# zener Flyback diodes issues and pull-in & hold current issues in this Relay circuit

Posted on Feb 5, 2014

Although this may be a basic question but I`m still struggling with it. In this schematic, two zener diodes D1 and D2 are connected back-to back across relay coil L1. The BVds = -30V for Q1. Can I use 15V(Vz = 15V) zeners for D1 and D2 instead of 5. 1 V zeners Will the relay coil or contacts can get damaged during turn-off of relay If required, I

`m using this relay (5V DC Standard Coil). Also, to reduce steady state current consumption of relay coil, I wanna use the RC ckt shown aside in schematic. As soon as Q1 turns-on, uncharged capacitor temporarily appears as a dead short, causing maximum current to flow through the relay coil and closing the relay contacts without chatter. As the capacitor charges, however, both the voltage across and the current through the relay coil decline. The circuit reaches steady state when the capacitor has charged to the point that all the current through the relay coil is moving through R1. The contacts will still remain closed until the drive voltage is removed. Which is the best place to put this RC ckt - section marked `A` or `B` in schematic. Will it make any difference Section-B seems to me the best choice, as when Q1 turns-off, capacitor C1 can discharge via R1 through ground. How will C1 discharge when instead I place RC ckt at section-A Am I missing something here Does putting this RC ckt has any side-effects Any better solution Say in above schematic I have 6V DC Standard coil(see datasheet above), 48. 5 ohm relay. And take C1 = 10uF say. Assume that R1C1 ckt is placed at section-A in schematic above. The power supply is at +5V. For a Drop of 3V(Hold-on voltage) across relay coil, the current must be 62mA approx. through coil. So drop across R1 at steady state is 2V. For a current of 62mA through relay coil at steady...

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