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I'm trying to create a delay circuit like this. When I snapp on the push button, then the current flows from +3.3V to GND and bypass the 220 Ohm resistor, which is my load.

But the problem here is that I want to have this current peaks like a square wave, PWM etc, not this slow slope.

Question:

What should I replace so this MOSFET got its voltage gate dropped to 0V when the gate voltag is under a certain threshold?

I will NOT use a mechanical relay and optocoupler will not work neither.

Digital circuits will work too. But I'm not expert at them.

enter image description here

Solution:

Schmitt-trigger

enter image description here

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    \$\begingroup\$ Remove capacitor. Use SPDT switch, common to transistor gate, two others to grounds and PS+. \$\endgroup\$
    – user263983
    Commented Mar 3, 2021 at 14:28
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    \$\begingroup\$ Use a digital output to drive that gate directly with 0 V (off) or 3.3 V (on). Why is there a capacitor if you want fast switching? It is like filling a car with heavy stones and then complaining it doesn't accelerate that fast. \$\endgroup\$
    – Bimpelrekkie
    Commented Mar 3, 2021 at 14:36
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    \$\begingroup\$ Define Delays for rising and falling edge and rise/fall time with tolerances ! \$\endgroup\$
    – D.A.S.
    Commented Mar 3, 2021 at 14:37
  • \$\begingroup\$ Hearing that you don't want that slope is confusing: Why exactly then are you using this exact circuit? \$\endgroup\$
    – Marcus Müller
    Commented Mar 3, 2021 at 14:53

1 Answer 1

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Your wire is not defined on the schematic. Typically Delays are made for Half Bridges to delay turn-on to avoid short circuit or shoot -thru and depend on load inductance and FET Capacitance which I modelled here for a power FET with Ciss.

The Turn-ON delay is circled and OFF is assumed to be x ns with low diode resistance.

enter image description here

You must define more details on FET parameters and load. I simply chose beta=1 and logic level FET with Vt=1.

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  • \$\begingroup\$ But you are using a PWM source at 400 kHz. I want to create a delay OFF function \$\endgroup\$
    – euraad
    Commented Mar 3, 2021 at 15:26
  • \$\begingroup\$ By the way! Have a look at my answer. \$\endgroup\$
    – euraad
    Commented Mar 3, 2021 at 15:32
  • \$\begingroup\$ Ok I guessed wrong what you were actually looking for and you still did not show the input to measure the delay \$\endgroup\$
    – D.A.S.
    Commented Mar 3, 2021 at 15:41

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