wimpy diode

How is that e-phemt Vgs bias point to change with temperature? Would the B-E junction TC even be in the right direction?

piglet

Or two schottky diodes in series?

piglet

BCX70_as_Diode.JPG

I use a BAV199W if I want a high forward drop or vanishingly small reverse current. Vf is not very well constrained by worst case limits in the datasheet though.

Allan

In some companies there could be a risk that someone in Marketing will change the LED colour to blue without asking you, because the blue LEDs fitted under his car look so good.

Right, though you've got no emitter resistor then, and are wholly dependant on tr characteristics.

| | R | | _|c +------(_) | |e D | | D D | | | +--------+---

NT

If base diodes temp rise is half as much as the tr, you're good :) Easily arranged, but of course short term power dissipation variations will not go so well, and T_amb is uncompensated.

NT

One of those 2mVs nicely compensates the tr. So halve the diode temp rise...

NT

I've got a graph from who knows where that shows 1N458 0.8v @ 10mA. FWIW.

NT

Not in my company! Manufacturing must use the BOM, and only an ECO can change the BOM, and I sign all the ECOs.

Add a TEC to compensate!

It's true that power dissipation in the transistor will warm it up, and change its Vbe. So a trick like this will never be really accurate. But it is cute.

or make the temp rise equal with 2mV LED and tamb is also compensated

-Lasse

Sorry, I've never figured out how to do that.

I suspect that it's about the right amount and direction. I suppose I should measure it. Snarl. Snap.

If you want crazy low reverse current, consider the c-b junction of a BFT25.

That reverse leakage was about at my measurement resolution limit.

I think for exactly 800mV I'd be tempted to just slap an AP2127 down there- SOT-23-5 and you get 800mV +/-2% with no additional parts (just an output cap). Less than 10 cents in quantity, and it can be used in other applications. Even has a shutdown input.

--sp

I find that Blue LED's create a blue fog of dispersed light vs. Green, amber or Red LED's.

It's particularly annoying.

Cheers

Thanks, but I don't need that precision, and we have the BCX70 in stock.

Putting more parts into stock is generally avoided. We have 6469 parts already, 3.03 million pieces.

Ouch. JIT.

NT

I think at one time JL said they had more than 100 types of LDO alone in stock.

--sp