1. UNIT – V APPLICATION ICs
PREPARED BY
V.SANDHIYA
LECT/ ECE

2. 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).

3. Zener as Regulator
A simple regulator circuit A regulator circuit with load resistance

4. 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.

5. 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.

6. Zener I-V Charateristic
Reverse biased region
Reverse breakdown region

7. Zener Diode Regulator
In 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.

8. Thevenin Equivalent Circuit

9. Zener Diode Three types of Zener analysis Fixed VS and RL
Fixed VS and variable RL
Variable VS and fixed RL

10. Zener Diode - Fixed VS and RL
The applied dc voltage is fixed, as the load resistor.
The analysis :
Determine the state of the Zener diode by removing it from the network and calculating the voltage across the resulting open circuit.

11. Zener Diode VL=VZ IZ = IR – IL PZ = VZ IZ
2. 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.

12. Zener Diode - Fixed VS and Variable RL
Step 1- get the RLmin so that zener is on. Rs + Vs -
- if RL ≥ RLmin, zener diode ‘on’, so that VL=VZ
Step 2: Calculate the IZ using KCL: 2 condition
1. If RLmin , then ILmax and IZmin because of constant I1
2. If RLmax, then ILmin and IZmax

13. Zener Diode or Where and ; Izmax taken from data sheet
Izmin = 0, if not given or
Where
and

14. Zener Diode - Variable VS and fixed RL
Step 1- get the VSmin so that zener is on. Rs + Vs -
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 IL
2. if VSmax, thenI1max and IZmax

15. Zener Diode
; Izmax= Pzmax/Vz or
where
and

16. IC Regulator
The 78xx (also sometimes known as LM78xx) series of devices is a family of self-contained fixed linear voltage regulator IC. The 78xx family is a very popular choice for many electronic circuits which require a regulated power supply, due to:
i. ease of use and
ii. Low cost.

17. Optocouplers

18. Optocouplers LED for emitter Air as barrier for isolation
Phototransistor for detector
Transformer is similar, but only for AC
Optocoupler can be used for DC

19. Emitter Incandescent lamp Much slower response time than LED
Can filter out high frequency noise
Lower lifespan than LED however

20. Parameters
Optocoupler’s bandwidth - determines the highest signal frequency that can be transferred through it
Typical opto-couplers with a single output phototransistor may have a bandwidth of kHz, while those with a Darlington pair are usually about 10 times lower, at around kHz.

21. Darlington Pair

22. The other main type of optocoupler is the type having an
output Diac or bilateral switch, and intended for use in
driving a Triac or SCR.
Examples of these are the MOC3020 and MOC3021.
Here the output side of the opto-coupler is designed to be
connected directly into the triggering circuit of the Triac
where it’s operating from and floating at full 120/240 VAC

23. A simple circuit with an opto-isolator.
Vcc
A simple circuit with an opto-isolator.
When switch S1 is open, LED D1 is off, so Q1 is off and no current flows through R2, so Vout = Vcc.
When switch S1 is closed, LED D1 lights.
Phototransistor Q1 is now triggered, so current flows through R2
Vout is then pulled down to low state.
This circuit, thus, acts as a NOT gate.