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How to interface PWM output from a dsPIC30F6012 microcontroller with power MOSFET TrenchFET like SiE818DF? I want use PWM to control the brightness of the LEDs. Four PWM channels, one PWM per channel.

PWM frequency 244Hz 
LED Voltage: 12V 
Total operating current: 5A 
1W LEDs with working current 350mA (4 banks of LED's)
Overcurrent protection on output of each channel.

Can TrenchFET be connected directly, or some matching IC circuits need be used?

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  • \$\begingroup\$ Read the required gate voltage for the FET and compare to what your microcontroller outputs. \$\endgroup\$ Apr 8, 2015 at 0:34
  • \$\begingroup\$ What do you plan to do with the MOSFET? Will you be PWMing it? If so, at what frequency? A MCU's weak GPIO driver is generally incapable of high-frequency PWM as the limited drive current capability cannot charge/discharge the gate capacitance quickly. Also you may need to drive it to a higher voltage than the +5V max of the dsPIC to get the Rds(on) minimized. \$\endgroup\$ Apr 8, 2015 at 0:39
  • \$\begingroup\$ @Adam Lawrence, MOSFET(TrenchFET) will be used to drive LEDs(12V, 1W). Yes, connecting PWM output to MOSFETs. PWM frequency I want 244Hz. \$\endgroup\$
    – minto
    Apr 8, 2015 at 20:14
  • \$\begingroup\$ Put these details into your original question please. \$\endgroup\$ Apr 8, 2015 at 20:16

1 Answer 1

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That's a rather overkill FET for the purpose. For lower current applications, and when you get a FET rated for lower voltage, which then has lower overall gate charge, you can sometimes drive the FET gate directly from a digital output.

However, in this case, you should use a FET driver. For example, the Microchip TC442x is a nice low side FET driver, although that particular one is dual channel. FET drivers take a digital signal as input and have output drivers specifically designed to provide the large pulses of current it takes to switch a FET gate quickly. Especially if this is a one-off project, just do it.

If this is a high volume project where cost is a high priority, I'd look around carefully to find a FET that just meets the requirements and has low enough gate charge and works well enough with 5 V gate drive to run directly from a dsPIC output. I have done that quite successfully a number of times, but 5 A is getting to where the tradeoffs may go the other way. Another possibility is to use two such direct-drive FETs and have each drive 2 banks of LEDs. Switching 2.5 A twice will be easier than switching 5 A once, especially if you can use two PWM outputs that are 1/2 period offset from each other.

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  • \$\begingroup\$ Well, SiE818DF possibly is a bit overkill for the purpose. What would be a more suitable FET for this application? \$\endgroup\$
    – minto
    Apr 11, 2015 at 12:58
  • \$\begingroup\$ @minto: My go-to FET for low voltage and direct digital drive applications is the IRFML8244, but it doesn't have quite enough current capability for this case. Two of them driven from two different PIC pins may be simpler and cheaper than driving one larger FET thru a FET driver, though. \$\endgroup\$ Apr 11, 2015 at 15:10
  • \$\begingroup\$ You mean two IRFML8244 per PWM channel? How to connect it in such a way? \$\endgroup\$
    – minto
    Apr 11, 2015 at 19:40
  • \$\begingroup\$ @min: Source to ground, drain to bottom end of valve coil, gate driven directly by a 0-5 V PWM output of the dsPIC. \$\endgroup\$ Apr 11, 2015 at 20:07
  • \$\begingroup\$ You mean connection like this? \$\endgroup\$
    – minto
    Apr 11, 2015 at 21:33

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