uA78HGA

[ChrisP58]

??? I said ground fixed at -5V; not floating??

Yes, you did.

But in post #6 the OP asked about floating the ground. That's what I was referring to in post #9.

 

[Pim Driessen]

Dear Forum Members,
It seems that bringing down the uA78HGA power supply voltage is not easy.
The way I came up with solving it might be a bit strange but it is a solution.
By adding an LM317 to the power supply and making it switchable between the LM317 and the uA78 HGA, you can now start with the LM 317 that can be used up to 5 volts and by switching to the uA78HGA, you can start from 5 volts to 30 volts.
It still needs to be checked whether it is possible to make a negative voltage of 1.2 volts with the transformers that are used in order to be able to use the LM317 from 0 volt to 5 volt, I think that is a condition. to start from 0 volts.
Below 2 diagrams with the switch positions, there was no 2-position switch available in the software, therefore the multi-position switch, but it will be a 2-position switch.

The LM109H are fictitiously chosen as an example only.

It will be a dual power supply from 0 to 30 volts.

What do you think of the idea?

Greeting
Pim

 

[sarahMCML]

The following diagrams show how the two options have been tried by me, but neither gives the correct result.View attachment 130361
View attachment 130362

Seems to me you need to take the bottom of R4 to pin4 of the uA78HGA, since the reference is effectively across those two points!

 

[Pim Driessen]

That is coincidentally, got the same tip this morning from another Forum.
But thank you very much for the response, I still have to try it out, but a response is coming back from me.
Greeting,
Pim

 

[Pim Driessen]

Seems to me you need to take the bottom of R4 to pin4 of the uA78HGA, since the reference is effectively across those two points!

It's great, it works.
I am very happy with that, thank you for the help.
Greeting,
Pim

 

[Pim Driessen]

Here the - 5 volt power supply along with the base power supply for the uA78HGA.

 

[Pim Driessen]

Dear Forum Members,
The power supply is now working.
With the possibility of the negative voltage of -5 volts it is possible to regulate from 0 volts, but to be able to regulate it from the 5 volts that the uA78HGA original supplies it has been made switchable.
Here are some pictures of the finished product
Thanks for the support.
Greeting,
Pim