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Author Topic: Know a good PIN Switching Diode?  (Read 903 times)
KG4SGP
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« on: November 05, 2008, 04:45:22 PM »

Hi!

I know this topic gets brought up over and over again, but some of the links I've found on eham are outdated. Currently I’m working on a T/R switch for a transceiver.

I am looking for a PIN Diode that can handle 50W or more in the HF Bands. It would be nice if it is reasonably priced too! Know any part numbers?

Also a low dissipation PIN Diode would be nice, I don’t need 50W for all of the switching.

Thanks
73 KG4SGP - Jim
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WD4HXG
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« Reply #1 on: November 05, 2008, 06:26:18 PM »

M/A-COM has a series MA4P4000 Series you might consider.
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W4BQF
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« Reply #2 on: November 06, 2008, 02:18:46 PM »

You might want to reconsider how you have your question stated? Along with forward power handling ability, an equally important parameter is the reverse voltage. If your putting out 50w or 100w into an open circuit, what will be the maximum voltage reflected back to the PIN? The PIN will HAVE to withstand that reflected (or reverse) voltage or it will go 'poof'!

And believe me, sooner or later you WILL operate your radio into an open circuit!

Tom - W4BQF
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TANAKASAN
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« Reply #3 on: November 13, 2008, 02:09:46 PM »

Motorola 1N4007 diodes, and they MUST be Motorola devices.

Tanakasan
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WB2WIK
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« Reply #4 on: November 14, 2008, 02:07:42 PM »

>RE: Know a good PIN Switching Diode?       Reply
by TANAKASAN on November 13, 2008    Mail this to a friend!
Motorola 1N4007 diodes, and they MUST be Motorola devices.

Tanakasan<

::That's silly.  A 1N4007 made by anybody is a lousy PIN device that might be used in a pinch but has too short a minority carrier lifetime to be effective; and, Motorola hasn't made a 1N4007 since the mid-90s.  They turned all that over to ON Semiconductor in '99, and since before that their 1N4007 could have been manufactured in any one of five different facilities around the world, none of whom use the same processes. An "original" Motorola 1N4007 as made by them using the old double diffused process on 3" wafers would probably have to go back to the 80s or before.

WB2WIK/6
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W8JI
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« Reply #5 on: November 15, 2008, 03:38:15 AM »

Jim,

You'd be amazed at how difficult it is to find a didode with enough carier lifetime at 160 or 80 meters.

Browse the Macom site and look at carrier lifetime ratings.

73 Tom

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TANAKASAN
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« Reply #6 on: November 15, 2008, 08:37:27 AM »

http://www.google.co.uk/search?hl=en&q=1n4007+pin+diode&btnG=Google+Search&meta=

Lots of information on using the 1N4007 as a PIN diode including this quotation, "Elecraft  successfully applies the IN4007 as an RF switch in their K2 transceiver design. They are able to achieve very good IMD performance with this low cost device. "

Tanakasan
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W8JI
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« Reply #7 on: November 15, 2008, 05:09:34 PM »

Tanakasan,

The 1N4007 does not make a good PIN diode, but that does not mean it can act like a switch.

I can get great IMD performance with a regular diode if I bias it forward enough.

Even some of the longer carrier lifetime real P-I-N diodes are terrible at lower HF. When I design swithing gear or attenuators, including pulse modulators, it is a PITA to find a P-I-N diode that really acts like a P-I-N diode on HF.

You would need a carrier lifetime several times the period of an RF cycle, normally a few microseconds. Unfortunately by the time we get into the 2 or 3 uS range or longer the diodes get pretty expensive.

My measurements on 1N4007 and 1N5408 diodes showed they were never good P-I-N diodes at all. One test would be to try to use the diode as a rectifier at the operating frequency.

One trick around having to use a good diode is to connect two diodes in parallel for RF but in series for DC, with the anode and cathode reversed in one diode. This way each half cycle of RF tends to turn one diode on while the other is turned off.

If you look at the Ameritron QSK-5 I used 4 diodes in parallel that way to handle the 1500 watt line. with high carrier lifetime diodes like the 4P506 258 package in a normal circuit, IMD and distortion was a problem even with 2 amperes of holding current on lower bands.

I tried many times to use a 4007 and never found any that were good. But I do agree that if you dump enough current through them, as with any diode, you can make them work.

I never tested above lower HF because that was always where the problem was, so they might act like a PIN diode at 30 MHz. They sure don't on lower HF though.

73 Tom

 

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