Could somebody tell me why someone would need circuit like that in supply rails?


I assume it is for making DC voltage smoother by parallel capacitor.

However, my 24V power supply has 500mA output (I am going to feed amplifier with 12-0-12 V instead of 15-0-15V).

So 10Ω does nothing in this case to decrease current level.

Do I need a minimum 100Ω or 1kΩ protection resistor or not? I read that an amplifier should have no more than 5mA current flowing. Or does that concerns only inputs?

If I put a 1kΩ resistor, should I change the capacitor?

  • \$\begingroup\$ the 10 ohm resistors are there for surge current limiting. the capacitors are there for voltage ripple reduction, supply decoupling for fast transient current surges. \$\endgroup\$ – KyranF Jul 24 '14 at 14:53

The resistors are not for current protection, but rather for noise filtering. Each resistor with its associated capacitor forms a low-pass filter on the supply line. 10 ohms with 10 uF will give you a cutoff frequency of about 1.6kHz. This will help the op-amp (assuming this is an op-amp) reject any high frequency noise on supply and keep it from getting to the output. Most op-amps have pretty good power supply noise rejection already, but it tends to get worse at higher frequencies. The 10uF caps are OK here, but I would think about putting some 0.1uF caps in parallel with them in order to help with high frequency decoupling. As for current protection, most op-amps have built-in output over current protection, so you can easily check to see if your amplifier does as well.

  • 1
    \$\begingroup\$ Yup, (though I'd call it power supply filtering.) I will sometimes do the same thing on the IC that is the source of the PS disruption, and add some C to ground on both sides of the resistor. \$\endgroup\$ – George Herold Jul 24 '14 at 15:07

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