HOW TO MAKE EASY TRANSFORMERLESS POWER SUPPLY

How to make Transformerless power supply

Generating Low voltage DC, from the 220v or 110v AC mains, is very useful and necessary in the field of electronics. Low voltage DC, like 5v, 6v, 9v, 12v, is used in electronics circuits, LED bulbs, toys and many household electronics items. Generally batteries are used to power them, but they need to be replaced time to time, which is not cost effective and also takes our time & energy. So the alternative is to generate the DC from AC mains, for which there are many AC-DC adapters are available, but what circuitry they are using inside?

The easy and straight forward approach is to use step-down transformer to low down the AC, but the disadvantages of using transformer are that they expensive in cost, heavy in weight and big in size. We have already covered this type of AC to DC conversion, using Transformer in this article Cell Phone Charger Circuit. And yes, we can also convert the High voltage AC into Low voltage DC, without using the Transformer, this is called Transformerless power supply. The main component of a Transformerless power supply circuit is Voltage dropping capacitor or X-rated capacitor, which are specially designed for AC mains. This X rated capacitor is connected in series of Phase line of AC, to drop the voltage. This type of Transformer less power supply is called Capacitor Power Supply.

Things we need:

X-Rated Capacitor

As mentioned they are connected in series with phase line of AC to lower down the voltage, they are available in 230v, 400v, 600v AC or higher ratings.

Below is the table for output current and output voltage (without the Load), of different values of X-rated capacitors:

Selection of voltage dropping capacitor is important, it is based on Reactance of Capacitor and the amount of current to be withdrawn. The Reactance of the capacitor is given by below formula:

X = 1 / 2¶fC

X = Reactance of Capacitor

f = frequency of AC

C = Capacitance of X rated capacitor

We have used 474k means 0.47uF capacitor and frequency of AV mains is 50 Hz so the Reactance X is:

X = 1 / 2*3.14*50*0.47*10-6 = 6776 ohm (approx)

Now we can calculate the current (I) in the circuit:

I = V/X = 230/6775 = 34mA

So that’s how the Reactance and Current is calculated.

Circuit Explanation

Circuit is simple, Voltage dropping capacitor of 0.47uF is connected in series with Phase line of AC, this is a non-polarised capacitors so it can be connected from any side. A 470k ohm resistor is connected in parallel of Capacitor, to discharge the stored current in the capacitor when circuit is switched off, thus preventing from electric shock. This resistance is called Bleeder resistance.

Further Bridge rectifier (combination of 4 diodes) has been used to remove the negative half component of AC. This process is called the Rectification. And 1000uF/50v capacitor has been used for Filtration, means removing the ripples in resulted wave. And finally a Zener diode of 6.2v/1w is used as voltage regulator. As we know this circuit provides approx. 12v output (see the table above), so this Zener diode regulate it to approx. 6.2v voltage and flow back the extra current. A different value of Zener diode can also be used for desired voltage like 5.1v, 8v etc. An LED is connected for indication and testing purpose. R3 (100 ohm) is used as a current limiting resistor.

Use 1 Watt or above (5w) rating resistor, especially resistor R4. Otherwise it will burn after some time. They are usually thicker than usual resistor. Below is the diagram for different type of resistors:

Advantages of this transformerless power supply over transformer based supply are that: It is cost effective, lighter and smaller.

Notes

· Make it on your own risk, its extremely dangerous to work with AC mains without proper experience and precaution. Do take extreme caution while building this circuit.

· Don’t replace X-Rated capacitor with normal capacitor, otherwise it will burst.

· If more output voltage and output current is required then use different value of X-Rated capacitor, according to the table.

· Only use 1 Watt or above (5w) rating resistor and Zener diode.

· A 1 ampere fuse can also be used before X-rated capacitor, in series with phase line, for safety purpose.

· IC voltage regulator can also be used in place of Zener diode for voltage regulation.