12v Transformerless Power Supply Circuit Diagram

Transformerless Power Supply Circuit 220-12v

Introduction

Instead of using a series resistor to drop the voltage, many circuits can be powered by a series capacitor. However, this approach usually only allows one half-cycle of the mains waveform to produce a DC voltage. To overcome this limitation, a bridge rectifier can be used for full-wave rectification, which increases the amount of current that can be supplied and reduces the size of the filter capacitor. The following circuit diagram of 12v Transformerless Power Supply shown below achieves this by cleverly utilizing a zener diode as a normal diode that conducts current in the forward direction. During one half-wave of the AC cycle, the current flows through specific diodes, and during the other half-wave, it flows through different diodes.

Circuit Diagram of 12v Transformerless Power Supply

This project can be designed using a few basic components. The circuit diagram of this project is shown below.

12v Transformerless Power Supply Circuit Diagram

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Components List of 12v Transformerless Power Supply

Following is the list of all components used in this project:

100 ohms 1W Resister x 1
0.22uf 250v Capacitor x 1
470uf 15V Capacitor x 1
1N4004 Diode x 2
12V 1W Zener Diode x 2

Explanation of 12v Transformerless Power Supply

When an uncharged capacitor is connected, it initially draws a high charging current. To prevent any damage, a resistor is used to limit this current to a safe value.

It is important to note that in this circuit, and in the bridge rectifier version, the DC voltage’s zero voltage reference is not directly connected to the neutral line of the 230V circuit. Consequently, this type of supply cannot be used to drive a triac, which typically requires such a connection. However, circuits that use relays can benefit from full-wave rectification.

The value of the supply voltage depends on the chosen zener diodes’ specifications, which can be selected as desired. Capacitor C2 must be able to handle at least this voltage. The amount of current that can be delivered depends on the capacitance of capacitor C1. In this circuit, with a capacitance of 0.22μF (220nF), the current is approximately 15mA. Please note that this circuit is directly connected to mains voltage, which is extremely dangerous. Under no circumstances should you come into contact with this circuit while it is connected to the mains! It is crucial to safely house this circuit in a suitable enclosure.

Conclusion

In conclusion, the 12v Transformerless Power Supply described offers an alternative to using a series resistor for voltage dropping, utilizing a series capacitor and bridge rectifier. While there are limitations in terms of only utilizing one half-cycle of the mains waveform, the clever use of a zener diode allows for more efficient rectification. Safety measures must always be taken when working with circuits connected to mains voltage.

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