Hi
I've been looking for a way to drive a load with 20 kHz PWM - 3A / 15V controled by a 3.3V µC but did not succeed. I've seen a lot of drivers (gate driver/Mosfet combi) but none of them can run at 20 kHz, so if any of you have a suggestion it is very welcome. It must be a high side / common ground konfiguration.
(I'm looking for a way to drive and dimm a series of LED's)
The ESP32 has 2 ways to generate PWM.
The LED PWM and the MCPWM modules accessible through the ESP32 API. API Reference - ESP32 - — ESP-IDF Programming Guide latest documentation.
The LED PWM can:
The LEDC can be used for generating signals at much higher frequencies that are sufficient enough to clock other devices, e.g., a digital camera module. In this case, the maximum available frequency is 40 MHz with duty resolution of 1 bit. This means that the duty cycle is fixed at 50% and cannot be adjusted.
The MCPWM can be ran at 1/2 the peripheral clock speed, 80Mhz/2.
I have used both the LED API and the MCPWM, works great lasts a long time.
Good luck with your hardware search.
Thanks 
The esp32 is exactly the one I'll be using - now hoping to find a good way to generate the 3A at 15V
You probably want a logic level N-channel MOSFET. Or you may try a NPN Darlington transistor but it will have to dissipate about 3 W which is quite a lot.
20 kHz is not so high frequency.
Hi,
Welcome to the forum.
Please read the post at the start of any forum , entitled "How to use this Forum".
OR
http://forum.arduino.cc/index.php/topic,148850.0.html.
What is the load?
Is it inductive?
Thanks.. Tom...
wittrockvita:
I've seen a lot of drivers (gate driver/Mosfet combi) but none of them can run at 20 kHz, s
This driver can work at 100KHz - https://www.mouser.com/datasheet/2/268/21946B-277918.pdf
alesam:
This driver can work at 100KHz - https://www.mouser.com/datasheet/2/268/21946B-277918.pdf
I looked at these drivers but they are categorized as low side drivers and I have therefore not given them any more attention. However, I have now come to think about whether they can be used to drive the gate on a P-channel mosfet as a high side, but I do not have enough knowledge about mosfets to use them and can not find any application notes about it. Is there anyone who can help me with that?
CrossRoads:
You can do this:
Use an NPN transistor is the buffer to pull the Gate of a P-channel MOSFET, like NDP6020, low to turn it on.
Use a resistor to pull it high to turn off.
Only need to go from 15V to 10V to be fully on.
I don't think it will work at 20 KHz due to the large gate capacitance of the mosfet - it has to be actively pulled up.
wittrockvita:
I've been looking for a way to drive a load with 20 kHz PWMI'm looking for a way to drive and dimm a series of LED's
Might have to go to DC dimming of a switching LED driver,
because basic 8-bit dimming with 20kHz PWM is already > 5Mhz (20000*256).
Or, a dim level of 1/256@20kHz is a ~200 nanoseconds wide pulse.
Why don't you give us all the details.
Is this one LED string, of how many LEDs, or more strings in parallel, or a COB LED?
Leo..
If I'm applying my math right, a frequency of 1/(2xPixRxC) Hz can be achieved with 1K pullup and the 1590pF gate capacitance:
1/(2 x 3.14159 x 1000 x .000000001590) = 100,097 Hz, 5 times faster than needed.
Hi,
What is the application?
Is there a specific reason it has to be high side switched?
There are high side drivers.
Google
high side mosfet driver
Tom...
@CrossRoads: You are not applying the math right. OP is driving a MOSFET, not trying to construct a low pass filter. To reduce switching losses you need to have the MOSFET in linear region for only a very short fraction of time.
OP: Why do you need high side switching? In general low side is better in every aspect.
CrossRoads:
If I'm applying my math right, a frequency of 1/(2xPixRxC) Hz can be achieved with 1K pullup and the 1590pF gate capacitance:
1/(2 x 3.14159 x 1000 x .000000001590) = 100,097 Hz, 5 times faster than needed.
You're right - sorry. I didn't calculate it before assuming.
Smajdalf:
OP: Why do you need high side switching? In general low side is better in every aspect.
I need the high side mode because I need a common ground.
@TomGeorge and others: I have to drive several strings of LEDs and all strings have to be connected to common ground. Therefore, low-side switching cannot be used (just as the dedicated LED drivers cannot because they are all low side drivers).
I have looked a lot at high side drivers but have not been able to find one that fits the purpose.
The solution I like best is to use e.g. a TC4423A, but I do not know if it can be used to control a p-channel mosfet in high side mode - can you help me to clarify that?
So why the 20kHz PWM.
Is that a number from a magician's hat?
How low do you want the brightness to go.
How do you control LED current.
Leo..
Wawa:
because basic 8-bit dimming with 20kHz PWM is already > 5Mhz (20000*256).
The ESP8266 PWM is 10 bit.
wittrockvita:
Hi
I've been looking for a way to drive a load with 20 kHz PWM - 3A / 15V controled by a 3.3V µC but did not succeed. I've seen a lot of drivers (gate driver/Mosfet combi) but none of them can run at 20 kHz
A gate driver chip into any standard MOSFET will handle 20kHz no problem, and be drivable from
3V or 5V logic.
Don't bother trying to roll your own with a transistor, go straight to a chip designed for the purpose,
a low-side MOSFET driver. My go-to device is the MIC4422 as it will drive any size MOSFET and is
available in through-hole. I'd run the 15V through a 7812 12V regulator to power the driver chip,
so that you can use a non-logic-level MOSFET.
MOSFET driver chips need proper decoupling, 1--10uF ceramic less than 10mm from the chip is going
to work. Keep the wiring between driver and MOSFET short.
RIN67630:
The ESP8266 PWM is 10 bit.
OP is using the ESP32. Could also be 10-bit PWM.
MarkT:
A gate driver chip into any standard MOSFET will handle 20kHz no problem, and be drivable from
3V or 5V logic.
But 20kHz PWM is not always a pulse width of 50us. Only at 50% PWM.
20kHz 10-bit PWM has ~50ns wide steps.
Leo..
ESP32 PWM LED API 13bit.
ESP32 MCPWM API 32bit.
See ESP32 API.
