This article covers the working, circuit, advantages, disadvantages and application of Transformerless power supply.
In general, DC power supplies convert Alternating current to Direct Current ( small DC voltage ) using step-down transformers or SMPS ( Switch Mode Power Supply ). These power supplies include many steps to step down DC. For small applications these steps acts major disadvantage. That are –
- High cost
- Needs bigger space
What is transformerless power supply ?
A transformer-less power supply is a circuit that converts high voltage AC input ( 230 v ) to low voltage DC at low current, without using a transformer. It is used where there is less space for circuit.
Working principle of Transformerless power supply
The working principle of transformerless power supply includes voltage divider circuit. It converts single phase AC voltage to desired low voltage DC. The concept of this power supply involves voltage division, rectification, regulation and current limit.
The capacitor 225j drops down the 230 V AC voltage to about 24 V Ac. The 1 MΩ resistor that shorts the capacitor is called bleeding resistor, the purpose of this resistor is to discharge the capacitor when the circuit is switched off.
Further, the circuit has bridge rectifier that converts alternating current to direct current. The Zener diode next to it regulates voltage to desired level and 470 µf capacitor smooth the flow of current. The 100 Ω resistor limits the flow of current in the circuit.
The components required for transformer less power supply are as follows
- 225j / 400 V capacitor
- 470 µf / 25 V capacitor
- In 4007 diode x 4
- Zener diode ( 5v / 9v / 12v / 15v )
- 1 Mega Ohm 0.25 W resistor
- 100 Ohm 2 W resistor
- Connecting wires
- Veroboard / Breadboard
The circuit diagram for the transformer less power supply
The capacitor ( 225j / 400v ) drops the voltage, rectifier converts it to DC, Zener diode regulates the voltage and resistor limits the current flow.
Connect the wires step by step as mentioned below –
- Take 225j capacitor and short its terminal using 1 MΩ discharging resistor.
- Make a bridge rectifier using in4007 diode as shown in circuit diagram.
- Now connect one terminal of 225j capacitor to bridge rectifier as shown.
- Connect 100 Ω resistor to bridge rectifier as shown.
- Connect Zener diode with voltage according to your need.
- Add a 470 µf / 25 V filter capacitor to DC output of bridge rectifier.
- Our circuit is now ready. Apply AC input to free terminals of 225j capacitor and 100 Ω.
- Small circuit
- Low current
- Dangerous ( no insulation / no galvanic isolation )
- Low current
Application of transformerless power supply
- Low current consumption devices that operates on low DC voltage.
- It has very small circuit that takes very small space. It can easily be fit into small devices.
- Used as charger in emergency lights and bug zapper, etc.
- This circuit is used as LED driver in cheap household LED bulbs.