How to make 0 to 12v Variable High Current Transformerless Electronic Power Supply or LED Driver or Electronic Dimmer which is Surge Free.

How to make a 0 to 12v Variable Transformerless Electronic Power Supply or LED Driver or Electronic Dimmer at home.

By: Alok kumar

In this post i am going to explain how to make a Electronic Dimmer or Transformerless Electronic Power supply or LED driver which can vary it output from o to 12v or even higher. This circuit can be a useful gadget for electronic hobbyist to test various appliances having different voltage rating for them. This circuit have a protection against Surge current while switched ON by Crowbar Network attached to its output. This design ensures that high current value is availabe at all voltage levels . So without wasting time lets get started....

I have previously explained various power supply on my blog but today we are going to learn a little bit about how to protect surge current from the circuit. 

Previously i had explained about how to make a variable high current, high voltage from 0v to 300v using a Mosfet and transistor.

Today we will see how to use Thyrister or SCR (Silicon Controlled Rectifier) for making a variable voltage high current surge free transformerless electronic power supply or Led driver or Electronic Dimmer by using a Crowbar Network.

Now lets start making this circuit.

Components Required:

Resistance: 1 Mega ohm, 22 ohm, 5k preset or potentiometer.

Diodes: four IN4007 diodes, 24v/400mW zener.

Capacitors: one 2uF/400V capacitor film type,  100uF/225V condensor DC.

Thyristor or SCR:  TIC 106,

Circuit Diagram

Here the 2uF/400V capacitor drawn high current and fixed voltage from mains as i already explained in my first blog. Lets review the working of capacitive or transformerless electronic power supply or LED Driver.

Here the capacitive reactance of capacitor(2uF/400V) connected at mains supply is:

x= 1/(2*pi*f*c)       where pi is 22/7, and f is the frequency of mains supply eg 50Hz or 60Hz 

then 

now rectance or impedence of whole ckt is = sqrt(R+x)                ehere R is the resistance or load attached in circuit

now current i=(v/z)                                   where v= mains voltage 220v or 111v 

So i think you have just recalled the concept lets move forward

Now we all know the output of capacitive circuit is unstable and have a surge current even when it is switched off.

So we are going to remove any surge current in circuit just by introducing a Croebar Network to above capacitive circuit. The network having SCR at extreme right of above diagram is the Crowbar circuit.

Lets understand the working of Crowbar Network.


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Working of Crowbar Network:

Here the zener along with R1(22ohm) OR P1(5k resistor) forms a king of voltage regulator or limiter which decide at what voltage level the Thyrister or SCR fires meand conducts.

Here P1 really varies the zener (24v/400mWatt)  from 0 to maximum rating which here is 24v approx(depends upon tje load attached).

Now by altering the the P1 we can set the firing angle of SCR according to requirement.

Let say, we set the value of P1 to get output of 12v then, when the main power is switched on the rectified DC voltage start appearing across D1 & P1.

At the moment when it reaches 12v barrier or level the SCR or Thyrister gets the sufficint power to get fired and when SCR fires it short circuit the output to ground leaving 0v output to output terminal

then charge stored in condenser (100uF/225V) get discharge and then scr will switched off due to unavailability of power for triggering on. Then charge on filter condenser starts accumulating again and this cycle starts repeating again and again.

In this way we get a controlled Output voltage and high current at output terminals.

If any surge current get generated it will be instantly passes through thyrister or SCR RESULTING IN short circuit and surge will be removed in this way everytime.

So enjoy making this cheap, easy and compact 0 to 12v variable high current transformerless electronic power supply or LED driver or small Electronic Dimmer.

Thank You for reading.