Summary of the invention
For overcoming the deficiency existing for existing LED drive chip employing linear voltage regulator step-down control, the invention discloses a kind of LED Drive and Control Circuit.
LED Drive and Control Circuit of the present invention, comprises direct-flow input end, DC output end, output voltage feedback end, the control loop controlling power tube duty cycle of switching according to output voltage feedback end and the power tube be connected with control loop;
Also comprise the first reference voltage, linear voltage regulator LDO, sampling resistor R4 and Correctional tube, described sampling resistor R4 is connected between DC output end VOUT and Correctional tube drain electrode, Correctional tube source electrode connects load LED, the control end of described Correctional tube is connected with linear voltage regulator output, and two inputs of described linear voltage regulator connect common port and first reference voltage of Correctional tube and sampling resistor respectively; The common port of described Correctional tube and load LED is as output voltage feedback end; Described second reference voltage is the divider resistance string be connected between direct-flow input end and ground.
Preferably, described control loop comprises logic drive circuit, PWM comparator, error amplifier, the second reference voltage and current sampling circuit, two inputs of described error amplifier connect the second reference voltage and output voltage feedback end respectively, two inputs of described PWM comparator connect the output of error amplifier and current sampling circuit respectively, the output of described PWM comparator connects logic drive circuit, and the output of described logic drive circuit connects power tube control end.
Preferably, described current sampling circuit comprises and is connected to current sampling resistor between power tube source electrode and ground and current-to-voltage convertor, and the input of described current-to-voltage convertor connects power tube source electrode, and output is as the output of current sampling circuit.
Preferably, the protective circuit that output is connected with logic drive circuit is also comprised.
The present invention is by being applied in booster type LED drive circuit in conjunction with switched-capacitor circuit and linear constant current LDO, control inputs is to the rechargeable energy path turn-on and turn-off of output capacitance, LDO realizes the ripple-free constant current of LED and fed-back output voltage to switching capacity loop, achieve transmitting energy to supply as required, adopt in direct current input feedback to error amplifier the Direct Sampling achieved input direct voltage, improve input response speed.
Embodiment
Below in conjunction with accompanying drawing, the specific embodiment of the present invention is described in further detail.
LED Drive and Control Circuit of the present invention, comprises direct-flow input end, DC output end, output voltage feedback end, the control loop controlling power tube duty cycle of switching according to output voltage feedback end and the power tube be connected with control loop;
Also comprise the first reference voltage V REF, LDO, sampling resistor R4 and Correctional tube M2, described sampling resistor is connected between DC output end and Correctional tube drain electrode, Correctional tube source electrode connects load LED, the control end of described Correctional tube is connected with LDO output, and two inputs of described LDO connect common port and first reference voltage of Correctional tube and sampling resistor respectively; The common port of described Correctional tube and load LED is as output voltage feedback end;
Described control loop comprises logic drive circuit, PWM comparator, error amplifier, the second reference voltage and alternating current sampling circuit, two inputs of described error amplifier connect the second reference voltage and output voltage feedback end respectively, two inputs of described PWM comparator connect the output of error amplifier and alternating current sampling circuit respectively, the output of described PWM comparator connects logic drive circuit, and the output of described logic drive circuit connects power tube control end.
Concrete, described current sampling circuit comprises and is connected to current sampling resistor R3 between power tube source electrode and ground and current-to-voltage convertor, and the input of described current-to-voltage convertor connects power tube source electrode, and output is as the output of current sampling circuit.
As shown in Figure 1, system is divided into two large divisions, and power tube M1 and output capacitance COUT forms the turn-on and turn-off of switching capacity controls transfer to COUT energy pathway.LDO and Correctional tube M2 is control LED output current, and it is connected with output LED string, and the energy of LDO and LED conducting is from output capacitance COUT.The drain terminal of M2 connects the anode LED+ of load LED strip, and LED+ can reflect the size of energy on COUT electric capacity in real time, and the positive input of LDO is connected with the first reference voltage.Correctional tube can be PMOS or PNP pipe.
Adopt the control mode of above-mentioned LDO and Correctional tube, eliminate the fluctuation of pressure drop because output voltage fluctuates on the load LED caused, make LED output current more stable, make the output voltage feedback end voltage constant being input to Inner Control Loop simultaneously, reduce the power loss of control loop.
Take input voltage as 220V civil power, output voltage is for driving 28-60 LED light-emitting diode, and output voltage is for example is tested in the excursion of 80-200V, and the loss of control loop only changes about 0.2W.Can think that loss and output voltage are substantially irrelevant.
Second reference voltage V REF2 is formed by the divider resistance string dividing potential drop be connected between direct-flow input end and ground, as shown in Figure 1, the common port of the first divider resistance R1 and the second divider resistance R2 is that divider node is as the second reference voltage, second reference voltage is obtained by the voltage of direct-flow input end, make in booster type LED drive circuit, the change of input voltage can rapid feedback to control loop, make the change of the change of control loop to input voltage timely Modulating Power pipe duty ratio.
Control loop preferably adopts current feedback form, described control loop comprises logic drive circuit, PWM comparator, error amplifier, the second reference voltage and alternating current sampling circuit, two inputs of described error amplifier connect the second reference voltage and output voltage feedback end respectively, two inputs of described PWM comparator connect the output of error amplifier and alternating current sampling circuit respectively, the output of described PWM comparator connects logic drive circuit, and the output of described logic drive circuit connects power tube control end.Wherein the first reference voltage V REF1 can be produced by bandgap voltage reference output voltage dividing potential drop, and dividing potential drop can adopt conventional electric resistance partial pressure form.
Preferably, can also protective circuit be set, such as overvoltage crowbar, overheating protection circuit etc., controls logic drive circuit when detecting that output voltage is excessive or power tube current is excessive and close power tube.
Previously described is each preferred embodiment of the present invention, preferred implementation in each preferred embodiment is if not obviously contradictory or premised on a certain preferred implementation, each preferred implementation can stack combinations use arbitrarily, design parameter in described embodiment and embodiment is only the invention proof procedure in order to clear statement inventor, and be not used to limit scope of patent protection of the present invention, scope of patent protection of the present invention is still as the criterion with its claims, the equivalent structure change that every utilization specification of the present invention and accompanying drawing content are done, in like manner all should be included in protection scope of the present invention.