Diode Circuits and Applications

Transcription

1 Diode Circuits and Applications

2 In this chapter, we will: Determine the operation and characteristics of diode rectifier circuits, which is the first stage of the process of converting an ac signal into a dc signal in the electronic power supply. Apply the characteristics of the Zener diode to a Zener diode voltage regulator circuit. Apply the nonlinear characteristics of diodes to create waveshaping circuits known as clippers and clampers. Examine the techniques used to analyze circuits that contain more than one diode. Understand the operation and characteristics of specialized photodiode and light-emitting diode circuits.

3 Block Diagram for ac to dc Converter The diode rectifier, filter, and voltage regulator are diode circuits.

4 Half-Wave Rectifier Voltage Transfer Characteristics

5 Signals of Half Wave Rectifier Input voltage Output voltage Diode voltage

6 Load Line Analysis A load line is used in graphical analysis of nonlinear electronic circuits, representing the constraint other parts of the circuit place on a non-linear device, like a diode or transistor. It is usually drawn on a graph of the current vs the voltage in the nonlinear device, called the device's characteristic curve.

7 Load Line Analysis Load line when v S is at its maximum forward voltage. Load line when v S is at its most negative value.

8 Load Line (con t) As v S varies with time, the load line also changes, which changes the Q-point (v D and i D ) of the diode.

9 Half-Wave Rectifier as Battery Charger

10 Full-Wave Rectifier Voltage transfer characteristics Input and output waveforms

11 Full-Wave Bridge Rectifier When v S is positive, D 1 and D 2 are turned on (a). When v S is negative, D 3 and D 4 are turned on (b). In either case, current flows through R in the same direction, resulting in an output voltage, v O, shown in (c).

12 Full-Wave Bridge Rectifier

13 Output Voltage of Full-Wave Rectifier with RC Filter The ripple on the dc output is V r = VM 2 frc where f = 1 2T P

14 Output Voltage of Full-Wave Rectifier with RC Filter t 1 2V = T π V M r Diode conducts current for only a small portion of the period.

15 Equivalent Circuit During Capacitance Charging Cycle i i C C, peak ω = t ω = CV = + M ω 2V V M CV r ωt M ω t

16 PSpice Schematic of Diode Bridge Circuit Steady state output voltage for a 60Hz sine wave input with peak value of 13.4V.

17 Demodulation of Amplitude-Modulated Signal Modulated input signal Detector circuit Demodulated output signal

18 Voltage Doubler Circuit

19 Equivalent Circuits for Input Cycles Negative input cycle Positive input cycle

20 Voltage Regulator I I I L I Z V = R = V = I PS I Z L V R i I L Z The characteristics of the Zener diode determines V L.

21 Voltage Rectifier with nonzero Zener resistance The Zener diode begins to conduct when V PS = V Z. When V PS V Z : V L = V Z I L = V Z /R L,, but V Z constant I 1 = (V PS V Z )/R i I Z = I 1 - I L

22 Voltage Transfer Characteristics of Limiter Circuit

23 2 Diode Circuit Voltage transfer characteristics

24 Problem-Solving Technique: Multiple Diode Circuits 1. Assume the state of the diode. a. If assumed on, V D = V γ b. If assumed off, I D = Analyze the linear circuit with assumed diode states. 3. Evaluate the resulting state of each diode. 4. If any initial assumptions are proven incorrect, make new assumption and return to Step 2.

25 Diode Logic Circuits: 2-Input OR Gate V 1 (V) V 2 (V) V O (V) V γ = 0.7V

26 Diode Logic Circuits: 2-Input AND Gate V 1 ( V ) V 2 ( V ) V O ( V ) V γ = 0.7V

27 Photodiode Circuit

28 Optoisolator

29 Design DC Power Supply Circuit

30 Diode Clippers A clipper (or limiter) is a circuit used to eliminate some portion (or portions) of a waveform. A series clipper is in series with its load. A shunt clipper is in parallel with its load.

31 Series Clippers

32 Negative Shunt Clipper Operation

33 A Positive Shunt Clipper When the diode is conducting: When the diode is not conducting: V L = V F V L = V in R L R L + R S

34 Biased Shunt Clippers

35 Diode Clampers A clamper (or dc restorer) sets (or restores) the dc reference of a waveform.

36 Clamper Operation

37 Biased clampers Biased clampers allow a waveform to shifted above or below a dc reference other than 0 V. The dc reference is determined by the biasing voltage (V B ) and the setting of the potentiometer (R 1 ).

38 Zener clampers The diodes in (a) are in a common-cathode configuration. The diodes in (b) are in a common-anode configuration.

39 Voltage Doublers A voltage doubler provides an output that is twice its peak input voltage.

40 Half-Wave Voltage Doubler The term half-wave reflects the fact that the output capacitor (C 2 ) is charges during one alternation of each input cycle and discharges during the other.

41 Half-Wave Voltage Doubler Operation

42 Full-Wave Voltage Doublers The term full-wave reflects the fact that the output capacitors are charged during alternate half-cycles of the input signal.

43 Voltage Tripler A voltage tripler provides a dc output voltage that is approximately three times the peak input voltage.

44 Voltage Quadrupler A voltage quadrupler provides a dc output voltage that is approximately four times the peak input voltage.

45 A Basic Dual-Polarity Power Supply The output voltages are approximately equal to the peak values of the input waveform.

46 LED Level Indicators The LED in circuit (a) lights when the driver output is +5 V. The LED in circuit (b) lights when the driver output is 0 V.

47 Multisegment Display Multisegment display A device used to display alphanumeric characters (numbers, letters, symbols, and punctuation marks). LED displays contain some number of diodes that are connected in a common-cathode or a common-anode configuration. A liquid crystal display (LCD) consists of segments that reflect (or do not reflect) ambient light when provided an active input.

48 Seven-Segment Displays The display uses LEDs that are arranged in a figure 8 configuration. The display represented below is a common-cathode display. Each LED lights when a positive voltage is applied to the appropriate pin.