Zener Regulation - how to clamp 36V ?

[ringo888]

Zener Regulation

Hi guys,

I have a switching regulator with a input range of 9-36V but the potential transient voltage input could exceed 100V. I thought of using a 36V Zenner across VIN and GND before the switching reg but when i try to simulate this using a spice program it doesn't clamp at the switching reg, am i missing something? also if the voltage from the battery were say 50V and i was using 36V zener to clamp, would this have a detrimental affect on the battery?

Thanks in advance,
Ringo

 

[hakeen]

Re: Zener Regulation

I guess if you correctly limit current sourced by battery, you will not only protect zener diode but also battery itself. There should be an intermediate stage between battery and diode (might be as simple as a resistor) to adjust voltage and limit power dissipation.

For Spice, do you use a general model or specific model?

Cheers

 

[ringo888]

Re: Zener Regulation

Thanks Hakeen,

Ahh yes i've now fitted a resistor in the spice before the zener and its performing as expected.

I'm using this for a high current application so don't really want to limit the current. Is there any other way of regulating (clamping) the voltage to 36V without fitting a series resistor to VIN? i've seen a transistor and zener (tied to the base) topology, is this the only other viable solution?

Would the zener circuit ont work if there was a resistive load after it? i.e. R(L)

Cheers,
Ringo

 

[FvM]

Re: Zener Regulation

The zener or surpressor diode can only provide overvoltage protection according to it's voltage/current characteristic.
You may want to consult the datasheet to learn about transient currents that can be handled by the device. Obviously, the characteristic
won't be changed by a load resistor.

But fortunately, no transient source has zero impedance, so some protection is even achieved without a series impedance. But
the overvoltage may be still too high. For the same reason, automotive qualified power electronic devices, e.g. voltage regulators
have also a higher surge withstanding. You'll possibly run into problems with a conventional device. In this case, a more complex
protection circuitry would be needed, e.g. an active disconnect switch, if you can't accept a simple series impedance. Using dedicated
automotive components is most likely a more promising method.