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Re: [Amps] Need Zener for 2KD-3

To: "Manfred Mornhinweg" <manfred@ludens.cl>, <amps@contesting.com>
Subject: Re: [Amps] Need Zener for 2KD-3
From: "Carl" <km1h@jeremy.qozzy.com>
Date: Tue, 3 Feb 2015 15:28:45 -0500
List-post: <amps@contesting.com">mailto:amps@contesting.com>


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From: "Manfred Mornhinweg" <manfred@ludens.cl>
Sent: Tuesday, February 03, 2015 8:36 AM
To: <amps@contesting.com>
Subject: Re: [Amps] Need Zener for 2KD-3

Bill,

I need a zener for my 2KD-3. It's a 1N4561. It appears that they are really hard to find and exorbitantly expensive when you do.

Power zeners are very much out of fashion. They have a tendency to burning out after some time, even when used perfectly within rated specs, and it seems that this made them impopular in new equipment.

>  Has anyone found a source for a replacement at a reasonable cost?

My way to replace power zeners is to use a common low power zener together with a power transistor and a small resistor. The zener goes collector to base, the resistor base to emitter. The transistor is selected to comfortably handle the voltage, current and power, the zener is a low power unit (typically either 1 watt or 0.4 watt) with a voltage 0.6V lower than the original power zener, and the resistor's value is chosen to bias the small zener to about 10% of its maximum current, with 0.6V across the resistor.

It's your choice whether to use an NPN or PNP transistor. If one side of the power zener goes to ground, it's often very convenient to select the transistor polarity so that its collector will be at ground. That way you can bolt it to the chassis for heatsinking, without needing any insulation. Of course you must connect the zener in the proper way, according to transistor polarity.

This solution has a more stable voltage than a series string of diodes, uses fewer components, and doesn't need any extra support, because the two small parts are simply soldered to the transistor, which is bolted to the chassis or a heat sink. It's also suited to replace higher voltage zeners, which is impractical using diode strings.

Manfred


Dentron did that as far back as the late production Clipperton L and there were likely others prior. The 10-50W zener is a joke

Carl
KM1H
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