Report on Exercises 2 - Diodes (1)

Tallinn University of Technology Department of Electrical Drives and Power Electronics
Report on Exercises 2 Diodes
Student ******* Code ****96 Group AAVB41
Tallinn 2012 2.1. Diode rectifier VD
f = 9 kHz U=6V U = 19.7 V R = 96 k
Figure 1. Circuit diagram
Figure 2. Timing diagram
VD
R = 96 k -
Figure 3. Replacement circuit
Forward biased : Reverse biased: Table 1. Volt-amphere characteristics
US, V UAC, V Measured Calculated US, V UAC, V Measured IA, µA IA, µA IA, µA 0,2 0,1999 0,0027 0 0,2 -0,199 0,6 0, 3657 1,252 0 0,6 -0,599 1 0,5183 5,107 0 1 -0,999 2 0,5469 15,311 0 3 -3 3 0,5602 25,465 25,414 5 -5 4 0,5691 35,922 35,738 9 -8,999 -1,776 5 0,5756 47,070 46,087 18 -17,998 -3,553 6 0,5809 56,093 56,448 25 -24,998 -3,553 14 0,6043 140,810 139,955 35 -34,997 -7,105 20 0,6139 202,999 201,938 50 -49,995 -7,105 250
200
Ia, µA 150
100
50 UKNEE 0 0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 -50 U ac, V 6 = =3 9 Figure 4. Volt-amphere characteristics, forward biased
0 -20 -15 -10 -5 0 -2 -4 -6 -8 Ia, µA
-10 -12 -14 -16 -18 -20 U ac, V
Figure 5. Volt-amphere characteristics, reverse biased
Conclusion
Multisim gave us a virtual diode with the idealized symmetrical output characteristic. This means that if the voltage drops across anode-cathode are bigger than the knee voltage, then the current increases rapidly. But if not, then only very small current occurs. In the reverse biased, the voltage across the diode could be large, but only a small current occurs. is obtained as 0,57V from figure 4, which is made by the data we can see from table 1. 2.2 Series clippers VD
f = 9 kHz R = 96 k US = 10 V UDC = 6V - Figure 6. Circuit diagram
UL
Figure 7. Voltage traces
VD
f = 9 kHz R = 96 k US = 10 V
- UDC = 6 V
Figure 8. Replacement circuit
UL
Figure 9. Voltage traces Conclusion The diode conducts while the current in the circuit is bigger than zero, in other words when the function generator voltage is bigger than the one apllied to the DC source. For the diode to conduct the current must be above zero. Therefore . If the dunction generator voltage drops below assigned reference voltage the diode stops conducting and the output remains 6 volts. In reverse biased, , where is the reference voltage and UVD is the voltage drop on diode. In other words, the function generator voltage is smaller than the one applied to the DC source, then the diode conducts. If the function generator voltage grows above the assigned voltage, the diode stops conducting and the output remains 6V. 2.3 Parallel clippers R = 9,6 k
f = 9 kHz VD R = 96 k US = 10 V
UDC = 6,7 V -
Figure 10. Circuit diagram
UL
Figure 11. Voltage traces
R = 9,6 k
f =9 kHz VD U = 10 V R =96 k UDC = 5,3 V -
Figure 12. Replacement circuit UL
Figure 13. Voltage traces
Conclusion Because the output voltage is parallel to the diode, the results are opposite to the results in series circuits. In the first case, the diode will conduct as long as In the second case, the diode will conduct as is the reference voltage and UVD is the voltage drop on the diode. 2.4 Diode limiters
f = 9 kHz US = 10 V R = 100 R = 100 R = 96 k
UDC1 = -0,7 UDC2 = 6 V V
Figure 14. Circuit diagram
UL1 UL2
Figure 15. Voltage traces
R = 100 f = 9 kHz US = 10 V R = 96 k UDC2 = 3,7 UDC1 = 5,3 V V Figure 16. Replacement circuit UL1 UL2
Figure 17. Voltage traces
Conclusion When the diodes are in series connection, then the DC voltages are -0,7 V and 6 V to get the wanted clipping voltages. Formula: = and = ( )
When the diodes are in parallel connection then the DC voltages are 5,3 V and 3,7 V to get the reference clipping voltages. UDC1= - and = 2.5 Zener diode R = 9,6 k
f = 9 kHz US = 10 V
VD; 6 V R = 96 k
Figure 18. Circuit diagram
UL1
Figure 19. Voltage traces
R = 9,6 k
f = 9 kHz US = 10 V VD1; 6 V R = 96 k
VD2; 6 V
Figure 20. Replacement circuit UL1
UL2
Figure 21. Voltage traces
Conclusion The Zener diode does not conduct while the function generators voltage is on the negative ide, only small leakage exists which is produced by the voltage drop. When the function generators voltage is on the positive side, the Zener diode conducts but only to the point where its breakdown voltage is reached. In the limiter circuit, the Zener diode limits the voltage according to the assigned reference breakdown voltage. In both directions the voltage is 0,5 volts bigger caused by the voltage drop on the diodes.