# How to find voltage on zener diode while there is a current source

simulate this circuit – Schematic created using CircuitLab

I'm confused about whether zener is on or off due to not being able to know voltage on V0. I tried to find by applying KCL & KVL, but current on the diode (Id) and the resistor (Ir) is not equal to each other. I'm using the shockley diode equation.(Id=Is(e^(Vd/Vt))). This current source being connected to zener diode instead of a voltage source makes something complicated. Which way should I follow to find V0? Hope one can give me a trick.

• I don't see Id or Ir marked on your schematic so I can't follow your reasoning. Also, please show all of the work you have done so far. – Elliot Alderson Dec 2 '18 at 21:08
• What would Vo be if you assume that the Zener is not conducting? Is it higher than the Zener voltage? – Phil G Dec 2 '18 at 21:12
• What I'm trying to do is that if I find the current flowing through resistor (here I use Id current for each branch one by one because Ir and Id are the same, but to find Id , Vd has to be known. The given Vd values is for constant voltage drop model that requires relatively higher voltage than ,in this circuit, V0 , therefore I am not sure whether to use it) I would find voltage on resistor so then the V0. – Klementayn Dec 2 '18 at 21:48
• @Klementayn Assume the zener is off. This just means that you have two resistors in parallel, or $\frac23$k, times 3 mA. This works out to 2 V. Add 600 mV for your diodes and this would account for the entire current. But at 2.6 V, the zener isn't going to conduct current (leakage only.) So the assumption is supported. Do you need to be more detailed than this? – jonk Dec 2 '18 at 21:49