I want lots of voltage drop at 100 mA or so.
A high voltage fast-recovery diode, like ES1G, might work.
I suppose I could just put two ES1Gs in series, but that's not sporting.
MMBD5004S is two wimpy diodes in series, in SOT-23. That would drop about 2 volts at 100 mA!
This is a supply sequencing dilemma with the LT6803. A long story.
A BAV99 is even worse, once it warms up a bit (1.05V typ at 100 mA and
40C). I bet you have 30k of them in stock, amirite? They also come in SC70.Cheers
Phil Hobbs
SOT-23, only 2300! But it is an impressively bad diode.
SiC would work, but they are impressively(expensive + unavailable)
Think of some other way. Diode solutions aren't all they're cracked up to be.
I am sure you'll find your way with the problem calling for the diode without any help. I am going to insert a rant-ish comment about the "long story".
Every time I have used some readily available convertor part, LTC, Maxim many ears earlier, there were long stories. Which is why to this day I make my own regulators, 1/2 74hc123 and 1/2 lmc6482, typically. Plus a mosfet and its driver of course. Somewhat more complex and the story may be long again on some occasions but the ending is happy and calls for a lot less compromise. Having control over the loop overall etc. gives you that.
I just need to drop about a volt. A diode would do that just fine. Better yet 2 diodes in series so I can tune the drop.
It's an electronic discussion group! In theory at least. Sometimes.
Home-made is a lot of parts. Lots of integrated switchers work fine.
Synchronous switchers can have bad EMI issues.
Some parts are poorly defined as regards cap ESR and loop stability.
Best to breadboard.
I was just making an excuse for the rant I was about to post, of course I did not mean your post was inappropriate, quite the contrary.
They take more part obviously but they don't take a much larger area on the board. I am sure lots of integrated switchers work fine, and the few (not more than 5-6) I remember using did work but had either stability issues or noise or whatever, I don't remember, I only remember there were issues beyond my control as they were integrated. I may have been too demanding, of course.
Breadboard does not help much with switchers where routing is essential. But I have found out that even for my "home made" switchers ltspice is reasonably accurate evaluating stability over load and input variations, as well as step response etc.
resistor and 5ish volt zener to ground?
Or, a diode and 10 ohm resistor in series.
The structure of a PIN diode should give fairly high forward resistivity, though I'm not sure where that'd be found in a datasheet.
I really like TPS54302. It's a tiny SOT23 switcher, spread-spectrum, well behaved. But I can't get the TI Pspice model to work in LT Spice and I haven't the energy to learn Tina. I'll breadboard it.
I think I can use it as a +7 to -7 converter.
HV diodes are usually PINs. That shows up in the I:V curve.
On a sunny day (Tue, 20 Sep 2022 11:04:03 -0700) it happened John Larkin snipped-for-privacy@highlandSNIPMEtechnology.com wrote in snipped-for-privacy@4ax.com:
Old color sets had a 4 kV rectfer for focus, consisted of a ceramic tube with a zillion ? diodes in series
I think one plate/junction of a selenium rectifier dropped about 2 volts.
Webench requires a login (why make people log in to sell stuff?) and doesn't work on my machines.
I suspect that LT Spice added a couple billion dollars to ADI's purchase price of LT. And it crushed the sales of several expensive simulators. Mike E says that LT Spice is used 1000 times more than all other circuut sim programs.
There are advantages to breadboarding tricky stuff like switchers, even if the sims work. EMI. Thermals. Caps. Inductors. Reality.
Someone used to sell a pseudorandom noise generator chip. This is one!
tirsdag den 20. september 2022 kl. 23.20.55 UTC+2 skrev John Larkin:
NPN and two resistors?
On a sunny day (Wed, 21 Sep 2022 07:34:49 -0700) it happened John Larkin snipped-for-privacy@highlandSNIPMEtechnology.com wrote in snipped-for-privacy@4ax.com:
You could make something with a transistor Vbe and diode in series: | ___ \ / --- | _________ | | | | [ ] X |c | |/ |------| NPN | |\/e [ ] 1k | | | --------- |
Yes, there are lots of ways to use a transistor here. Don't need the upper series diode.
A small Darlington would give me more drop. Or one of those "logic transistors" with internal resistors.
The only darls we have in stock are ancient TO-92, hand load and solder stuff. Yuk. Mosfets pretty much made darlingtons obsolete.
A logic-threshold mosfet like FDV301, drain to gate, would sort of work. Roughly 2 volts at 200 mA; 400 mW is a bit much for a SOT23.
That would work, but is more parts than two diodes. I'd probably need something bigger than a SOT23.
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