F0810NH thyristor

I didn't see a data sheet for the F0810NH, at least not easily, so the only thing I have to go on is a (correct?) 5.1A rating (and an extortionate GBP18.50 price, beside the "out of stock" notice), and that it has to be faster than the ST TYN812 (tgt = 2usec typical).

Based on (only) that perhaps you could look at the IR 10TTS08 which has a tgt of 800ns (typical).

Hopefully you have a bit more information to compare. The IR parts are cheap (about 1.50 US one-off) and in stock (in TO220) at Digikey.

Best regards, Spehro Pefhany

Spehro Pefhany wrote (in ) about 'F0810NH thyristor', on Fri, 15 Apr 2005:

I found a data sheet at:

tgt is typically 2 us, but the TYN812 doesn't trigger; ITrms is 8 A and VDRM is 800V. So the 10TTS08 is a good substitute.

Yes, I now have the data. Thank you very much. Maybe there is another fault. So far, I've replaced a 7556, a PNP small-signal transistor and the thyristor. This suggests to me a surge picked up by the fence, due to a fairly distant lightning strike, and there are several diodes in the circuit that might be damaged. The trigger pulse is reaching the gate, but its duration may be very short indeed; since it happens only about once every two seconds, it's a bit difficult to tell.

Are you sure it's not the gate *current*? The TYN812 needs 15mA at

Best regards, Spehro Pefhany

Spehro Pefhany wrote (in ) about 'F0810NH thyristor', on Fri, 15 Apr 2005:

No, I'm not sure of much about this. The F0810NH IGT spec is min 10 mA, max 25 mA. The gate is driven like this (use Courier font):

--+--| gate; source is grounded. | [1k] | Gnd

The charge dump from the 100 nF is presumably limited to about 1 A(!) with a 12 V supply. I can look at the voltage across the 10 ohm with a DB scope to see what current is actually flowing, if any.

I wonder if the Zetex xistor or the 10R could be damaged. Maybe measure the latter in-circuit and pull the ZTX450 and check hFE in your multimeter? This would be more plausible if the SCR failed with an open to the cathode, thus allowing current to flow back to the drive circuit.

Best regards, Spehro Pefhany

Spehro Pefhany wrote (in ) about 'F0810NH thyristor', on Fri, 15 Apr 2005:

I checked the transistor. But I found why the thyristor wasn't firing; the gate wasn't in contact with its pad, which is very small. I should learn to solder, or rather see, better. Now it fires, but at about 34 V on the storage capacitor, and I suspect that should happen at about 200 V.

The plot thickens.

Limitations are also due to input pulse amplitude, as this is an emitter-follower.

RL

legg wrote (in ) about 'F0810NH thyristor', on Sat, 16 Apr 2005:

It was firing at 34 V because the 1 ohm resistor that senses the storage capacitor charging current was open-circuit. It all works now.

Thanks to all for help and interest. I'm leaving this NG now, because I can't spare the time to keep up, but I may be back one day.