that means the Zener diode is on that means the Zener diode is off

Basic zener regulator V

i

and R

L

Fixed

2. Substitute the appropriate equivalent circuit and solve for the desired unknowns.

V L



V Z I R



I Z



I L I Z



I R



I L I L



V L R L I R



V i



V L R P Z



V Z I Z

Fixed V

i

, Variable R

L 1- Finding R Lmin : Using VDR

R L

min OR : If Izmin is given:

I Z



I R



I L I L

max 

I R



I Z

min 

V i RV Z



V Z

2- Finding R Lmax :

I R V R R L

min  

V R V R i



V z



V Z I L

max

I L

min

R L

max 

I R

 

I Z

max

V Z I L

min

Fixed R

L

, Variable V

i

• • The minimum value of Vi must be sufficiently large to turn the Zener diode on .

Using VDR

V i

min  (

R L



R L R

)

V Z

The maximum value of Vi limited by maximum Zener current

I ZM I ZM



I R



I L I R V R

 

V R V i R



V z I R

max

V i

max 

I ZM



I L



I R

max

R



V Z

Applications

Simple square-wave generator

AC Limiter Protection circuit

Applications

Half Wave Voltage Doubler

High Voltage transformers are expensive and impractical at voltages above 1000V The peak inverse voltage PIV across each diode is 2Vp

Half Wave Voltage Doubler

First Half Cycle – D 1 charged. C 2 conducting, C 1 remains uncharged because of the reverse biased D2 Second Half Cycle – D 2 conducting, C 2 charged by (source + C1) – about twice the source voltage Next Half Cycle – Repeat of first stage with the addition that C 2 can now discharge through R L . Notice that C 2 is charged once/cycle, so output has the same frequency as input.

Full Wave Voltage Doubler

• When the secondary voltage is positive, D 1 is forward-biased and C 1 charges to approximately Vp • During the negative half-cycle, D 2 forward-biased and C 2 charges to approximately Vp. The output capacitors in series.

is voltage 2Vp- is taken across the two The peak inverse voltage PIV across each diode is 2Vp

Voltage Tripler

• • The addition of another diode-capacitor section to the half-wave voltage doubler creates a voltage tripler. The operation is as follows: On the positive half-cycle of the secondary voltage. C 1 charges to Vp, through D1. During the negative half-cycle, C 2 charges to 2Vp through D2 as described for the doubler. During the next positive half-cycle, C 3 charges to 2Vp through D3 the tripler output is taken across C 1 and C 3.

Voltage Quadrupler

The addition of still another diode-capacitor section produces an output four times the peak secondary voltage. C 4 charges to 2Vp through D 4 negative half-cycle. The 4V p output is taken across C 2 and C 4 on a , as shown. In both the tripler and quadrupler circuits. the PlV of each diode is 2Vp

Voltage Quadrupler • Can extend this circuit to produce extremely high voltages (~750kV).

Voltage Quadrupler

Special Purpose Diodes

Varactor Diodes

A

varactor diode

is best explained as a variable capacitor. Think of the depletion region a variable dielectric. The diode is placed in reverse bias. The dielectric is “adjusted” by bias changes.

Varactor Diodes

The varactor diode can be useful in filter circuits as the adjustable component.

Other Diode Types

The

Schottky diode’s

significant characteristic is it’s fast switching speed. This is useful for high frequencies and digital applications. It is not a typical diode in the fact that it does not have a p-n junction, instead it consists of a heavily doped n-material and metal bound together.

Other Diode Types

The

PIN diode

is also used in mostly microwave frequency applications. It’s variable forward series resistance characteristic is used for attenuation, modulation, and switching. In reverse bias exhibits a nearly constant capacitance.

Other Diode Types

The

tunnel diode

is also used for fast switching applications. This is achieved by reduced doping at the junction.

Other Diode Types

The

laser diode

(light amplification by stimulated emission of radiation) produces a monochromatic (single color) light. Laser diodes in conjunction with photodiodes are used to retrieve data from compact discs.