# voltage regulator

#### isha

Joined Sep 16, 2005
36
consider a circuit in which power supply voltage is of +12V
a zener diode [Vz=9.1V] is connected to power supply through a resistance of 100ohms
Izk=5mA, load current can vary from 0mA to 15mA
when we connect a load resistance of 100ohms across zenerdiode then diode is drop out of the circuit and voltage drop across RL become 6Volts
Can we design voltage regulater circuit using zener diode such that when we connect load of 100ohms,its voltage drop remains 9 volt , i.e;zener diode operates normally???????

#### Gorgon

Joined Aug 14, 2005
113
Originally posted by isha@Oct 29 2005, 04:06 AM
consider a circuit in which power supply voltage is of +12V
a zener diode [Vz=9.1V] is connected to power supply through a resistance of 100ohms
Izk=5mA, load current can vary from 0mA to 15mA
when we connect a load resistance of 100ohms across zenerdiode then diode is drop out of the circuit and voltage drop across RL become 6Volts
Can we design voltage regulater circuit using zener diode such that when we connect load of 100ohms,its voltage drop remains 9 volt , i.e;zener diode operates normally???????
[post=11324]Quoted post[/post]​
Hi,
If your +12v is stable you could use a zener diode of 3.0V in series with your supply and get 9V with 'any' load. A 1W zener could supply about 300mA. A resistor of 100 ohm only draw 90 mA on 9V.

This way no extra power is wasted through the 'shorting' zener.

TOK Joined Jan 19, 2004
220
wats izk?

edited: never mind i figured it out...k stands for knee

Joined Jan 19, 2004
220
assuming izk is the same as iz..one way to solve ur problem is like this
I thru load must be 90mA... therefore I from supply is 95mA...by reconfiguring the 100 ohms internal supply resistance to a value much smaller 9V output can be achieved... that value would be around (12-9)/0.095 ohms

a similar approach can be followed if iz is taken as 2*izk...

#### n9352527

Joined Oct 14, 2005
1,198
Originally posted by Gorgon@Oct 29 2005, 03:24 PM
Hi,
If your +12v is stable you could use a zener diode of 3.0V in series with your supply and get 9V with 'any' load. A 1W zener could supply about 300mA. A resistor of 100 ohm only draw 90 mA on 9V.

This way no extra power is wasted through the 'shorting' zener.

TOK [post=11335]Quoted post[/post]​
Just be careful when you have a voltage sensitive application that draws _very_ little current then the voltage would be close to 12V instead of the expected 9V. As I once found out with a catastrophic result. Have a look at the Iz v Vz graph of the zener.

#### mozikluv

Joined Jan 22, 2004
1,437
hi

i have attached a common zener regulator configuration. as always the value of R1 will depend on your load current requirement. in your case, your load is 100ohms at 9.1vdc will draw about 91ma. hence your R1 will have a value of 27ohms 0.5w and a 3w or 5w zener diode. these values were derived assuming that your supply source is an unregulated full wave bridge. zener current will vary between 290ma to 325ma and its voltage will vary between 8.6vdc to 9.6vdc.

moz