Hello Everyone.

In recent i'm getting zener failures in one power supply. Its a 27V, 5%, 1W zener having 30K, 2W series resistor. All the failures are similar (early regulation). At 145-150V i/p this should start the regulation but it is starting 110-135V.

Please explain what was the causes for the failure of zener.

Izt : 9.5mA
Izm : 34mA

 

Why should regulation start with an input of 145-150V?

 

Umm... schematic? My ESP isn't working so well this lifetime.

 

Why should regulation start with an input of 145-150V?

It is using as an input higher voltage cutoff switch. When the input exceeds 145 has to regulate to cut off the output voltage. But in this case it was starting regulation early to the limit

 

It is using as an input higher voltage cutoff switch. When the input exceeds 145 has to regulate to cut off the output voltage. But in this case it was starting regulation early to the limit

Very interesting.

I still have no idea what "it" is without a schematic.

 

If the zener fails it likely has too much current flowing through it, i.e. greater than 34mA.

 

It would REALLY help if you posted some kind of a schematic. It would also help to know if the voltages you are talking about are all DC voltages.

Assuming DC voltages, then if you have the 27 V zener in series with a 30 kΩ resistor and have a nominal knee current of 9.5 mA, then at that current your total voltage across the zener and resistor would be 312 V.

What current are you shooting for in the zener at your 140 V to 150 V?

Keep in mind that zener specs usually do not guarantee a current below which the voltage isn't within spec, instead they give a current by which point the voltage IS within spec. This means that, in practice, the diode will be in spec at a current well below that.

 

Hello Everyone.

In recent i'm getting zener failures in one power supply. Its a 27V, 5%, 1W zener having 30K, 2W series resistor. All the failures are similar (early regulation). At 145-150V i/p this should start the regulation but it is starting 110-135V.

Please explain what was the causes for the failure of zener.

Izt : 9.5mA
Izm : 34mA

What diode are you using?
What are you expecting to happen?
Schematic, please.