jeffbro
Well-known member
To assist anyone interested enough to look at the attached schematic, all this text is copied there.
The V+ and V- regulators in this PSU track each other and each will shut down if the other fails. I want to individually troubleshoot and test them but I want to make sure I understand how they track and how I can 'separate' them without the risk of unpleasant surprises.
It appears that when the V- rail goes down, the lack of a voltage at R47 causes Q3 to turn on and rob U5 of its input at pin 5, turning off the V+ rail.
It also appears that the 723 in the -18V regulator gets its pin 5 input signal not from the 723's internal reference voltage (pin 6) as is typical but instead from a voltage divider hanging off the V+ regulator's output rail. So, if the V+ rail goes down there is no input to the 723 and it turns off the V- rail.
If I understand this correctly then...
It seems that I could make the V+ rail operate independently by lifting one end of R46 so the loss of V- can't turn on Q3.
To make the -V rail independent I could add a temporary 4K7 resistor between U7 pins 5+6 and lift the ends of R61 and 62 that join at pin 5.
Am I on the right track here or is there a simpler way of making the +/- regulators operate independently?
The V+ and V- regulators in this PSU track each other and each will shut down if the other fails. I want to individually troubleshoot and test them but I want to make sure I understand how they track and how I can 'separate' them without the risk of unpleasant surprises.
It appears that when the V- rail goes down, the lack of a voltage at R47 causes Q3 to turn on and rob U5 of its input at pin 5, turning off the V+ rail.
It also appears that the 723 in the -18V regulator gets its pin 5 input signal not from the 723's internal reference voltage (pin 6) as is typical but instead from a voltage divider hanging off the V+ regulator's output rail. So, if the V+ rail goes down there is no input to the 723 and it turns off the V- rail.
If I understand this correctly then...
It seems that I could make the V+ rail operate independently by lifting one end of R46 so the loss of V- can't turn on Q3.
To make the -V rail independent I could add a temporary 4K7 resistor between U7 pins 5+6 and lift the ends of R61 and 62 that join at pin 5.
Am I on the right track here or is there a simpler way of making the +/- regulators operate independently?
