Guru
Joined: 21/06/2018
Location: AustraliaPosts: 1231
| Posted: 03:06pm 29 Oct 2020 |
Yes Techie007, thanks for reverse engineering & posting the circuit, an excellent effort.
I am fairly confident though that there is an error with the over current protect sense part of the schematic. The 2K resistor on pin 5 of the LM358 should go to the load side of the current shunt (the same as the connection net Csense ), else it cant see the actual output current. The circuit appears to act as a maximum output foldback current limiter (limits the PWM duty cycle once the threshold is exceeded), the input under-voltage appears to operate in a similar fashion reducing output PWM to reduce power throughput.
I assume the output shunt is around 1.2 to 1.3 mOhms which would allow for an output current ~ 40A+ before the over current protect kicks in.
The first regulator also appears to be shown pinned incorrectly. I believe the 13.5V regulator IC is an AP1609 or exact equivalent and the pinning is out by 180 degrees.
For the sake of adding a few buffer transistors to properly drive the 3 indicator LEDs from the 13.5V supply I think it could have ended up a much better design.
Lastly to remove ambiguity of exactly how to perform the modifications, a few pictures would help to ensure what needs to be done for the less technical readers.