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VOLTAGE REGULATOR - Dronacharyaggn.dronacharya.info/.../Section-B/SectionB-4_Voltage_regulator.pdf · Voltage Regulator Zener diode is a voltage regulator device because it is able

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Page 1: VOLTAGE REGULATOR - Dronacharyaggn.dronacharya.info/.../Section-B/SectionB-4_Voltage_regulator.pdf · Voltage Regulator Zener diode is a voltage regulator device because it is able
Page 2: VOLTAGE REGULATOR - Dronacharyaggn.dronacharya.info/.../Section-B/SectionB-4_Voltage_regulator.pdf · Voltage Regulator Zener diode is a voltage regulator device because it is able

Voltage Regulator Zener diode is a voltage regulator device

because it is able to fix the output voltage at a constant value (DC voltage).

RS is to limit the zener current, IZ so that it is less than the maximum current, IZM (to avoid the zener diode from broken).

Page 3: VOLTAGE REGULATOR - Dronacharyaggn.dronacharya.info/.../Section-B/SectionB-4_Voltage_regulator.pdf · Voltage Regulator Zener diode is a voltage regulator device because it is able

Zener as Regulator

+

VS

-

+

VS

-

+VZ

-

+VZ

-

RS RS

RL

A simple regulator circuit A regulator circuit with load resistance

Page 4: VOLTAGE REGULATOR - Dronacharyaggn.dronacharya.info/.../Section-B/SectionB-4_Voltage_regulator.pdf · Voltage Regulator Zener diode is a voltage regulator device because it is able

Voltage Regulator

How to determine whether the zener acts as a regulator or not?? Use Thevenin Theorem See example

If VTH<VZ, regulation does not occur.

Page 5: VOLTAGE REGULATOR - Dronacharyaggn.dronacharya.info/.../Section-B/SectionB-4_Voltage_regulator.pdf · Voltage Regulator Zener diode is a voltage regulator device because it is able

Voltage Regulator…. Referring to zener I-V charateristic curve, if the

voltage across the zener diode zener is between 0-VZ, the zener diode is operating in the reverse bias region, thus it DOES NOT functioned as a regulator.

VTH must at least the same value as VZ (VTH ≥ VZ)so that the diode CAN function as a voltage regulator because it is operating in reverse breakdown region.

Page 6: VOLTAGE REGULATOR - Dronacharyaggn.dronacharya.info/.../Section-B/SectionB-4_Voltage_regulator.pdf · Voltage Regulator Zener diode is a voltage regulator device because it is able

Zener I-V Charateristic

Reverse biased region

Reverse breakdown

region

Page 7: VOLTAGE REGULATOR - Dronacharyaggn.dronacharya.info/.../Section-B/SectionB-4_Voltage_regulator.pdf · Voltage Regulator Zener diode is a voltage regulator device because it is able

Zener Diode RegulatorIn this simple illustration of zener regulation circuit, the zener diode will “adjust” its impedance based on varying input voltages and loads (RL) to be able to maintain its designated zener voltage.

Zener current will increase or decrease directly with voltage input changes. The zener current will increase or decrease inversely with varying loads. Again, the zener has a finite range of operation.

Page 8: VOLTAGE REGULATOR - Dronacharyaggn.dronacharya.info/.../Section-B/SectionB-4_Voltage_regulator.pdf · Voltage Regulator Zener diode is a voltage regulator device because it is able

Thevenin Equivalent Circuit

Page 9: VOLTAGE REGULATOR - Dronacharyaggn.dronacharya.info/.../Section-B/SectionB-4_Voltage_regulator.pdf · Voltage Regulator Zener diode is a voltage regulator device because it is able

Examples of zener as voltage regulator

Page 10: VOLTAGE REGULATOR - Dronacharyaggn.dronacharya.info/.../Section-B/SectionB-4_Voltage_regulator.pdf · Voltage Regulator Zener diode is a voltage regulator device because it is able

Cases in Zener Regulator Circuits

Page 11: VOLTAGE REGULATOR - Dronacharyaggn.dronacharya.info/.../Section-B/SectionB-4_Voltage_regulator.pdf · Voltage Regulator Zener diode is a voltage regulator device because it is able

Zener Diode Three types of Zener analysis

Fixed VS and RL

Fixed VS and variable RL

Variable VS and fixed RL

Page 12: VOLTAGE REGULATOR - Dronacharyaggn.dronacharya.info/.../Section-B/SectionB-4_Voltage_regulator.pdf · Voltage Regulator Zener diode is a voltage regulator device because it is able

Zener Diode- Fixed VS and RL

The applied dc voltage is fixed, as the load resistor.The analysis :1. Determine the state of the Zener diode by removing it from the network and

calculating the voltage across the resulting open circuit.

Page 13: VOLTAGE REGULATOR - Dronacharyaggn.dronacharya.info/.../Section-B/SectionB-4_Voltage_regulator.pdf · Voltage Regulator Zener diode is a voltage regulator device because it is able

Zener Diode2. Substitute the appropriate equivalent circuit and solve for the

desired unknowns.

- For the on state diode, the voltages across parallel elements must be the same.

VL=VZ

The Zener diode current is determined by KCL:IZ = IR – IL

The power dissipated by the Zener diode is determined by:PZ = VZ IZ

- For the off state diode, the equivalent circuit is open-circuit.

Page 14: VOLTAGE REGULATOR - Dronacharyaggn.dronacharya.info/.../Section-B/SectionB-4_Voltage_regulator.pdf · Voltage Regulator Zener diode is a voltage regulator device because it is able

Zener Diode- Fixed VS and Variable RL

+Vs-

Rs

Step 1- get the RLmin so that zener is on.

LS

LL RR

VsRV+

=ZS

ZSL VV

VRR−

=min

- if RL ≥ RLmin, zener diode ‘on’, so that VL=VZ

Step 2: Calculate the IZ using KCL: 2 condition1. If RLmin , then ILmax and IZmin because of constant I12. If RLmax, then ILmin and IZmax

Page 15: VOLTAGE REGULATOR - Dronacharyaggn.dronacharya.info/.../Section-B/SectionB-4_Voltage_regulator.pdf · Voltage Regulator Zener diode is a voltage regulator device because it is able

Zener Diode

minmaxconstant1maxmin orLorZ III −=

S

ZS

RVVI −

=1

minmax

L

ZL R

VI =min

maxL

ZL I

VR =Where or

Page 16: VOLTAGE REGULATOR - Dronacharyaggn.dronacharya.info/.../Section-B/SectionB-4_Voltage_regulator.pdf · Voltage Regulator Zener diode is a voltage regulator device because it is able

Zener Diode- Variable VS and fixed RL

+Vs-

Rs

Step 1- get the VSmin so that zener is on.

LS

LL RR

VsRV+

=L

ZSLS R

VRRV )(min

+=

if VS ≥ VSmin, zener diode will ‘on’, so that VL=VZ

Step 2: Calculate the IZ using KCL: 2 condition

1. if VSmin , then I1min and IZmin because of constant IL2. if VSmax, thenI1max and IZmax