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Guest

Thu Feb 07, 2019 1:45 am   



Hi

I need a supercheap fast diode (sub 1ns)

Been looking at MMBD1705A, and it's cheap

https://media.digikey.com/pdf/Data%20Sheets/Fairchild%20PDFs/MMBD170x(A).pdf

But, a regular BC847 is even cheaper and my application has less than 4V reverse voltage

Anyone know the reverse recovery time?

Cheers

Klaus

piglet
Guest

Thu Feb 07, 2019 8:45 am   



On 06/02/2019 11:46 pm, klaus.kragelund_at_gmail.com wrote:
Quote:
Hi

I need a supercheap fast diode (sub 1ns)

Been looking at MMBD1705A, and it's cheap

https://media.digikey.com/pdf/Data%20Sheets/Fairchild%20PDFs/MMBD170x(A).pdf

But, a regular BC847 is even cheaper and my application has less than 4V reverse voltage

Anyone know the reverse recovery time?

Cheers

Klaus


Pease "Troubleshooting Analog Circuits" page 69 suggests 0.1ns for
2N3904 see:

<https://www.dropbox.com/s/lhg4p0c5xlkl4tf/PeaseQdiodeE-BC.jpg?dl=0>

piglet

Winfield Hill
Guest

Thu Feb 07, 2019 4:45 pm   



klaus.kragelund_at_gmail.com wrote...
Quote:

I need a supercheap fast diode (sub 1ns)
Been looking at MMBD1705A, and it's cheap


You'll do much better with a Schottky diode,
they don't have significant reverse recovery.
You appear to also want low capacitance. Our
diode table, page 32, suggests the classic
1N6263 and 1N6263W, but there are other good
newer low-capacitance choices. For example,
the Skyworks SMS7621 has only 0.3pF near 0V.

For more current, to 15mA, try the classic
1N5711, only 1.4pF. For up to 350mA, I like
BAT54, but it has 10pF at low voltages.

I like the sensible SOD-323 package for diodes
(BAT54WS, 1N5711WS, SMS7630-011LF), about the
same size as the relatively-large 0805 part.


--
Thanks,
- Win

Winfield Hill
Guest

Thu Feb 07, 2019 5:45 pm   



Winfield Hill wrote...
Quote:

klaus.kragelund_at_gmail.com wrote...

I need a supercheap fast diode (sub 1ns)
Been looking at MMBD1705A, and it's cheap

You'll do much better with a Schottky diode,
they don't have significant reverse recovery.
You appear to also want low capacitance. Our
diode table, page 32, suggests the classic
1N6263 and 1N6263W, but there are other good
newer low-capacitance choices. For example,
the Skyworks SMS7621 has only 0.3pF near 0V.

For more current, to 15mA, try the classic
1N5711, only 1.4pF. For up to 350mA, I like
BAT54, but it has 10pF at low voltages.


The BAS70, BAS170 is similar to the IN5711,
and available in more variations. The 3pF BAS40,
BAS140 is intermediate between BAS70 and BAT54.

Quote:
I like the sensible SOD-323 package for diodes
(BAT54WS, 1N5711WS, SMS7630-011LF), about the
same size as the relatively-large 0805 part.


The 3-lead SOT-23 diode package is wasteful of
space, and common two-lad SOD-123 looks huge
next to the popular 0805 res / cap package.
Hence the SOD-323, even tho it has wimpy leads.
I have a roll of Bourns 0805 diodes, but stopped
using them after they discontinued it. :-(


--
Thanks,
- Win

Tim Williams
Guest

Thu Feb 07, 2019 11:45 pm   



Probably not good
https://www.seventransistorlabs.com/Images/2N3904_Recovery_BE.jpg

Much better B+C "diode" strapped.

Second the options others suggested: BAS70, 1N5711, etc. You didn't mention
forward drop or leakage so we have no choice but to assume those are exactly
what you're looking for... :-)

Tim

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

<klaus.kragelund_at_gmail.com> wrote in message
news:5a348a6f-defc-4130-9205-b80ec1cb1452_at_googlegroups.com...
Quote:
Hi

I need a supercheap fast diode (sub 1ns)

Been looking at MMBD1705A, and it's cheap

https://media.digikey.com/pdf/Data%20Sheets/Fairchild%20PDFs/MMBD170x(A).pdf

But, a regular BC847 is even cheaper and my application has less than 4V
reverse voltage

Anyone know the reverse recovery time?

Cheers

Klaus



Guest

Fri Feb 08, 2019 12:45 am   



On Thursday, 7 February 2019 15:55:49 UTC+1, Winfield Hill wrote:
Quote:
klaus.kragelund_at_gmail.com wrote...

I need a supercheap fast diode (sub 1ns)
Been looking at MMBD1705A, and it's cheap

You'll do much better with a Schottky diode,
they don't have significant reverse recovery.
You appear to also want low capacitance. Our
diode table, page 32, suggests the classic
1N6263 and 1N6263W, but there are other good
newer low-capacitance choices. For example,
the Skyworks SMS7621 has only 0.3pF near 0V.


I have been using the BAT54, but it has too much capacitance

The skyworks one is nice, but the price is, ahem, skyhigh ;-)

Quote:

For more current, to 15mA, try the classic
1N5711, only 1.4pF. For up to 350mA, I like
BAT54, but it has 10pF at low voltages.

I like the sensible SOD-323 package for diodes
(BAT54WS, 1N5711WS, SMS7630-011LF), about the
same size as the relatively-large 0805 part.

Cheers


Klaus


Guest

Fri Feb 08, 2019 12:45 am   



On Thursday, 7 February 2019 23:00:24 UTC+1, Tim Williams wrote:
Quote:


Nice measurement

Quote:

Much better B+C "diode" strapped.


Yes. I tried the B+E, but that was bad. B+C is a lot better than a BAT54
Quote:

Second the options others suggested: BAS70, 1N5711, etc. You didn't mention
forward drop or leakage so we have no choice but to assume those are exactly
what you're looking for... Smile


Nice hints, thanks

Cheers

Klaus

Winfield Hill
Guest

Fri Feb 08, 2019 4:45 am   



klaus.kragelund_at_gmail.com wrote...
Quote:

On Thursday, 7 February 2019 23:00:24 UTC+1, Tim Williams wrote:
Probably not good
https://www.seventransistorlabs.com/Images/2N3904_Recovery_BE.jpg

Nice measurement

Much better B+C "diode" strapped.

Yes. I tried the B+E, but that was bad. B+C is a lot better than a BAT54

Second the options others suggested: BAS70, 1N5711, etc. You didn't
mention forward drop or leakage so we have no choice but to assume
those are exactly what you're looking for... :-)

Nice hints, thanks


2N3904 50ns recovery time is better than BAT54's zero recovery time?
Lower capacitance, yes, that's why I suggested 1.4 and 3 pF parts.


--
Thanks,
- Win

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