Hi,
I am a recent graduate who has been asked by my employer to reverse engineer a power supply for a linear power operational amplifier.
The power supply appears to be very simple, it consists of a fused 230Vac input to the primary side of the transformer, the secondary side is a 45-0-45V output which then feeds into a bridge rectifier followed by a 33K resistor and 2200u cap in parallel which leads to the output terminal.
As I have no datasheet or any other kind of information on the power supply I decided to measure the voltage out to see what it was suppling. This is where things started to get confusing.
The output voltage of the power supply measured at +/- 64V (no load) and +/- 61V (measured at input to actual load).
Therefore my query is how can a 45-0-45V secondary side output produce a 61-0-61V supply by only using a rectifier, resistor and capacitor?
My thoughts so far are:
- The transformer has the wrong rating sticker on it. (I will check this when I get a chance by measuring the voltage directly on the transformer)
- The transformer has a single 20V output (which as far as I can see has been left unconnected), maybe this has been connected to the 45V winding in some why to produce 61V but based on my current understanding this would not be possible.
- There is some wizardry going on with the other components that I am yet to fully understand.
Any help would be much appreciated.
Thanks,
N0blea
Also as an aside; the 2200u capacitors are only rated to 63V. Seems strange to me that if the power supply is intended to produce around 60V, why would you fit a 63V cap instead of a 80V cap, size and cost are not issues.
