Issues with Latching switch using push button


I'm trying to make a latching power switch based off this schematic (source: EDN) push button latching power circuit

I emulated the circuit in Falstad and everything works like it should (link to simulation).

However, it doesn't work when assembled on a PCB. When I click the button, I see a sudden spike at Vout from 0 to 0.2V and then it quickly settles back to zero. I'm seeing no behavior that is similar to the simulation. I'm now starting to think I selected the wrong MOSFET/Transistor for the job, but I'm not sure which property would effect the circuit.

Here are some more details about my imlementation:

  • Vs – LiPo Battery (3.9 to 4.2 V Nominal)
  • Desired Vout – mirrors +Vs
  • Mosfet – FDN352AP
  • Transistor – MMBT2222A

Any thoughts? This is the first analog circuit I've built (simulated a few), so not really sure where to start looking.

Best Answer

This issue is solved. The circuit was failing due to a faulty isolation diode earlier in the circuit.