Maker Pro
Maker Pro

Help needed with a Power Latch circuit

belbao

Sep 4, 2023
1
Joined
Sep 4, 2023
Messages
1
Hi All,
I'm troubleshooting power issues on a device and have narrowed the issue down to this Power-Latch circuit (I think). Proper functioning should be:
-Toggle switch activates Mosfet (unifying grounds) and sends PWR_BUTTON signal to the ESP32 microcontroller.
-ESP32 then maintains a High PWR_HOLD voltage to keep the Mosfet enabled and grounds unified.
The issue is that the Q5 transistor is not fully activated with the 3.2V PWR_HOLD coming from the ESP32. And the Q1 Mosfet is not a-> Leading to Ground being 0.7V higher than RPP-. I am seeing issues with charging circuit and spooky happenings elsewhere.
Full battery is at 8.2V - Low is around 6.8V
The ESP32 is connected to 3.3V and Ground.
The device turns off when the ESP32 sends PWR_HOLD Low as espected
The charging circuit is controlled by a BQ24005 connected to ground
How can I saturate these two components, Q5 and Q1, to fully activate them?
Please let me know if more info is needed
Needless to say I am an amateur/student and may not know what I'm talking about :)

r/AskElectronics - Help needed Power-latch circuit



r/AskElectronics - Help needed Power-latch circuit
 

Attachments

  • 1693858809808.png
    1693858809808.png
    128.4 KB · Views: 1

Harald Kapp

Moderator
Moderator
Nov 17, 2011
13,645
Joined
Nov 17, 2011
Messages
13,645
The issue is that the Q5 transistor is not fully activated with the 3.2V PWR_HOLD coming from the ESP32.
The gate-source threshold voltage of Q4 can range from 2.4 V to 3.6 V. With 3.2 V at the base of Q5, the emitter of Q1 and thus the gate of Q4 will be at ~ 2.6 V. This is not sufficient to ensure Q4 is on.
One way to remedy this is:
  • insert a diode with anode to the base of Q5, cathode to the ESP's PWR_HOLD.
  • add a pull up from the base of Q5 to Battery+, e.g. 10 kΩ
Leading to Ground being 0.7V higher than RPP-.
Very likely a measuring error. Where should a voltage less than 0 V come from?
 
Top