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I'm doing a 12V to 230V push pull inverter design & need to drive it via two MOSFETs for each transformer tapping. Mosfets feeds by an optocoupler PC817. The frequency is 50Hz coming from a PIC microcontroller. Going to do as below. enter image description here

Am I driving it correctly? Any improvements?

Thanks

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    \$\begingroup\$ Missing individual gate resistors! \$\endgroup\$
    – winny
    Commented May 2, 2022 at 14:47
  • \$\begingroup\$ Yet again in MOSFET designs, gate capacitance ignored. \$\endgroup\$
    – TonyM
    Commented May 2, 2022 at 16:16
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    \$\begingroup\$ Closed too quick. At any rate this link may be helpful: homemade-circuits.com/how-to-design-inverter-basic-circuit The optocoupler isn’t necessary, you need good push-pull gate drive to deal with gate capacitance. You could also consider using NPNs instead of FETs. \$\endgroup\$ Commented May 2, 2022 at 17:32

2 Answers 2

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  1. You probably want a push pull or totem pole method between OC1 and your power MOSFETs. Direct opto drive might be insufficient for PWM at 50Hz, It certainly would be in
  2. I would omit OC1 and only have the aformentioned totem pole or push-pull driver. The opto does little and there aren't safety issues because the transformer is low V on your primary. sufficient at 1kHz+.
  3. 50Hz square wave would saturate your transformer I think because the DC level is applied for too long.
  4. You might want some form of snubbing to protect T1 and T2 from excessive voltage spikes.
  5. The voltage labels at your transformer primary are incorrect.
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  • \$\begingroup\$ It seems there was an unintended cut/paste between items 1 and 2 \$\endgroup\$
    – devnull
    Commented May 2, 2022 at 14:47
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This topology will not work for several reasons:

  1. It has no back EMF diode clamp
  2. The driver impedance is not low in the off state and even with diodes is not sufficiently low compared to this FET to regulate voltage with a load transformed (divided by) \$R_{load}/N^2\$. The ratio of source to load impedance determines the "% voltage load regulation error" This is critical to your understanding of boost converters and means the source impedance must be very low (in both hi and lo voltage states).
  3. The primary current should be symmetrical to improve power quality , reduce EMI and load resonance, eliminate DC, and preferably sine wave or 3 level switches.

Complexity of AC inverters is far greater than this and you might study how it is done before trying to DIY. A DC powered centre tap and dual Nch end coil low-side switches with BEMF clamping is a better topology. https://www.edaboard.com/attachments/12v-220v-gif.62924/

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