Amps
[Top] [All Lists]

Re: [Amps] Zener Diodes

To: amps@xxxxxxxxxxxxxx
Subject: Re: [Amps] Zener Diodes
From: MU 4CX250B <4cx250b@xxxxxxxxxxx>
Date: Sun, 28 May 2017 16:22:09 -0600
List-post: <mailto:amps@contesting.com>
Mike needed this as a replacement cathode bias diode in an old
homebrew 8877 amp with 2600V on the plate.  Manfred's suggestion is
the more contemporary solution, but in any case a 50W zener is way
overkill. A 10W zener would work just fine, and these are still
available without spending a fortune.
73,
Jim w8zr

Sent from my iPad

> On May 28, 2017, at 4:01 PM, Ron Youvan <ka4inm@xxxxxxxxx> wrote:
>
>>  On 05/28/2017 12:35 PM, Manfred Mornhinweg wrote:
>>
>> Mike,
>
>>> I need to know where to get a 8 volt 50 watt stud mount Zener diode 1n3303
>
>> Such 50W Zener diodes seem to have fallen out of favor with designers, 
>> because of their poor reliability. I have seen lots of them fail, in various 
>> applications. I wonder if any company is even making them anymore.
>
>> If you can't find some old stock, probably your best option is to use a 
>> common small (1W) Zener connected between collector and base of a suitable 
>> power transistor. Add a resistor (anything between about 47 and 68 ohm) from 
>> base to emitter, to bias the Zener into its plateau.
>
>> You can use either an NPN or PNP power transistor. I choose between them   
>> depending on which side of my Zener replacement I want to ground or attach 
>> to the heatsink. For a Zener replacement having the negative end attached to 
>> a grounded heatsink you want a PNP transistor.
>
>> TIP35 and TIP36 transistors are cheap, widely available, and typically
>
>  The TIP120 and TIP125 will each dissipate 65 Watts if properly heat
> sunk and they are Darlington type with a dc gain of approaching 1,000.
>
>> work well in this circuit, but their gain is a little on the low side, so 
>> they might overtax a small Zener if the load current is high. The 2SC5200 
>> and 2SA1943, available from Digikey, seem better choices, but I haven't yet 
>> used them. Same thing for the FJA4213 and FJA4313.
>
>> The Zener used should have a nominal voltage roughly 0.6V lower than the 
>> actual voltage you need.
>
>> Such a transistor + small Zener + resistor combination costs far less than a 
>> 50W Zener, if you can find one, and in my experience is more reliable.
> --
>  Ron  KA4INM - Youvan's corollary:
>                Every action results in unwanted side effects.
> _______________________________________________
> Amps mailing list
> Amps@xxxxxxxxxxxxxx
> http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@xxxxxxxxxxxxxx
http://lists.contesting.com/mailman/listinfo/amps

<Prev in Thread] Current Thread [Next in Thread>