- Objectives To Recognize Zener Diodes In Various Physical Forms And To Distinguish The M From Rectifying Diodes To Unde 1 (127.67 KiB) Viewed 38 times
- Objectives To Recognize Zener Diodes In Various Physical Forms And To Distinguish The M From Rectifying Diodes To Unde 2 (73.92 KiB) Viewed 38 times
- Objectives To Recognize Zener Diodes In Various Physical Forms And To Distinguish The M From Rectifying Diodes To Unde 3 (136.11 KiB) Viewed 38 times
- Objectives To Recognize Zener Diodes In Various Physical Forms And To Distinguish The M From Rectifying Diodes To Unde 4 (24.33 KiB) Viewed 38 times
Objectives: To recognize zener diodes in various physical forms and to distinguish the m from rectifying diodes. To understand the constant-voltage characteristic of a reverse-biased zener diode. To understand the use of a zener diode in a simple voltage regulator circuit. The Zener Diode Reverse Characteristics Construct the circuit of Fig. 3.1. 0-20V d.c. variable v, V 1ะบะพ, V high-resistance met er 10V dc VA BZY88 C7V5 OV Fig 3.1 . The method obtaining the voltage-current characteristics is the similar to that of Assignment 1 but notice that the zener diode is reverse biased. U=sing the p ower supply variable control, set Vs to the values given in Table 3.1. For each value record V, then calculate: V. V = V, -V, and / = -= V,mA 100 0 0 d Copy the results table as shown in Table 3.1. Table 3.1. V. (V) 0 0 V=Vs-V, (V) I=V, (mA) P = Vo*ld (mW) 0 0 0 Vs (V) 0 0 2 2 4 6 6.5 7.0 7.5 8.0 8.5 9.0 10.0 15.0 0 215mV 755mV 1.260V 1.700V 2.750V 7.60V 20.0 12.50V โข Plot Vd against Id and also plot Vs against Pd in Fig. 3.2.
L P. (mW) la (mA) 100 20- 90 18 80 16 70 14 60 12 50 10 40 8 30 6- 20 4 - 10 2 0 2 V&V,(V) 0 4 6 8 10 12 14 16 18 20 Fig 3.2. The Zener Diode Characteristic Questions 1. From Fig 3.2 describe the characteristics in your own words. 2. The nominal voltage of the BZY887V5 is 7.5V. Does your graph agree with this exactly? If not, can you suggest a reason for any difference? 3. Why is the series resistor in Fig 3.1 necessary? 4. The power dissipated in the diode for each value of V, and Id is calculated and enteredinto the last column of your Table 3.1. The maximum allowable power dissipation of type BZY88 is 400 mW. Does your maximum value of Pd approa ch this limit?
. A Simple Zener Diode Voltage Regulator The Zener diode has a region in its reverse characteristics of almost constant voltage regardless of the current through the diode. This can be used to regul ate or stabilize a voltage source against supply or load variations. A Zener diode whose breakdown voltage is the desired constant voltage is con nected across the load as shown in Fig 3.3. 33 R 0-20V dc variable Id 100mA d.c. 27 R 20V dc v 10 mA d.c. or 1A d.c. RL 220 R ฮฟฮฝ ฮ Fig 3.3. A Simple Zener Diode Regulator . Construct the circuit of Fig 3.3. โข Copy the results table as shown in Table 3.2. Vs (V) 12 14 16 18 20 Table 3.2 IL (m A) 0 6.02mA 6.22mA 6.38mA 6.46mA 6.48mA All readings are for Va ju stequal to the Zener volt age. โข Now set the potentiometer temporarily to make I L=0, and then slowly increase Vsuntil the diode just begins to conduct current, say 1mA. Record Vs and I =0 i n the first row of the table. โข Now set the potentiometer to maximum (clockwise). The extra current drawn by RL will reduce the diode current to below 1mA. . Increase Vs to 12V; the diode current will increase above 1mA. Then adjust RLU ntil the diode current just returns to approximately 1mA. Again record Vs and I Repeat this for Vs=14, 16, 18 and 20V. Suat SELI
เญฎ Plot I against Vs. (mA) 400 350 3001 250 200 150 100 50 0 2 4 6 Vs (V) 8 10 12 14 16 18 20 Fig 3.4. Suat SELI 6 L CONCLUSIONS: