Q/A about power supply

[luffy]

I was asked by my teacher to produce a schematic diagram of a triple output power supply which supply output voltages of 15v
-15v and -5 v of not more than 15 component. After looking through different electronics forums and web page i manage to come out with this diagram. I just want to ensure that the circuit in the diagram will net me my desire voltage. Thanks
(meanwhile i will be writing a report)

 

[luffy]

As i was writing the report, question starts to surface, i was told that the diode from the negative side of the power supply should be place in the opposite direction relativeto that of the positive side. Why is this so?

 

[luffy]

Issit becos by placing the diode in that position, when the -15v and the gnd pin is connected, current will flow from the GND pin to the external circuit and back to the -15 v pin, hence making the the voltage negative.