--------------------------------------------------
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
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|