* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download plans - Warren Mar
Power factor wikipedia , lookup
Spark-gap transmitter wikipedia , lookup
Mercury-arc valve wikipedia , lookup
Power over Ethernet wikipedia , lookup
Ground (electricity) wikipedia , lookup
Electrical ballast wikipedia , lookup
Solar micro-inverter wikipedia , lookup
Immunity-aware programming wikipedia , lookup
Electric power system wikipedia , lookup
Electrification wikipedia , lookup
Variable-frequency drive wikipedia , lookup
Current source wikipedia , lookup
Pulse-width modulation wikipedia , lookup
Audio power wikipedia , lookup
Power inverter wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Earthing system wikipedia , lookup
Electrical substation wikipedia , lookup
Power engineering wikipedia , lookup
Distribution management system wikipedia , lookup
Amtrak's 25 Hz traction power system wikipedia , lookup
Transformer wikipedia , lookup
Surge protector wikipedia , lookup
Three-phase electric power wikipedia , lookup
Stray voltage wikipedia , lookup
Power MOSFET wikipedia , lookup
Power electronics wikipedia , lookup
Voltage regulator wikipedia , lookup
History of electric power transmission wikipedia , lookup
Opto-isolator wikipedia , lookup
Transformer types wikipedia , lookup
Buck converter wikipedia , lookup
Power supply wikipedia , lookup
Alternating current wikipedia , lookup
Voltage optimisation wikipedia , lookup
Audio Amplifier Design Warren Mar January 11, 2011 1 Design Criteria The human audible range is 20 Hz - 20 kHz. 2 Power Supply To drive the 8 Ω, we need a supply voltage of at least 28.3 V. RL = 8 Ω 1 2 50 W(RMS) = Vpeak RL 2 Vpeak = 28.3 V Ipeak = 3.6 A To get the DC voltage to power the LM4780 chip, we need to convert the 120 VAC 60 Hz building supply into ±40 V by using a AC to DC converter composed of a center tapped transformer with some rectifying diodes and a voltage regulator. The transformer turns the 120 V to 40 V. The rectifying diodes, convert the AC into bumps, which gets smoothed out by large capacitors. This smoothed out bumping signal then gets further regulated into a stable supply. Noise in the power supply can couple into noise in the output. A stable power supply is a must. A dual-polarity power supply will give us what we need as seen in Figure 1. A sample netlist is provided in Listing 1. 1 Figure 1: Dual-polarity power supply [3] Listing 1: Dual power supply netlist Dual Power Supply VIN 1 0 SIN ( 0 120 60 0 0 ) RS 1 2 0 . 1 LP1 2 0 90m LP2 2 0 90m LS1 4 0 10m LS2 0 5 10m K1 LP1 LS1 0 . 9 9 9 9 9 K2 LP2 LS2 0 . 9 9 9 9 9 D1 6 4 D2 4 7 D3 6 5 D4 5 7 ∗ 7 v+ 6 v− RL 7 6 50 C1 7 0 10m C4 0 6 10m ∗ analysis .TRAN 1m 0 . 1 . PRINT TRAN V( 1 ) V( 4 ) V( 5 ) V( 6 ) V( 7 ) .END 2 2.1 Transformer Toroidal geometry results in less lost form stray fields. V1 V2 = N1 N2 , where V1 is the voltage and N1 is the number of windings. To go from 120 V to 40 V. N1 = 3N2 , so the primary windings will be triple that of the secondary windings. Since it is difficult to get the core and laborious to wind a toroidal transformer yourself, buy you can easily buy one such as the one seen in Figure 2. 500 VA means Vrms Irms < 500 for safe operations. Figure 2: Avel Y236804 500VA 40V+40V Toroidal Transformer from partsexpress.com [2] 2.2 Rectifying Diode Bridge For the rectifying diodes used in the bridge, we need ones that have a low turn on voltage to minimize losses and able to support enough current. Minimum current around 10A. There are rectifying bridge modules that can be purchased, but they usually are designed to higher requirements for voltage and current, so it will be cheaper to go with individual diodes to make our bridge. 3 150 Line Voltage Secondary Positive Secondary Negative 100 Voltage (V) 50 0 −50 −100 −150 0 0.005 0.01 Version0.025 of MATLAB0.03 0.015Student 0.02 Time (s) Figure 3: Center-tapped transformer 4 Figure 4: Avel Y23 transformer series connection diagram [?] 5 Figure 5: Rectified positive supply output 6 2.3 Regulation The rectified voltage needs to be smoothed out for it to be DC. At minimum capacitors are needed. A voltage regulator can also be added, but some efficiency is lost, because it regulates by dumping excess current to ground. Q = CV I=C 3 dV dt Amplifier Circuit Humans can hear from 20 Hz to 20 kHz. The ability to hear higher frequencies gets lost as one ages. The audio source is mostly a CD, so that’s 44.1 kHz at 16-bits, which gives you 22500 Hz as your highest frequency and 20 ∗ log(21 6) = 96.3dB of dynamic range. Having a noise level less than 96 dB, won’t make much of a difference. LM4780 is composed of two LM3886. Output Power/Channel ??with 0.5% THD+N, 1kHz into 8 60W (typ) THD+N at 2 x 30W into 8 (20Hz - 20kHz) 0.03% (typ) The amplifier can be thought as a simple opamp. Since we want to use the two opamps in different configurations, we need the proper switches to wire it up. Mute and soft turn on. The PCB traces will be designed with ExpressPCB. The LM4780 datasheet has a lot of information. When selecting resistors, measure them and choose the ones that are the closest. 7 Figure 6: Stereo circuit diagram [1] Figure 7: Mono circuit diagram 8 Figure 8: Bridged circuit diagram [1] Figure 9: Mute soft start [1] 9 Figure 10: LM4780 PCB 10 4 Chassis Metal chassis to shield against electromagnetic interference acting as a faraday cage. The power supply should be on the opposite side of the incoming signal lines to reduce noise for EMI and capacitive coupling. The front panel will be designed with front panel express. Figure 11: a) Front Panel b) Back Panel References [1] Lm4780 datasheet. [2] www.parts-express.com. [3] Paul Horowitz and Winfield Hill. The Art of Electronics. Cambridge University Press, 1989. 11