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Hello if unregulated power supply (transformer, bridge and main caps) is 30 cm away from the circuit to feed, is it better to put the voltage regulator close to the circuit (long input and short output) or close to the power supply (short input and long output)?

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  • \$\begingroup\$ I'd say it depends on the input and output specification (voltage, amperage and noise requirements). \$\endgroup\$ – Arsenal Jan 2 '18 at 22:41
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    \$\begingroup\$ If you have long leads from the psu cap to the circuit then it is a good idea to place a capacitor across the circuit supply after the lead. But whether you want to let the ac-cable or the dc-cable be 30cm longer (That is how I understand your question?) This is the difference; On the AC side the cable does not need to be as thick to transfer the same power because the voltage is higher, but it depends a lot on your application, if you have large output current then place the psu close to the circuit. I would genarally say put the PSU close to the circuit and let the ac cable be 30cm longer \$\endgroup\$ – Vinzent Jan 2 '18 at 22:49
  • \$\begingroup\$ It is only unregulated DC long 30 cm. Trafo caps and bridge are together \$\endgroup\$ – Gianluca G Jan 3 '18 at 5:27
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If your DC currents are high and the regulator is at the power supply then you will either need to use heavy cables and connectors or you may experience voltage drops along the wires that make the supply voltage too low.

However, 30cm is by no means long for power cables.

If the supply is only used on the target board it is generally better to do the regulation on the board itself so your wiring and connector resistances are a bit less critical. It also alleviates you of the necessity of having a separate PCB to house the bridge rectifier and capacitors which can also be located on the target board.

If the power supply is shared across multiple boards, sensors, indicators etc, it may be more appropriate to have a central power regulator rather than add additional connectors to the main board. However, when you do that you have to pay special attention to ground and power loops that may introduce noise issues.

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