CN112104234A - Ia protection level intrinsic safety type power supply circuit with constant voltage output for coal mine - Google Patents
Ia protection level intrinsic safety type power supply circuit with constant voltage output for coal mine Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
- H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
- H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
- H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
- H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
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- H02M1/32—Means for protecting converters other than automatic disconnection
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Abstract
The invention discloses an intrinsically safe power circuit with constant voltage output for ia protection level coal mine, which comprises: the isolation type power supply conversion circuit comprises an isolation type power supply conversion circuit (1), a current limiting circuit (2) and an overvoltage protection circuit (4) which are connected in sequence; the input end of the isolation type power supply conversion circuit (1) is connected to an input power supply, the output end of the isolation type power supply conversion circuit (1) is connected to the input end of the current limiting circuit (2), the output end of the current limiting circuit (2) is connected to a load, and the current limiting circuit (2) is used for limiting current output to the load. The power supply realizes the high-power constant-voltage output of the ia protection level intrinsic safety power supply within a certain load range, and better solves the problem that the traditional ia protection level intrinsic safety power supply is seriously insufficient in carrying capacity.
Description
Technical Field
The invention belongs to the field of coal mine explosion-proof electrical and electronic circuit design, and relates to an ia protection level coal mine intrinsically safe power circuit with constant voltage output.
Background
The underground coal mine is an environment with explosive dangers such as gas, coal dust and the like, and the intrinsically safe power supply is widely applied to various electronic equipment, measuring instruments, control instruments, electric transmission equipment and the like of the coal mine. According to the requirements related to GB3836, electrical equipment used in the environment generally has an ib protection level, and a power supply arranged in a gas extraction pipeline and associated with equipment such as a gas transmission monitoring system and the like reaches an ia protection level. The intrinsically safe circuit in ia protection level electrical equipment requires that it should not ignite explosive gases in normal operation, in the case of applying one counting failure point, in the case of applying two counting failure points and in the case of non-counting failure under the worst conditions, respectively. GB3836.4 has definite limits and requirements on output voltage and current of an intrinsic safety circuit, and according to the requirements, an ia protection level intrinsic safety power supply has to realize reliable current limiting of the circuit by adopting a protection mode of a series power resistor, and then triple redundant overvoltage protection is arranged to meet the requirement of no ignition under the most severe fault condition.
With the progress and development of the technology, especially the development requirements of building intelligent mines, intelligent mines and underground 5G networks, more and more advanced equipment enters coal mines to protect the safety of the coal mines, and meanwhile, greater impact is brought to underground intrinsic safety power supply.
Fig. 3 shows a circuit schematic of a conventional ia protection class intrinsically safe power supply. The circuit consists of a power supply conversion circuit, a voltage regulation feedback circuit, a current limiting resistor and a triple overvoltage protection circuit connected in parallel. The power supply conversion circuit is a power supply module with fixed voltage output, and the output voltage of the power supply conversion circuit is set through the voltage regulation feedback circuit; the voltage regulating feedback circuit is arranged in front of the current limiting power resistor, and samples and feeds back the output voltage of the power conversion circuit, so that the power conversion circuit outputs constant voltage. The conventional ia protection level intrinsically safe power supply is limited by necessary protection modes, the current limiting resistor causes a large amount of power loss, the output characteristic of the power loss is linear (as shown in fig. 4), namely, the voltage transmitted to a terminal is sharply reduced along with the increase of a load, and the load capacity is seriously insufficient.
Disclosure of Invention
Aiming at the problems of the traditional ia protection level intrinsic safety type power supply, the invention provides an ia protection level intrinsic safety type power supply circuit with constant voltage output, which realizes high-power constant voltage output of the ia protection level intrinsic safety type power supply within a certain load range and better solves the problem that the traditional ia protection level intrinsic safety type power supply is seriously insufficient in carrying capacity.
According to an embodiment of the present invention, there is provided an intrinsically safe power supply circuit for an ia protection class coal mine having a constant voltage output, including: the isolation type power supply conversion circuit comprises an isolation type power supply conversion circuit (1), a current limiting circuit (2) and an overvoltage protection circuit (4) which are connected in sequence; the input end of the isolated power supply conversion circuit (1) is connected to an input power supply, the output end of the isolated power supply conversion circuit (1) is connected to the input end of the current limiting circuit (2), the output end of the current limiting circuit (2) is connected to a load, the current limiting circuit (2) is used for limiting current output to the load, the input end of the first voltage feedback control circuit (5) is connected to the input end of the current limiting circuit (2), the output end of the first voltage feedback control circuit (5) is connected to the feedback input end of the isolated power supply conversion circuit (1), the input end of the second voltage feedback control circuit (6) is connected to the output end of the current limiting circuit (2), and the output end of the second voltage feedback control circuit (6) is connected to the feedback input end of the isolated power supply conversion circuit (1), the overvoltage protection circuit (4) is used for enabling the voltage output to the load not to exceed a preset overvoltage protection threshold value, and the first voltage feedback control circuit (5) is used for sampling the voltage of the output end of the isolated power supply conversion circuit (1) and sending a first feedback control signal to the feedback input end of the isolated power supply conversion circuit (1) according to a sampling result; the second voltage feedback control circuit (6) is used for sampling the voltage at the output end of the current limiting circuit (2) and sending a second feedback control signal to the feedback input end of the isolated power supply conversion circuit (1) according to the sampling result; the isolated power conversion circuit (1) is used for adjusting the voltage of the output end of the isolated power conversion circuit (1) according to the first feedback control signal and/or the second feedback control signal received through the feedback input end.
The embodiment of the invention has the advantages and beneficial effects that:
1. by introducing terminal voltage feedback, constant voltage output is realized, and the problem that the carrying capacity of the traditional ia protection level intrinsic safety type power supply is insufficient is solved;
2. the limitation of the highest output voltage and the highest output current is realized by simultaneously setting the highest output voltage of the power conversion circuit, and better intrinsic safety parameters are easy to determine;
3. the circuit is reasonably isolated, so that the isolation voltage-resistant performance is better, and higher safety performance is realized;
4. the power supply has the advantages of high power supply conversion efficiency, simple circuit, low cost and easy production and realization.
Drawings
Fig. 1 is a functional block diagram of an ia protection level intrinsically safe power supply circuit having a constant voltage output according to an embodiment of the present invention;
FIG. 2 is a schematic circuit diagram of a ia protection level intrinsically safe power supply circuit with constant voltage output according to an embodiment of the present invention;
FIG. 3 is a schematic circuit diagram of a conventional ia protection class intrinsically safe power supply;
fig. 4 is a graph comparing the output characteristics of a ia protection level intrinsically safe power supply and a conventional ia protection level intrinsically safe power supply according to an embodiment of the present invention.
Detailed Description
In the following, preferred embodiments of the present invention will be described in further detail with reference to the attached drawings, the present invention is not limited to the embodiments, and various modifications can be made to the idea of the present invention to extend various implementation forms within the scope of the present invention.
First, the principle of the solution of the invention is outlined with reference to fig. 1.
Fig. 1 is a functional block diagram of an ia protection level intrinsically safe power supply circuit having a constant voltage output according to an embodiment of the present invention.
The power supply circuit according to the embodiment of the invention mainly comprises an isolated power supply conversion circuit 1, a reliable current limiting circuit 2, a voltage stabilizing circuit 3, a triple overvoltage protection circuit 4 and two feedback control circuits which are connected in sequence, namely: a highest output voltage feedback control circuit 5 arranged between the input end of the reliable current limiting circuit and the isolated power supply conversion circuit; and a constant voltage output feedback control circuit 6 arranged between the output end of the reliable current-limiting resistor and the isolated power supply conversion circuit.
The isolated power conversion circuit 1 has an output voltage adjustment terminal, which electrically isolates an input power from a subsequent output power, receives feedback control signals from the two voltage feedback control circuits (the highest output voltage feedback control circuit and the constant voltage output feedback control circuit) in an isolated manner (e.g., via an optical coupler (photocoupler)), and forms a closed-loop feedback with any one of the voltage feedback control circuits, thereby enabling constant voltage output at a power output terminal (an input terminal of a reliable current limiting circuit) and at a load terminal (an output terminal of a reliable current limiting circuit), respectively.
The reliable current limiting resistor 2 is connected in series in the power output loop and determines the maximum current of the output circuit.
The voltage stabilizing circuit 3 stabilizes the peak clipping processing of the terminal output voltage (load terminal voltage) in a set range, on one hand, the power supply voltage stability of the electric equipment is ensured, and on the other hand, the hidden trouble that the power supply output cannot be recovered after the fault is eliminated due to the fact that transient peak voltage easily triggers the malfunction of a rear-stage overvoltage protection circuit in the moment of recovery after the output short circuit is avoided.
The triple overvoltage protection circuit 4 realizes overvoltage protection by a redundant parallel circuit, and when rare faults occur and the output end exceeds a set safe voltage, the overvoltage protection circuit acts to directly return current to a power supply ground, so that the risk of igniting explosive gas by sparks due to overvoltage is eliminated.
The maximum output voltage feedback control circuit 5 is configured to limit the highest voltage at the power output end, sample the voltage at the power output end (the input end of the reliable current limiting circuit), and feed back the voltage comparison result to the adjusting end of the isolated power conversion circuit 1 in an electrical isolation manner, where the isolated power conversion circuit 1 adjusts the voltage at the power output end thereof accordingly, thereby achieving voltage limitation at the power output end.
The constant voltage output feedback control circuit 6 is used for realizing constant voltage output of a load end, sampling voltage of the load end (the output end of the reliable current limiting circuit 2), feeding a voltage comparison result back to the adjusting end of the isolated power supply conversion circuit in an electrical isolation mode, and realizing the constant voltage output of the load end by adjusting the voltage of the power supply output end.
According to the power supply circuit disclosed by the embodiment of the invention, the isolation conversion between the input and the output of the power supply is realized, the electrical isolation between the feedback control signal and the output end is realized, the higher isolation voltage-resistant level is easy to realize, and the safety is higher. The constant voltage output characteristic of its realization has promoted the on-load ability greatly. The maximum output voltage of the circuit is limited by the arrangement of the maximum output voltage, and the maximum output current of the circuit is limited by the arrangement of the maximum output voltage and the reliable current limiting resistor. The voltage stabilizing circuit and the triple overvoltage protection circuit eliminate risks caused by rare fault overvoltage of the circuit, meet the requirement of automatic power supply recovery of the circuit after short-circuit fault elimination, and simultaneously ensure stable voltage output by external power supply.
Hereinafter, embodiments of the present invention are described in detail with reference to the accompanying drawings.
Fig. 2 is a schematic circuit diagram of a ia protection level intrinsically safe power supply circuit with constant voltage output according to an embodiment of the present invention.
As shown in fig. 2, the intrinsically safe power supply circuit includes, as an example: the protection circuit comprises an isolation type power supply conversion circuit 1, a reliable current limiting circuit 2 formed by a power resistor R (current limiting resistor), a voltage stabilizing circuit 3 formed by a voltage stabilizing diode D6, and a triple overvoltage protection circuit 4 formed by a silicon controlled rectifier Q, a voltage stabilizing tube V and the like.
In addition, the operational amplifier U2 and the voltage reference U3 constitute the maximum voltage feedback control circuit 5 as core devices, and the voltage reference chip U4 constitutes the constant voltage output feedback control circuit 6 as a core device. Feedback signals of the highest output voltage feedback control circuit 5 and the constant voltage output feedback control circuit 6 are respectively isolated by the optical couplers E1 and E2 and then input to the adjusting end (pins 1 and 8 shown in the figure) of the isolated power conversion circuit 1.
The isolated power conversion circuit 1 is a single-ended flyback AC/DC power conversion circuit, which realizes voltage conversion through a flyback transformer T, and simultaneously realizes isolation of an output power supply from an input power supply, and can realize higher withstand voltage isolation by adopting a transformer mode.
The operation principle of the isolated power conversion circuit 1 is specifically described below.
The intrinsically safe alternating current is converted into pulse direct current through an electric bridge B, firstly, a pulse width modulation chip U1 (for example, a PWM controller with the model of UC 3842) is charged through a resistor R1, a pulse width modulation signal (OUT end and pin 6) is generated after the chip U1 is charged and started, a switching tube N (N-MOS tube) is conducted, and a primary winding of a transformer T, the switching tube N and the resistor R7 form a loop. Current flows through the primary winding of the transformer T and continues to increase with increasing time. Because the current in the inductor can not change suddenly, the magnetic flux of the transformer T tends to increase according to the Faraday's law of electromagnetic induction, the primary winding of the transformer T generates a reverse electromotive force opposite to the current, and the homonymous end of the secondary winding also generates a reverse induced electromotive force in the same direction as the current. Due to the action of the diode D5, no current is output from the circuit at this time.
When the chip U1 turns off the switch tube N, the current at the terminal of the primary winding of the transformer T is instantaneously reduced from the maximum value to 0, the magnetic flux of the transformer T has the tendency of reduction according to the Faraday's law of electromagnetic induction, a forward electromotive force is induced in the primary winding, a forward induced electromotive force in the same direction as the forward induced electromotive force is also generated at the same-name end of the secondary winding, the diode D5 is switched on, and the circuit outputs voltage. Meanwhile, the primary auxiliary winding also generates positive induced electromotive force, the current is limited by a resistor R2-2 and then the current is supplied to the chip U1 instead of the resistor R1, and the chip U1 is maintained to work and continuously generate pulse width modulation signals. The high-frequency pulse width modulation signal generated by the chip U1 controls the switch tube N to be switched on and off, so that the constantly induced current is output to the rear stage in a reciprocating manner, and the ripple waves are filtered by the filter capacitor C10 to form stable direct current output.
The chip U1 is a power supply pwm management chip, which controls that when the switching tube N is turned off, the induced current in the primary winding of the transformer T will disappear, the current will change, and a forward induced current will be generated, the secondary winding will generate a reverse induced current, the output will be cut off, when the switching tube N is turned on, the reverse induced current will be generated again, the secondary winding will generate a forward induced current again and output through the diode D5, and thus the current will be output to the subsequent stage repeatedly.
The highest voltage feedback control circuit 5 is arranged at the input front end of the reliable current limiting circuit 2, and feedback control of the highest output voltage of the isolated power supply conversion circuit 1 is achieved.
In the maximum output voltage feedback control circuit 5, the output voltage (the voltage at the VA point, output through the diode D5) is divided and sampled by the resistors R12 and R13, and the divided voltage of the maximum output voltage Vmax (the maximum voltage at the VA point) of the isolated power conversion circuit 1 should be equal to the voltage source reference (which may be 2.5V) of the operational amplifier U2, and the relationship may be:
2.5V ═ Vmax × R13/(R12+ R13) formula (1)
Therefore, according to equation (1), the highest output voltage Vmax, e.g., 26V, is set by the resistors R12, R13.
The chip U3 is a 2.5V voltage reference chip, the VA point is subjected to current-limiting power supply through a resistor R10 to generate 2.5V voltage reference, the in-phase input end of an operational amplifier U2 is connected, the voltage of the VA point is subjected to voltage division and sampling through resistors R12 and R13 to obtain an output voltage sampling value of the VA point, the reverse input end of the operational amplifier U2 is connected, the operational amplifier U2 continuously compares the sampling voltage with the voltage reference Vref to generate output, when the output voltage sampling value is larger than 2.5V, the output end of the operational amplifier U2 drives an optocoupler E1 to be switched on, when the output voltage sampling value is lower than 2.5V, the operational amplifier U2 enables the optocoupler E1 to be switched off, a feedback signal isolated by the optocoupler is transmitted to the chip U1, the duty ratio of a pulse width modulation signal.
The constant voltage output feedback control circuit 6 is arranged at the rear end of the output of the reliable current limiting circuit 2 to realize the feedback control of the constant voltage output.
By utilizing the current voltage control characteristic of the current source U4, the fluctuation of the voltage at the output end is fed back to the power supply pulse width modulation management chip U1 through the optical coupler E2, and the chip U1 adjusts the driving pulse width of the switching tube N, so that the output voltage is stabilized at a set value.
Here, as an example, the on voltage reference of the current source U4 may also be 2.5V, and the divided voltage of the constant voltage output Vcv (for example, 18V) at the VB point should be equal to the on voltage reference of U4:
2.5V ═ Vcv × R18/(R17+ R18) formula (2)
Here, the constant voltage output voltage Vcv is set by the resistors R17 and R18 according to the formula (2).
Based on the adjustment principle, fig. 2 is a schematic diagram of a specific implementation of a dual adjustment mode having a constant voltage output feedback control circuit and a highest output voltage feedback control circuit according to an embodiment of the present invention. In fact, the two feedback control modes are different specific implementation modes of the voltage regulation feedback control, that is, the circuit structures of the highest output voltage feedback control circuit 5 and the constant voltage output feedback control circuit 6 can be the same, interchanged, or implemented by using any other voltage comparison circuit. The maximum output voltage feedback control circuit 5 and the constant voltage output feedback control circuit 6 are respectively designed at the input end and the output end of the reliable current limiting circuit 2, and an isolation optocoupler E1 and an isolation optocoupler E2 are respectively arranged at the input end and the output end of the reliable current limiting circuit, and the electrical independence of the current limiting resistor R front and back feedback circuits is realized while the optocoupler is isolated from the power input end, because the power part passing through the reliable current limiting circuit and the triple overvoltage protection circuit is an intrinsic safety circuit, and the intrinsic safety circuit and the previous circuit are electrically independent.
The embodiment has double regulation of constant voltage output feedback control and a highest output voltage feedback control circuit, wherein the highest output voltage Vmax is the upper limit of the output voltage at the VA point, the constant voltage output set value Vcv is the constant voltage output value at the VB point, and in application, Vmax is larger than Vcv.
When the circuit is in no-load, the voltage output of a VB point is Vcv (18V), the voltage of a VA point is the same as that of the VB point, the voltage of the VA point is lower than the set highest output voltage Vmax (26V), E1 is kept open, the highest output voltage feedback control circuit 5 does not work, the constant voltage output feedback control circuit 6 works, a control signal of the constant voltage output feedback control circuit is fed back to a power supply management chip U1 through an optical coupler E2, and the chip U1 repeatedly adjusts the duty ratio of the output signal to adjust the on-off of a switching tube N so that the VB point outputs stable voltage.
When the load increases, i.e. the current flowing through the current limiting resistor R increases, the voltage drop across the resistor R increases, the voltage at point VA will gradually increase (from 18V), and because of the closed-loop control action of the constant voltage output feedback control circuit 6, the output voltage at the point VB is still kept at Vcv until the voltage at the point VA reaches the highest voltage set value Vmax, the highest output voltage feedback control circuit 5 will act, the control signal is fed back to a power management chip U1 through an optical coupler E1, the chip U1 repeatedly adjusts the duty ratio of the output signal to adjust the on-off of a switching tube N, the output voltage of a VA point is stabilized at Vmax and is not increased, due to the voltage division effect of the current-limiting resistor R, the voltage at the VB point is reduced, so that the sampling voltages on the resistors R17 and R18 are lower than 2.5V, the voltage reference U4 is cut off, the optical coupler E2 is not conducted any more, and the constant-voltage output feedback control loop 6 loses effect.
As the load continues to increase, the voltage drop falling on the current limiting resistor linearly rises, the voltage at the point VB linearly falls until the load approaches a short circuit, and the output voltage at the point VB is 0.
The present embodiment discloses the technical solution in a better way, and does not limit the specific implementation manner at all, and the above working principle has a better effect also under the DC/DC power conversion.
Further, the circuit configurations of the highest voltage feedback control circuit 5 and the constant voltage output feedback control circuit 6 in fig. 2 are merely examples, and any circuit (a circuit having a voltage feedback control function, for example, a voltage feedback control circuit implemented by a voltage dividing circuit and a voltage comparator) that achieves the same function may be employed instead of the highest voltage feedback control circuit 5 and/or the constant voltage output feedback control circuit 6, and the technical solutions thereof also fall within the scope of the present invention.
Similarly, the specific components of the regulator circuit 3 and the over-voltage protection circuit 4 are also only examples, and those skilled in the art can arbitrarily adopt circuits with the same functions to replace the regulator circuit 3 and the over-voltage protection circuit 4, and the technical solutions thereof also fall within the scope of the present invention.
The reliable current limiting circuit of the circuit is formed by adopting power resistors required by relevant standards of explosion-proof electricity. The circuit adopting the power resistor for limiting the current is particularly important for temperature management and heat dissipation treatment, as the further optimization of the technical scheme disclosed by the invention, a temperature protection circuit can be arranged in front of or behind the power resistor, and a temperature control switch is arranged near a power conversion circuit or the power resistor with concentrated heat during implementation, so that the overtemperature power-off protection is realized, and the intrinsic safety of the power supply is further improved.
As a further optimization of the technical scheme disclosed by the invention, before the reliable current limiting circuit, a plurality of overvoltage protection circuits can be arranged to further reliably limit the highest voltage applied to the reliable current limiting circuit.
As a further optimization of the technical scheme disclosed by the invention, before and after the reliable current limiting circuit, the current limiting circuit can be arranged, and the highest output current is arranged on the target load by a certain coefficient and is lower than the maximum output current of the invention. Further improving the intrinsic safety characteristics of the output current.
The above-mentioned optimization is further optimized and extended by the conventional techniques according to the concept of the present invention, and is not an essential part of the present invention, i.e. the simple modification and extension by the conventional techniques according to the concept of the present invention should fall into the protection scope of the present invention.
In the following, an 18V ia protection level intrinsically safe power supply with constant voltage output capability is designed in combination with the schematic circuit diagram provided by this embodiment, so as to further explain the working principle of the power supply.
As will be readily appreciated from the embodiments of the present invention, it is preferable to set the constant voltage output voltage Vcv to 18V, the maximum output voltage Vmax to 26V, the triple over-voltage protection circuit protection threshold to Vp 18.5V, and the power resistance to 25 Ω/50W in the design, so that:
Uo＝Vp＝18.5V；
Io＝Vmax/R＝26V/25Ω＝1.04A；
namely, UO in intrinsic safety parameters: 18.5V, Io: 1.04A.
When the circuit works, the voltage at the VB point is divided and sampled by the resistors R17 and R18 to obtain a voltage signal, the voltage signal is higher than the conduction voltage of the current source U4 by 2.5V, that is, when the voltage at the VB point exceeds the set 18V, the current source U4 is turned on, the light emitting tube in the optical coupler E2 is lit, the internal triode is turned on, the pwm management chip in the power conversion circuit 1 adjusts the pwm driving switch tube N to reduce the output voltage, when the voltage at the VB point is lower than the set 18V, the internal triode in the optical coupler E2 is opened, the pwm management chip in the power conversion circuit 1 adjusts the pwm driving switch tube N to increase the output voltage, in this process, the feedback signal drives the switch tube N through the pwm management chip U1 to form closed-loop control on the power circuit 1, so that VB is 18V, that is Vcv 18V.
When the circuit is idle, the current is zero, the feedback signal of the constant voltage output feedback control circuit 6 at the point VB is active, at this time, VA is 18V, which is far less than the maximum output voltage Vmax (26V), and the feedback signal of the maximum output voltage feedback control circuit 5 is inactive.
When the load current increases, i.e. the intrinsically safe output current gradually increases, the voltage at the point VB decreases, the feedback signal of the constant voltage output feedback control circuit 6 acts, thereby increasing the voltage of the VA point, further recovering the voltage of the VB point and maintaining the 18V constant voltage output, due to the existence of the power resistor R, the voltage drop on the power resistor R is larger and larger along with the increase of the load current, the feedback control makes the voltage at the point VA higher and higher until the maximum output voltage Vmax set is reached, which is 26V, the feedback signal of the feedback control circuit 5 for the highest output voltage will act, the voltage is fed back to the power conversion circuit 1 through an optical coupler E1 to form new closed-loop control (VA is stabilized at 26V, and VB is lower than 18V), the voltage at the VA point is not increased any more, and the voltage drop at the point VB is lower than 18V due to the voltage drop effect of the power resistor, and the feedback signal of the constant-voltage output feedback control circuit 6 is not effective (because E2 is opened/closed).
The current in the power supply circuit continues to increase, and the output voltage at the point VB after the power resistor R will linearly decrease because the voltage at the point VA reaches Vmax, which is 26V and does not increase any more. Until the output end reaches the short circuit critical point, the voltage at the VB point is close to 0V. When the output is short-circuited, the transient current is 1.04A/R, the transient voltage is 0V, and the released energy is not enough to ignite explosive gas, namely, the intrinsic safety characteristic is met.
On the other hand, when the load current drops to raise the voltage at the VB point to be higher than 18V, E2 is turned on to lower VA (E1 is opened), and then VB drops to form a new closed-loop control, VB is stabilized at 18V, and VA is lower than 26V.
From the above process, the power supply circuit of the present invention has a constant voltage output characteristic within a certain range.
Fig. 3 shows a conventional ia protection class intrinsically safe power supply circuit comprising a power conversion circuit, a voltage regulation feedback circuit, a current limiting power resistor and a parallel triple overvoltage protection circuit. The power supply conversion circuit is a power supply module with fixed voltage output, and the output voltage of the power supply conversion circuit is set through the voltage regulation feedback circuit; the voltage regulating feedback circuit is arranged in front of the current limiting power resistor, and samples and feeds back the output voltage of the power conversion circuit, so that the power conversion circuit outputs constant voltage.
For convenience of explaining the advantages of the present invention, a conventional 18V intrinsically safe power supply with a conventional ia protection class having the same intrinsic safety parameters as the embodiment of the present invention is designed to illustrate the operating characteristics of the conventional power supply and perform comparative analysis.
From intrinsic safety parameter Uo: 18.5V, Io: 1.04A, the current-limiting power resistor Ro of the available traditional power supply should be set as:
Ro＝Uo/Io＝18.5V/1.04A＝18Ω；
obviously, the triple over-voltage protection threshold should also be set to 18.5V, and the fixed voltage output maximum ripple voltage of the power conversion circuit may be close to 18.5V but may not reach 18.5V, and generally, should be a rated 18V for the design target, i.e., Va ═ 18V.
When the output is open, the output voltage Uout is 18V;
when the output is short-circuited, the output voltage Uout is 0V, and the transient maximum short-circuit current is:
Imax＝Va/R＝18V/18Ω＝1A；
in normal operation, due to the voltage dividing effect of the current-limiting power resistor Ro, the voltage output Uout will be linearly reduced with the increase of the load current.
The power supply voltage of the mining intrinsically safe electric equipment is generally 9-24V of direct current. To this end, alignment analysis was performed using the above examples.
The output characteristic curve of the ia protection level 18V intrinsically safe power supply realized by the embodiment of the present invention and the above-described conventional scheme is shown in fig. 4, in which the solid line is the output characteristic curve of the ia power supply realized by the embodiment of the present invention, and the dotted line is the output characteristic curve of the ia power supply realized by the conventional scheme.
As shown in fig. 4, which is easily demonstrated by the above embodiments, point a is the turning point of the ia power supply output voltage from the constant voltage to the linear drop realized by the embodiment of the present invention, i.e. the constant voltage output in the load range of 0mA to 320mA, wherein:
Ua＝18V；
Ia＝(Vmax-Vcv)/R＝(26V-18V)/25Ω＝320mA；
c. point e is the power output of the ia power supply implemented with the embodiment of the present invention and the ia power supply implemented with the conventional scheme, respectively, when the lowest supply voltage of 9V output is reached, where:
Ic＝(Vmax-(Vcv-9V))/R＝(26V-9V)/25Ω＝680mA；
Ie＝(Va-9V)/R＝(18V-9V)/18Ω＝500mA；
point b is the power output of ia power supply realized by the embodiment of the present invention when comparing with 500mA load, and the voltage at the output terminal is:
Ub＝Vcv-(Ib-Ia)*R＝18V-(500mA-320mA)*25Ω＝13.5V；
point d is the power output of ia power supply realized by adopting the traditional scheme when comparing with 320mA load, and the output end voltage is:
Ud＝Vcv-Ia*R＝18V-320mA*18Ω＝12.24V；
in conclusion, by comparing the output characteristic curves of the power supply and the power supply, the load carrying capacity of the ia protection level intrinsic safety power supply realized by the embodiment of the invention is far better than that of the traditional ia protection level intrinsic safety power supply, and the problem that the load carrying capacity of the traditional ia protection level intrinsic safety power supply is seriously insufficient is solved.
The reliable current limiting circuit is formed by adopting a power resistor required by the relevant standard of the current explosion-proof electricity. The circuit adopting the power resistor for limiting the current is particularly important for temperature management and heat dissipation treatment, and as further optimization of the technical scheme disclosed by the invention, a temperature protection circuit can be arranged in front of or behind the power resistor, and a temperature control switch is arranged near a power conversion circuit or the power resistor with concentrated heat during implementation, so that overtemperature power-off protection is realized, and the intrinsic safety of the power supply is further improved.
As a further optimization of the technical scheme disclosed by the invention, multiple overvoltage protection circuits can be arranged at the input front end of the reliable current limiting circuit, so that the highest voltage applied to the reliable current limiting circuit is further reliably limited.
As a further optimization of the technical scheme disclosed by the invention, a current limiting circuit can be arranged at the output rear end of the reliable current limiting circuit, and the highest output current is arranged above the target load by a certain coefficient and is lower than the maximum output current of the invention. Further improving the intrinsic safety characteristics of the output current.
In conclusion, the embodiment of the invention not only meets the circuit structure requirements of relevant standards in the field of explosion-proof electricity on reliable current-limiting and triple overvoltage protection of the ia protection level intrinsic safety power circuit of the coal mine, but also realizes constant voltage output in a certain load range through the arrangement of the constant voltage output feedback control circuit, thereby greatly improving the load capacity of the ia power supply. Meanwhile, the safety, the reliability, the power conversion efficiency and the like are greatly improved.
The above description is only a general embodiment of the present invention, and is not intended to limit the present invention, and any modifications, alterations, equivalent structural changes, etc. made by the above implementation according to the technical principle of the present invention still belong to the protection scope of the technical solution of the present invention.
Claims (9)
1. An intrinsically safe power supply circuit with constant voltage output for ia protection level coal mines, comprising: the isolation type power supply conversion circuit comprises an isolation type power supply conversion circuit (1), a current limiting circuit (2) and an overvoltage protection circuit (4) which are connected in sequence; and a first voltage feedback control circuit (5) and a second voltage feedback control circuit (6),
the input end of the isolated power supply conversion circuit (1) is connected to an input power supply, the output end of the isolated power supply conversion circuit (1) is connected to the input end of the current limiting circuit (2), the output end of the current limiting circuit (2) is connected to a load, the current limiting circuit (2) is used for limiting the current output to the load,
the input end of the first voltage feedback control circuit (5) is connected to the input end of the current limiting circuit (2), the output end of the first voltage feedback control circuit (5) is connected to the feedback input end of the isolated power supply conversion circuit (1),
the input end of the second voltage feedback control circuit (6) is connected to the output end of the current limiting circuit (2), the output end of the second voltage feedback control circuit (6) is connected to the feedback input end of the isolated power supply conversion circuit (1),
the overvoltage protection circuit (4) is used for enabling the voltage output to the load not to exceed a preset overvoltage protection threshold value,
the first voltage feedback control circuit (5) is used for sampling the voltage at the output end of the isolated power supply conversion circuit (1) and sending a first feedback control signal to the feedback input end of the isolated power supply conversion circuit (1) according to the sampling result;
the second voltage feedback control circuit (6) is used for sampling the voltage at the output end of the current limiting circuit (2) and sending a second feedback control signal to the feedback input end of the isolated power supply conversion circuit (1) according to the sampling result;
the isolated power conversion circuit (1) is used for adjusting the voltage of the output end of the isolated power conversion circuit (1) according to the first feedback control signal and/or the second feedback control signal received through the feedback input end.
2. An ia protection level intrinsic safety type power supply circuit for coal mine with constant voltage output according to claim 1, further comprising a voltage stabilizing circuit (3) connected between the current limiting circuit (2) and the overvoltage protection circuit (4) for reducing voltage fluctuation at the output terminal of the current limiting circuit (2).
3. An ia-protection-level intrinsically-safe power supply circuit with constant-voltage output as claimed in claim 1, wherein the overvoltage protection circuit (4) is a triple overvoltage protection circuit.
4. The ia protection level intrinsic safety type power supply circuit with the constant voltage output for the coal mine as claimed in claim 1, wherein the first feedback control signal and the second feedback control signal are respectively input to the feedback input end of the isolation type power supply conversion circuit (1) after passing through a first optical coupler (E1) and a second optical coupler (E2).
5. An ia protection level power supply circuit for coal mine with constant voltage output as claimed in claim 1, wherein the current limiting circuit (2) is a power resistor (R).
6. The ia protection level intrinsic safety type power supply circuit with constant voltage output for coal mine according to claim 4, wherein if the voltage at the output terminal of the isolated power supply conversion circuit (1) is higher than a first threshold value, the first voltage feedback control circuit (5) sends a first feedback control signal with a level for dropping the voltage at the output terminal of the isolated power supply conversion circuit (1), and can form closed loop control with the isolated power supply conversion circuit (1) to maintain the voltage at the output terminal of the isolated power supply conversion circuit (1) at the first threshold value.
7. The ia protection level intrinsic safety type power supply circuit for coal mine with constant voltage output according to claim 6, wherein if the voltage at the output terminal of the current limiting circuit (2) is higher than a second threshold value, the second voltage feedback control circuit (6) sends a second feedback control signal with a level for dropping the voltage at the output terminal of the isolated power conversion circuit (1), and can form closed loop control with the isolated power conversion circuit (1) to maintain the voltage at the output terminal of the current limiting circuit (2) at the second threshold value.
8. The ia protection level intrinsic safety type power supply circuit with constant voltage output for coal mine according to claim 6 or 7, wherein the isolation type power conversion circuit (1) is a single-ended flyback AC/DC power conversion circuit and comprises a PWM controller (U1) and a switch transistor (N), and the PWM controller (U1) is used for generating a pulse width modulation signal for driving the switch transistor (N) according to the level of a first feedback control signal and/or a second feedback control signal so as to control the voltage of the output end of the isolation type power conversion circuit (1).
9. The ia-protection-class intrinsically safe power supply circuit with constant-voltage output as claimed in claim 4 or 6, wherein the first voltage feedback control circuit (5) and the second voltage feedback control circuit (6) respectively comprise voltage comparison circuits for comparing the sampled voltages with respective reference voltages and outputting driving signals to a first optical coupler (E1) and a second optical coupler (E2) respectively according to the comparison results.
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| CN202011049717.7A CN112104234A (en) | 2020-09-29 | 2020-09-29 | Ia protection level intrinsic safety type power supply circuit with constant voltage output for coal mine |
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