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Lesson 2402-8 Topic 26 – The Zener Diode as a Voltage Regulator (Part II)

Transistor Circuits XIV - Electronics – Online Distance ... · First example •If the zener diode is disconnected from the source, what is the load voltage?

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Page 1: Transistor Circuits XIV - Electronics – Online Distance ... · First example •If the zener diode is disconnected from the source, what is the load voltage?

Lesson 2402-8

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

Page 2: Transistor Circuits XIV - Electronics – Online Distance ... · First example •If the zener diode is disconnected from the source, what is the load voltage?

Diagram

15 V

470Ω

1.5kΩPower

Supply

+

_

24 V

Page 3: Transistor Circuits XIV - Electronics – Online Distance ... · First example •If the zener diode is disconnected from the source, what is the load voltage?

Equations for circuit analysis

• 𝐼𝑆 =𝑉𝑆−𝑉𝑍

𝑅𝑆 (𝐸𝑞𝑢𝑎𝑡𝑖𝑜𝑛 1)

• 𝑉𝑇𝐻 =𝑅𝐿

𝑅𝑆+𝑅𝐿𝑉𝑆 (𝐸𝑞𝑢𝑎𝑡𝑖𝑜𝑛 2)

• 𝑉𝐿 = 𝑉𝑍 (𝐸𝑞𝑢𝑎𝑡𝑖𝑜𝑛 3)

• 𝐼𝐿 =𝑉𝐿

𝑅𝐿 (𝐸𝑞𝑢𝑎𝑡𝑖𝑜𝑛 4)

• 𝐼𝑍 = 𝐼𝑆 − 𝐼𝐿 (𝐸𝑞𝑢𝑎𝑡𝑖𝑜𝑛 5)

Page 4: Transistor Circuits XIV - Electronics – Online Distance ... · First example •If the zener diode is disconnected from the source, what is the load voltage?

First example

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

Page 5: Transistor Circuits XIV - Electronics – Online Distance ... · First example •If the zener diode is disconnected from the source, what is the load voltage?

First example work

• 𝑉𝑇𝐻 =𝑅𝐿

𝑅𝑆+𝑅𝐿𝑉𝑆 =

1.5kΩ

470Ω+1.5kΩ24V =

1.5k

1.97k24 =

18.274V

Page 6: Transistor Circuits XIV - Electronics – Online Distance ... · First example •If the zener diode is disconnected from the source, what is the load voltage?

Second example

• Calculate all three currents.

Page 7: Transistor Circuits XIV - Electronics – Online Distance ... · First example •If the zener diode is disconnected from the source, what is the load voltage?

Second example work

• 𝐼𝑆 =𝑉𝑆−𝑉𝑍

𝑅𝑆=

24V−15V

470Ω=

9

470=

19.149mA

• 𝑉𝐿 = 𝑉𝑍 = 15V

• 𝐼𝐿 =𝑉𝐿

𝑅𝐿=

15V

1.5kΩ= 10mA

• 𝐼𝑍 = 𝐼𝑆 − 𝐼𝐿 = 19.149mA − 10mA =9.149mA

Page 8: Transistor Circuits XIV - Electronics – Online Distance ... · First example •If the zener diode is disconnected from the source, what is the load voltage?

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.

Page 9: Transistor Circuits XIV - Electronics – Online Distance ... · First example •If the zener diode is disconnected from the source, what is the load voltage?

Third example work

• 𝑅𝑆 − 5% = 446.5Ω

• 𝑅𝐿 + 5% = 1.575k

• 𝐼𝑆 =𝑉𝑆−𝑉𝑍

𝑅𝑆=

24V−15V

446.5Ω=

9

446.5= 20.157mA

• 𝐼𝐿 =𝑉𝐿

𝑅𝐿=

15V

1.575Ω= 9.524mA

• 𝐼𝑍 = 𝐼𝑆 − 𝐼𝐿 = 20.157mA − 9.524mA =10.633mA

Page 10: Transistor Circuits XIV - Electronics – Online Distance ... · First example •If the zener diode is disconnected from the source, what is the load voltage?

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.

Page 11: Transistor Circuits XIV - Electronics – Online Distance ... · First example •If the zener diode is disconnected from the source, what is the load voltage?

Fourth example work

• 𝐼𝑆 =𝑉𝑆−𝑉𝑍

𝑅𝑆=

40V−15V

470Ω=

25

470=

53.191mA

• 𝑉𝐿 = 𝑉𝑍 = 15V

• 𝐼𝐿 =𝑉𝐿

𝑅𝐿=

15V

1.5kΩ= 10mA

• 𝐼𝑍 = 𝐼𝑆 − 𝐼𝐿 = 53.191mA − 10mA =43.191mA

Page 12: Transistor Circuits XIV - Electronics – Online Distance ... · First example •If the zener diode is disconnected from the source, what is the load voltage?

Fifth example

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

Page 13: Transistor Circuits XIV - Electronics – Online Distance ... · First example •If the zener diode is disconnected from the source, what is the load voltage?

Data Sheet information

Page 14: Transistor Circuits XIV - Electronics – Online Distance ... · First example •If the zener diode is disconnected from the source, what is the load voltage?

Fifth example work

• 𝑉𝐿 = 𝑉𝑍 = 12V

• 𝐼𝑆 =𝑉𝑆−𝑉𝑍

𝑅𝑆=

24V−12V

470Ω=

12

470=

25.532mA

• 𝐼𝐿 =𝑉𝐿

𝑅𝐿=

12V

1.5kΩ= 8mA

• 𝐼𝑍 = 𝐼𝑆 − 𝐼𝐿 = 25.532mA − 8mA =17.532mA

Page 15: Transistor Circuits XIV - Electronics – Online Distance ... · First example •If the zener diode is disconnected from the source, what is the load voltage?

Process for solving

Analyzing a Loaded Zener Regulator

Process Comment

Step 1 Calculate the series current (Eq. 1) Apply Ohm’s 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 Ohm’s Law to RL

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

Page 16: Transistor Circuits XIV - Electronics – Online Distance ... · First example •If the zener diode is disconnected from the source, what is the load voltage?
Page 17: Transistor Circuits XIV - Electronics – Online Distance ... · First example •If the zener diode is disconnected from the source, what is the load voltage?

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