Following circuit drives a 24V LED strip. Vin is a 3.3V 1kHz PWM signal coming from an ESP32 GPIO. The MCP1416 MOSFET driver converts the input signal to a 5V PWM with low output impedence. The MOSFET SQ2362ES drives the LED strip with a max drain current of 1A. A TVS diode SMAJ10CA+ provide the overvoltage protection for the gate, while the flyback diode is a SS115 schottky. The 5V and 24V come from 2 bench power supply.
I tested the circuit both on breadboard and on the final PCB, here the graph of Vin and Vds when the MOSFET turns off:
Regarding the ringing:
- Why this huge ringing up to 70V the driver?
- What can I do to suppress it? Placing a 100 ohm resistor between driver output gate reduces the ringing to 50V. Adding a 0.1u ceramic cap between L1 connector and ground gives a further reduction to 15V. Should I place the gate resistor? Should I place a decoupling cap? A film cap could work better? What about an electrolitic one?
Regarding Vds with MOSFET off:
- Vds should be 24V. Why do I measure 9V? Is it due to the scope probe?
- If so, how should I measure this voltage?
- Placing the probe on the LED connectors results in a stable 24 V signal, without PWM, and the LEDs are fully switched on. Why this behavior?
Here the arrangement of the components on the breadboard. The MOSFET is a IRF520, but the behaviour is the same with the original MOSFET. I added also a 10 Ohm gate resistor and 4x 0.47uF decoupling cap on 24V rail. The circuit was also tested on a PCB with same results. The image shows also the scope probes (x10).