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I am putting a power mosfet to control my power output. It is a pure DC application. I dont need to switch the mosfet fastly. Turn on & turn off will happen once a day or something like that. Once ON, it will stay ON.

My doubt is, with all the time I have to charge my Gate capacitance, Do I need to supply high current(1A) to charge the Gate. If I have time & i dont need switching, can i go ahead with a 100mA current to charge the Gate. Datasheet of power mosfet is :-

https://toshiba.semicon-storage.com/info/docget.jsp?did=35760&prodName=TPHR6503PL

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  • \$\begingroup\$ It ultimately depends on the switch on time you require and the accompanied losses due to RDSon during that time. \$\endgroup\$ – PlasmaHH Aug 19 '16 at 10:22
  • \$\begingroup\$ I am okay with the switch on time. How can I analyze the RDSon losses? \$\endgroup\$ – Oshi Aug 19 '16 at 10:23
  • \$\begingroup\$ @Oshi Look for an SOA curve in the datasheet, thermal impulse diagram and/or impulse current rating. If you switch slow enough, it's easy to burn out the MOSFET from excessive power dissipration. At 1 A and switched once, it should be near impossible on the other hand. \$\endgroup\$ – winny Aug 19 '16 at 10:30
  • \$\begingroup\$ @Oshi , yes you can , you can even go lower 1mA or 10mA \$\endgroup\$ – ElectronS Sep 8 '16 at 11:13
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The datasheet says:

  1. Features
    (2) Small gate charge: QSW = 30 nC (typ.)

With a constant current of 100 mA, this would result in a switching time of 300 ns. The current will not actually be constant, but this is much smaller than the smallest pulse width shown in the SOA graph, and probably safe for the VDS and ID values that your circuit uses:

TPHR6503PL SOA

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As general rule of thumb the ratio of drain to peak gate current should be < 500 to minimize self heating during switching if using high power loads.

Taken to extremes at high switching speeds, some designs reduce this ratio to 50 and some as low as 10 and require several stages.

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