CA2298428C - Battery charging circuit - Google Patents
Battery charging circuit Download PDFInfo
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- CA2298428C CA2298428C CA002298428A CA2298428A CA2298428C CA 2298428 C CA2298428 C CA 2298428C CA 002298428 A CA002298428 A CA 002298428A CA 2298428 A CA2298428 A CA 2298428A CA 2298428 C CA2298428 C CA 2298428C
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- signal
- battery
- battery charging
- circuit
- rectified
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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
- H02M3/33507—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 with automatic control of the output voltage or current, e.g. flyback converters
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Dc-Dc Converters (AREA)
- Charge And Discharge Circuits For Batteries Or The Like (AREA)
Abstract
A battery charging circuit uses a simplified design for converting AC to DC and powering a flyback transformer.
The switch of the flyback transformer operates at a high frequency and the time of the transformer is controlled to achieve a high power factor. The flyback transformer is fed a rectified AC signal which has not been smoothed in the traditional manner using a bulk hold capacitor and in rush limiting resister. Any treating to smooth the charging current for the battery is carried out on the secondary side. In many cases, no smoothing of the charging current is necessary. The time on of the switch is changed if necessary, slowly, relative to the pulsating input signals powering the primary winding. With a fixed T on, or slowly varying T on, dramatic fluctuations in the charging current are avoided.
The switch of the flyback transformer operates at a high frequency and the time of the transformer is controlled to achieve a high power factor. The flyback transformer is fed a rectified AC signal which has not been smoothed in the traditional manner using a bulk hold capacitor and in rush limiting resister. Any treating to smooth the charging current for the battery is carried out on the secondary side. In many cases, no smoothing of the charging current is necessary. The time on of the switch is changed if necessary, slowly, relative to the pulsating input signals powering the primary winding. With a fixed T on, or slowly varying T on, dramatic fluctuations in the charging current are avoided.
Description
WH-10,757CA
TITLE: BATTERY CHARGING CIRCUIT
FIELD OF THE INVENTION
The present invention relates to battery charging circuits, and in particular, to a battery charging circuit having a high power factor.
BACKGROUND OF THE INVENTION
Recent advances in rechargeable batteries have greatly extended the number of products which can be powered by a relatively small battery. In many of these products it is desirable to have a charging circuit associated with the product to allow convenient recharging of the battery. As most of these devices are portable, weight and size of the charging circuit are important factors, and from a marketing point of view, the cost of the circuit is also important.
The growth of rechargeable battery operated devices have also forced utilities to reconsider specifications for charging circuits as many of the early designs had relatively poor power factor corrections. As the number of products increase, this has become a concern for the utilities and thus, the specification, with respect to recharging circuits is changing.
Switching power supply devices of a type without power factor correction have been used. These devices rectify an AC voltage and process the rectified AC voltage using a bulk holdup capacitor to smooth it to a DC voltage.
This smoothed DC signal is then provided to a flyback transformer circuit which is controlled by a switch.
Feedback is provided from the charging current of the secondary winding and the feedback circuit is relatively fast to maintain a desired, instantaneous charging current.
WH-10, 75.7CA
The smoothing of the rectified AC signal has the advantage that the signal provided to the primary winding for powering thereof is more constant, and thus, the charging current provided by the secondary winding is more consistent. The charging current may be closely monitored and fast correction of variations in the charging current is provided by the feedback mechanism and a control arrangement associated with the switch of the flyback transformer. Unfortunately, this design has a relatively poor power factor. In addition, the design includes a number of bulky and expensive components for smoothing of the input signal which further increases the cost of the charging circuit.
The present invention provides a simplified circuit which has desirable characteristics with respect to achieving a predetermined power factor, has improved space utilization, and is cost effective.
SUMMARY OF THE INVENTION
A battery charging circuit according to the present invention comprises means for receiving an AC input signal, means for rectifying the AC input signal to produce a non constant DC signal and providing said non constant DC
signal to an input of a flyback transformer circuit. The flyback transformer circuit comprises a primary winding in series with a switch, and a secondary winding associated with said primary winding, and having a diode. The secondary winding produces a current for charging of a battery. A control arrangement controls the opening and closing of the switch and thereby defines a time on and time off of the switch. The control arrangement controls the time on as required to meet a predetermined power factor specification.
TITLE: BATTERY CHARGING CIRCUIT
FIELD OF THE INVENTION
The present invention relates to battery charging circuits, and in particular, to a battery charging circuit having a high power factor.
BACKGROUND OF THE INVENTION
Recent advances in rechargeable batteries have greatly extended the number of products which can be powered by a relatively small battery. In many of these products it is desirable to have a charging circuit associated with the product to allow convenient recharging of the battery. As most of these devices are portable, weight and size of the charging circuit are important factors, and from a marketing point of view, the cost of the circuit is also important.
The growth of rechargeable battery operated devices have also forced utilities to reconsider specifications for charging circuits as many of the early designs had relatively poor power factor corrections. As the number of products increase, this has become a concern for the utilities and thus, the specification, with respect to recharging circuits is changing.
Switching power supply devices of a type without power factor correction have been used. These devices rectify an AC voltage and process the rectified AC voltage using a bulk holdup capacitor to smooth it to a DC voltage.
This smoothed DC signal is then provided to a flyback transformer circuit which is controlled by a switch.
Feedback is provided from the charging current of the secondary winding and the feedback circuit is relatively fast to maintain a desired, instantaneous charging current.
WH-10, 75.7CA
The smoothing of the rectified AC signal has the advantage that the signal provided to the primary winding for powering thereof is more constant, and thus, the charging current provided by the secondary winding is more consistent. The charging current may be closely monitored and fast correction of variations in the charging current is provided by the feedback mechanism and a control arrangement associated with the switch of the flyback transformer. Unfortunately, this design has a relatively poor power factor. In addition, the design includes a number of bulky and expensive components for smoothing of the input signal which further increases the cost of the charging circuit.
The present invention provides a simplified circuit which has desirable characteristics with respect to achieving a predetermined power factor, has improved space utilization, and is cost effective.
SUMMARY OF THE INVENTION
A battery charging circuit according to the present invention comprises means for receiving an AC input signal, means for rectifying the AC input signal to produce a non constant DC signal and providing said non constant DC
signal to an input of a flyback transformer circuit. The flyback transformer circuit comprises a primary winding in series with a switch, and a secondary winding associated with said primary winding, and having a diode. The secondary winding produces a current for charging of a battery. A control arrangement controls the opening and closing of the switch and thereby defines a time on and time off of the switch. The control arrangement controls the time on as required to meet a predetermined power factor specification.
WH-10,757CA
The charging circuit of the invention recognizes that the rectified AC signal can advantageously be used for powering of the primary winding without any extensive smoothing of the signal. Such smoothing of the signal typically has been accomplished in prior art devices using a large, relatively expensive bulk holdup capacitor.
With the present invention, the time on is controlled to achieve or meet a predetermined power specification. The time on, in some applications, can be constant or where it is desired to vary the time on to appropriately increase or decrease the charging current, the time on is varied slowly and thus, high power factor correction is possible.
The present invention recognizes that the input signal to the primary winding can vary, and the resulting charging current for charging of the battery can vary in each cycle, and that satisfactory charging of the battery is possible. The battery is quite tolerant to variation in the charging current. In most cases, the charging current only need to be controlled to not exceed some maximum level. Therefore, the time on can be set to achieve a desired maximum current for the maximum voltage provided by the input signal. By controlling the time on to achieve the acceptable characteristics for the charging current, effective charging of the battery can occur. The charging circuit of the present invention is quite simple in design and has relatively few components. This combination is space efficient, weight efficient, and has a controllable power factor correction. This is also highly desirable for portable products.
A battery charging circuit according to an aspect of the invention, has the control arrangement control the rate of change of time on to meet the predetermined power factor specification.
The charging circuit of the invention recognizes that the rectified AC signal can advantageously be used for powering of the primary winding without any extensive smoothing of the signal. Such smoothing of the signal typically has been accomplished in prior art devices using a large, relatively expensive bulk holdup capacitor.
With the present invention, the time on is controlled to achieve or meet a predetermined power specification. The time on, in some applications, can be constant or where it is desired to vary the time on to appropriately increase or decrease the charging current, the time on is varied slowly and thus, high power factor correction is possible.
The present invention recognizes that the input signal to the primary winding can vary, and the resulting charging current for charging of the battery can vary in each cycle, and that satisfactory charging of the battery is possible. The battery is quite tolerant to variation in the charging current. In most cases, the charging current only need to be controlled to not exceed some maximum level. Therefore, the time on can be set to achieve a desired maximum current for the maximum voltage provided by the input signal. By controlling the time on to achieve the acceptable characteristics for the charging current, effective charging of the battery can occur. The charging circuit of the present invention is quite simple in design and has relatively few components. This combination is space efficient, weight efficient, and has a controllable power factor correction. This is also highly desirable for portable products.
A battery charging circuit according to an aspect of the invention, has the control arrangement control the rate of change of time on to meet the predetermined power factor specification.
WH~10, 75~7CA
According to yet a further aspect of the invention, the circuit includes an input arrangement for entering a battery charging specification and the control arrangement varies the time on to meet the battery charging specification. Typically, the specification can be set according to the maximum charging current relative to voltage of the battery and these conditions can be monitored to meet the charging specification.
A battery charging circuit according to the present invention has the rectified AC signal applied directly to the primary winding and this signal continuously varies from 0 volts to a maximum voltage and the charging current produced by the secondary winding continuously varies as a function of the rectified AC signal.
A battery charging circuit according to an aspect of the invention allows for considerable variation in the instantaneous charging current and this charging current can vary at least 25 per cent during each cycle. The changing current can be smoothed if desired by processing after the secondary winding.
According to yet a further aspect of the invention, the rectified AC signal used to power the primary windings pulses and the battery charging current produced by the secondary winding varies as a function of the rectified AC
pulsating signal.
The battery charging circuit of the present invention is advantageously used in combination with the charging of different types of batteries, including nickel cadmium batteries or lithium batteries.
BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the invention are shown in the drawings, wherein:
According to yet a further aspect of the invention, the circuit includes an input arrangement for entering a battery charging specification and the control arrangement varies the time on to meet the battery charging specification. Typically, the specification can be set according to the maximum charging current relative to voltage of the battery and these conditions can be monitored to meet the charging specification.
A battery charging circuit according to the present invention has the rectified AC signal applied directly to the primary winding and this signal continuously varies from 0 volts to a maximum voltage and the charging current produced by the secondary winding continuously varies as a function of the rectified AC signal.
A battery charging circuit according to an aspect of the invention allows for considerable variation in the instantaneous charging current and this charging current can vary at least 25 per cent during each cycle. The changing current can be smoothed if desired by processing after the secondary winding.
According to yet a further aspect of the invention, the rectified AC signal used to power the primary windings pulses and the battery charging current produced by the secondary winding varies as a function of the rectified AC
pulsating signal.
The battery charging circuit of the present invention is advantageously used in combination with the charging of different types of batteries, including nickel cadmium batteries or lithium batteries.
BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the invention are shown in the drawings, wherein:
WH-10,757CA
Figure 1 shows a simplified charging circuit;
Figure 2 is a schematic of a simplified charging circuit with some additional components; and Figure 3 shows various signals of the signal.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The battery charging circuit 2 of Figure 1 receives an AC input signal at 4 and rectifies the AC signal at 6 to produce a pulsating rectified AC signal generally shown at 7. This signal is provided to a flyback transformer circuit comprising the primary winding 10, the controlled switch 14, the secondary winding 24, and the current rectifying diode 16. The secondary winding 24 provides a charging current for the rechargeable battery 30. This battery can be a lead acid battery, a nickel cadmium battery or a lithium battery or other rechargeable battery.
A feedback arrangement 29 preferably provides feedback with respect to the present voltage of the battery as well as the charging current. This information can be provided to the control arrangement 18. The control arrangement opens and closes switch 14 in a predetermined manner and defines an on time of the switch (Ton), indicated as 19, and an off time of the switch (Toff) indicated as 21. The on time charges the primary winding and is discharged during the off time. This is the typical operation of the flyback transformer.
The rectified AC signal has a frequency of approximately 120 Hz and the switch 14 is opened and closed at a rate at least 10 times this frequency. The control arrangement 18 can vary the charging current provided to the battery 30 by varying the on time. In order to provide a high power factor, the rate of change of time on is slow relative to the rectified AC signal 7. A very high power factor close to unity can be obtained if the rate of change of time on is 25 Hz or less, and preferrably, 12 Hz or WH-10,757CA
less. This slow rate of change of Ton is quite acceptable for charging of the battery 30.
As can be seen from the circuit of Figure 1, the traditional flyback transformer and charging circuit, does not include a bulk hold capacitor nor an in rush resistor to smooth the DC signal that is provided to the primary winding 10. This modification of the circuit significantly reduces the cost of the circuit due to a reduction in relatively expensive components and also allows for the improved power factor.
The feedback arrangement 29 for some application may provide very little feedback, if any. For example, for some battery applications, it may be sufficient to use a constant Ton such that the battery 30 is exposed to the same current throughout the charging cycle. The charging cycle can be stopped once the battery achieves a predetermined voltage. For other applications, it will be desirable to have a battery charging profile. Such profiles are desirable with some nickel cadmium batteries, as well as lithium batteries. In this case, a predetermined battery charging profile can be provided to the control arrangement 18 as indicated by the profile 32.
Such a profile can be a battery voltage relates to maximum charging current relationship and the control arrangement 18 can vary Ton relatively slowly to on average, achieve a desirable charging current. In this way, the maximum charging current is maintained below a certain level.
It can be appreciated from the circuit of Figure 1 that the pulsating signal provided to the primary winding 10 will result in a pulsating charging current for charging of the battery. Some smoothing of that charging current can be provided if desired on the secondary side, however, for most battery applications, this is not necessary. In any event, the recognition that the pulsating input current to the primary winding 10 is satisfactory allows vast WH-10,757CA
improvement in the power factor, excellent control of the charging characteristics of the battery, reduction in costs of the circuit due to fewer components, as well as reduced space requirements due to lesser components.
The charging circuit 2a of Figure 2 merely includes some additional components but basically operates in the same manner as Figure 1. On the input side, a small capacitor 31 has been provided to eliminate high frequency noise signals caused by the opening and closing of the switch 14. This is not a bulk hold capacitor. It merely prevents the high frequency signal being fed back to the power system. The primary side of the circuit has also been modified to include a circuit branch 33 across the switch 14 which acts as a clamp for flyback protection of switch 14 protecting it against over voltage.
The circuit of Figure 2 also shows an auxiliary power arrangement 41 used to provide power to the control arrangement 18. On the battery side of the circuit, a battery filter arrangement 43 is shown which can modify and smooth the charging current to the battery 30, if necessary. A feedback arrangement 29 is also provided.
The simplified charging circuit of Figures 1 and 2, has particular application for applications up to 250 to 300 watts. This power limitation is primarily determined by the availability of suitable components for the circuit at reasonable costs. If there is an application for higher power requirements, rather than increasing the circuit components, it may be preferrable to parallel the design.
The power factor is easily controlled as the rate of change of Ton necessary to achieve a particular charging of a battery is quite tolerant, and thus the feedback arrangement can be slow, relative to the input signal.
This allows an average or dampened feedback response and avoids wide variations in Ton. Most of the WH-10,757CA
benefits with respect to the power factor correction have been achieved due to the elimination of the in rush resistor and the bulk hold capacitor of the traditional flyback transformer charging circuit.
Basically, the design accepts the pulsating DC
signal provided to the primary winding and if necessary or desired, suitable filtering of the charging current can occur on the secondary side of the circuit.
It can fully be appreciated that the electronic power switch shown as 14 can be any of the traditional devices such as bi-polar transistor mosfet transistor, IGBT
transistor, etc. The circuit design of Figures 1 and 2, allows for variation of the duration of Ton, however, any changes therein are relatively slow. This, to a large extent, provides the circuit with a generally constant duty signal. The power factor specification is met by slowly varying any change in Ton. Basically, Ton is constant as the input signal to the primary winding varies from one minimum through a maximum, to the next minimum. In fact, in the preferred embodiments, Ton would not change for several cycles of this signal. Ton can also be controlled by distinct steps and is general constant between steps.
_ g WH-10,757CA
The transferred power to the battery generally follows the following equation.
(Vin*Ton)2*Frequency Battery Power Out = ------------------------2* (Primary Inductance of T1) Where:
* means multiply Vin is the instantaneous voltage across T1 and the Electronic Switch Ton is the on time, in seconds Frequency is the frequency of the electronic switch operation in Hertz Primary Inductance of T1 is the primary inductance of T1 Battery Charger Power Out is the power delivered to the battery ignoring losses When Vin, the instantaneous rectified line voltage is integrated over one complete line cycle, the output power of the charger is Battery Charger Power Out = (Line Voltage in rms)2* Constant The power factor correction will occur so long as the duty of the control circuit maintains nearly a constant duty when averaged over one half cycle of the AC input line voltage.
The output filter circuit of the flyback converter is designed to reduce as required the output ripple current as seen by the battery being charged. It can be nothing, a filter capacitor, combination of passive devices or may even include some form of active electronic circuit. The feedback circuit monitors the charging of the battery, sends a signal back to the electronic switch control circuit and adjusts the duty to increase or decrease the output power delivered to the battery.
_ g -wH-10,757CA
The operation of the charging circuit has been described with respect to a feedback arrangement where Ton is slowly varied relative to the input signal. It is also possible to vary the frequency of the switch 14 to thereby vary the charging current for the battery. It is also possible to use a combination of the variation of the frequency and the variation of Ton to achieve a desired charging characteristic. Varying the time on of the switch is more traditional and easier to accomplish, and as such, is the preferred control.
Modulation of time on or the switching frequency will result in the modulation of the input source current, thereby degrading the power factor.
If time on and frequency are held constant, a high power factor (better than .93) in practical implementation of the circuit is achieved. Power factors of better than .80 are easily obtained with slow modulation of time on or switching frequency.
In many cases, the switch 14 will operate at a frequency in the order of 100 KHz. The feedback for variation of Ton is preferrably of the order of 10 Hz. It is also possible to have different profiles for Ton that vary as a function of time. The important thing is that Ton over a number of cycles of the input signal does not widely vary and as such, a high power factor power is achieved. If certain applications do not require a high power factor correction, then the rate of change of Ton can approach the frequency of the input signal. Therefore, the rate of change of time on and/or frequency of the switch is controlled to meet a particular power factor specification.
Figure 3 shows various signals of the circuit.
WH-10,757CA
The charging circuit has been described with respect to charging a battery, however, the circuit can be used for other applications which can accept the output waveform of this circuit directly or modified on the secondary side of the circuit.
Although various preferred embodiments of the present invention have been described herein in detail, it will be appreciated by those skilled in the art, that variations may be made thereto without departing from the spirit of the invention or the scope of the appended claims.
Figure 1 shows a simplified charging circuit;
Figure 2 is a schematic of a simplified charging circuit with some additional components; and Figure 3 shows various signals of the signal.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The battery charging circuit 2 of Figure 1 receives an AC input signal at 4 and rectifies the AC signal at 6 to produce a pulsating rectified AC signal generally shown at 7. This signal is provided to a flyback transformer circuit comprising the primary winding 10, the controlled switch 14, the secondary winding 24, and the current rectifying diode 16. The secondary winding 24 provides a charging current for the rechargeable battery 30. This battery can be a lead acid battery, a nickel cadmium battery or a lithium battery or other rechargeable battery.
A feedback arrangement 29 preferably provides feedback with respect to the present voltage of the battery as well as the charging current. This information can be provided to the control arrangement 18. The control arrangement opens and closes switch 14 in a predetermined manner and defines an on time of the switch (Ton), indicated as 19, and an off time of the switch (Toff) indicated as 21. The on time charges the primary winding and is discharged during the off time. This is the typical operation of the flyback transformer.
The rectified AC signal has a frequency of approximately 120 Hz and the switch 14 is opened and closed at a rate at least 10 times this frequency. The control arrangement 18 can vary the charging current provided to the battery 30 by varying the on time. In order to provide a high power factor, the rate of change of time on is slow relative to the rectified AC signal 7. A very high power factor close to unity can be obtained if the rate of change of time on is 25 Hz or less, and preferrably, 12 Hz or WH-10,757CA
less. This slow rate of change of Ton is quite acceptable for charging of the battery 30.
As can be seen from the circuit of Figure 1, the traditional flyback transformer and charging circuit, does not include a bulk hold capacitor nor an in rush resistor to smooth the DC signal that is provided to the primary winding 10. This modification of the circuit significantly reduces the cost of the circuit due to a reduction in relatively expensive components and also allows for the improved power factor.
The feedback arrangement 29 for some application may provide very little feedback, if any. For example, for some battery applications, it may be sufficient to use a constant Ton such that the battery 30 is exposed to the same current throughout the charging cycle. The charging cycle can be stopped once the battery achieves a predetermined voltage. For other applications, it will be desirable to have a battery charging profile. Such profiles are desirable with some nickel cadmium batteries, as well as lithium batteries. In this case, a predetermined battery charging profile can be provided to the control arrangement 18 as indicated by the profile 32.
Such a profile can be a battery voltage relates to maximum charging current relationship and the control arrangement 18 can vary Ton relatively slowly to on average, achieve a desirable charging current. In this way, the maximum charging current is maintained below a certain level.
It can be appreciated from the circuit of Figure 1 that the pulsating signal provided to the primary winding 10 will result in a pulsating charging current for charging of the battery. Some smoothing of that charging current can be provided if desired on the secondary side, however, for most battery applications, this is not necessary. In any event, the recognition that the pulsating input current to the primary winding 10 is satisfactory allows vast WH-10,757CA
improvement in the power factor, excellent control of the charging characteristics of the battery, reduction in costs of the circuit due to fewer components, as well as reduced space requirements due to lesser components.
The charging circuit 2a of Figure 2 merely includes some additional components but basically operates in the same manner as Figure 1. On the input side, a small capacitor 31 has been provided to eliminate high frequency noise signals caused by the opening and closing of the switch 14. This is not a bulk hold capacitor. It merely prevents the high frequency signal being fed back to the power system. The primary side of the circuit has also been modified to include a circuit branch 33 across the switch 14 which acts as a clamp for flyback protection of switch 14 protecting it against over voltage.
The circuit of Figure 2 also shows an auxiliary power arrangement 41 used to provide power to the control arrangement 18. On the battery side of the circuit, a battery filter arrangement 43 is shown which can modify and smooth the charging current to the battery 30, if necessary. A feedback arrangement 29 is also provided.
The simplified charging circuit of Figures 1 and 2, has particular application for applications up to 250 to 300 watts. This power limitation is primarily determined by the availability of suitable components for the circuit at reasonable costs. If there is an application for higher power requirements, rather than increasing the circuit components, it may be preferrable to parallel the design.
The power factor is easily controlled as the rate of change of Ton necessary to achieve a particular charging of a battery is quite tolerant, and thus the feedback arrangement can be slow, relative to the input signal.
This allows an average or dampened feedback response and avoids wide variations in Ton. Most of the WH-10,757CA
benefits with respect to the power factor correction have been achieved due to the elimination of the in rush resistor and the bulk hold capacitor of the traditional flyback transformer charging circuit.
Basically, the design accepts the pulsating DC
signal provided to the primary winding and if necessary or desired, suitable filtering of the charging current can occur on the secondary side of the circuit.
It can fully be appreciated that the electronic power switch shown as 14 can be any of the traditional devices such as bi-polar transistor mosfet transistor, IGBT
transistor, etc. The circuit design of Figures 1 and 2, allows for variation of the duration of Ton, however, any changes therein are relatively slow. This, to a large extent, provides the circuit with a generally constant duty signal. The power factor specification is met by slowly varying any change in Ton. Basically, Ton is constant as the input signal to the primary winding varies from one minimum through a maximum, to the next minimum. In fact, in the preferred embodiments, Ton would not change for several cycles of this signal. Ton can also be controlled by distinct steps and is general constant between steps.
_ g WH-10,757CA
The transferred power to the battery generally follows the following equation.
(Vin*Ton)2*Frequency Battery Power Out = ------------------------2* (Primary Inductance of T1) Where:
* means multiply Vin is the instantaneous voltage across T1 and the Electronic Switch Ton is the on time, in seconds Frequency is the frequency of the electronic switch operation in Hertz Primary Inductance of T1 is the primary inductance of T1 Battery Charger Power Out is the power delivered to the battery ignoring losses When Vin, the instantaneous rectified line voltage is integrated over one complete line cycle, the output power of the charger is Battery Charger Power Out = (Line Voltage in rms)2* Constant The power factor correction will occur so long as the duty of the control circuit maintains nearly a constant duty when averaged over one half cycle of the AC input line voltage.
The output filter circuit of the flyback converter is designed to reduce as required the output ripple current as seen by the battery being charged. It can be nothing, a filter capacitor, combination of passive devices or may even include some form of active electronic circuit. The feedback circuit monitors the charging of the battery, sends a signal back to the electronic switch control circuit and adjusts the duty to increase or decrease the output power delivered to the battery.
_ g -wH-10,757CA
The operation of the charging circuit has been described with respect to a feedback arrangement where Ton is slowly varied relative to the input signal. It is also possible to vary the frequency of the switch 14 to thereby vary the charging current for the battery. It is also possible to use a combination of the variation of the frequency and the variation of Ton to achieve a desired charging characteristic. Varying the time on of the switch is more traditional and easier to accomplish, and as such, is the preferred control.
Modulation of time on or the switching frequency will result in the modulation of the input source current, thereby degrading the power factor.
If time on and frequency are held constant, a high power factor (better than .93) in practical implementation of the circuit is achieved. Power factors of better than .80 are easily obtained with slow modulation of time on or switching frequency.
In many cases, the switch 14 will operate at a frequency in the order of 100 KHz. The feedback for variation of Ton is preferrably of the order of 10 Hz. It is also possible to have different profiles for Ton that vary as a function of time. The important thing is that Ton over a number of cycles of the input signal does not widely vary and as such, a high power factor power is achieved. If certain applications do not require a high power factor correction, then the rate of change of Ton can approach the frequency of the input signal. Therefore, the rate of change of time on and/or frequency of the switch is controlled to meet a particular power factor specification.
Figure 3 shows various signals of the circuit.
WH-10,757CA
The charging circuit has been described with respect to charging a battery, however, the circuit can be used for other applications which can accept the output waveform of this circuit directly or modified on the secondary side of the circuit.
Although various preferred embodiments of the present invention have been described herein in detail, it will be appreciated by those skilled in the art, that variations may be made thereto without departing from the spirit of the invention or the scope of the appended claims.
Claims (10)
1. A battery charging circuit comprising means for receiving an AC input signal means for rectifying said AC signal to produce a non constant DC signal and providing said rectified signal to an input of a fly back transformer circuit, said fly back transformer circuit comprising a primary winding in series with a switch and a secondary winding associated with said primary winding and having a diode, said secondary winding providing a current for charging a battery, a control arrangement controlling the opening and closing of said switch and thereby define a time on and a time off of said switch, said control arrangement controlling said time on as required to meet a defined power factor specification.
2. A battery charging circuit as claimed in claim 1 wherein said control arrangement controls the rate of change of time on to met the defined power factor specification.
3. A battery charging circuit as claimed in claim 1 wherein the rate of change of time on is slow relative to the frequency of the AC input signal.
4. A battery charging circuit as claimed in claim 3 wherein the rate of change of time on is slowly varied by said control arrangement to met said power factor specification and to met a predetermined battery charging specification.
5. A battery charging circuit as claimed in claim 4 wherein said circuit includes an input arrangement for entering a battery charging specification and said control arrangement varies time on to met the battery charging specification.
6. A battery charging circuit as claimed in claim 1 wherein said rectified AC signal applied to said primary winding continuously varies from about zero volts to a maximum voltage and a charging current produced by said secondary winding continuously varies as a function of said rectified AC signal.
7. A battery charging circuit as claimed in claim 6 wherein the percentage variation of said charging current during each time off is at least 25%.
8. A battery charging circuit as claimed in claim 1 wherein said rectified AC signal is used to power said primary windings to expose the windings to the pulsating characteristic of said rectified signal and a battery charging current produced by said secondary winding varies as a function of said rectified AC signal.
9. A battery charging circuit as claimed in claim 1 in combination with a nickel cadnium battery or a lithium battery, and wherein said circuit is charging said battery.
10. A battery charging circuit as claimed in claim 9 wherein said rectified AC signal is used to power said primary windings to expose the windings to the pulsating characteristic of said rectified signal and a battery charging current produced by said secondary winding varies as a function of said rectified AC signal.
Priority Applications (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002298428A CA2298428C (en) | 2000-02-10 | 2000-02-10 | Battery charging circuit |
| CA 2306438 CA2306438A1 (en) | 2000-02-10 | 2000-04-20 | Dc power supply |
| CA002331916A CA2331916A1 (en) | 2000-02-10 | 2001-01-22 | Dc power supply |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002298428A CA2298428C (en) | 2000-02-10 | 2000-02-10 | Battery charging circuit |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2298428A1 CA2298428A1 (en) | 2000-05-23 |
| CA2298428C true CA2298428C (en) | 2000-11-14 |
Family
ID=31722345
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002298428A Expired - Fee Related CA2298428C (en) | 2000-02-10 | 2000-02-10 | Battery charging circuit |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2298428C (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2019224136A1 (en) * | 2018-05-21 | 2019-11-28 | Scandinova Systems Ab | Output rectifier and arrangement comprising an output rectifier |
-
2000
- 2000-02-10 CA CA002298428A patent/CA2298428C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| CA2298428A1 (en) | 2000-05-23 |
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| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed |