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Old 5th October 2007, 12:43 AM   #1
hags is offline hags  United States
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Default Zener regulated power supply

Excuse my ignorance on the subject.
I see zener regulated power supplies still in use, the Aleph P P/S comes to mind. I was wondering what if any advantage, using a shunt regulator with zeners would have over say a three pin device?
Is this thought to provide higher performance in audio applications? Why not use something like a 78** instead of the zeners?
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Old 6th October 2007, 01:30 PM   #2
AndrewT is offline AndrewT  Scotland
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Hi,
I think a shunt gives better high frequency performance than series, particularly when trying to make it cheaply with less than perfect components.

I also think that a CCS source with shunt gives valuable short circuit immunity that is difficult to achieve otherwise. Guess what I would use for the CCS? Yes, a 317+R.

Zener, if the inherent noise can be reduced low enough, is certainly very cheap.
A transistor multiplier wrapped around a zener gives enormous dissipation capacity with just three components, Z+C+Q.
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Old 8th October 2007, 12:33 PM   #3
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Hi,
for using zener for regulating voltage, the disadvantage is it cannot provide high current, there must be a resistor in serious with the cct.
zener is only good for voltage reference. another product TL431 is precision voltage reference, try to understand this component.
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Old 8th October 2007, 03:58 PM   #4
AndrewT is offline AndrewT  Scotland
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Hi,
a Zener shunt has to handle the CHANGE in current demand from the downstream circuit.
If, as with most small discrete circuits it is ClassA, then the change in current might be just a few mA.
Set the CCS to slightly exceed the the circuit quiescent demand and the zener then pulls the extra current that the circuit does not require. Or the zener takes less when the circuit demand increases.

Let's suppose the circuit needs 80mA +-10mA.
Set the CCS to 95mA. The Zener then passes 15mA+-10mA.
The maximum dissipation in the Zener is when the circuit is at minimum and this is 25mA*Vout. The circuit is also short circuit proof since the CCS is set to 95mA.
If Vin=24V and Vout=15V the CCS dissipation is 9V*95mA=0.86W and maximum Zener disspation is 15V*25mA=0.38W. Just about possible with a 400mW Zener.
But, you must never disconnect the amp from the shunt or you will burn out the Zener.
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