Figure 1.  Schematic Diagram for a Simple DC Voltage Ripple Remover

Figure 1 shows a simple circuit for removing an AC ripple from a DC voltage. The main component of the circuit is an operational amplifier configured as a simple amplifier in common-mode operation.  This means that both the inverting and non-inverting inputs of the op-amp get the same input voltage, i.e., a DC voltage Vin with an AC ripple Vripple.  The only difference is that the inverting input has an input capacitor that blocks the DC voltage.

Since the op-amp amplifies just the difference between the voltages at its two inputs, it cancels out the AC ripple (which appears at both inputs).  On the other hand, the op-amp amplifies the DC voltage Vin since this is only present at the non-inverting input. However, the op-amp is configured to have a DC voltage gain equal to 1, so the output of this circuit is just equal to Vin.

Since the AC ripple can only be cancelled cleanly if both op-amp inputs have equal gains, the 10K potentiometer is used to compensate for any inherent differences between the inputs' gains.

See Also:  Operational Amplifiers

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