Voltage Mode Buck Converter Output Voltage

crutschow

Joined Mar 14, 2008
25,132
Have you looked at a typical buck-converter circuit and understand how they work?
They have a free-wheel diode (usually a Schottky type) from the output of the MOSFET (cathode) to ground.
This carries the inductor current when the MOSFET is off.
 

Thread Starter

T.B.

Joined Jun 19, 2020
9
Have you looked at a typical buck-converter circuit and understand how they work?
They have a free-wheel diode (usually a Schottky type) from the output of the MOSFET (cathode) to ground.
This carries the inductor current when the MOSFET is off.
Sorry, I should have removed it accidentaly. I add new analysis results with diode as reply on post.
 

Thread Starter

T.B.

Joined Jun 19, 2020
9
If you attach your spice file we could fix it.
P-MOSFET is installed wrong.
Gate drive is wrong.
Missing diode.
Sorry, I should have removed it accidentaly. I add new analysis results with diode as reply on post.
Have you looked at a typical buck-converter circuit and understand how they work?
They have a free-wheel diode (usually a Schottky type) from the output of the MOSFET (cathode) to ground.
This carries the inductor current when the MOSFET is off.
Sorry for my wrong.
I should have removed diode accidentally.
I attached analysis with diode and file.
 

Attachments

crutschow

Joined Mar 14, 2008
25,132
M1 source and drain are still backward.

And for a 50V input, the MOSFET gate drive also has to go to 50V, which that comparator can't provide.
 

Thread Starter

T.B.

Joined Jun 19, 2020
9
M1 source and drain are still backward.

And for a 50V input, the MOSFET gate drive also has to go to 50V, which that comparator can't provide.
So should I increase the comparators supply , or is there any solutions for it ?
 

ronsimpson

Joined Oct 7, 2019
726
V1. Started at 50V. I changed it to start at 0 and take 100nS to reach 50V. Things were blowing up at startup.
S1. The mosfet was backwards. The gate drive was very wrong. So I just put in a switch that can be driven from 0/5V.
Added diode.
OP-amp was fast while the comparator was slow.
C2 to slow down the amp.
Removed the -5V supply.
1592608190886.png
Give this a try. Good Luck ronS
 

Attachments

Thread Starter

T.B.

Joined Jun 19, 2020
9
V1. Started at 50V. I changed it to start at 0 and take 100nS to reach 50V. Things were blowing up at startup.
S1. The mosfet was backwards. The gate drive was very wrong. So I just put in a switch that can be driven from 0/5V.
Added diode.
OP-amp was fast while the comparator was slow.
C2 to slow down the amp.
Removed the -5V supply.
View attachment 210221
Give this a try. Good Luck ronS
Thanks for your help ,I will try this .
 
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