arrow said:
Hi All
I am a newbie to electronics. I would like to setup a constant voltage without using a voltage regulator. My V supply is fluctuating.
I thought of using a zenner diode by just connecting
a zenner with a R=300kOhm across a fluctuating Voltage.
My aim is to get a fixed voltage, say 1.5V where the R and zenner meet.
Its not working :<
Can someone please tell me what I am doing wrong?
The voltage across a zener is quite dependent on the current through it, you should aim to arrnage for the current through the zener to be constant (if possible), and for the current to be on the best part of the zeners curve.
Also, 1.5V sounds rather low for a zener?.
Another point is the resistor you mentioned?, 300KOhm, this sounds FAR too high a value, unless you are feeding it off hundreds of volts (or thousands?).
You also don't mention what load you are using either?, really you don't give any of the required information?.
For a general design, the zener would normally be designed to draw around five times the current the load takes!.
So, the basic things you need to know:
Supply voltage
Zener voltage
Load current
Specification of zener diode
From those you can work out the resistor and zener needed, and indeed if it's practical or not!.