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I would like to control LED strips using MOSFETs. I've got recommendation to use PSMN9R0-30YL and drive it using MIC4427. So I bought these, but right now, I'm unsure about two things - (a) how to actually use it and (b) how much current will this control consume.

(a) The LED strip (and power supply) is made for 24V. However the MIC4427 maximum supply voltage is 18V (absolute maximum according to the datasheet is 22V). I expect I've got bad recommendation, right? Or is there a way how to correctly use this pair of MOSFET with this gate driver? Maybe, if you can recommend me a better alternative to the driver. It's going to be feed with TTL PWM from atmega328 or similar.

(b) What's power consumption when using MOSFETs with gate drivers? Does it depends on PWM frequency?

Thank you for your hints and advices and sorry for little bit stupid question - I'm learning slowly.

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    \$\begingroup\$ You can use 24V with 18 V max components if you add a series inductor plus diode to implement a buck converter. This must never fail on if you are to avoid destroying the load - or have protection against doing so such as zener diode and fusing. \$\endgroup\$
    – Russell McMahon
    Nov 4, 2020 at 0:22

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This driver is meant to switch FETs fast (less than 25ns according to datasheet) which is what you want for DC-DC converters running at high frequency. However your use case is different, if you use PWM on LEDs it won't be 500kHz, more likely it will be at most 25kHz if you want to avoid audible frequency, or 5kHz if you just want to avoid any flicker.

At such lower frequency, switching very fast is not necessary to minimize switching losses... and it is actually a problem because this will send high dv/dt and di/dt into the wires and the LED strip which will then radiate this as EMI. In other words, if you make your FET switch at 10-20ns and you're not sticking an inductor right there to make a buck converter but instead connect that to wires without any filter, you're really making a wideband radio jammer with the LED strip acting as antenna.

Since the FET has a gate charge of 17nC, with say 4mA gate drive it will switch in 4µs and with 20mA it will switch in 1µs, which is both fast enough to produce negligible switching losses at a PWM frequency suitable for LEDs, and slow enough to radiate much less EMI.

Your MOSFET is a good choice for 5V gate drive since it specifies about 10 mOhms RdsON at Vgs=4.5V.

If you use a 5V microcontroller, you can drive the FET gate directly from it with a resistor, say 220 ohms, that should switch in ~1-2µs.

If you use a 3V3 microcontroller, you can use your MIC4427 powered from 5-10V to drive the FET, but you'll need to add a gate resistor to slow it down. That's a bit of a waste of a FET driver, but if you already have it, why not... A cheaper option, especially if you have several channels, is to just use 74HCT or 74ACT logic gate as voltage level translator from 3V3 to 5V, powered from a 5V supply that you probably already have.

If you don't have the necessary supply voltage, just use a linear regulator from +24V. You can't power that driver chip from 24V.

Unless you intend to run a huge number of amps through it you don't need to increase Vgs to more than 5V to scrape off the last bit of RdsON. So if you already have 5V somewhere it'll be fine.

PS: is you need to convert 24V down to 5V consider one of these instead of an old 7805.

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    \$\begingroup\$ Hi, thanks for the reply - I've marked it as accepted, as it's most broad and mentioned even EMI radiation. Though all answers were great and helped me understand better how the relation between Vgs and RdsON works. As I'm going to use 5 channels of PWM (RGB + CW + WW) and maximum sink/source current through amtega328 is 200mA, I'll use little bigger resistor (maybe 460Ω?), which should allow me to stay inside safe area of MCU and still enough fast switching time to achieve non-flickering light. Am I right? \$\endgroup\$
    – Mike S.
    Nov 9, 2020 at 6:10
  • \$\begingroup\$ Yes, this is correct. \$\endgroup\$
    – bobflux
    Nov 9, 2020 at 9:09
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Not a stupid question - good catch on your part. The parts cannot be used with a 24-volt supply without damage for two reasons: the MIC4427 voltage rating which you have pointed out, and the PSMN9R0-30YL which has a maximum gate-source voltage of 20 volts. Choices are: IXYS makes a 35-volt version of the part (IX4427) which you could use to drive a voltage divider and cut the voltage in half going into the gate (at the cost of the voltage divider current), or you can make a 12-or 15-volt separate supply for the gate drive part of your circuit. The 4427 parts draw only a few milliamps.

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You can't use the MIC4427 with a 24V source voltage and you can't power the gate of the PSMN9R0-30YL with more than 20V.

What you need is some intermediate voltage. This will be based on how much current is flowing into your leds. You can find that value in the graphs associated with the PSMN9R0-30YL.

5V VGS should be okay for most mosfet currents (Make sure the voltage source for the gate driver can provide enough current). This graph shows the resistance of the mosfet with respect to Vgs.

The current draw will be based on gate capacitance (17.8 nC for the PSMN9R0-30YL). Power consumption is simple, but requires a little math. How to calculate it is here (page 6-7): https://toshiba.semicon-storage.com/info/docget.jsp?did=59460

The uC can't provide the amount of current required to quickly turn on and off a mosfet and that's the reason for gate drivers. Bad quick drawing but strong = more current weak = less current.

enter image description here

I'm new to answering questions. Let me know if anything isn't clear.

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    \$\begingroup\$ No need to hand-draw. There's a excellent circuit drawing tool right there in top bar where you enter your answer. \$\endgroup\$ Nov 3, 2020 at 20:18

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