minimum zenner current

[Simon]

What would the minimum current be for a zenner to clamp at ? I'm not too fussed about accuracy as it is protective only not for regulation. what would this be called on a datasheet ?

[hacklordsniper]

What would the minimum current be for a zenner to clamp at ? I'm not too fussed about accuracy as it is protective only not for regulation. what would this be called on a datasheet ?

I usually use the test current in the datasheet as reference and keep arround it, but most of the time im taking maximal current and derate it by 10-25 %. However you have a specifical request.

[eternal_noob]

Isn't that around 10 to 20uA or so (at it's rated voltage. It will begin to clamp before that)? I'll guess it depends a bit on the manufacturer, but it is fairly low anyway.

[amspire]

What voltages and peak currents do you need?

For low current applications, a small signal base emitter junction are often used.

Depending on the device, the Zener voltage is usually between 5v and 8v. Should be useable down to a uA or so.

Richard.

[Balaur]

If you look at the I/V characteristic curve for a Zener diode, there is a minimal Iz(min) at which the Zener/avalanche effect is engaged. However, this is not relevant for your clamping application. As an indication, Iz(min) is considered to be 5-10% of Iz(max).

Either:
a) the source that drives the input you want to clamp has enough current capability to engage the diode and thus the input will be clamped. The current will go up until the diode burns or the source reaches his limitations.
b) the source will not provide enough current (too much internal resistance) to reach the breakdown zone and the diode is almost linear, like a resistor. Forcefully, the voltage on the diode will be less than the breakdown voltage.

Cheers,
Dan

[Simon]

basically I want to protect the gate of a mosfet, my voltage will start low and rise so I want to feed the voltage through a resistor and put the zenner in parallel with the gate, so all I'm worried about is that the zenner conducts before the max Vgs is reached.

[ejeffrey]

For that application there is no minimum current.  You should look at the zener data sheet and look for the maximum current at the stated voltage, the set your resistor to limit the current to less than or equal to that value.

[Zero999]

Yuo still haven't provided enough information: MOSFET part number, gate drive voltage, frequency etc.

If it's just a low frequency application where the drive voltage is fairly constant then a simple potential divider will do.

[Simon]

The voltage will start at 0.7 volts (my mosfet has a Vgs threshold of 0.4V) and the voltage will then rise to 12v and stay there, the mosfet will trigger other circuitry that will cause the higher voltage to come on so once on i need to protect the gate - so a divider is no good