Hello Members,

I am trying to regulate voltage delivered to an inductive load using a Semikron SCR of 100A connected in anti parallel configuartion

I am attaching my circuit for firing scr , the problem is that the scr goes out of control after firing the circuit for about 2 to 3 times for 3 to four cycles (50hz) .It passes full current through the load , though the input is proper 200us pulses.

We are using a pic to generate a 5Khz pulse. R1 & R2 are 10 ohms 1W , I do not know how to calculate it,I have selected it randomly , also if you observe the output it is not proper as per the input, after introducing the diode the spikes were reduced (Which I have not depicted ).

I have used a snubber across the scr .

Please help me , I need some proper write ups about designing a firing card with pulse transformer (1:1:1) ,

With regards

 

Your circuit is incomplete. What drives the TIP122?

 

I am using PIC microcontroller which drives the TIP via a opto-coupler 4n35

 

Hello,

I posted this schematic a while ago. It may help.

Daniel.

http://forum.allaboutcircuits.com/attachment.php?attachmentid=834&d=1178300984

 

Thank you Dear Lightingman,
The problem is the output across 4 -3 & 5- 6 terminals.
On Turn On there is a sharp spike of about 5 V and then it falls back. I feel this determental for the inductive load we are firing.
I will post the DSO o/P when I go back to office.

 

Are you saying the SCR turns on and stays on?

 

I am firing the thyristor after detecting the zero Cross of the utility.

The SCR Turns On & OFF but in between it will conduct full voltage instead of what is desired.

 

Since this does not effect the turn on as per our further analysis Please close this topic

 

Thank you Dear Lightingman,
The problem is the output across 4 -3 & 5- 6 terminals.
On Turn On there is a sharp spike of about 5 V and then it falls back. I feel this determental for the inductive load we are firing.
I will post the DSO o/P when I go back to office.

I'm not surprised if you have seen sharp spikes at outputs as you are using the pulse transformer in flyback connection. It WILL generate high voltage spikes.

It should be connected as shown below.