SG1468T voltage regulator - voltage adjust

[jeroen79]

I found this voltage regulator.
Normally it will give +/- 15V but according to the datasheet it has a voltage adjust pin that can adjust both outputs between 9 and 20V.

In the circuit diagram the voltage adjust goes to the base of one of a pair of transistors.
The other transistor's base is linked to a zener diode going to ground and a resistor going to positive supply.

As far as I can see this pair will control the current mirror above it.
With the voltage adjust not connected the right transistor would always be off, right?

How do I use the voltage adjust? The datasheet doesn't specify this.
I can use it to turn the right transistor on before or alongside the left transistor but I cannot force the left transistor open or closed.
This puzzles me as the datasheet says I can adjust the voltage up and down.

Datasheet: http://www.eoo-bv.nl/documentatie/SG1468T.pdf

Extra question: How does this regulator compare to an LM78xx or LM317 and their negative counterparts?
Is it useful to make a small split rail powersupply?

[Tac Eht Xilef]

Check out the datasheet for the equivalent (original?) Motorola MC1468/MC1568, which has some little detail on using it as an adjustable regulator.

Though, from the application circuits it looks like it can only be configured for 8v-14.5v or 14.5v-20v, not 9-20v - which makes sense from your understanding/explanation of the internals.

[jeroen79]

Thank you.
That datasheet has some more information.

Here there is connection between the transistor's base, the voltage adjust pin and a stack of zeners and resistors between Vsense and ground indicated by a little 'knot' that is not there on the SG datasheet.
I suppose the potentiometer can be used to tweak this stack.