The domestic market, despite the car stereo program source has been expanded from a single radio , dual tape machine developed to join the single disc or multi disc changer CD, but the basic car stereo amplifier has changed little for , still in radio, tape drives , and the composition of the integration of audio CD machine . Such integration of audio , regardless of the manufacturer of the 2 * 35W or 200W +200 W, in fact still early two-channel amplifier , its output effective power per channel is not really greater than 20W, ordinary product will not exceed 2 * 6W . Recently, domestic electronic newspapers have published reports of car audio upgrade that car owners have not met, then wanted to know the latest car audio trends abroad . To this end, membership in this article to a car audio enthusiast describes a family . The current status of the foreign car stereo has the following characteristics . DC converter Teng jumped back The reason why DC converters , " Teng jumped back "because of the last century 40's era tube radio , tube to the car radio to provide high -voltage power supply, has been widely used in a " vibrator " converter, this Converter principle is composed of two-way mechanical switch contacts will be transformed into two-way 12V DC square wave , and then pulse voltage transformer capital increase , and then rectified , filtered into high voltage direct current , the basic principle of the circuit with the existing transistors DC-DC converter is the same, difference is the mechanical switch commutation, the pulse frequency only in the 1KHZ the following , but also low frequency . This mechanical vibration sub- converter has been applied to the semiconductor device is quite advanced, that the radio tubes to transistors before disappearing from the car stereo . As the car stereo by the 12V power supply constraints , both the output power or sound field effect is difficult to further increase . In this case , from the end of the century , the production of car audio in Europe began to use DC-DC converters, 12V battery power supply will be transformed to ± 24V-± 50V, providing power to the car stereo . Currently , DC-DC converters , compared with the mechanical converter , has shrunk , its switching frequency up to 100KHZ above , efficiency is nearly 90%. Car audio power supply used in DC-DC converters, instead of the boost switching power supply is the result of careful consideration. Part of a modern transistor amplifier class AB amplification is still its working current fluctuations with the signal proportional to change , so changes in the scope of PA practice constitutes a great load . In order to avoid the amplifier output signal distortion produced decapitation , required power supply sufficient energy reserves , when the signal peaks can provide immediate large transient current ( general PMOP shall instantaneous peak power of the amplifier nominal ) . Obviously, also includes a power supply transient output current capability. No matter PWM switching power supply , or PCM, the energy output is converted by the formation of electromagnetic pulse transformer , switch turns on , magnetic energy storage to the pulse transformer , switch closed , the magnetic energy into electrical energy to the load voltage . Even if the instantaneous load current increases the output voltage drops , the regulator control system can only control the switch conduction interval extension for the next -time , to be set only after the switch , the output voltage increases to map the impact of increasing load current compensation . However, the music is ever-changing fluctuations , sometimes substantially out of the signal is instantaneous, if the signal Chongji come O'clock , switching power supplies fail to provide high current , output voltage Biran formation decreased with the large-signal waveform , the signal on the red Limited , resulting in waveform distortion , etc. After the impact signal , PWM circuit until the output signal rise , switching power supply further reduces the output voltage to its output voltage . Unfortunately , all too late in the process output signal distortion is inevitable , but also increases the supply ripple pulse , so that the amplifier noise increases . DC-DC converter is different converter switch to set the pulse width is always work , as long as the switch has enough switching current , it can provide its rated power at any time within the voltage . From this point , the DC-DC converter and transformer rectifier power supply is no different , and lower the internal resistance of DC-DC converter , on the momentary high current and adaptable . In fact converter is not regulated system switching circuit , switching power supply to remove any pulse modulation , sampling error amplification part of the substance shall Converter . According to this principle , the end of the century , Europe began to configure the DC-DC converter car audio , car amplifier and matching . In 1980, German production of Monacor HPB150 car amplifier , equipped with a 12V and ± 25V DC-DC converter , the maximum output current of up to 10 to 15A, so that the effective output power of amplifier 2X40W, or BTL Connection , the output power of 150W. Another , called "Jensen" car amplifier used on the converter , you can transform the 12V voltage output of ± 30V/15A dual power supply can power four -channel amplifier , the effective power output 4 * 60W which "Monacor HPB150 for the first product, the power amplifier converter using discrete components assembled into a self-excited push-pull converter , using a total of 13 transistors, the circuit more complex alignment is not easy . In addition, self -excited oscillation circuit whose Frequency changes with load current , pulse interference suppression is also more difficult. Jensen power converters , switching power supply which is the traditional drive -excited drive four MOS FET switch composed of parallel push-pull circuit , the amplifier converter circuit as shown in photo . The car tube amplifier using MOS FET as the switch , can improve the efficiency of the power transformer , is conducive to impulse noise suppression , but also can reduce the size of the power transformer . Converter oscillator and control systems are all integrated in the IC (TL494) inside . TL494 original design for its Switching Power drive controller , except with the internal oscillator, pulse-width modulator , there are reference voltage regulator circuit , dead time control circuit and the comparator group consisting of error detection circuit . TL494 constitute the circuit of forward converter , using only its oscillator and drive circuit for driving the pulse switch signal source , and therefore have no regular use . In this circuit , TL494 first time constant circuit external 5,6 feet (C3, R5), oscillator 80kHZ the pulse signal , bistable flip-flop by the TL494 internal control, into a different drive two-way timing pulse , the drive Two sets of driver amplifier . TL494 internal groups driver level , 9,10 feet from the first positive pulse output timing difference . In order to avoid two-way push-pull switch pulse alternating Department VT3, VT5 and VT2, VT4 same turn , TL494 fourth pin external R6, C2, R4 set the dead time . A driving pulse to turn one arm push-pull circuit , the gap between a dead time , when it issued another set of drive pulses to the other arm turn ( the fourth leg higher the voltage, the longer the dead time ) . 1,2 feet TL494 amplifier for the two -phase sampling and the inverting input , to control the composition of the internal comparator to set the duty cycle pulse width modulator . In the converter , TL494 function and application of the foot as follows : 1 foot for the first group of the error amplifier inverting input . Grounding circuit to R2 , so that is low . 2 feet for the first group of the error amplifier inverting input. R7 access from the 5V reference voltage . Output when the first 2 feet high , the error amplifier output ( pin 3 ) output a constant low , the level of internal control in the TL494 PWM comparator consisting of modulator, the output pulse width 45% maximum , and the remaining 5% Seek death -time . In addition, add 2 feet for the soft-start capacitor C4 , C4 boot instant instant charge to 2 feet for the low , the error amplifier output high , with the C4 charge voltage increases , voltage rise 2 feet , 3 Pin voltage is lower , so that PWM output pulse width compared to the nominal pulse width increases slowly , to avoid the impact of current damage to the boot switch . 3 feet for the error amplifier output , external R3, C1 is designed to avoid the error amplifier oscillation . 4 feet for the dead-time control side , through R6, R4 voltage divider from the 5V reference voltage by 0.05V dead-time control of voltage pulses between the two sets of drivers accounted for 5% of the gap width . 4 foot level to 0.3V , the driving pulse is turned off . S 5,6 for the oscillation frequency control pin end , add R5, C3 set the oscillator 's oscillation about 80KHZ pulse logo R5 can adjust oscillation frequency 100KHZ. C3, R5 and the relationship between the oscillation frequency is : f (kHZ) = 1.2 / R (kO) · C (µF). 7 feet for the public to side .