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What I'm trying to do is allowing the current to move through only one component. In the circuit shown, DC voltage is running two components (Z & C), also charging the capacitor
When voltage cut, then capacitor give current to Z & C. What I want to do is allowing the current to flow through only C but not Z. I tried to put zener diode on the line indicated by light blue but the current still flowing through Z (zener diode is not working).
How can I make this work? What can be the problem?
No Zener diodes need to be abused:
When V1 is present, it will supply current for R1, R2, and charge cap C1.
When V1 is disconnected, the cap will supply current to R2 but not R1. Of course the energy in the cap is limited, and the voltage across R2 will decay exponentially towards zero over time.
There will also be a voltage drop across the diode, even when it is forward biased. For example, if V1 is 10 V, then there might only be 9.6 V or so across R2, depending on the current. If this is not acceptable, then a more complicated topology that switches a FET is needed.
A Schottky diode as D1. Be careful of the voltage and current specifications of the Schottky you choose. In this case: at least 40V and 2A to be safely above maximum ratings.
Using a standard diode (eg in4007) should work for your application.
And the current in Z is because the Zener is operating in breakdown region. So either you need to select a Zener which has cut off voltage greater than 28V or just use one of the standard diodes as mentioned above. A standard diode should work perfectly for your circuit.
