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Integrated power supply without main light
A transformerless or capacitive power supply can provide low DC voltage without a main light by using a series capacitor and rectification, suitable for small electronic circuits.
How It Works
A transformerless power supply, also called a capacitive power supply, steps down AC mains voltage without using a bulky transformer. It relies on a high-voltage capacitor in series with the AC input to limit current through capacitive reactance. The AC voltage is then rectified using diodes, and a Zener diode stabilizes the output voltage to a safe DC level for low-power electronics . Unlike typical designs with an indicator LED, a supply without a main light simply omits the LED, reducing power consumption and simplifying the circuit. The capacitor still controls current, and the Zener diode ensures voltage regulation.
Key Components
- Series Capacitor: Determines the current limit; must have a voltage rating higher than the AC peak (e.g., 400V for 220V mains) .
- Bridge Rectifier: Converts AC to DC.
- Zener Diode: Stabilizes the output voltage according to the load requirements.
- Optional Resistor: Can be added for surge protection or to discharge the capacitor safely when the supply is off .
Safety Considerations
- The output is not isolated from mains, so direct contact is extremely dangerous .
- Only suitable for low-power applications (typically <100 mA).
- Must be enclosed in a strong insulated box to prevent accidental contact .
- Avoid using for devices requiring galvanic isolation or high current.
Applications
- Small electronic circuits like ambient sensors, IoT devices, or low-power switches.
- Situations where space and cost constraints prevent using a transformer.
- Circuits where a main light or LED indicator is unnecessary, reducing power draw.
Limitations
- Cannot safely power high-current devices.
- No isolation from mains, so risk of electric shock is high.
- Voltage regulation depends on load; large variations in current can affect output stability . By carefully selecting the capacitor and Zener diode, a compact, transformerless power supply without a main light can reliably power small electronics while minimizing size and cost .
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