Lesson 2402-8

Topic 26 The Zener Diode as a Voltage Regulator (Part II)

Diagram

15 V

470

1.5kPower

Supply

+

_

24 V

Equations for circuit analysis

=

( 1)

=

+ ( 2)

= ( 3)

=

( 4)

= ( 5)

First example

If the zener diode is disconnected from the source, what is the load voltage?

First example work

=

+ =

1.5k

470+1.5k24V =

1.5k

1.97k24 =

18.274V

Second example

Calculate all three currents.

Second example work

=

=

24V15V

470=

9

470=

19.149mA

= = 15V

=

=

15V

1.5k= 10mA

= = 19.149mA 10mA =9.149mA

Third example

Assuming a tolerance of 5 percent in both resistors, what is the maximum zener current?

To maximize the current, we need to find the lower tolerance for RS and the upper tolerance for RL.

Third example work

5% = 446.5

+ 5% = 1.575k

=

=

24V15V

446.5=

9

446.5= 20.157mA

=

=

15V

1.575= 9.524mA

= = 20.157mA 9.524mA =10.633mA

Fourth example

Suppose the supply voltage can vary from 24 to 40 V. What is the maximum zener current?

Calculate the values at the maximum supply voltage.

Fourth example work

=

=

40V15V

470=

25

470=

53.191mA

= = 15V

=

=

15V

1.5k= 10mA

= = 53.191mA 10mA =43.191mA

Fifth example

The zener diode is replaced with a 1N963B diode. What are the load voltage and the zener current?

Data Sheet information

Fifth example work

= = 12V

=

=

24V12V

470=

12

470=

25.532mA

=

=

12V

1.5k= 8mA

= = 25.532mA 8mA =17.532mA

Process for solving

Analyzing a Loaded Zener Regulator

Process Comment

Step 1 Calculate the series current (Eq. 1) Apply Ohms Law to RS

Step 2 Calculate the load voltage (Eq. 3) Load voltage equals diode voltage

Step 3 Calculate the load current (Eq. 4) Apply Ohms Law to RL

Step 4 Calculate the zener current (Eq. 5) Apply the current law to the diode

Any questions?

Contact us at:

1-800-243-6446

1-216-781-9400

Email:

faculty@cie-wc.edu

mailto:faculty@cie-wc.edumailto:faculty@cie-wc.edumailto:faculty@cie-wc.edu