# Zener diodes in parallel

#### FuneralHomeJanitor

Joined Oct 12, 2019
54
Hey everyone, this might be a silly question but if I use a series resistor and two 1W;12v zener diodes in parallel, will those diodes let me use up to 2W With 12 V regulation?

#### BobTPH

Joined Jun 5, 2013
8,989
It would be better if you used a series resistor for each one. This would make allowance slightly different breakdown voltages. If you don’t, one will take more current than the other and exceed its rating.

#### dl324

Joined Mar 30, 2015
16,924
if I use a series resistor and two 1W;12v zener diodes in parallel, will those diodes let me use up to 2W With 12 V regulation?
If you're talking about 2 zeners in parallel sharing a single current limiting resistor, that's not advisable. If the voltages are far enough apart, the lower voltage diode could fail. Then the other diode will fail if the first diode fails open.

Post a schematic showing your 12V regulator circuit.

#### crutschow

Joined Mar 14, 2008
34,454
You can use two 6V Zeners in series to get 12V.
That way there can't be any current hogging by one.
Also, the 6V Zener has a much lower temperature coefficient, so the voltage will be more stable with temperature (below).

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#### FuneralHomeJanitor

Joined Oct 12, 2019
54
If you're talking about 2 zeners in parallel sharing a single current limiting resistor, that's not advisable. If the voltages are far enough apart, the lower voltage diode could fail. Then the other diode will fail if the first diode fails open.

Post a schematic showing your 12V regulator circuit.
my goal is to precede this stage with a boost converter to step up 9v, the boost converter will be switched by an arduino mcu, and I was hoping to use this stage to regulate the voltage at 12 v but currently have 1W zeners to play around with, this is for a school project, I will use the zener regulator to provide a 12 v supply an amplifier of some kind, most likely darlington pair, based on 10 programmed settings from the arduino.

for example, setting 1 could be 10% power, and the arduino will send an input voltage to be amplified with a 12v max output in proportion to that input

I am not too well versed with power supplies, Ihaven’t done much with them especially hands on so assume I am an idiot on this subject, and although Ihave a few textbooks as resources they can’t answer the questions like these

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#### dl324

Joined Mar 30, 2015
16,924
I will use the zener regulator to provide a 12 v supply an amplifier of some kind, most likely darlington pair
A zener diode isn't an appropriate "voltage regulator" for a high power circuit. All of the power to the "load" needs to go through the series resistor Rs.

#### FuneralHomeJanitor

Joined Oct 12, 2019
54
A zener diode isn't an appropriate "voltage regulator" for a high power circuit. All of the power to the "load" needs to go through the series resistor Rs.
Zener isn’t appropriate for 3W? I have to order parts today for my project, I have decided to go with a zener that had a high enough power rating, I currently own 1W zeners and was hoping to experiment or do some basic tests. I wasn’t concerned about the resistors because I can put a few in parallel to divide the current among them, but I don’t see why a zener isn’t sufficient for a few watts, especially one that is rated appropriately for that kind of power. I also don’t intend to run the pump I am driving for long periods of time, I hope this reaches you soon because you’re the only thing stopping me from placing the order and I value your input despite me questioning it a bit, I only questioned you so I can better understand, not because I am disagreeing or looking to argue

#### dl324

Joined Mar 30, 2015
16,924
Zener isn’t appropriate for 3W?
If you have a 3W amplifier being supplied by the zener, at 100% efficiency, the amplifier would draw 250mA. That current, in addition to about 10mA required for the zener to regulate, has to go through the series resister. Since you haven't specified a supply voltage, I can't calculate power dissipation in the series resistor.

Assuming that the amplifier can be turned off, that 250mA would have to go through the zener. The zener would have to be larger than 3W.

You can't use 4 1W zeners in parallel and, for what it would cost you to buy a 5W zener, you could buy a 12V regulator.

#### BobTPH

Joined Jun 5, 2013
8,989
Zener isn’t appropriate for 3W? I have to order parts today for my project, I have decided to go with a zener that had a high enough power rating,
Why not use a 12V regulator? Is the something you think is better about using a Zener?

#### Alec_t

Joined Sep 17, 2013
14,318
You could use just one 12V Zener to control the base voltage for an NPN power transistor, then supply your amplifier from the transistor's emitter (albeit at about 11V).

#### BobTPH

Joined Jun 5, 2013
8,989
Ignored again.

#### MisterBill2

Joined Jan 23, 2018
18,535
It would be better if you used a series resistor for each one. This would make allowance slightly different breakdown voltages. If you don’t, one will take more current than the other and exceed its rating.
A zener diode voltage regulator is the very least efficient scheme possible, in addition to being a poor regulator . A 12 volt zener can work quite well as the reference source in a simple series pass regulator circuit.
Posts #6, #8, and #10 are applicable. If you don't follow the advice be prepared for less satisfactory results.