Why does the pwm drive signal from my mosfet become constant voltage at the outp - Page 1
Forum section: electronics / beginners

author: man1
author_rank: Contributor
timestamp: April 14, 2025, 03:10:30 pm
content: I use a 28335 to generate a pwm signal. It drives my MOSFT through the driver module. but my pwm signal to the output side of the driver module becomes constant voltage. And there is no current in my main power circuit when voltage is applied to it and the voltage is the sum of the driver voltage and power circuit voltage, what is the situation. I am attaching my driver circuit schematic and main power circuit schematic below

author: Terry Bites
author_rank: Super Contributor
timestamp: April 14, 2025, 05:04:21 pm
content: You've got a kind of peak hold circuit here. Put the cap across the load to get an averaged current.

author: man1
author_rank: Contributor
timestamp: April 15, 2025, 01:56:01 am
content: I want him to have pwm control not constant voltage

author: man1
author_rank: Contributor
timestamp: April 15, 2025, 01:58:07 am
content: Quote from: Terry Bites on April 14, 2025, 05:04:21 pmI want him to have pwm control not constant voltage

author: xavier60
author_rank: Super Contributor
timestamp: April 15, 2025, 09:46:13 am
content: Measure some voltages With Respect To the GND in the driver diagram.Including both ends of D3.

author: Zero999
author_rank: Super Contributor
timestamp: April 15, 2025, 10:35:30 am
content: What's the load?What does C3 do?

author: xavier60
author_rank: Super Contributor
timestamp: April 15, 2025, 10:39:58 am
content: The driver looks like it's meant to drive a high-side MOSFET.

author: Zero999
author_rank: Super Contributor
timestamp: April 15, 2025, 11:50:08 am
content: Quote from: xavier60 on April 15, 2025, 10:39:58 amThat's true. The IR2127 is a bootstrap driver, designed for high side operation.https://www.infineon.com/dgdl/Infineon-ir2127-DS-v01_00-EN.pdfI might be wrong, but it should be possible to configure it for low side, although the OP should change it for a low side driver.

author: xavier60
author_rank: Super Contributor
timestamp: April 15, 2025, 12:14:31 pm
content: A high side driver can definitely be used on the low side. Even a high side MOSFET needs to be able to be turned on while its Source is at ground voltage.

author: man1
author_rank: Contributor
timestamp: April 16, 2025, 11:27:46 am
content: Quote from: xavier60 on April 15, 2025, 12:14:31 pmSo it's the chip?

author: xavier60
author_rank: Super Contributor
timestamp: April 16, 2025, 12:46:38 pm
content: Quote from: man1 on April 16, 2025, 11:27:46 amNo. Did you do the tests asked for in Reply #4?

author: man1
author_rank: Contributor
timestamp: April 17, 2025, 02:19:07 am
content: Quote from: xavier60 on April 16, 2025, 12:46:38 pmI removed D3 and connected the 4.5 pins together, the chip output has a pwm waveform, but the back part of the connection is still not what is the reason?

author: xavier60
author_rank: Super Contributor
timestamp: April 17, 2025, 02:31:44 am
content: Quote from: man1 on April 17, 2025, 02:19:07 amI dont know what that means. Bridging D3 would make sense. Is this what you did?What frequency is the PWM? Showing waveforms can be helpful.