I'm trying to build uninterrupted power bank for my 9V 1A router and 12V 0.9A ONU. I have made a circuit Mindmap. But I think I have done some questionable things in it. Such as, I don't know the efficiency of the LM317 based 12V to 9V linear voltage regulator. I think I'm loosing 50% of power during the conversions. So there isn't much power to run this devices and charge the 18650 lithium battery simultaneously.

Joint box means only wire joints.

|<, >| This are diode symbols.

On 2nd mind map the relay cut's off when the battery is changing.

Mindmap of Mini ips

Which one is better than other from the above? What can I do to improve the better one even more?

Is there any good quality diagram exist for this application?

What type of diode should I use, like, zener diode?

Also I want to build this as cheaply as possible. Thanks in advance for the support.

  • 3
    \$\begingroup\$ An LM317 is not a buck converter. \$\endgroup\$
    – uglyoldbob
    Jul 24, 2020 at 23:08
  • \$\begingroup\$ I know, it's a linear voltage regulator. I was saying that in general. \$\endgroup\$ Jul 25, 2020 at 4:33

1 Answer 1


If your current out of the LM317 is Iout you are dissipating 3V*IoutA power at the LM317 as heat. Also, check what are your current ratings of your router and your ONU to calculate your power requirements and check if your supply can handle it. Measure the voltage and current at the 5V supply output to see if it is able to support the load.


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