Transcript Slide 1
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 (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 Anode N Cathode Department of Electronics and Communication Engineering, Manipal Institute of Technology, Manipal, INDIA Zener diode Department of Electronics and Communication Engineering, Manipal Institute of Technology, Manipal, INDIA Zener Diode characteristics • V-I characteristics: I VZ IZK IZM Department of Electronics and Communication Engineering, Manipal Institute of Technology, Manipal, INDIA V 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 VZ, 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 • 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 – Department of Electronics and Communication Engineering, Manipal Institute of Technology, Manipal, INDIA Zener Diode characteristics • Equivalent circuits of zener diode N – Vγ + N RR ≈ RF P N P Forward + VZ – N RZ P Reverse P Breakdown • Note: RZ is usually very small, hence it can be neglected 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 + Vi IR RS + IZ VZ – IL RL – Department of Electronics and Communication Engineering, Manipal Institute of Technology, Manipal, INDIA Vo Zener diode circuit • Step 1: – Remove the zener diode from the circuit, and calculate the voltage V across the resulting open circuit Vi RL V RS R L – 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) Department of Electronics and Communication Engineering, Manipal Institute of Technology, Manipal, INDIA Zener diode circuit + IR RS + Vi VZ – – , Vo IL RL , IL RL IZ = ( IR – IL) where, Vi VZ IR RS IZ Vo VZ Department of Electronics and Communication Engineering, Manipal Institute of Technology, Manipal, INDIA Vo Zener diode circuit 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 + Vi IR RS + VZ – IZ IL RL – Department of Electronics and Communication Engineering, Manipal Institute of Technology, Manipal, INDIA Vo 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, RS = 120Ω, RL = 250Ω and VZ = 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, RS = 10Ω, VZ = 10V, Vi = 25V. Find the minimum and maximum current through zener when RL is varied between 10Ω and 100Ω Department of Electronics and Communication Engineering, Manipal Institute of Technology, Manipal, INDIA End of module 5 Department of Electronics and Communication Engineering, Manipal Institute of Technology, Manipal, INDIA