The content of the invention
To overcome the shortcomings of that existing LED drive chip is existing using linear voltage regulator decompression control, the invention discloses
A kind of LED drive controls circuit.
LED drive controls circuit of the present invention, including direct-flow input end, DC output end, output voltage feedback end, root
The power tube for controlling the control loop of power tube duty cycle of switching according to output voltage feedback end and being connected with control loop;
Also include the first reference voltage, linear voltage regulator LDO, sampling resistor R4 and adjustment pipe, the sampling resistor R4 to connect
Be connected between DC output end VOUT and adjustment pipe drain electrode, adjustment pipe source electrode connection load LED, the control terminal of the adjustment pipe with
Linear voltage regulator output end connects, and two inputs of the linear voltage regulator connect the public of adjustment pipe and sampling resistor respectively
End and the first reference voltage;The adjustment pipe is with loading LED common port as output voltage feedback end;The second benchmark electricity
Press to be connected to the divider resistance string between direct-flow input end and ground.
Preferably, the control loop includes logic drive circuit, PWM comparators, error amplifier, the second reference voltage
And current sampling circuit, two inputs of the error amplifier connect the second reference voltage and output voltage feedback respectively
End, two inputs of the PWM comparators connect the output end of error amplifier and current sampling circuit, the PWM respectively
The output end connection logic drive circuit of comparator, the output end connection power tube control terminal of the logic drive circuit.
Preferably, the current sampling circuit includes the current sampling resistor and electricity being connected between power tube source electrode and ground
Electric pressure converter is flowed, the input connection power tube source electrode of the current-to-voltage convertor, output end is as current sampling circuit
Output end.
Preferably, in addition to the protection circuit that is connected with logic drive circuit of output end.
The present invention is applied in booster type LED drive circuit by combining switched-capacitor circuit and linear constant current LDO, control
The rechargeable energy path turn-on and turn-off to output capacitance are inputted, LDO is realized to LED ripple-free constant current and fed-back output voltage
Switching capacity loop is given, transmission energy is realized and supplies on demand, is realized using direct current input feedback into error amplifier pair
The direct sampling of input direct voltage, improves input response speed.
Embodiment
Below in conjunction with the accompanying drawings, the embodiment of the present invention is described in further detail.
LED drive controls circuit of the present invention, including direct-flow input end, DC output end, output voltage feedback end, root
The power tube for controlling the control loop of power tube duty cycle of switching according to output voltage feedback end and being connected with control loop;
Also include first reference voltage V REF, LDO, sampling resistor R4 and adjustment pipe M2, the sampling resistor is connected to directly
Flow between output end and adjustment pipe drain electrode, adjustment pipe source electrode connection load LED, the control terminal and LDO output ends of the adjustment pipe
Connection, two inputs of the LDO connect the common port and the first reference voltage of adjustment pipe and sampling resistor respectively;The tune
Homogeneous tube is with loading LED common port as output voltage feedback end;
The control loop includes logic drive circuit, PWM comparators, error amplifier, the second reference voltage and exchanged
Sample circuit, two inputs of the error amplifier connect the second reference voltage and output voltage feedback end respectively, described
Two inputs of PWM comparators connect the output end of error amplifier and alternating current sampling circuit respectively, the PWM comparators
Output end connects logic drive circuit, the output end connection power tube control terminal of the logic drive circuit.
Specifically, the current sampling circuit include being connected to current sampling resistor R3 between power tube source electrode and ground and
Current-to-voltage convertor, the input connection power tube source electrode of the current-to-voltage convertor, output end is as current sample electricity
The output end on road.
As shown in figure 1, system is divided into two large divisions, power tube M1 and output capacitance COUT form switching capacity controlling transmission
To the turn-on and turn-off of COUT energy pathways.LDO and adjustment pipe M2 is control LED output currents, and it is with exporting LED string string
The energy of connection, LDO and LED conductings comes from output capacitance COUT.The anode LED+, LED+ of M2 drain terminal connection load LED strip can
Reflect the size of energy on COUT electric capacity in real time, LDO positive input is connected with the first reference voltage.Adjusting pipe can be
PMOS or PNP pipe.
Using above-mentioned LDO and adjustment pipe control mode, eliminate and loaded caused by being fluctuated due to output voltage on LED
Fluctuation of pressure drop, make LED output currents more stable, while make the output voltage feedback terminal voltage for being input to Inner Control Loop
It is constant, reduce the power attenuation of control loop.
Using input voltage as 220V civil powers, output voltage is used to drive 28-60 LED light emitting diode, and output voltage exists
Tested exemplified by 80-200V excursion, the loss of control loop only changes 0.2W or so.It is considered that loss with
Output voltage is substantially unrelated.
Second reference voltage V REF2 is formed by the divider resistance string partial pressure being connected between direct-flow input end and ground, such as Fig. 1
Shown, the first divider resistance R1 and the second divider resistance R2 common port is divider node as the second reference voltage, the second base
Quasi- voltage is obtained by the voltage of direct-flow input end so that in booster type LED drive circuit, the change of input voltage can
Rapid feedback makes change of the control loop to input voltage adjust the change of power tube dutycycle in time to control loop.
Control loop preferably uses current feedback form, and the control loop includes logic drive circuit, PWM compares
Device, error amplifier, the second reference voltage and alternating current sampling circuit, two inputs of the error amplifier connect respectively
Two reference voltages and output voltage feedback end, two inputs of the PWM comparators connect error amplifier and exchanged respectively
The output end of sample circuit, the output end connection logic drive circuit of the PWM comparators, the output of the logic drive circuit
End connection power tube control terminal.Wherein the first reference voltage V REF1 can be produced by bandgap voltage reference output voltage partial pressure,
Partial pressure can use conventional electric resistance partial pressure form.
Preferably, protection circuit, such as overvoltage crowbar, overheating protection circuit etc. can also be set, it is defeated when detecting
Go out controls logic drive circuit to close power tube when voltage is excessive or power tube current is excessive.
Previously described each preferred embodiment for the present invention, if the preferred embodiment in each preferred embodiment
It is not obvious contradictory or premised on a certain preferred embodiment, each preferred embodiment can any stack combinations
Use, the design parameter in the embodiment and embodiment merely to clearly state the invention verification process of inventor, and
The scope of patent protection of the limitation present invention is not used to, scope of patent protection of the invention is still defined by its claims, all
It is the equivalent structure change made with the specification and accompanying drawing content of the present invention, similarly should be included in the protection model of the present invention
In enclosing.