Choosing MOSFET gate driver for PWM logic signal

Thread Starter

ilium007

Joined Aug 24, 2013
112
I am putting together a small board to drive some N channel MOSFETs to control a 24V DC load from an ESP8266 running Tasmota for a home automation project. I will use these boards to control 24V gardening solenoids and also to PWM dim 24V DC LED lights.

I was thinking about isolating the load power supply from the micro controller power supply via an optoisolator and found the Vishay VOM1271 Photovoltaic MOSFET Driver. When I compare the VOM1271 with the LM5111 that I have used previously I notice the rise and fall time of the VOM1271 to be orders of magnitude slower than the non-isolated LM5111 gate driver

Datasheets:
https://www.vishay.com/docs/83469/vom1271.pdf
https://docs.rs-online.com/1906/A700000006905993.pdf

I have put together an initial design (incomplete, no de-coupling etc, will need an I2C hardware PWM driver to get the PWN freq I want) and would welcome some suggestions on the MOSFET gate driver and whether it would better to use the LM5111 with a separate open collector type optoisolator between the ESP8266 and LM5111. I am not quite sure on calculating the propagation delays.

Schematic_Home Automation_2020-10-03_12-07-39.png
 

Solar Mike

Joined Apr 26, 2018
24
Isolating your CPU from the high power outputs is a good idea.

The Vom1771 is a very low current isolated voltage generator mosfet driver, thus very slow and better suited to solid state relay's, I wouldn't use it for PWM.

Use your LM5111 with a high speed opto-coupler like a TLP2361, or better one of the new isolated capacitor coupled drivers like the UCC53550SB. Just make sure they accept 3.3v logic input as a valid level.

Cheers
Mike
 

Solar Mike

Joined Apr 26, 2018
24
Yes that non-inverting opto buffer would be quite suitable for isolation.
I see LCSC also sell the UCC21520DWR mosfet isolated driver, it is compatible with 3v logic and can be configured for dual low side operation, I have used another version of them in the past for synchronous buck converters.
 

Ian0

Joined Aug 7, 2020
750
The board will be used to switch/dim DC LED lights as well.
I see - I thought you meant some outputs were switching and others were PWM.
Are the two power supplies (24V for load and 3.3V/5V for microcontroller and WiFi module entirely separate?
I would not have thought linking their 0V terminals would cause problems, hence removing the need for isolation.

Thank you for bringing the ESP8266 to my attention - it looks interesting!
 

Thread Starter

ilium007

Joined Aug 24, 2013
112
I see - I thought you meant some outputs were switching and others were PWM.
I was trying to design one board to do both but now have just realised I am switching 24VAC solenoids so I guess I will be designing two boards. The 24VAC solenoids will use relays.

I'll be using two power supplies, one for the microcontroller and the other for the load.
 
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