Subject Code : ECE – 101/102 BASIC ELECTRONICS COURSE MATERIAL For 1st & 2nd Semester B.E.

1. Subject Code : ECE – 101/102 BASIC ELECTRONICS COURSE MATERIAL For 1st & 2nd Semester B.E. (Revised Credit System) DEPARTMENT OF ELECTRONICS & COMMUNICATION ENGINEERING

2. Zener diode is heavily doped P-N junction diode Designed to operate in reverse breakdown region Each zener diode has specific breakdown voltage (VZ). Value of VZ depends on doping level Zener diodes are available with VZ ranging from 1.8V to 200V, power ratings from 250mW to 50W Symbol of zener diode: P N Anode Cathode Zener Diode

3. Zener diode

4. V-I characteristics: I VZ V IZK IZM Zener Diode characteristics

5. V-I characteristics: When zener diode is forward biased, it acts like ordinary diode – i.e., until certain voltage Vγ is reached, current is zero, then afterwards, current rises exponentially When zener diode is reverse biased, until the breakdown voltage is reached, current is zero or negligible When reverse voltage equals zener voltage, current rises exponentially in reverse direction After the breakdown has occurred, voltage across zener diode remains almost constant at VZ, only the current increases with the increase in applied reverse bias Zener Diode characteristics

6. PZM = VZ.IZM where PZM is Maximum Power dissipation across the zener diode Zener diode is always connected such that it is reverse biased and it is in zener breakdown region IZ + VZ – Zener Diode characteristics

7. Equivalent circuits of zener diode Forward Reverse Breakdown Note: RZ is usually very small, hence it can be neglected N N N N + – VZ Vγ + – RR ≈  RF RZ P P P P Zener Diode characteristics

8. Analysis of networks employing zener diodes is similar to analysis of ordinary diodes First, the state of the diode (ON, OFF or breakdown) must be determined, followed by substitution of correct model Figure shows a simple circuit employing a zener diode RS IR IZ IL + + Vi VZ RL Vo – – Zener diode circuit

9. Step 1: Remove the zener diode from the circuit, and calculate the voltage V across the resulting open circuit If V ≥ VZ, the zener is ON, appropriate equivalent model is substituted If V < VZ, the zener is OFF, open circuit equivalent is substituted Step 2: Substitute the appropriate equivalent model and solve for the desired unknown Suppose that we get V ≥ VZ, then zener is in breakdown region, and equivalent model is VZ (neglecting RZ) Zener diode circuit

10. IZ = ( IR– IL) where, RS IR IZ IL + + Vi VZ RL Vo – – Zener diode circuit , ,

11. Problem: For the zener network, Vi= 16 V, RS= 1 K ohm, VZ= 10 V and RL= 3K ohm. Determine Vo, IZ and PZ . Repeat for RL= 1.2K ohm RS IR IZ IL + + Vi VZ RL Vo – – Zener diode circuit

12. Line Regulation is the capability to maintain a constant output voltage level on the output channel of the power supply despite the changes in the input voltage level Problem on Line regulation In a Zener network, RS = 120Ω, RL = 250Ω and VZ = 5V. Find the minimum and maximum current flowing through zener when input varies from 9V to 15V. Line Regulation

13. Load regulation is the capability to maintain a constant voltage level on the output channel of the power supply despite the changes in the load Problem on Load regulation For a Zener network, RS = 10Ω, VZ = 10V, Vi = 25V. Find the minimum and maximum current through zener when RL is varied between 10Ω and 100Ω Load Regulation

14. End of module 5