Wide input 350mA LED driver circuit based on NCL30000

Circuit explanation:

1. The input filter circuit plays a two-way filtering role, filtering out the interference from the power grid to the power circuit and the interference from the power circuit to the power grid. The filter inductors L2 and L3 in parallel with the resistors R2 and R3 play a damping and absorption role;

2. The anti-input peak interference suppression varistor suppresses the impact of the power grid input peak interference voltage on the normal operation of the power circuit;

3. The R CD absorption loop plays an absorption role to avoid generating a high peak voltage at the drain of the power switch Q3 and causing damage to the power switch Q3;

4. The flyback transformer can play the role of primary and secondary isolation of the switching power supply, and the value of the output voltage can be adjusted by adjusting the turns ratio. The auxiliary windings 1-2 of the flyback transformer can be used to power the NCL30000 after the NCL30000 completes startup, reducing the Power consumption generated by supplying power to the Q2 circuit;

5. The starting circuit and auxiliary power supply circuit are composed of peripheral components such as Q2, D9, D7, etc. D7, D8, R14 constitute the power supply circuit of the collector of photoelectric coupler U2; Q2, D9 and other peripheral components constitute a series voltage stabilizing circuit , which is NCL30000 Once the startup is completed, the NCL30000 is powered by the auxiliary power supply winding 1-2 circuit;

6. Rectifier and filter circuit 6 is an output rectifier and filter circuit;

7. Q4 and D11 form a series voltage stabilizing circuit to supply power to U3, U2 and U4;

8. The output overvoltage protection circuit is composed of D12 and Q5. Once the output DC voltage is higher than the regulated value of D12, Q5 is saturated and turned on. The COMP pin of the NCL30000 is made low through U2, and the NCL30000 stops working;

9. U4 is a reference voltage generating circuit, which provides a reference voltage for the third pin of U3 through U4. This reference voltage is used for the CV control loop of U3;

10. Complete the demagnetization detection of the flyback transformer through the auxiliary winding 1-2 of the flyback transformer, the resistor R16 and the Z CD pin of the NCL30000. Once the flyback transformer completes the magnetic reset, a new switching working cycle begins;

11. The external capacitor C9 connected to the 3rd pin Ct of NCL30000 is used to adjust the output characteristics of the power circuit, such as the position of the output current change point and the smoothness of the output change;

12. Q1 and thermistor RT1 (PTC) act as circuit over-temperature protection control. Once the circuit temperature exceeds the allowable operating temperature, the base potential of Q1 increases due to the voltage dividing effect of RT1, and Q1 becomes saturated and conducts, thereby turning off the NCL30000. The work of the voltage-stabilizing power supply circuit Q2 causes the NCL30000 to stop working;

13. The external capacitor C9 connected to the 3rd pin Ct of NCL30000 is used to adjust the output characteristics of the power circuit , such as the position of the output current change point and the smoothness of the output change;

14. Power switch tube Q3 source current detection resistor, the detection voltage is sent to the 4th pin CS of NCL30000 through resistor R18, which plays the role of over-current limitation and protection of power switch tube Q3;

15. Y capacitor C10 (4.7nF) plays the role of filtering the power supply noise signal. It is a high-voltage withstand capacitor and has an obvious filtering effect of the power supply noise signal;

16. Resistors R30 and R31 are the input balancing resistors of the operational amplifier in the CC/CV control loop in the NCL30000 to ensure the low offset operating current of the operational amplifier;

17. Optocoupler U2 plays the role of primary and secondary isolation of the circuit to ensure reliable transmission of feedback sampling control signals;

18. Resistor R19 is the load operating current sampling resistor. The sampling signal is sent to the 6th pin of NCL30000 through resistor R30 and sent to the internal operational amplifier for CC control;

19. U3 uses LM2904 dual operational amplifier circuit to complete the CC/CV control of the circuit;

20. Capacitor C16 is the output filter capacitor.

Original circuit diagram