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I just read about 'decoupling capacitors' to stabilize the voltage. I have some small voltage drops on this schematic when I made it into a PCB.

Can capacitors would solve the problem?

If yes, where do I have to put them?

enter image description here

Here's the PCB view. Maybe there is something wrong with it: enter image description here

I measured on the M1/M2/M3 outputs. When I press SW1, I've 5.2V. When I press SW1 & SW2 I'm at 5.0V. When I press SW1 & SW2 & SW3 I land at 4.8V. Measured on the same (M1) output with both probes on GND and VCC of the connector.

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    \$\begingroup\$ Where exactly you are measuring voltage drops? And doesn't the regulator already have enough bypassing? \$\endgroup\$
    – Justme
    Jan 16 at 12:15
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    \$\begingroup\$ Unlikely that the caps would solve the voltage drops. (They would help with transients, not DC issues). My bet is that you are measuring the voltage of the transistor when its on. \$\endgroup\$
    – Wesley Lee
    Jan 16 at 12:22
  • \$\begingroup\$ I measure on the M1/M2/M3 outputs. When I press SW1, I've 5.2V. When I press SW1 & SW2 I'm at 5.0V. When I press SW1 & SW2 & SW3 I land at 4.8V. Measured on the same (M1) output with both probes on GND and VCC of the connector \$\endgroup\$
    – dessi
    Jan 16 at 12:25
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    \$\begingroup\$ Do you have the motors connected to M1, M2, and M3? \$\endgroup\$
    – JRE
    Jan 16 at 12:44
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    \$\begingroup\$ Likely your circuit as a load has nothing to do with voltage drops and the voltage drop comes from the power supply itself or the wiring when load is added. Just measure the power supply itself when there is no load or some load. \$\endgroup\$
    – Justme
    Jan 16 at 12:58

1 Answer 1

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You already have a decoupling (bypass) capacitor (C1) where it's needed (across the supply of U4). So, no, you don't need more.

Also, no, it won't solve your long-term voltage drop problem. Small decoupling capacitors supply short bursts (~microseconds) of power, not long-term power.

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