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
- Bulky
- 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.
Components Required
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
Circuit Diagram
The circuit diagram for the transformer less power supply
The above figure shows transformerless power supply. It is converting 220v AC to 5v, 9v, 12v, 15v with the use of capacitor (capacitive reactance ), resistor, bridge rectifier and Zener diode.
The capacitor ( 225j / 400v ) drops the voltage, rectifier converts it to DC, Zener diode regulates the voltage and resistor limits the current flow.
Connection
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.
Advantages
- Small circuit
- Cheap
- Low current
Disadvantages
- 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.
Author
Akash Sharma
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This is by far the best explanation I’ve found for a transformerless Ac to Dc converter.
Thank You.
Very simple, cheap, and brilliant design a bjg thank you Akash from Lusaka Zambia
Welcome.
Good article: I found a power supply of this type in a Vegas multicooker that came from Ukraine to the UK. The 11.2 V output was achieved by using two 5.6 V Zeners in series, after the bridge rectifier. It had blown both Zener diodes and to repair it, I used two replacement Motorola Zeners and also added a large resistor in parallel with the Zener chain, to draw away some microamps and prevent the Zener diodes from running too hot when there was no applied load on the DC output. I did not like the approach of having two Zener diodes in series as this is never an ideal design approach and depends on very good matching of the two diodes.
It’s very cheap and amazing circuit but can you tell me how much Ampere he provide?
0.1A
Please how do l increase the ampere to 1A as 0.1A will not charge the battery fast
Use transformer or SMPS.
Please how do l increase the ampere to 1A as 0.1A will not charge the battery fast
Sir I made the circuit 3 times but got 0v output. Is their any problem that i connected wrong phase and neutral. But when I changed according to the circuit diagram it does not work .
You can check the connection of bridge rectifier.