SCR unwanted spurious firing.
SCR unwanted spurious firing.
(OP)
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.

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.





RE: SCR unwanted spurious firing.
Link
RE: SCR unwanted spurious firing.
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RE: SCR unwanted spurious firing.
Keith Cress
kcress - http://www.flaminsystems.com
RE: SCR unwanted spurious firing.
RE: SCR unwanted spurious firing.
Heres another video, where fault is more obvious:
Link
Snubber is already there, as u can see in the attached circuit diagram.
Load is 500 watts a hand driller, with 100uf capacitor in parallel.
RE: SCR unwanted spurious firing.
RE: SCR unwanted spurious firing.
As ITSMOKED and BRIANE22 already pointed, voltage rising rate across SCR anode-cathode,
was re-firing my SCR.
Snubber was there, but no really working...
20 ohms resitor (1 watt,sorry), in series with .1uf capacitor, was indeed open because
of heat.
Will keep testing the circuit to be sure thats is OK now, and
RE: SCR unwanted spurious firing.
RE: SCR unwanted spurious firing.
1W seems too low a rating for that. You might consider bumping it up to 3 or 5W. What happens is the 1W can run within its rating but still be so *(&#*$ hot as to oxidize and kill the solder joints holding it to the board.
Keith Cress
kcress - http://www.flaminsystems.com
RE: SCR unwanted spurious firing.
No spurious at all!
Thanks again to eng-tips ppl for your help
RE: SCR unwanted spurious firing.
After a couple of positive half cycles, triac cannot block negative half cycles,
So load (DC motor), stops turning and starts oscillating in its place under AC current.
(red window).
RE: SCR unwanted spurious firing.
Yuck. In some cases dVdT breakdowns can damage the triac and the damage can grow quickly to outright failure.
Keith Cress
kcress - http://www.flaminsystems.com
RE: SCR unwanted spurious firing.
Now i am a bit concerned about SCR and Triac erratic temper.
An spurious low angle firing, may cause the load to receive a lot of current.
Guess will try to control my motor, with a PWM signal driving an IRF840 at 310Vcc!
RE: SCR unwanted spurious firing.
RE: SCR unwanted spurious firing.
This time is not that bad, because its inside IRF840 SOA.
look:
RE: SCR unwanted spurious firing.
RE: SCR unwanted spurious firing.
Keith Cress
kcress - http://www.flaminsystems.com
RE: SCR unwanted spurious firing.
way to detect zero cross, and be sure that unwanted firing is 100% unlikely.
May be, I will try something with a PIC to avoid fake zero cross detections.
i like SCR because of its incredible current withstand capability.
Triac turn-off failure picture, was not from this motor control project, but from a coffee
expresso machine that I am trying to fix.
So far, pwm with irf is ok.Vcc was not raised to 310vdc, but just 160volts
because Mosfet in not mounted on the heatsink yet.
I keep in touch, Thanx.
RE: SCR unwanted spurious firing.
RE: SCR unwanted spurious firing.
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.
RE: SCR unwanted spurious firing.
Virtually all of them require properly sized snubbers.
Keith Cress
kcress - http://www.flaminsystems.com
RE: SCR unwanted spurious firing.
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!
RE: SCR unwanted spurious firing.
That constant ringing on the positive part of the your FET waveforms would be rather concerning to me.
RE: SCR unwanted spurious firing.
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.
RE: SCR unwanted spurious firing.