This capacitor power supply can provide 12 volts DC current and 100 mA to power low current devices. It has surge protection and is completely isolated from the electrical network using two capacitors on the phase and neutral lines. Therefore, the connected device is safe even if the phase and neutral lines change.
Transformerless power supply is used to reduce the size and cost of electronic devices. Only low current devices can work on transformerless power supply since the output current is low. Unlike the resistive type power supply, the capacitive power supply isolates the mains from the circuit and reduces the mains to low voltage AC without generating heat. Therefore, energy loss due to heat generation is negligible. The power supply operates safely unless the capacitor burns out due to too high a surge current. Expensive equipment should not be connected to capacitive power supplies.
Do not use this power supply for testing prototypes or as a battery charger.
Don't build this on the breadboard. Use common PCB.
Circuit Description
1. A 250 Volt MOV is connected between phase and neutral as a surge protector.
2. Capacitors C1 and C2 are in series with the phase and neutral lines to reduce AC. C1 and C2 are 225 J, 600 volt AC capacitors that reduce 230 volts AC to low voltage AC through the property of capacitive reactance. The capacitor's output voltage varies slightly depending on the input AC voltage. The output current is around 100 -120 mA. The output current depends on many factors such as the quality of material used in the capacitor, the input AC voltage, etc. Therefore, accuracy in voltage and current will not be available in capacitor power supply. As a rule, every 1 uF can deliver a current of 80-100 mA.
3. R1 and R2 are bleeder resistors to remove stored current from C1 and C2 at shutdown. These capacitors can store over 400 volts which must be removed to avoid shock using the bleed resistor.
4. D1 to D4 forms a full wave bridge rectifier to convert AC to DC. IN 4007 diodes can handle up to 1 amp of current.
5. C3 is the smoothing capacitor to remove ripples from the rectified voltage. As a rule, the nominal voltage of the smoothing capacitor should be three times greater than the rectified voltage. Here a 60 volt capacitor is used. DC smoothing depends on the capacitor value. A default value is 470 uF. But clean, ripple-free DC will be available if the value increases to 1000 or 2200 uF.
6. Resistor R3 is the current limiter of the Zener diode ZD.
7. ZD is the 12 volt 1 watt Zener diode to regulate the output voltage to 12 volts DC. The Zener diode requires more than 2 volts more than its rated voltage for fast breakdown.
8. LED indicates output current. If LED is used at the output, there will be some voltage drop (about 1.6-1.8 volts) at the output. If 12 volts are required, omit the LED.
Fig. 1: Image of capacitor power supply
Note: 1.4 volt drop is due to LED
Circuit diagrams
| Capacitor Power Supply-circ_06 |  |
