Latch ckt not working

[deepak.midri]

Attached is latch circuit for powering a microcontroller.

"External Switch" is trigger pressed by user which will turn on the device and wake up MCU.
Once its done, MCU will pull ground to right switch and output should turn off.

On simutaltion this ckt is not working, whats wrong in it?
Even without pressing trigger, I can read output voltage.

[Benta]

1 M is far too high. MOSFETs have significant leakage current.

[deepak.midri]

I am simulating with 12V input dc at the moment for testing.

Since 3.6V mosfets are not available in simulation software.



I think its leakage current issue. Can it be solved by using Bjt instead of mosfets?

[Renate]

Put a load resistor on your simulator.

[deepak.midri]

This seems to be working. Instead of N mosfet, NPN is added.
Whenever latch is pressed, output will be seen, and MCU is powered up. Now MCU pin is made inout high impedence.
When need to turn off, this MCU pin is made output low. This will eventually cut off the latch.
Will this work as intended?

We need to make as low power as it can be.

[deepak.midri]

Ok will the circuit work as intended?

1. Input dc range is 2V-3V. Will the selected fet work for this range?
2. Whenever latch is pressed, output will be seen, and MCU is powered up. Now MCU pin is made inout high impedence.
When need to turn off, this MCU pin is made output low. This will eventually cut off the latch.
Will this work as intended?
3. Load current is only 100mA so 36ohm resistor is connected.

[Wimberleytech]

Ok will the circuit work as intended?

1. Input dc range is 2V-3V. Will the selected fet work for this range?
2. Whenever latch is pressed, output will be seen, and MCU is powered up. Now MCU pin is made inout high impedence.
When need to turn off, this MCU pin is made output low. This will eventually cut off the latch.
Will this work as intended?
3. Load current is only 100mA so 36ohm resistor is connected.

Seems to me, U1B should be a PMOS transistor.

>>LOL...I need better glasses...it is a PCH device<<

[deepak.midri]

Another doubt is in schematic load is shown as R5=36 for simplicity.

In actual its "Boost + MCU",  boost have input/output capacitors of 47uF each, can they can any issue?

Since they will charge in their time constant, and power will go MCU which will then wake up and put MCU pin in high impedecne?

During this time it may happen pin of MCU may behave weird?

[Benta]

It will work with a load, without load it will be marginal.
In that case, the leakage current through U1B will flow into the base of Q1 and turn the circuit on.