Capacitor step-down LED drive circuit diagram using varistor

The figure shows a practical LED drive circuit 9 that uses capacitors to step down the voltage. The difference between this circuit and most current application circuits is that it is connected with a varistor (which can also be a transient voltage suppression diode), a varistor ( Or transient voltage suppression diode) can effectively discharge the sudden change of current during sudden voltage changes (such as lightning, starting of large power equipment, etc.), thereby protecting LEDs and other transistors. The response time of transient voltage suppressors is typically in the nanosecond range.

Figure Capacitor Buck LED Circuit

In the figure, the function of capacitor C1 is to step down and limit current; the function of VD1~VD4 is to rectify. For VD1~VD4 to rectify the alternating current, 1N4007 series rectifier diodes can be selected. The function of C2 and C3 is to filter the rectified pulsating DC voltage into a stable DC voltage. The withstand voltage of C2 and C3 should be determined according to the load voltage, which is generally 1.2 times the load voltage. The capacitance capacity depends on the load current. The function of the varistor Rv (or transient voltage suppression diode) is to discharge the instantaneous pulse high voltage in the input power supply to the ground, thereby protecting the LED from being broken down by the instantaneous high voltage.

The number of LEDs connected in series depends on their forward voltage (VF), and can reach up to about 80 in a 220V AC circuit. The withstand voltage of the capacitor is generally required to be greater than the peak value of the input power supply voltage. In a 220V/50Hz AC circuit, polyester capacitors or paper capacitors with a withstand voltage of more than 400V can be selected.