Firing circuit with AVR

Thread Starter

Far

Joined May 11, 2009
20
Hi all:)
I'm trying to design a Firing circuit to drive a simple Low voltage rectifier and inverter (1phase, 1A, ). now I need to know that I should design it in PWM mod?
and can I use an AVR to generate 6 pulse out?
it's my wonder if you could help me!
 

Thread Starter

Far

Joined May 11, 2009
20
dear all
I want to design an evaluation set for Industrial Electronics laboratory.
I need to design such a firing circuit to Excite thyristors in a low voltage(24 VAC, 12 VDC) rectifier & inverter circuits(in full bridge design).
the Inverter output is a square wave. since these circuits work in low power mod, it doesn’t make any problem!
now I want to know if I could design a digital firing circuit using AVR ?
regards
 

Wendy

Joined Mar 24, 2008
23,415
The problem is you are assuming we know what you are talking about. AVR? That and a schematic to base your question on would go a long ways.
 

R!f@@

Joined Apr 2, 2009
9,918
Thyristors are used in really powerful inverters . they go in the range of KW.
You should consider IGBJT's or MOSFET's
 

Thread Starter

Far

Joined May 11, 2009
20
24 VDC input/12 V-50 Hz sinusoidal wave in output/using Bridge 1phase design with 4 Thyristors or power MOSFET/ RL load(R=1 Ohm, L=10 mH)
enough information? or u wanna know how does it work?!:D
 

Thread Starter

Far

Joined May 11, 2009
20
Thanks for your constructive Help!:cool:
I cope with my problem by explain it to the other:)
if u found any problem in power electronics, I'm here to help you.
 

DickCappels

Joined Aug 21, 2008
10,153
I think you question would get a better reception on www.avrfreaks.net.

To fire a thyristor (through a transformer?), you should do it by sending a "picket fence" series of firing pulses that start at the phase that you would like the thyristor to start firing. I really doubt you can get the PWM outputs in any of the AVRs to do this for you without tricky real time firmware intervention. Instead, I think you would be better off to use a timer interrupt to create the dealy from zero crossing, then either the same timer again, or a better yet, a different timer interrupt to time the firing interval. The pulses themselves can be only a couple or few us wide, depending on the thyristor, and that can be timed in firmware.

Rather than timing directly from sensed zero crossings, I recommend using a timer in a free-running mode along with a zero crossing detector and some servo firmware (such as PID controller) to make a digital phase locked loop, locked to the power line zero crossings, and then time your thyristor firing from that. This way, you will greatly reduce the risk of accidentally firing from a glitch on the power line.

And one more thing...while debugging, use an isolation transformer if at all possible, but most importantly, remember to keep one hand in your back pocket (seriously!)
 
Top