Electronic – MOSFET switch with two on/off momentary buttons — asking for critique

mosfetpowerschematicsswitches

I want a "power button" that is actually two buttons; one on, one off.
This needs to switch on the order of 15 V and up to 10 A, for a LiFePO4 battery powered device.
I don't want to use a hardwired switch where this is mechanical, because I later also want soft (MCU-based) control of the same on/off functions.
I don't want to use a relay because 60 mA for a typical coil current is a lot (the typical load is perhaps 500 mA, but peak load on the device is 10 A.)

This is the best I could come up with. De-bouncing the buttons is not needed. When first connected, I think it enters "off" state because the gate is weakly pulled to ground through the load (output) — and even if it isn't, the main power P-channel FET isn't going to have any gate charge.

I'm asking for two things here:

  1. If you want to spend a few minutes helping out a poor n00b on circuit design, please critique this design and suggest whatever you think needs improving in this circuit. (Three FETs? really?)
  2. If you think my diagram is hard to read (I got that last time 🙂 then please at least critique exactly what you think is poor about the diagram, so that I can better communicate in the future.

Thanks in advance for any help!

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Best Answer

Could it be that what you had in mind was this?

enter image description here

Purpose of components:

  • Q5 - P-channel MOSFET, high side power switch
  • SW1 - momentary normally open OFF switch, which drives the gate high. Since it's connected directly to the gate of Q5, it will overpower the ON switch, which is connected through 1kΩ.
  • R32 - pull up, makes sure that the circuit is off when it's not on.
  • SW2 - momentary normally open ON switch. When pressed, the gate of Q5 is driven low and Q5 starts to conduct. Output drives the gate of Q12 high.
  • Q12 - N-channel MOSFET, keeps the gate of Q5 low when SW2 is released and SW1 not pressed.
  • R30 - pull down, makes sure that the output is pulled to ground when the circuit is off and load is disconnected. Because of R30, the gate of Q12 can't float up and turn the circuit on spontaneously.