* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Bollen - Jan Bollen`s Homepage
Immunity-aware programming wikipedia , lookup
Transistor–transistor logic wikipedia , lookup
Standby power wikipedia , lookup
Regenerative circuit wikipedia , lookup
Thermal runaway wikipedia , lookup
Index of electronics articles wikipedia , lookup
Surge protector wikipedia , lookup
Power MOSFET wikipedia , lookup
Cellular repeater wikipedia , lookup
Operational amplifier wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Current mirror wikipedia , lookup
Distortion (music) wikipedia , lookup
Radio transmitter design wikipedia , lookup
Power electronics wikipedia , lookup
Audio power wikipedia , lookup
Valve RF amplifier wikipedia , lookup
Switched-mode power supply wikipedia , lookup
POWER AMPLIFIER Bollen 1 AGENDA Power amplifier Signals / definitions DC power supply AC signal power Efficiency Classes Class A type CE Class A type CC Push Pull Bollen Cross over distortion Vbe Multiplier Thermal runaway Emitter resistors Temperature dependent Bias voltage Short circuit protection 2 Power Amplifier Power amplifier = current amplifier Rloudspeaker = 8 Ohm, P for 50 Watt >> I = 2,5 Ampere Bollen I R Power IN = DC power Power out = AC power 2 3 Signals / definitions 1/3 DC supply power DC-power = DC value for supply voltages, Bollen And Average for current waves 4 Signals / definitions 2/3 AC Signal power U U signal 2 I signal Bollen I 2 5 Signals / definitions 3/3 efficiency = efficiency / for definition see below AC signalpower delivered to load DC power from DC source So, POWER SUPPLY delivers DC or average power And the LOAD gets SIGNAL power (use root mean square value) Bollen 6 ɳ Bollen 7 Classes Class-A Output device(s) conduct through 360 degrees of input cycle (never switch off) - A single output device is possible. The device conducts for the entire waveform Class-B Output devices conduct for 180 degrees (1/2 of input cycle) - for audio, two output devices in "push-pull" must be used Class-AB Halfway (or partway) between the above two examples (181 to 200 degrees typical) - also requires push-pull operation for audio. Bollen 8 Classes Class-C Output device(s) conduct for less than 180 degrees (100 to 150 degrees typical) - Radio Frequencies only - cannot be used for audio! This is the sound heard when one of the output devices goes open circuit in an audio amp! Class-D Quasi-digital amplification. Uses pulse-widthmodulation of a high frequency (square wave) carrier to reproduce the audio signal. Bollen 9 Class A type CE The configuration is a common emitter The load / loudspeaker is in the collector If there is no signal there is a quecient current to adjust Vc = ½ Vcc for symmetrical use of voltage range If there is no signal, the power supply should deliver power to the circuit The efficiency is very low Bollen The lost power is just dissipation: heating of components: so you need to 10 cool for high power Class A Vcc = 40 Volt Rload = 8 Ohm Quesientpoint Uc = 20 volt I bias = 2,5 A I signal max = 2,5 A 1 Vcc I q AC signalpower 2 2 2 DC power Vcc I q Bollen 1 Vcc I q 4 0,25 Vcc I q 11 Class A type CC The configuration is a common collector The load / loudspeaker is connected to the emitter If there is no signal there is a quecient current to adjust Ve = ½ Vcc for symmetrical use of voltage range If there is no signal, the power supply should deliver power to the circuit The efficiency is very low Bollen The lost power is just dissipation: heating of components: so you need to 12 cool for high power Vcc = 40 Volt Class A Rload = 8 Ohm Quesientpoint Uc = 20 volt Isignal max = 2,5 Ampere 1 Vcc I q AC signalpower 2 2 2 DC power Vcc I q 1 Vcc I q 4 0,25 Vcc I q Bollen 13 Push Pull idea If you need water; open Q1 If you deliver water; Open Q2 Q1 and Q2 never opens at the same time Bollen 14 Push Pull with transistors Here the BJT are complementary (NPN and PNP) Each device amplify the opposite halves of the input signal At the output you get the total signal. excellent efficiency But small mismatch between the two halves of the signal Bollen 15 Push Pull in realisation Vcc Vcc = +20 Volt Vee = -20 Volt Rload = 8 Ohm Uin = 0 Volt Uout = 0 Volt Vee Bollen So no bias current 16 Push Pull in realisation Vcc Vcc I Psignal 2 2 20 2,5 25 Watt 2 2 Pdc 2 Vcc 24 Vee Bollen 2,5 I 32 Watt 25 0, 78 32 17 Cross-over distortion Dead zone = 1,4 Volt Bollen 18 Eliminating Cross-Over Distortion Shift NPN 0,7 Volt to left Shift PNP 0,7 Volt to right Bollen 19 Eliminating Cross-Over Distortion Bollen 20 Eliminating Cross-Over Distortion Shift 1,4 Volt Or Shift 2,8 Volt Or Something else … Bollen 21 Vbe multiplier Base current is negligible, so: VBE I R1 I R 2 R2 VBE VBE R1 VR1 I R 2 R1 R2 Vbias Vbias Bollen R1 R2 RV 1 BE VR1 VR 2 VBE VBE R2 R2 R1 R2 0.7 R2 Inverse voltage divider !!! 22 Vbe multiplier Bollen 23 Thermal runaway Fit a bigger heatsink. Use series emitter-resistors. Use a temperature dependent bias voltage. The latter two are preferred methods. Both introduce negative feedback. Bollen 24 Emitter resisters 2Vbias VBE1 VEB 2 2VRE By symmetry: VBE1 VEB 2 Vbias VRE Vbias I C RE So, if IC rises, VBE falls and IC is reduced. Note RE should be small compared with RL to minimise power wasted. Bollen 25 Temperature dependent bias voltage If junction temperature rises but IC stays the same, VBE must fall causing Vbias to fall also. Negative thermal feedback achieved if the transistor is in close contact with the output devices. Especially suitable for integrated circuits where close thermal contact is guaranteed. Bollen 26 Short circuit protection Current limitation Rx is a current measuring resistor T1 Rx If URx> 0,7 the T1 switches ON Then output current in limited !! Bollen 27