I need to design a circuit to charge a capacitor from 0 to 2V. The circuit should not be that complicated and no matter the type of capacitor, it should never exceed 2.7 V when charging. The capacitor that I have to charge can be charged between the range of 1nF to 1F and have a not too bad efficiency and not consume much current because I have a limit of 40mA of load. Also, I need it not to download when it is loaded.

This is the design I thought of, but I think it's very simple and there are better ones.

Circuit Diagram for Chargin Supercap

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    \$\begingroup\$ define "not too bad efficiency" It will always be low going from 5V to 2V with a resistor. Your max supply current and load currents must be separate specs.. The cap must have some other reason for being there as a transistor can amplify C values if needed for a time constant. \$\endgroup\$ Sep 1 at 13:45
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    \$\begingroup\$ That circuit may have a problem if the reverse leakage current of the Zener diode > leakage current of the capacitor. If it does then C1 will continue to charge. \$\endgroup\$
    – Transistor
    Sep 1 at 13:46
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    \$\begingroup\$ Always think in terms of input and output specs with a given purpose before considering any configuration.... then tell us what they are \$\endgroup\$ Sep 1 at 13:47
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    \$\begingroup\$ A 2V low quiescent current LDO linear regulator with a 50 ohm resistor in series with the cap (2V/40mA) might be a good solution. Something like this: digikey.com/en/products/detail/ablic-inc/S-812C20AY-B2-U/… . But, more details are needed to be sure. \$\endgroup\$
    – Mattman944
    Sep 1 at 14:06
  • \$\begingroup\$ @TonyStewartEE75 Well I have to design and create a circuit that charges a capacitor from 0V to 2V and the circuit must be safe for both the operators and the devices. The circuit can use up to two Arduino Uno digital outputs to deliver energy .No other energy source is allowed. The circuit should work for devices with capacitances from 1nF to 1F. The circuit should never surpass 2.7V, regardless of the capacitor. The circuit must not draw more than 20 mA per digital pin. \$\endgroup\$ Sep 1 at 14:45

1 Answer 1


Assuming a regulator with low quiescent current, this will have almost no wasted power after the cap is charged. Use the minimum value for C1 and C2 from the datasheet. For the part I chose, C2 min is zero.

A constant current would charge the cap faster, you may be able to find a single part that will regulate current to your requirement and have a constant voltage output.

For charge time, charging through a resistor is not optimum. A 1 Farad cap will take about 3 minutes to charge to 95%.


simulate this circuit – Schematic created using CircuitLab

  • \$\begingroup\$ i made your circuit and im receving the 2v as output but when i connect the capacitor it does not stay charged. What can i do? \$\endgroup\$ Sep 1 at 23:27
  • \$\begingroup\$ @CarloDavid006 - If you need the cap to stay charged after you remove the GPIOs, you need to list that as a requirement. You could try a diode in series with the resistor, but you will need to use a larger voltage regulator to compensate. \$\endgroup\$
    – Mattman944
    Sep 2 at 1:49

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