As a learning project, I'm trying to create a simple linear power supply using LM317. The basic circuit is well documented on internet, but I want to create a variant that allows me to have multiple output channels.

One of these output channels is for internals of the power supply: powering up an INA219 to measure current drawn, an atmega328 and an LCD for display.

Ideally I want to have two independant variable output channels (1.25V - 12V) and a single internal output channel (5V).

I think the following circuit should work, on paper, but I am not sure it will be really usable in practice. I have the feeling that sharing the same input lines (and grounds) between all channels will create undesirable side effects between them, especially with ICs using spike currents like the LCD.

Here is my take at a circuit diagram: Multiple output channel variable linear power supply

The top part is the variable output channel, the bottom part is the internal 5V channel. They are both forked from the 15V input from a switching wall adapter.

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    \$\begingroup\$ To prevent input spikes to leak through ground, you may use the concept known as star ground, which means run separate ground conductors and join all the ground conductors at a single point (usually the input or center tap in a transformer), the great book "Electromagnetic compatibility engineering" by Ott explains this very well. \$\endgroup\$ – S.s. Dec 5 '18 at 3:04
  • \$\begingroup\$ As an economic matter, I'd suggest to just use three 317's instead of two 317's and one 7805. Generally prices go down on these parts pretty quickly as you buy higher volumes, so it's a good idea to re-use part numbers when you can. \$\endgroup\$ – The Photon Dec 5 '18 at 4:20

Try adding input and output caps to the "precision" regulator because if you don't it may bounce current back and forth with the current drawn by lm317. if you're not familiar with pcb traces and decoupling it's recomended to add one regulator for the digital 5v line and one another for the opamp. or powerup the opamo directly from the arduino? depending the power cycles consumed. that may add complexity to the design but provide a perceptual of higher quality design isolation from 15v.

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    \$\begingroup\$ What does "bounce current back and forth with the current drawn by lm317" mean? The circuit shown is almost identical to the datasheet recommended configuration. \$\endgroup\$ – Jack Creasey Dec 5 '18 at 5:20

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