iceblu3710
Member level 3
I have recently received several power supplies ranging from 8V/5A to 18V/3A and one has fantastically stable output regulation. I have done a bunch of tests and their is almost no measurable ripple and on overload the the current ever rises above the variable set point and the voltage drops without a single spike!
Two others however do not have these wonderful features and their analog meters have non linear movement. I would like to diagnose the problem and understand how the system works.
I have the schematic below, My first task next week will be to trace the pcb out and place the resistance, cap, diode, and transistor values on the schematic. After I do this what would be the best way to go about understanding the system?
I have Multisim 10 and can build the circuit in there but other than guessing and testing the transistor interaction is a bit confusing to me. A few questions I have just by looking at the schematic are:
1) lowercase a comes from the (+) terminal output to the winding shield of the transformer secondary. The transformer is isolating but then why isn't the output ground to the secondary shield?
2) (H) and (J) are at the same potential while (J) goes to output terminal (+) and (H) is the neutral center tap on the secondary. This makes me think the variable voltage happens by lowering the potential of the (-) terminal and the (+) one is fixed. However that can not be as it is clearly obvious that the upper block is the transistors allowing a percentage of the voltage from the xformer to the (+) terminal.
Thats just the beginning of my confusion, the more I look the less I understand. If I where to make a PSU myself I would use op-amps however that design requires a series resistor to pull the current off of for overload protection while this complex circuit seems to not have that limitation.
Anyways, what steps would you guys take to understand this PSU operation?
Two others however do not have these wonderful features and their analog meters have non linear movement. I would like to diagnose the problem and understand how the system works.
I have the schematic below, My first task next week will be to trace the pcb out and place the resistance, cap, diode, and transistor values on the schematic. After I do this what would be the best way to go about understanding the system?
I have Multisim 10 and can build the circuit in there but other than guessing and testing the transistor interaction is a bit confusing to me. A few questions I have just by looking at the schematic are:
1) lowercase a comes from the (+) terminal output to the winding shield of the transformer secondary. The transformer is isolating but then why isn't the output ground to the secondary shield?
2) (H) and (J) are at the same potential while (J) goes to output terminal (+) and (H) is the neutral center tap on the secondary. This makes me think the variable voltage happens by lowering the potential of the (-) terminal and the (+) one is fixed. However that can not be as it is clearly obvious that the upper block is the transistors allowing a percentage of the voltage from the xformer to the (+) terminal.
Thats just the beginning of my confusion, the more I look the less I understand. If I where to make a PSU myself I would use op-amps however that design requires a series resistor to pull the current off of for overload protection while this complex circuit seems to not have that limitation.
Anyways, what steps would you guys take to understand this PSU operation?