Hi Experts,

Need your expertise for this circuit. Well I'm trying to figure out what is the main purpose of diodes (all are 1n5060) connected in +in to out of regulators CR1 to CR3 also for the resistors R1 and R2, is it for current sensing? Plus my other problem is if tried to power only U1 (for +12V regulation) it is working fine, same goes for U2 (-12V regulation) it is working fine but if I applied power to both of them the -12V is turning to +12V.

Thanks

 

Your schematic is missing a bit of information, namely, where are the voltages coming from.

 

Well I'm trying to figure out what is the main purpose of diodes (all are 1n5060) connected in +in to out of regulators CR1 to CR3 also for the resistors R1 and R2, is it for current sensing?

No. They are for voltage regulator reverse break down protection.

Plus my other problem is if tried to power only U1 (for +12V regulation) it is working fine, same goes for U2 (-12V regulation) it is working fine but if I applied power to both of them the -12V is turning to +12V. Thanks

You cannot power both the circuit(U1 and U2) with the same power supply of +20V.

You'll need to have a dual output power supply of +/-20V, i.e. a +20V to common(PGND) and a -20V to common, three wires connection, or a total of 40V between two of the wires.

A normal power supply of just +20V and common will not work and as you have just found out, it can power only one part of the circuit at a time.

 

Yes I am using dual power supply, +20V and -20V as my input and pgnd as my common. if diodes are for protection how about the resistors?

 

Yes I am using dual power supply, +20V and -20V as my input and pgnd as my common. if diodes are for protection how about the resistors?

I would guess the resistors are a cheap shot to reduce the heat dissipation of the voltage regulators.

Never seen any other design with such resistors fitted. The +12V and -12V outputs would rise to +/-20V if there is no loading on the power rail.

 

Ok so to sum up

The module receives inputs and outputs through the connector strip. It receives +20volts on pins 4/5 and -20 volts on pins 2/3 pins 6/7 and 14 are zero (ground).

From these supplies R1 and R2 provide approximately 1/4 amp of unregulated bypass current to the outputs.
In addition current through R1 also supples U3 , the 5 volt regulator.

Regulators U1 and U2 provide regulated 12 volts supplies to output pins U1 to 8/9/10 at +12 volts and U2 to 1/11/16 at -12 volts.
U1 also supplies any additional current to regulator U3.

The +12 and -12 supplies are independent and can operate without the other present. The 5 volt supply is fed from the same 20v positive supply as the +12 volt and so requires this. It can operate up to 1/4 amp independently of the 12 volt supply.

The diodes provide a discharge path for the electrolytics C4/C5/C6 strapped across each input in the event of sudden removal of the 20 volts supplies. The output caps will discharge through the load.