Switching Vs. Zener controlled supply

[LucasBS]

What are the pros an cons of a Switching mode power supply Vs. a zener controlled power supply (also known as emitter follower voltage regulator) ?

Everyone knows the first one. Here's a picture of the second one:

http://www.radio-electronics.com/in...erence-diodes/zener-psu-series-transistor.gif

 

[VEBill]

Switching is typically more efficient.

This is because the switching device is either on (low voltage drop, thus low power dissipation), or off (no current, thus low power dissipation).

In contrast, the linear regulator uses voltage drop over the transistor to control the output voltage. So high current and voltage drop at the same time, power dissipated as heat.

 

[ScottyUK]

Linear supplies are inherently quieter, whereas switchers can be made fairly quiet through careful design.

 

[OperaHouse]

Zener based supplies are becoming rare these days. They are neither accurate because of
transistor gain or zener tolerance. They can easily be replaced by a single part of the
78XX type that are offered in a variety of voltages and currents. They can also be adjusted
to any voltage above the base voltage by the addition of two resistors. Low drop out varieties
also allow a smaller differential between input and output voltages. If going the zener route,
consider using a LM431 as a replacement for the zener. Last couple hundred I bought only cost
about 3 cents each.

 

[Skogsgurra]

Of course, switchers are more efficient. But efficiency is not everything. For low power applications where you need a measly few hundred microamps at 3.3 V or so, a zener supply is OK. Even if you need one mA with occasional short pulses of higher current. And, yes, the LM431 is great. Doesn't cost much, is stable and low noise (which you can't say about zeners) and can easily be made to deliver any voltage at or above base voltage.

Gunnar Englund

http://www.gke.org

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