A zener regulator has an input voltage in the range 15V-20V and a load current in the range of 5mA-20mA. If the zener voltage is 6.8V, the value of the series resistor should be:
This is a very confusing situation for me. If the input voltage were constant, then I would be able to understand that by varying load resistance, I can change the current through it, such that the drop across the load = Vz = 6.8V.
But the input voltage is also not constant. So what am I to understand? The 5-20mA range is for what voltage?
I only know:
If Vs is source voltage, then
Vs- I*Rs - 6.8=0
So, I*Rs = Vs-6.8
So, Imax = (20-6.8)/Rs
Imin = (15-6.8)/Rs
This is total current through series resistor. Some of it will run through zener and some through load. But load itself is variable.
Please show me some way.
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