1. Diode Circuits

2. Outline Large-Signal and Small-Signal Operation
Application of Diodes (Up to 3.5.1)

3. c03f19
How does a small increase in Vad affect Vout?

4. c03f20
(Slope)

5. Small Signal Resistance
Small Signal Resistance: ID/VT

6. Measured Diode Voltage

7. Small Signal Resistance
VF (V)
IF (Computed)
0.70
5.74 mA
0.748
13.8 mA
Dynamic Resistance from the measurement:
( )/(13.8 mA-5.74 mA)= 48 mV/8.06 mA =5.95 Ohms
From the manufacture’s specification=8.33 Ohms, using data from 0.7V
and V in Figure 4.
( )/(13.8 mA-5.74 mA)= 48 mV/8.06 mA =5.95 Ohms

8. c03f22
Using Small Signal Model in a Small Signal Calculation

9. c03f23

10. Small Signal Model of Adaptor
c03f25
Change in Vad

11. c03f26
Change in Vout
due to a drop in
c03f26

12. c03f27
c03f27

13. c03f28 Half-Wave Rectifier Assume constant voltage model for diodes
Voltage offset
Diode is off for Vin < VD,on
Assume constant voltage model for diodes

14. c03f29
On for Vin less than –VD,on

15. c03f31
An AC-DC Converter Circuit
Ideal Diode Model

16. c03f30 An AC-DC Converter Circuit
Constant Voltage Diode Model
Issue: It remains to be seen whether it can provide a current to a load

17. How should a load be conceptualized?
A laptop consumes an average power of 25 W with a supply
voltage of 3.3 V. Determine the average current drawn from
the batteries or the adaptor.
P=VI
I= 7.56 A
If the laptop is modeled by a resistor, then RL is Ohms.

18. c03f32 Rectifier Driving a Resistive Load The diode is turned on again
ripples
Vin begins to fall after t1 because RL provides
a discharge for C1.
C1 must be sufficient large so that the current
drawn by RL does not reduce Vout significantly.

19. c03f33
C1 is called smoothing capacitor

20. c03f34
Magnitude of the Ripple
Tin

21. c03f35 The Maximum Forward Bias Current
Maximum Forward Current Occurs at the point when the diode turns on (t1)
C1dVout/dt is maximum
The current supplied to RL is (Vp-VD,on)/RL

22. Screen Shots

23. Smoothed Capacitor