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low-capacitance high-voltage diode

Started by Winfield Hill June 28, 2016
 I'm looking for a good low-capacitance SMT 600V diode.
 For example, Vishay says a 1N4005 is about 5pF at 100V.
 ON Semi says under 3pF.  Diodes, Inc says about 1.5pF.
 What to think?  I suppose new SMTs are similar to oldies.
 An RGL34J MELF shows about 1.5pF.  Small die is better,
 and I don't need a 1A rating.  Why not a 50mA rating?

 A Vishay Ultrafast UF4005 plot says about 6pF.  Ouch.

 Soft-recovery would be nice.  Diodes' CMR1U-06 part
 doesn't give its capacitance, but an app note says
 it's 80pF.   Whoa, that's way too much.

 Suggestions, favorites?


-- 
 Thanks,
    - Win
On 28 Jun 2016 12:22:38 -0700, Winfield Hill
<hill@rowland.harvard.edu> wrote:

> > I'm looking for a good low-capacitance SMT 600V diode. > For example, Vishay says a 1N4005 is about 5pF at 100V. > ON Semi says under 3pF. Diodes, Inc says about 1.5pF. > What to think? I suppose new SMTs are similar to oldies. > An RGL34J MELF shows about 1.5pF. Small die is better, > and I don't need a 1A rating. Why not a 50mA rating? > > A Vishay Ultrafast UF4005 plot says about 6pF. Ouch. > > Soft-recovery would be nice. Diodes' CMR1U-06 part > doesn't give its capacitance, but an app note says > it's 80pF. Whoa, that's way too much. > > Suggestions, favorites?
I did a 1400 volt flyback switcher and used MMBD5004S's in the C-W multiplier. That's a dual 400-volt diode in SOT23, 300 mA rating. They ran cool, unlike some other diodes that had a lot of reverse-recovery losses. The Diodes Inc data sheet claims 0.6 pF typ per diode at 0 volts. That's 800 volts and 0.3 pF for the diodes in series! https://dl.dropboxusercontent.com/u/53724080/PCBs/T840_E1.jpg -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On 06/28/2016 03:22 PM, Winfield Hill wrote:
> I'm looking for a good low-capacitance SMT 600V diode. > For example, Vishay says a 1N4005 is about 5pF at 100V. > ON Semi says under 3pF. Diodes, Inc says about 1.5pF. > What to think? I suppose new SMTs are similar to oldies. > An RGL34J MELF shows about 1.5pF. Small die is better, > and I don't need a 1A rating. Why not a 50mA rating? > > A Vishay Ultrafast UF4005 plot says about 6pF. Ouch. > > Soft-recovery would be nice. Diodes' CMR1U-06 part > doesn't give its capacitance, but an app note says > it's 80pF. Whoa, that's way too much. > > Suggestions, favorites? > >
Isn't "low-capacitance, high-voltage" sort of like a delicious, fat-free diet cheeseburger?
Winfield Hill <hill@rowland.harvard.edu> wrote:

> I'm looking for a good low-capacitance SMT 600V diode. > For example, Vishay says a 1N4005 is about 5pF at 100V. > ON Semi says under 3pF. Diodes, Inc says about 1.5pF. > What to think? I suppose new SMTs are similar to oldies. > An RGL34J MELF shows about 1.5pF. Small die is better, > and I don't need a 1A rating. Why not a 50mA rating? > > A Vishay Ultrafast UF4005 plot says about 6pF. Ouch. > > Soft-recovery would be nice. Diodes' CMR1U-06 part > doesn't give its capacitance, but an app note says > it's 80pF. Whoa, that's way too much. > > Suggestions, favorites?
Use several in series to reduce the capacitance, the increased conduction losses won't matter much at high voltage. -- ~ Adrian Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk
On Tue, 28 Jun 2016 13:06:30 -0700, John Larkin
<jjlarkin@highlandtechnology.com> wrote:

>On 28 Jun 2016 12:22:38 -0700, Winfield Hill ><hill@rowland.harvard.edu> wrote: > >> >> I'm looking for a good low-capacitance SMT 600V diode. >> For example, Vishay says a 1N4005 is about 5pF at 100V. >> ON Semi says under 3pF. Diodes, Inc says about 1.5pF. >> What to think? I suppose new SMTs are similar to oldies. >> An RGL34J MELF shows about 1.5pF. Small die is better, >> and I don't need a 1A rating. Why not a 50mA rating? >> >> A Vishay Ultrafast UF4005 plot says about 6pF. Ouch. >> >> Soft-recovery would be nice. Diodes' CMR1U-06 part >> doesn't give its capacitance, but an app note says >> it's 80pF. Whoa, that's way too much. >> >> Suggestions, favorites? > >I did a 1400 volt flyback switcher and used MMBD5004S's in the C-W >multiplier. That's a dual 400-volt diode in SOT23, 300 mA rating. They >ran cool, unlike some other diodes that had a lot of reverse-recovery >losses. > >The Diodes Inc data sheet claims 0.6 pF typ per diode at 0 volts. >That's 800 volts and 0.3 pF for the diodes in series! > >https://dl.dropboxusercontent.com/u/53724080/PCBs/T840_E1.jpg
I have 6000 in stock if you need a few. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
John Larkin wrote...
> > Winfield Hill wrote: > >> I'm looking for a good low-capacitance SMT 600V diode. > > I did a 1400 volt flyback switcher and used MMBD5004S's > in the C-W multiplier. That's a dual 400-volt diode in > SOT23, 300 mA rating. They ran cool, unlike some other > diodes that had a lot of reverse-recovery losses. > > The Diodes Inc data sheet claims 0.6 pF typ per diode > at 0 volts. That's 800 volts and 0.3 pF for the diodes > in series! > >https://dl.dropboxusercontent.com/u/53724080/PCBs/T840_E1.jpg
Hey, those are awesome! About 0.4pF each at 100V, and 1/2 0.52pF at 50V = 0.25pF at 100V, even better yet! What's-more I had saved the datasheet after seeing you use them in your T840 (but without useful identifying info). I had thought you were using a '4004 variant. They'll be perfect, thanks! -- Thanks, - Win
I was gonna tease with "tube" something or other, but 6AL5 is a couple pF, 
even 1X2A (not that you could handle the voltage drop).  2-01C maybe, but 
they're really rare (Eimac microwave diode -- for RF voltmeter probes, it 
goes in the probe end).

In my defense, you can get a very accurate peak reading -- Vf(If = 0) is a 
little negative in fact, so there's no "0.6V" to worry about.

How many can you series up?  That's kind of along JL's idea.

I think HV diodes (>kV -- stacks of dies) are in that territory, but they 
often have crappy recovery, and obviously the voltage drop is high.  They're 
also kind of scarce.

Tim

-- 
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
Website: http://seventransistorlabs.com


"Winfield Hill" <hill@rowland.harvard.edu> wrote in message 
news:nkuipu027b1@drn.newsguy.com...
> > I'm looking for a good low-capacitance SMT 600V diode. > For example, Vishay says a 1N4005 is about 5pF at 100V. > ON Semi says under 3pF. Diodes, Inc says about 1.5pF. > What to think? I suppose new SMTs are similar to oldies. > An RGL34J MELF shows about 1.5pF. Small die is better, > and I don't need a 1A rating. Why not a 50mA rating? > > A Vishay Ultrafast UF4005 plot says about 6pF. Ouch. > > Soft-recovery would be nice. Diodes' CMR1U-06 part > doesn't give its capacitance, but an app note says > it's 80pF. Whoa, that's way too much. > > Suggestions, favorites? > > > -- > Thanks, > - Win
On Tue, 28 Jun 2016 18:28:09 -0500, "Tim Williams"
<tiwill@seventransistorlabs.com> wrote:

>I was gonna tease with "tube" something or other, but 6AL5 is a couple pF, >even 1X2A (not that you could handle the voltage drop). 2-01C maybe, but >they're really rare (Eimac microwave diode -- for RF voltmeter probes, it >goes in the probe end). > >In my defense, you can get a very accurate peak reading -- Vf(If = 0) is a >little negative in fact, so there's no "0.6V" to worry about. > >How many can you series up? That's kind of along JL's idea. > >I think HV diodes (>kV -- stacks of dies) are in that territory, but they >often have crappy recovery, and obviously the voltage drop is high. They're >also kind of scarce. > >Tim
I used to use 1B3 HV rectifier tubes as rectifiers and variable resistors, to charge an oil cap from a neon sign transformer. I drove the filament from a D-cell and a wirewound rheostat (with a long insulated shaft!), turned the knob until I got 7KV DC on the cap. So a 1B3 is a low-bandwidth amplifier with the filament voltage as the input. Amazing I'm still alive. A 1B3 with no filament power makes a nice 30KV capacitive probe. TEK used some tiny wire-lead pencil tubes as the HV rectifiers in their old tube scopes. An MMBD5004S costs 4 cents, 50 u$ per volt. Official HV diode stacks do tend to be expensive. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On Tuesday, June 28, 2016 at 12:22:47 PM UTC-7, Winfield Hill wrote:
> I'm looking for a good low-capacitance SMT 600V diode.
> A Vishay Ultrafast UF4005 plot says about 6pF. Ouch.
BAW101V is a dual, presumably matched in leakage, rated for series connection. As I read it, it's under 1 pf for series connection. <http://www.diodes.com/_files/datasheets/ds32178.pdf>
For me HV means a big gap, depletion region, distance.
which looks like HV ... C = e_0*Area/distance.
I know zilch about HV diodes. 

George H.