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I have a circuit that uses regular diodes, and I only have zener diodes in hand. As I understand, zener will conduct after a certain voltage in reverse, so all I have to do, is pick a voltage that is slightly higher than my circuit will send to the diode, and it should not conduct in reverse, and work like a regular diode. Am I right?

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  • \$\begingroup\$ I don't immediately see any problem with this, though I would recommend picking a zener voltage substantially higher than your operating voltage, not just slightly. There may be some pitfall I don't see, too. \$\endgroup\$ – Hearth Mar 16 at 20:00
  • \$\begingroup\$ Why substantially higher? The foward voltage need to stay in my operation range. (I don't have the spec of my diodes, picked them on ebay a while ago...) \$\endgroup\$ – Eradash Mar 16 at 20:04
  • \$\begingroup\$ @Eradash The Zener voltage and forward voltage are largely unrelated to one another. I say substantially higher because you want to avoid your diodes operating in the breakdown region, and it's good to have plenty of room between your normal operating state and a failure mode. \$\endgroup\$ – Hearth Mar 16 at 20:14
  • \$\begingroup\$ Substantially like how much? I need 5V to be passing one way, but not the other. Should I chose like 5.6V zener diode or more like 10V diode? \$\endgroup\$ – Eradash Mar 16 at 20:14
  • \$\begingroup\$ If you don't need a ton of diodes, consider salvaging them from something. Can't sell warrantied product that way but it could get your project working to spec while you wait for your order to arrive. \$\endgroup\$ – K H Mar 16 at 20:29
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If your circuit requires a small signal type diode that operates at extremely low leakage current in the reverse bias direction then a Zener diode may not be the best choice as they could have higher or lower reverse current. The only way to be sure is to study data sheets from reputable suppliers or to measure sample lots of diodes in an application circuit to ensure operation at acceptable levels of leakage.

Even though simulation is not the same as reading data sheets for worst case conditions it can shed some light on my point that you need to be careful about this. Using this simulation circuit with some common part simulation models:

enter image description here

You can see that the Zener as D1 has many orders of magnitude more leakage than the other two diodes. In addition to that notice that the 6.2V zener shows better under simulation conditions than the common 1N4148 signal diode.

enter image description here

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