SCR unwanted spurious firing. 3

[danielsoy]

Hi ppl, need advice to find out, what is causing this unwanted SCR firing.

Look:
Link

There u can see the signal at my BT152 SCR gate, that sometimes shows spurious firing,that
looks like a bridge, between two firing points.


If some one can help to discover the culprit, i may upload my circuit diagram.

Thanks a lot.

 

[danielsoy]

Heres a picture of the Drain-Source oscillogram, at 280vdc,
tested during a couple of seconds to avoid mosfet overheating.

Motor is no loaded, but running free.

Would like to know, if rise and fall time are ok, or must be improved.
IRF is working without snubber by now.

 

[itsmoked]

I'm not sure why you're wasting time on the 'other' method if you want a functional TRIAC method. There are a hundred million products out there using TRIACs successfully. There are scads of schematics and almost every TRIAC maker has extensive application notes on using their products. Find one and use it.

Virtually all of them require properly sized snubbers.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[danielsoy]

Thats right, I may even get a working dimmer for pennies,
but the fact is that i want learn something in the way about switching mosfets,
scrs and the like.


You are very kind to help me, thanx a lot!.

 

[LionelHutz]

I'm not sure what *.ms12 files are but if you want suggestions on your circuit then try posting a file type people can open.

That constant ringing on the positive part of the your FET waveforms would be rather concerning to me.

 

[danielsoy]

Hi Lionel, thanks for your reply.

Those are Msim files.

Overshoot is caused, at some point by gate drive from ne555 pwm and because of the lack of snubber across
mosfet.

That is an issue that I can deal with.

IRF is working good now and heating is moderate.

 

[danielsoy]

Look what I ´ve found about Mosfet´s ringing.