Forums

need really bad diode

Started by John Larkin September 20, 2022
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.

John Larkin wrote:
> 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 -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
On Tue, 20 Sep 2022 15:49:14 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>John Larkin wrote: >> 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)
On Tuesday, September 20, 2022 at 2:04:11 PM UTC-4, John Larkin wrote:
> 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.
Think of some other way. Diode solutions aren't all they're cracked up to be.
On 9/20/2022 21:04, John Larkin wrote:
> 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. >
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.
On Tue, 20 Sep 2022 13:46:39 -0700 (PDT), Fred Bloggs
<bloggs.fredbloggs.fred@gmail.com> wrote:

>On Tuesday, September 20, 2022 at 2:04:11 PM UTC-4, John Larkin wrote: >> 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. > >Think of some other way. Diode solutions aren't all they're cracked up to be.
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. https://www.dropbox.com/s/j72tytvzae0ubf2/T660_Regs_Sep_20.jpg?raw=1 Reg3 has an abs max input of 6 volts. I want at least 6.5 for my linear regs. I can't use 3.3 as the input to reg3 because +1 FPGA core has to come up before 3.3.
On Wed, 21 Sep 2022 00:13:29 +0300, Dimiter_Popoff <dp@tgi-sci.com>
wrote:

>On 9/20/2022 21:04, John Larkin wrote: >> 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. >> > >I am sure you'll find your way with the problem calling for the >diode without any help.
It's an electronic discussion group! In theory at least. Sometimes.
>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.
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.
On 9/21/2022 0:59, John Larkin wrote:
> On Wed, 21 Sep 2022 00:13:29 +0300, Dimiter_Popoff <dp@tgi-sci.com> > wrote: > >> On 9/20/2022 21:04, John Larkin wrote: >>> 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. >>> >> >> I am sure you'll find your way with the problem calling for the >> diode without any help. > > It's an electronic discussion group! In theory at least. Sometimes.
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.
> >> 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. > > Home-made is a lot of parts. Lots of integrated switchers work fine.
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.
> > Synchronous switchers can have bad EMI issues. > > Some parts are poorly defined as regards cap ESR and loop stability. > > Best to breadboard. >
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.
On 9/20/22 17:20, John Larkin wrote:
> On Tue, 20 Sep 2022 13:46:39 -0700 (PDT), Fred Bloggs > <bloggs.fredbloggs.fred@gmail.com> wrote: > >> On Tuesday, September 20, 2022 at 2:04:11 PM UTC-4, John Larkin wrote: >>> 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. >> >> Think of some other way. Diode solutions aren't all they're cracked up to be. > > 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. > > https://www.dropbox.com/s/j72tytvzae0ubf2/T660_Regs_Sep_20.jpg?raw=1 > > Reg3 has an abs max input of 6 volts. I want at least 6.5 for my > linear regs. I can't use 3.3 as the input to reg3 because +1 FPGA core > has to come up before 3.3. >
resistor and 5ish volt zener to ground? -- Regards, Carl
On Tuesday, September 20, 2022 at 11:04:11 AM UTC-7, John Larkin wrote:
> I want lots of voltage drop at 100 mA or so. > > A high voltage fast-recovery diode, like ES1G, might work.
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.