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I want to drive a mosfet using a mosfet-driver (TC4428). The frequency of turning on-off of mosfet is 5-10 Hz (yes Hz) and duty cycle is 10-20%. I use PC817 as below to make isolation: enter image description here

As you see, if FLASH1 STROBE be 4.8 volts, voltage of collector will be 0.18 volt. FLASH1 STROBE comes from a ATMEGA16 port. Is there any problem with this design? I mean 0.18 volt on collector and 4.8 volt on FLASH1 STROBE.

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  • \$\begingroup\$ What is the PC817's Vcc? 5v? What is the TC4428's Vcc? 12v? \$\endgroup\$ – rdtsc Sep 20 at 18:58
  • \$\begingroup\$ There is no Vcc pin for PC817. The Vdd for TC4428 is 9 volts. \$\endgroup\$ – Babak.Abad Sep 20 at 19:34
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There are two problems normally optoisolators in this setup: - Rise times - Not a low enough V_IL for the gate driver

Rise times aren't going to be a problem at 5 to 10Hz. The V_IL is 0.8V for the TC4426 so if the optoisolator pulls down to 0.2V you should be fine.

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  • \$\begingroup\$ Is there any to make 0.2 V be less? I'm worry about that noises make it more than this value (and it reaches ~0.8 V). \$\endgroup\$ – Babak.Abad Sep 20 at 19:41
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    \$\begingroup\$ I think your fine, you have 0.6V of headroom, that should be enough. If your getting ground noise or Vcc noise larger than 0.1V then you'll have many other problems. \$\endgroup\$ – Voltage Spike Sep 20 at 20:00

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