OnSemi ThermalTrak

Anybody has any interest in using OnSemi's ThermalTrak devices as the output devices in a Leach-clone?

They are not necessary the best method for biasing an output stage as evidenced by D.Self's work (Chapter Output Stage I) but I'd like to experiment with them. Besides, OnSemi claims measurable improvement.

If there is interest, then we can discuss them here. If not, I can proceed with trying them out and reporting in later. Got the parts in hand, so it'll be wasteful to not try them out.


One immediate question I have is whether to use a modified Vbe bias circuit (as per Leach) or use the internal diodes directly and forgo adjustment capability.

Thanks for looking.


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I was surprised myself at how fast OnSemi was. I ordered them last Friday and they came in today from Arizona.

I really didn't expect them to send any because I truthfully told them my sample request was for lab use, not production product.

Well I suppose it helps if you are currently an OnSemi customer, which I am. Hopefully you'll get yours soon.
Well, a quick exercise with the simulator shows a few possibilities. Think I'll use a modified VBE amplifier bias generator with the 6 diodes (3 output pairs) in the base-collector leg. Now all I need to do is try it out to see how well it tracks.


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2005-08-22 4:31 pm
I was surprised myself at how fast OnSemi was. I ordered them last Friday and they came in today from Arizona.

This is because the parts come from Digi-Key, next day air. Motorola has arrangements with Digi-Key to ship most of their samples from there.

I hope to God Motorola does very well financially, otherwise they may stop doing this.
Well, I use OnSemi parts at work and I can say that their sample service is never that fast (unless it's a part from their preferred 24hr program).

Many times, the parts come out of Asia. Even parts from within the US have about a one week turn.

Anyhoo, you're right. Digikey stocks them now and they're about the same as the regular MJL parts in price.

About using the thermal traks themselves, I was thinking of using them (their internal diodes that is) in a modified VBE multiplier, except for one device. That last device will be the temp sensor for the protection circuit. That means one output stage junction will be uncompensated. Assuming equal current sharing, I think that'll be ok. Comments, anyone?