PMOS on Zeta Converter

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Firenze02

Joined Sep 1, 2018
45
Hi,

I'm studying the Zeta Converter topology for Photovoltaic Applications.

In every documents, it is specified that the switch is PMOS. I don't understand why a PMOS is needed. Which are its advantages?

Being a switch, is it possible to use an NMOS instead of PMOS? Obviously, an isolated driver is needed.

Here some notes from TI about this topology:

https://www.ti.com/lit/an/slyt372/slyt372.pdf?ts=1605336852595

Thank you.
 

Ian0

Joined Aug 7, 2020
3,198
The driver is tricky for an N-channel device, because the drain of the P-channel (or the source of the N-channel) goes below the negative supply when the device is off. So you are correct about the isolated driver, because the charge-pump drivers don't like the output below their negative supply.
I don't see any other problems.
But if you can choose which is the "common" terminal of your system then there's nothing stopping you implementing the zeta converter for a negative supply (with an N-channel device with the output on the drain). Vin becomes negative, the diodes and electrolytics turn round. Then you can use an ordinary low-side driver. The problem then moves to how to sense the output voltage.
 
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