Electronic – Imposing AC ripple on DC voltage


I am trying to impose an AC ripple of 0.9V peak to peak (1kHz) on 36 volts DC supply for one of the test using following circuit.

Without any load connected, I get the proper AC imposed DC voltage but as soon as I connect a resistive or capcitive load to the output, the AC ripple of 0.9V just vanishes. Only 36 volts is left behind. The AC current source is capable of sourcing 400mA which is much higher than my actual current requirement of 280mA DC input current of load.

What could be the reason of vanishing of AC ripple when the load is connected ?

  • Do I need to use higher current sourcing AC source?

  • Does the value of the coupling capacitor need to be increased to reduce the output the impedance?

Any other means to achieve the functionality are also welcome!!

enter image description here

Best Answer

For simulation, just connect the two voltage sources in series. You can do the same with the AC source directly, as vangelo says, but it's more obvious on the schematic if you do it with two voltage sources.

For a real circuit you can do the same if at least one of your voltage sources is not grounded.

If the voltage sources are grounded, then you could add a series inductance (a few, say 3H) in place of the diode and something like 1000uF/50V electrolytic low-impedance blocking capacitor in series with the AC source, however the AC source needs to be protected against the 36V surge at power-on and capable of supplying the load current plus reactive current through the 3H inductor.