Hi guys,

Quick question regarding a circuit containing a diode and capacitor in parallel with each other. In the schematic you can see that in one situation the DC takes the path from terminal 11 to terminal 3 as traced through the green highlight. The voltage is 125 VDC with positive at terminal 11. I'm just wondering what the purpose is of this configuration. Is the capacitor there to provide some extra "oomph" so to speak to the load (not pictured) downstream? If so, why is there not the same configuration on the outputs of terminals 1 & 2? Terminals 1, 2, and 3 all energize the same load individually at certain conditions, never concurrently. If it helps this is a circuit used in protective relaying for transmission lines. The eventual load is the trip coil for a circuit breaker.

Thanks,
Dave

 

From what is shown one would think that once the capacitors charge to some peak voltage the diode stops conducting, and since the circuit is AC coupled the diode appears to have no function.

It might help to see some context for the circuit. Is this an RF circuit? What is the bigger picture?

 

Here is another picture with more context. Sorry about the quality, it's all i could find. So the circuit is not AC coupled, it's pure 125 VDC. The coil is the highlighted component. I don't know the values of the cap or the coil at the moment, but the coil is supposed to operate and open it's associated contact in roughly 48 milliseconds at the soonest if that helps. If needed I may be able to get those values. This picture is the same circuit but with three devices in parallel.

 

See post #3 in this thread.

 

Two possibilities come to mind.

The circuit needs the diode and the capacitor is there to absorb switching spikes, or the capacitor is needed and the diode is there to clamp the voltage in one direction at no more than a diode drop. Which, if either, of these is the intended purpose can be difficult to determine from just a schematic.

 

Capacitors are sometimes placed across solid state rectifiers in the power supplies of radio transmitters and receivers to prevent the rectifiers from modulating rf leaking into the power lines and ground as that can produce hum.