# simple clamp circuit resistor calculation

#### khatus

Joined Jul 2, 2018
93
Hello guys i want to calculate the resistor R in this circuit.Can anybody help me?

The value of zener diode(VZ)=4.8 volt.

well i try to simplify it

My question is is my solution is right??If not then what will be the value of R?

#### ericgibbs

Joined Jan 29, 2010
18,212
hi k,
This looks like a College problem assignment, can you confirm.??

Moderation moved to Homework.

Last edited:

#### kubeek

Joined Sep 20, 2005
5,791
Are you talking about the resistor that is connected to the zener, or the resistor that "should be there"?

#### khatus

Joined Jul 2, 2018
93
Are you talking about the resistor that is connected to the zener, or the resistor that "should be there"?
the resistor that is connected to the zener

#### kubeek

Joined Sep 20, 2005
5,791
That resistor is there only to ensure that the leakage current of the zener doesn´t go through the BE junction when the zener is below its rated voltage drop.
A zener´s voltage is usually specified at 5mA, so I would choose a resistor R=0.7V/1mA=140 ohms or higher, but higher resistor will make the zener react at a little bit lower voltage.