class b amplifier design
DESCRIPTION
Slide show developed as part of school project. My contribution to group, in addition to engineering and circuit design, was creating and organizing a Power Point presentation to summarize our design.TRANSCRIPT
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Class B Amplifier Design Proposal
Evan Bare Andrew Cook Lee Kusy Joe Morrow Khiem Nguyen Michael West
Ingram School of EngineeringTexas State UniversitySan Marcos, TXDecember 5th, 2011
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Class B Characteristics
High efficiency High gain Push/pull transistors Power Amplifier
› Av ≈ 1
› Ai > 1
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Class B Pros/Cons
Advantages:› Ideally, no quiescent current› High efficiency (max efficiency of 78.5%)
Disadvantages:› Crossover distortion› Requires a biasing current› Q point stabilization
D.J. Bates, A. Malvino. "Power Amplifiers," in Electronic Principles, 7th ed. New York: McGraw-Hill, 2007. pp. 392-397.
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Design Considerations
Input: Sinusoidal voltage, 50 Ω resistance
Output: 2 – 16 Ω speaker Onboard 12 V supply High power gain High efficiency Minimum cost Single layer PCB Minimum PCB area
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Power Supply (12 V)
0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.070.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
Time (s)
Volt
age (
V)
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Alternate Power Supply (USB)
Provides 5 V±5%, max 500 mA› Limits input signal to max 2.5 Vpk
› Sufficient power Additional Cost
› USB connector› Additional PCB area
"7.3.2 Bus Timing/Electrical Characteristics". Universal Serial Bus Specification. USB.org
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Proposed Design
vinvout
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Transistor Biasing
› VCB = 0.7 V
› VBE = 0.7 V
› Place each base 0.7 V above/below emitter voltage
½ Vcc ½ Vcc
½ Vcc + 0.7V
½ Vcc - 0.7V
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Stability
Avoid thermal runaway Stabilizing capacitor between bases
› Keeps base voltages stable with AC swings
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Maximum Efficiency
D.J. Bates, A. Malvino. "Power Amplifiers," in Electronic Principles, 7th ed. New York: McGraw-Hill, 2007. pp. 392-397.
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Actual Efficiency
7 Vpk, 1 kHz input, 16 Ω load:
110 mA x 12.0 V = 1.32 W
245 mA x 3.93 V = 963 mW
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Power Gain
From Multisim:› pout = 523 mW
› pin = 27.96 mW
Improvements?› Op-Amp
𝐴𝑝=𝑝𝑜𝑢𝑡
𝑝𝑖𝑛
𝑝𝑖𝑛=𝑣 𝑖𝑛×𝑖𝑖𝑛
𝑝𝑜𝑢𝑡=𝑣𝑜𝑢𝑡× 𝑖𝑜𝑢𝑡
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1E+0 1E+1 1E+2 1E+3 1E+4 1E+5 1E+6 1E+7 1E+8 1E+90
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Input Frequency (Hz)
Frequency Response
Audible Range
(20 Hz – 20 kHz)
fC1 = 16 Hz fC2 = 15 MHz
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Load Variations v Power5 Vpk, 1 kHz Sinusoidal Input Signal
0 0.00005 0.0001 0.00015 0.0002 0.00025 0.0003 0.00035 0.0004 0.000450
0.5
1
1.5
2
2.5
2 Ohm
4 Ohm
8 Ohm
16 Ohm
Time (s)
pou
t (W
)
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Cost Analysis
Single Prototype: $8.55 + PCBComponents # per Circuit Unit Price ($) Cost ($)
1 kΩ resistor 5 0.33 1.65
500 µF capacitor 5 0.48 2.40
2N3904 transistor 3 0.43 1.29
2N3906 transistor 1 0.46 0.46
1N4002GP diode 4 0.50 2.00
100 µF capacitor 1 0.48 0.48
1N5242B Zener 1 0.27 0.27
Total: $8.55
Pricing from http://www.digikey.com as of Dec 3rd, 2011
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Cost Analysis
Mass Production: $0.756 + PCBComponents # per Circuit Unit Price ($) Cost ($)
1 kΩ resistor 5 0.036 0.18
500 µF capacitor 5 0.039 0.195
2N3904 transistor 3 0.033 0.099
2N3906 transistor 1 0.033 0.033
1N4002GP diode 4 0.048 0.192
100 µF capacitor 1 0.039 0.039
1N5242B Zener 1 0.018 0.018
Total: $0.756
Pricing from http://www.digikey.com as of Dec 3rd, 2011
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PCB Requirements
9 mm
50 mm
PCB Area: 9 x 50 = 450 mm2
30 units per 10 x 16 cm board
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Summary
Transistor-biased design $0.76/unit Minimal PCB area Amplification throughout audible range High efficiency Ap 20
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Web Resources
http://www.qrp.pops.net/AF-Basics.asp
http://www.digikey.com
http://www.ece.drexel.edu/courses/ECE-E352/ClassABAmp.pdf
http://vijayatronics.info/Notes/ch-2%20ampli.pdf
http://www.electronics-tutorials.ws/amplifier/amp_6.html
http://www.usb.org
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Acknowledgements:
Dr. Semih AslanIngram School of Engineering
Texas State University
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Questions?Diagram Supply Biasing Stability Efficiency
Gain Frequency Load Cost PCB