# Minimum Current for Zener to Clamp Vgs of Mosfet?

simulate this circuit – Schematic created using CircuitLab

When it comes to zener diodes I find it hard to get information about minimal currents needed for it to breakdown so I thought I would ask here.

In my project I have a 12S Li-ion battery, whose voltage can vary between 50V and 36V. This is quiet a big voltage difference to layout a resistor divider, so I decided to put a zener between gate and source to limit the voltage to maximum 16V.

The capacitor is there to limit in inrushcurrent for capacitve load.

About the zener diodes I can't find information in the datasheet about the minimum current needed for it to breakdown.

For the worst case I assume a Vbatt voltage of 36V, Vgate would then be 20V (Vs-Vz). The current through the diode is then 20V / 100k = 200uA.

Would that be enough current to limit the Vgs to 16V ? If not I'd have to use lower value resistors, a bigger cap and have bigger static power consumption which is not ideal for battery operated systems.

The diode I'm planning to use is MMSZ5221BT1.

Is there some information I'm missing in the datasheet or some general rule how much current a zener needs to breakdown?

– Big6
Aug 31, 2019 at 1:42
• In your datasheet you have both Izk and Izt. I tend to use a value between those two. If you want better regulation, may want to move close to Izt, otherwise shift more toward Izk
– Big6
Aug 31, 2019 at 1:46