Department of Electronics and Communication Engineering, Manipal Institute of Technology, Manipal, INDIA Subject Code : ECE – 101/102 BASIC ELECTRONICS COURSE MATERIAL For 1st & 2nd Semester B.E. (Revised Credit System) DEPARTMENT OF ELECTRONICS & COMMUNICATION ENGINEERING

Department of Electronics and Communication Engineering, Manipal Institute of Technology, Manipal, INDIA Zener Diode Zener diode is heavily doped P-N junction diode Designed to operate in reverse breakdown region Each zener diode has specific breakdown voltage (V Z ). Value of V Z depends on doping level Zener diodes are available with V Z ranging from 1.8V to 200V, power ratings from 250mW to 50W Symbol of zener diode: AnodeCathode PN

Zener diode Department of Electronics and Communication Engineering, Manipal Institute of Technology, Manipal, INDIA

Department of Electronics and Communication Engineering, Manipal Institute of Technology, Manipal, INDIA Zener Diode characteristics V-I characteristics: VZVZ I ZK I ZM I V

Department of Electronics and Communication Engineering, Manipal Institute of Technology, Manipal, INDIA Zener Diode characteristics 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 V Z, only the current increases with the increase in applied reverse bias

Department of Electronics and Communication Engineering, Manipal Institute of Technology, Manipal, INDIA Zener Diode characteristics P ZM = V Z.I ZM where P ZM 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 VZVZ + – IZIZ

Department of Electronics and Communication Engineering, Manipal Institute of Technology, Manipal, INDIA Zener Diode characteristics Equivalent circuits of zener diode ForwardReverseBreakdown Note: R Z is usually very small, hence it can be neglected VγVγ RFRF R R ≈  RZRZ VZVZ – +– + N P NN N PPP

Department of Electronics and Communication Engineering, Manipal Institute of Technology, Manipal, INDIA Zener diode circuit 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 RLRL VoVo VZVZ + – + – ViVi RSRS ILIL IZIZ IRIR

Department of Electronics and Communication Engineering, Manipal Institute of Technology, Manipal, INDIA Zener diode circuit Step 1: –Remove the zener diode from the circuit, and calculate the voltage V across the resulting open circuit –If V ≥ V Z, the zener is ON, appropriate equivalent model is substituted –If V < V Z, 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 ≥ V Z, then zener is in breakdown region, and equivalent model is V Z (neglecting R Z )

Department of Electronics and Communication Engineering, Manipal Institute of Technology, Manipal, INDIA Zener diode circuit I Z = ( I R – I L ) where, RLRL VoVo VZVZ + – + – ViVi RSRS ILIL IZIZ IRIR,,

Department of Electronics and Communication Engineering, Manipal Institute of Technology, Manipal, INDIA Zener diode circuit Problem: For the zener network, V i = 16 V, R S = 1 K ohm, V Z = 10 V and R L = 3K ohm. Determine V o, I Z and P Z. Repeat for R L = 1.2K ohm RLRL VoVo VZVZ + – + – ViVi RSRS ILIL IZIZ IRIR

Department of Electronics and Communication Engineering, Manipal Institute of Technology, Manipal, INDIA Line Regulation 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, R S = 120Ω, R L = 250Ω and V Z = 5V. Find the minimum and maximum current flowing through zener when input varies from 9V to 15V.

Department of Electronics and Communication Engineering, Manipal Institute of Technology, Manipal, INDIA Load Regulation 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, R S = 10Ω, V Z = 10V, V i = 25V. Find the minimum and maximum current through zener when R L is varied between 10Ω and 100Ω

Department of Electronics and Communication Engineering, Manipal Institute of Technology, Manipal, INDIA End of module 5