N-channel MOSFET MCH3478-TL-H with back to back zener diode

[dann11]

MCH3478-TL-H is a n-channel MOSFET with back-to-back zener diode at its gate and source pin? what is the purpose of the back-to-back zener didoe? Is it ok if I will use MCH3478-TL-H as my switching transistor for my buck converter?

 

[KlausST]

Hi,

Electronics is all about "volts" and "amperes".

Read the datasheet.
You will see the specifications are mainly about "volts"and "amperes".

Now you need to compare those specifications with the values of your buck converter circuit.
This is the (only) way to check if this Mosfets suits to your application.

In your post there is not a single value ---> therefore it's impossible for us to answer your question.

Klaus

 

[malli_1729]

Check this
https://www.diystompboxes.com/smfforum/index.php?topic=100760.10;wap2

Basically ESD Protection.

 

[dann11]

Does the back to back zener diode does not affect the regular voltage operation of the MOSFET? For example, in a buck converter for a battery charger, lets say I have an input voltage of 20V and the output battery is arround 12V, wont there be any possibility that the battery will trigger the gate on?

 

[Easy peasy]

Max gate to source voltage protection.......

 

[KlausST]

HI,

Again: Read datasheet.

For example, in a buck converter for a battery charger, lets say I have an input voltage of 20V and the output battery is arround 12V, wont there be any possibility that the battery will trigger the gate on?

You talk about 20V. But these 20V are not at the gate. So it is not relevant for the back-to-back zeners.

Whether the mosfet is conductive or not depend on gate-source voltage.
The threshold voltage (here called cutoff voltage) is at about 0.9V.
As the max. gate-source-voltage is specified with +/-12V .. it is far away from 0.9V.

But you have to ensure, that the gate-source voltage never exceeds the specified +/-12V.

** Function of zeners:
The gate is very high impedance. But inside the MOSFET the isolation barrier to source is small and sensitive against overvoltage.
Any V_GS overvoltage may harm the isolation barrier and thus may kill the MOSFET. (The problem is: the fault (=killing) may be immediately or it may be within months)
Therefore they manufacturer installs the zeners to limit V_GS.

The zeners don´t affect usual operation, otherwise you could see this in the specifications.

Klaus