Variable Power Supply controlled by microcontroller

[gkthebigj]

Hello all,

I am trying to deisgn a 0-12 and 0- -12v adjustable power supply.
I am using LM2574 to generate adjustable +12v and LM337 to generate -12v.
Please see the schematic attached.
View attachment 63399

I recently found out i cannot use the digital pot mcp4462 in here because the tolerable
voltage is only 5.5v with these pots.
Can someone tell me alternate ways to control the output voltages through a microcontroller in
these cases?

 

[alec_t]

Here's how I'd try to do it, assuming (a) +15V and -15V fixed supplies are available, (b) the digital pots have a maximum resistance of 100k each, and (c) independent control of the + and - adjustable supplies is required.
R1 and R4 are selected to prevent the digital pot voltage rising above ~ 3V, for compatibility with the micro controller .
U1 and U3 are unity-gain buffers. One can be omitted if a single pot is required to control both variable supplies so that they track each other.
U2 and U4 are respectively non-inverting and inverting amplifiers, each with a gain of ~ 4. The opamps need to be rail-to-rail I/O types if a wide control range is required.
M1 and M2 provide power gain. Feedback is taken from across the loads to stabilise the output voltages.

 

[gkthebigj]

Thanks for the suggestion.
I also need to make sure a maximum current output of 500 mA for both the supplies.
Can you tell me the current can be sourced by this circuit in worst case?
Also, do i need to add a short circuit protection?
Thanks in advance?

 

[alec_t]

Can you tell me the current can be sourced by this circuit in worst case?

Many Amps, depending on the 15V supply and the FET ratings.

I also need to make sure a maximum current output of 500 mA for both the supplies.

I'll have a think about that and get back to you.

Also, do i need to add a short circuit protection?

That's for you to decide. But won't current limiting to 500mA provide that?

 

[alec_t]

Here's the circuit with current-limiting. Even with a max 0.5A limit the FETs will get hot and will need substantial heat-sinks.

 

[gkthebigj]

thanks a lot for your help.
This design seems really cool fro my purpose.

Actually i m designing a Power supply board for general lab purpose.
It will have +15v fixed(500mA), -15v fixed(500 mA), 5v fixed(1.5A) and +- 12 adjustable.
I was stuck on the adjustable ones. After lot of searching i found these ICs LM337 and LM2574.
The problem is i have already bought the compenets (all the ICs). I will see the prices of the ICs you
suggested and take a decision based on budget.

Thanks again for your help. God bless

 

[alec_t]

I will see the prices of the ICs you suggested

The ICs and FETs in the circuits I posted are just selections from the LTSpice simulation collection, chosen to suit the simulation. I'm not recommending any particular manufacturer. I haven't checked their package type, price etc. Many alternatives are available. Feel free to substitute other types.