Understanding a Power supplies voltages-Help please.

[djsb]

I'm trying to simulate this power supply using Qucs-s,  LTspice and Micro-Cap 12. I can't figure out how it works and if the 0v rail is positive and at what voltage.
I basically want to provide another circuit with the same voltages WITHOUT having to build/simulate this power supply.  I can usually reduce a supply like this to batteries. Not this time. Can someone help me to figure it out? Thanks.

[George Edmonds]

Hi

This supply provides -12VDC and -18VDC the ground/0V is tag point 6 or U1/6

Hope this helps

George

[james_s]

Voltage is always relative, 0V just denotes the reference point, in other words it's "ground".

[George Edmonds]

3. 1 .8. SUPPLY
The plus potential of the - 1 2 V and - 1 8 V supply a re connected to circuit zero. Both sources are stabilized.
The un stabilised voltages are produced by rectifier 405 on unit 2. The output voltage, divided by resistors
637/638/639, is compared with the reference voltage across zener diode 404 via operational amplifier 322.
The output voltage of operational amplifier 322 controls series transistor 3 1 1 v ia current amplifier 3 1 2 .
The offset-voltage of the operational amplifier is reduced b y resistor 64 1 . The short-circuit it current of the - 1 2 V
supply is l limited by resistor 645.
The stabilizing circuit for the - 1 8 V supply is the same as given for the - 1 2 V suppy. The reference voltage is
the - 1 2 V supply. The output voltage is compared with the reference voltage via voltage divider 635/636.
A separate secondary winding of the mains transformer supplies the voltage for the scale illumination ( lamps
8 1 1 ... 8 1 3) and for the il illumination of the indicator via switch 803/1 A ( button CAL).

This is the explanation given in the service manual

The circuit zero (0V) is U1/6  which is the instruments common which may or may not be connected to the metal case work or the incoming mains supply CPC (earth)

George G6HIG

[coromonadalix]

Your ground is "indeed"  pin 6  or u1/16


You could say :  your supply / floating ground is  pin3 of the board going to the transformer pin 12, when you debug psus like this  you tend to go on the common point of the 2 main capacitors (1000uf) for the meter ground

Sure you will have the 12volt difference and the 18 volt too, relative to the floating ground,  it could play some tricks with the circuit ground, if you dont know where to take your measurements

They used   the pin 6  u1/16 pin as a ground to simplify the op amps supply pins ... thats the way i see it, no need for additional psu voltages for them.

my 2 cents