Clamper adding +5 V DC level

A clamper circuit (dc restorer) is a circuit that shifts an ac waveform up or down by adding a dc level to it, without changing the waveform's shape. It is made of a capacitor, a diode, a resistor and, when needed, a dc battery.

Clamper that adds +5 V

Assumption: "adds +5 V" is taken to mean that the negative peak of the output is clamped at +5 V (ideal diode), so the whole waveform is moved upward.

                C
 Vin o---------| |--------+--------+---o Vout
                          |        |
                        -----      |
                         / \   D   R
                        /___\      |
                          |        |
                        + |        |
                        -----      |
                         ---  5 V  |
                        - |        |
 GND o--------------------+--------+---o

The diode anode connects to the positive terminal of the 5 V battery (battery negative to ground) and its cathode to the output node. The resistor R is across the output.

Working (Vin = Vm sin ωt, ideal diode)

• The diode turns ON whenever Vout tries to go below +5 V. In the first negative half cycle, the capacitor charges to Vc = Vm + 5 V.
• Afterwards the diode is OFF and the capacitor holds this voltage (RC ≫ T).
• Output: Vout = Vin + (Vm + 5)

For example, for Vm = 10 V, Vc = 15 V and Vout ranges from +5 V to +25 V.

If the aim is to add exactly a +5 V dc component to the signal (mean level = +5 V, i.e. Vout = Vin + 5), the battery value should be 5 − Vm (a negative value, i.e. a reversed battery, when Vm > 5 V).

For a real silicon diode, the clamped level is reduced by 0.7 V.