0V-15V to -5V|+5V question

[MegaWatt]

Hello everybody, I have designed a circuit to convert a 0-15V power supply to a -5V|+5V supply. You can see it on this picture:

The voltages that I have written there are the voltages I measured when I built the circuit. Obviously this is not correct and I cannot find why, I would expect the inputs of the voltage regulators to be at +/-7.5V and the output at +/-5V, but that is not the case. I have already disconnected the diodes to check if they were causing problems but the result was the same. Can anybody see what I might be doing wrong? Thanks in advance!

[Dave]

The way I see it, you only have 2 input connections, right?
You need to provide an unregulated positive supply rail, negative rail, AND ground. Just connecting 15V between positive and negative rail won't cut it.
If your load doesn't require much power, you could try using a supply rail splitter. I said low power, because this circuit isn't too efficient.

[MegaWatt]

Yes you are right, I see my mistake, very stupid. Thanks a lot!

[Dave]

Hey, you make mistakes and you learn from them. Don't worry about it.
You are welcome.

[hlavac]

As to why it does not work, see which way does the current have to go to charge each input cap,
you will find it needs to go thru the opposite side regulator and load...

Read up on the concept of "virtual ground". You need a way for current to bypass the side that requires less current.

Fix could be as simple as putting two ~8V zeners across the input caps to bypass the other side unloaded regulator. Make sure that together the zener voltages are slightly higher than your supply voltage.

[Zero999]

How much current do you need? 15V doesn't give you much headroom for the dropout voltage.

The zeners are probably the simplest option but transistors would enable it to work from a wider voltage range.
http://www.learningelectronics.net/circuits/discrete-virtual-ground-circuit.html