esp8266mosfetmosfet-driverpwm
I am building an RGBW controller for my room. I will be using an ESP32 with four MOSFETs for each channel. I want to know which is best for fast switching. Do I need to use a MOSFET driver IC such as the ICL7667 with IRFZ44n or is it better to use a lower VGS MOSFET such as the AO3400, or something entirely different?
I'm open for suggestions.
What are the cons and pros for both, since it's only one time investment cost is not the issue?
I will make the PCB, so I prefer SMD components.
So, the friendly folks at IR got back to me, and suggested I swap out the IRS2001 with a IRS2301. The IRS2301 has a VCC requirement of just under 5V, and will thus work for my application.
Now I just have to wait for the priority mail from Digi-Key...
Since you're just switching a magnet, you don't need high speed, or high gate current. However, since your MCU operates on 3.3 volts, you do need some sort of driver to guarantee that your MOSFET gets turned on strongly, and 3.3 volts on an output just won't do that.
For a simple case like this, all you need is a transistor and a few resistors, and
simulate this circuit – Schematic created using CircuitLab
this will do, as long as you don't mind the fact that the signal is inverted. That is, a high output at the MCU will turn the relay off, not on. Note a few things. R2 and R3, when the transistor is off, set the gate drive at 12 volts. Without the combination, using only R2 would apply a maximum of 24 volts to the gate, and this exceeds the maximum specification. Also, D1 is called a flyback diode, and you should always use one when switching anything with a coil. If you don't, when you turn off the relay you'll get a big voltage spike across it, and you may well kill your transistor. Worse, sometimes it will take multiple operations to kill the transistor, so you think you've got a working circuit, but you can't understand why it's unreliable. The diode should be rated for whatever current the relay coil draws, and have a higher voltage rating than the power supply.
Best Answer
You don't want fast switching to drive LED strips! If the FET switches in a couple tens of nanoseconds, you will send very high di/dt currents into your wires which will radiate electromagnetic interference and essentially act like a broadband radio jammer. Remember a signal with 10ns edges has bandwidth extending to hundreds of MHz...
On the contrary, you want slow edges, like 0.5µs - 1µs. This increases switching losses, but your PWM frequency is going to be low anyway, so switching losses, which are proportional to frequency, will be low too. Let's check the math:
Conduction losses = RdsON * I^2 * DutyCycle
For 2 amps and a duty cycle of 1 (100%) a FET with RdsON of 40 mOhms dissipates 0.16W -- you can use a FET with lower RdsON if you want.
Switching losses = V * I * SwitchingTime * Frequency
For 12V, 2A, 500ns, 10kHz losses will be 0.12W.
Note these losses are already a bit high for a SOT23 FET. I'd use a SO8 single or dual FET instead, they have better dissipation and they're pretty cheap.
Say you want to switch an AO3400 in T=500ns, total gate charge is Qg=7nC so gate drive current will be roughly Qg/T = 14mA. For this you don't need a specialized gate drive IC.
If you have 5V available, you can use a 74HCT logic gate as voltage translator between your 3V3 micro and a 5V "logic level" MOSFET. It's cheap and it'll work.
If you only have 3V3 available and no 5V, and you don't want to bother with a separate 5V supply, then it makes sense to use a FET that is compatible with 3V3 drive. Depending on the gate drive current required, and the output drive capability of your micro, you might want to add a logic gate as a buffer too. 74LVC for example.