Power amplifier design using discrete components

1, power amplifier basic circuit characteristics

OTL power amplifier complementary symmetrical basic circuit shown in Figure ①. Where: C1 is the signal input coupling element, should be noted that the actual circuit polarity should be consistent in the potential situation. R1 and R2 bias circuit composed of BG1, BG1 provides static work point to the same time, the circuit also played the role of DC negative feedback. R1 is greater than the current required by the base current BG1 at least 5 times, in accordance with the β for the 100, Ic1 calculated for the 2mA, R1 should be no more than 6k, it is given for the 5.1k; C1, accordingly, given to 22μ, it 20Hz signal on the impedance of 362Ω; R2 must be in accordance with the specific voltage of the power to determine, approximately R1 (E/2-0.6) / 0.6, in accordance with the 32V voltage value should be taken as about 120K, the exact value of the actual debugging by making BG1 collector voltage of 15.4V to get.

C2 and R3 form the bootstrap circuit, asked R3 × C2> 1 / 10, (R3 + R4) × Ic1 = E/2-1.2, R4 is BG1 exchange for the load resistance, as far as possible to take bigger, R3 generally take the 1k within. In accordance with the 32V supply voltage value and Ic1 calculated to 2mA, R3 and R4 of and for the 7.2k, is actually the R3 to 820Ω, R4 to the 6.8k, Ic1 was 1.94mA; C2 is therefore desirable to 220μ.

R5 and D are BG2, BG3 complementary bias control circuit elements, to BG2, BG3 static work together to provide an appropriate point, to eliminate crossover distortion as much as taking a small value, usually based on the experimental results obtained in the 3mA ~ 4mA; R5 resistance to change can BG2 and BG3 voltage drop between the base of the static work to achieve changes in the adjustment, and R5 in series D is to compensate for BG2, BG3 emitter threshold voltage changes with temperature, preferably two only diodes connected in series Complementary tube emitter threshold voltage changes with temperature so that the static operating point stability control complement each other. Simplify the use of a diode circuit is omitted. Parallel in BG2, BG3 base between the C4, can reduce the dynamic work of ΔUAB, generally taken to be 47μ; C3 is to prevent the BG1 produce high-frequency self-excited AC negative feedback capacitor, generally taken as the 47P ~ 200P.

BG1 from the voltage amplification in the circuit is known as incentive level, required Buceo> E, Iceo ≤ Ic1/400 = 5μA, β = 100 ~ 200, it should use low-power low-noise transistor. BG2 and BG3 are highly complementary current amplification, respectively, and BG4, BG5 constitute a composite tube to amplify the output current require Buceo> E, Iceo ≤ Ic2/100 = 30μA, β = 100 ~ 200. In BG4, BG5 using ordinary high-power three pipes instead of power within the compound has been made of the case of three pipes, BG2 and BG3 need to provide after-class high-power three-level control over 100mA peak drive current, it should Use the power of three tubes. BG4 and BG5 is responsible for the amplified output current of the power control, quiescent current is desirable in 10mA ~ 30mA, asked Buceo> E, Iceo ≤ Ic4/100 = 0.1mA, β = 50 ~ 100. BG4 and BG5 the maximum current Imax should limit the maximum amplitude than the output current times the big one, can ensure the maximum amplitude of the output current when β> 10.

R6 and R7 are BG4 and BG5 shunt resistors to adjust the static working point, dynamic work of the streaming effect is negligible. In Ube4 and Ube5 standard parameters are equal to 0.6V when the current zoom level from the complementary static current to take in the 3mA ~ 4mA, R6 and R7 should be calculated taking as 220Ω. In fact, the power may be a difference of three large pipe Ube, BG4 and BG5 of Ube be paired through the measured use of the bootstrap circuit to work with half the total current magnification composite pipe should be higher than without the aid of the work of the bootstrap circuit The other half of the composite pipe is smaller.

R8 and R9 BG4 and BG were to prevent excessive flow of current limiting resistor, usually taken between the 0.2Ω ~ 0.5Ω. Will be 200mm long with a diameter of φ0.08 of enameled wire ends were welded over the 1k resistor at both ends, to fold up the enameled wire can be wrapped around the resistor. Equivalent to fuse the role of the insurance management, among the most simple non-smart way of limiting the protection blown.

C5 and C6 is the output capacitor, with a small capacitor in parallel with the large capacitor up and use, and can eliminate the internal capacitor inductance with the larger obstacles for high-frequency signals. Note that it is actually played the role of mid-point of the floating power supply, so the capacitance is not in accordance with the right pass the bottom fight Dai impedance AC signal to be what its terms, and that the output power according to the number of required energy consumption calculation. In the mid-point of the floating power supply voltage fluctuations as a result of the output current of the output signal chopper, they will have serious clipping. According to the energy storage capacitor is proportional to voltage squared, the midpoint of the floating power of the output capacitor, the total power supply capacity should be 4 times the energy storage capacitance.

C9 and R10 is the exchange of negative feedback network, and R2, R1 together form the voltage of the negative anti-parallel shame. R2 and R1 form a negative anti ashamed of DC voltage can total magnification is equivalent to R2 divided by 1.2k (equal to R1 and BG1 the emitter dynamic resistance in parallel), in accordance with the plan design parameters ① about 100 times, adding C9 and R10 exchange of negative feedback network, the total magnification is equivalent to the voltage and the R10's parallel resistance R2 divided by the 1.2k, is about 18 times. Practice shows that the work in this way the voltage performance of parallel negative effect of very good anti-ashamed.

Power amplifier design using discrete components

Second, the basic circuit for power amplifier

Shown in Figure ① OTL power amplifier complementary symmetric basic circuit, the signal input excitation level resistance only 1k, impedance conversion can be done with the majority, the high impedance signal source match. Incentive-level input signal directly into composite pipe is the easiest way, composite pipe connected in a variety of specific circuit, the best solution is shown in Figure ② Connection. Additional pre-class practice is equivalent to a simple voltage-controlled current-mode operational amplifier, BG0 the base and emitter equivalent to the positive op amp input and negative input, positive input of the dynamic resistance has been increased to more than 10K. Meanwhile, the output from the power amplifier input emitter receiving negative feedback resistor R10 and the sampling resistor R11 determines the ratio of the total voltage magnification.

Power amplifier design using discrete components

Debug circuit elements are adjusted into a first short-circuit 0 resistor R5 situation to BG2 ~ BG5 is off, with two 1K/2W resistance were received from both ends of the total power output was the mid-point voltage. Replaced with a 200K potentiometer R1 or R2 connected to the circuit board, with wires to the input capacitor C1 and to short circuit the input signal. Switched on, measuring BG1 collector to emitter voltage drop Uce, 200K potential regulation allows Uce equal E/2-0.6; the total power supply voltage of 32V at the time, BG1 static Uce should be equal to 15.4V ± 0.1V. 200K potentiometer and measuring the resistance in which the actual value, replace the fixed resistor with resistance value replace the potentiometer, then the static measurement BG1 Uce should be within 15.4V ± 0.2V. Determine the static Uce good BG1, then adjust from small to large to BG4 and BG5 R5 quiescent operating current is 15mA. For insurance purposes, R8 and R9 may be connected into 100Ω/2W for resistance, R8 and R9 on the first measurement of the static voltage drop should be 1.5V. Disconnect the power supply, adjustable resistor R5 actual measurement in which the resistance value, will be replaced with the same resistance R5 fixed resistors, removed earlier from the output ends are connected to a power resistor 1k/2W points. Plug in the power, R8 and R9 on the measurement of the static voltage drop should be kept between 1.2V ~ 1.8V. The mid-point level measurement of the output should be between the 16V ± 0.5V. The input capacitor C1 and to disconnect the input signal vacant, measuring the voltage drop across R8 and R9, C1 encounter with the screwdriver when the R8 and R9 input on the voltage drop was bigger. Then replaced 0.3Ω resistor R8 and R9, connected to the horn audition. Power on due to C0 charge, midpoint voltage output rose slowly from nothing, which produced only a slight impact on sound. 2 seconds later, the hand-touch input C1 speaker will be issued when the "Woo" and hum. The C1 input and ground (negative power supply side) short circuit, speakers should not sound practical to issue a slight background white noise or a very low voice communication hum. Shown in Figure ② OTL power amplifier to improve complementary symmetrical circuit, there is a clear disadvantage is that the input signal DC level than the midpoint voltage to low output 2V ~ 3V, the public has not IC op amp and transistor components using high cost 80 early 20th century, it has been very good to use a single power amplifier practical circuit. The mid-20th century, 80, op amp IC first introduced, people began to use as a pre-op amp IC to a very great and inspiring. Typical circuit shown in Figure ③, without adjustment for op amp IC quiescent operating point, as long as BG2 ~ BG5 adjust R5 so that the quiescent current of 10mA ~ 20mA can. Note that although the op amp IC not need to adjust the static working point, but in BG2 ~ BG5 is off, by the R8, R9 and BG3, BG5 emitter is the wizard through to the negative input of op amp IC is set to high, transport, let IC output low, so by BG3 emitter to the negative input of op amp IC is set to low, the output op amp IC turned into a high result in the output variable of the low-frequency oscillation state can not provide stable The reference to the midpoint level. In this situation, adjust BG2 ~ BG5 of quiescent current, operational amplifier IC output is high when the regulation is invalid R5; the op amp IC output is '0 BG5 can not turn on, adjust R5 can only BG2, BG3 , BG4 into the work area, BG2 actually only played the role of the diode, the current through BG4 and BG2 direct all poured into the op amp IC output, resulting in BG2 and the op amp IC for over-current damage! (I have owned at that time a few hand-made in the op amp IC and the power of three dozen full damage control, also failed to adjust the static working point out.) Must first IC op amp with a wire to the negative input and output connectivity, temporarily connected to the negative feedback resistor R6, so that op amp IC to follow a stable reference output device means the mid-point level, in this state, adjust R5 so that BG2 ~ BG5 the quiescent current of 15mA, the R5 fixed resistance into the same resistance is recognized BG2 ~ BG5 quiescent operating current in between 10mA ~ 20mA, and then the negative op amp IC input and output of reason and open to feedback resistor R6 access circuit.

IC op amp used as a front-most and inspire great, the best to BG2 ~ BG5 of quiescent current bias points form replaced by the transistor and resistor constitute the regulator, this can be changed greatly in the power supply voltage under remain almost the same quiescent current. Figure ④ that is, after the improved circuit, BG1 emitter threshold voltage and BG2, BG3, BG4 the threshold voltage with temperature change itself may play a role in temperature compensation. To reduce the output of op amp IC's quiescent current, the output of op amp IC gifts added to the end of the shunt resistor to R10. With the shunt resistor, adjusted BG2 ~ BG5 quiescent operating current can not access the first op amp IC, directly from one of R7, R8 and R10 partial pressure of the approximate midpoint of the reference level. Start with 0 and R5 big adjustment to make BG2 ~ BG5 the quiescent current of 10mA ~ 20mA in between, then access to op amp IC, the circuit that is able to work properly. In addition, IC op amp output current limiting resistor in series a 1k R15, can ensure that op amp IC output is '0 BG5 will not enter the closed state.

Power amplifier design using discrete components

IC op amp used as a front-most and inspire great, the biggest advantage is that the output DC level and DC level input signal strict agreement, a difference of no more than ± 0.05V. This can create a form from the two reverse OTL power amplifier output BTL power amplifier and the output DC level and DC level input signal are significant differences between cases are the two OTL power amplifier, inverting output DC level is often a difference of more than 0.5V, significantly affect the equilibrium position of speaker of the work. BTL power amplifier is, inverse DC level output DC level difference must be less than 0.1V, trumpet the work of the apparent equilibrium position will not deviate from the free position of equilibrium. Speaker balance the work obviously deviate from the free location of the equilibrium position, the positive and negative direction of the mechanical vibration amplitude asymmetry, issued by the unnatural sound will produce distortion. In addition, the output DC level and the input signal DC level strict consensus, which makes the use of positive and negative dual power supply for OCL power amplifier becomes a reality. Otherwise, the result of the power output DC level and the disparity in the mid-point level, will lead to a good speaker can not work properly.

As most of the op amp IC's operating voltage is not high, the good performance of high-voltage op amp IC varieties of small, high prices, people can also be used with front IC op amp differential amplifier circuit the same level to achieve the same purpose. Figure ⑤ differential amplification method that is used to do most of the typical pre-circuit than shown in Figure ① OTL complementary symmetrical circuit power amplifier basic requirement features more consistent with two of the transistor, as shown in the improved than the complementary graph ② symmetric OTL power amplifier with a more practical transistor circuits. Whichever that is not that people do not know how to design power amplifiers, but by the device selection constraints, in different historical periods can only use the appropriate circuit design. In the 20th century, late 80's, people began to more easily find properties matching using the same transistor. Because most of the quiescent current of differential amplification circuit design parameters can be accurately given, do not adjust the differential amplification of quiescent current. Circuit in Figure ⑤ use 32V power supply situation, front differential amplification of the quiescent current of 0.51mA ~ 0.52mA, adjust R12 to BG1 as long as the first collector to the ground side of the voltage dropped to 15.4V, and then adjust R5 so that BG2 ~ BG5 quiescent operating current can be in between 10mA ~ 20mA.

Power amplifier design using discrete components

BG1 quiescent current adjustment, the same must first be adjusted into a short circuit 0 resistor R5 situation to BG2 ~ BG5 is off, they will not access the negative feedback resistor R10, with a wire to BG6, BG0 the base short-circuit. Switch on the power, adjust R12 so that BG1 first collector to ground terminal voltage dropped to 15.4V ± 0.2V, and then adjust R5 so that BG2 ~ BG5 the quiescent current of 15mA. For insurance purposes, the first R8 and R9 for access into 100Ω/2W resistor, R8 and R9 on the measurement of the static voltage drop should be 1.5V. Disconnect the power supply, adjustable measuring resistor R5 and R12 in which the resistance of the actual value of resistance will change them for the same fixed resistor. Switched on, measuring R8 and R9 on the static voltage drop should be kept between 1.2V ~ 1.8V. The mid-point level measurement of the output should be between 16V ± 0.3V. Disconnect the power, will BG6, BG0 the inter-connection wires removing its base, the negative feedback resistor R10 access circuit. Plug in the power, R8 and R9 on the measurement of the static voltage drop should be kept between 1.2V ~ 1.8V. The mid-point level measurement of the output should be between 16V ± 0.2V, the greater the difference in charge current magnification, the signal output DC level and the smaller the difference between the input DC level. C1 touch with the screwdriver when the R8 and R9 input on the voltage drop was bigger. Then replaced 0.3Ω resistor R8 and R9, connected to the horn audition. Output power on the mid-point voltage required increased slowly from zero, which produced only a slight impact on sound. 2 seconds later, the hand-touch input C1 speaker will be issued a "Woo" and hum. The C1 input and ground (negative power supply side) short circuit, speakers should not sound practical to issue a slight background white noise or a very low voice communication hum.

Third, improve the practical circuit of the power amplifier

Using the bootstrap power amplifier circuit design is relatively simple although the circuit, but there is lower frequency cut-off point. The introduction of the bootstrap circuit is to avoid the half-wave current zoom is not enough time available to control the use of complementary, no shortage of transistors used in the case, you can ensure a constant current source Lai zoom in on the half-wave will have sufficient time governing the use of current available to the complementary. At the same time, the differential amplifier is also designed to provide operating current by the constant current source, can greatly improve noise rejection ratio of state and relax the requirements on the accuracy of the supply voltage. Figure ⑥ is to use a typical constant current source power amplifier circuit, including: BG3 and BG4 constitute a standard constant current source, the former to the front differential amplification to provide extremely 1mA constant total current, 2 only a thin charge of BG1, BG2 all be 0.5mA of quiescent current; which provides 2mA constant current, and encouragement very BG5 2mA quiescent operating current equal to the amplifier output Q of the static resistance of the mid-point voltage is entirely the same partial pressure of R13 and R14 determine the out, not too large deviation from E / 2. R14 series below the D1 was the top composite pipe to compensate for the threshold pressure ratio below the threshold of a single drop more of a complementary pipe PN junction voltage drop, to ensure the same by the resistance R13 and R14 divider out to determine the midpoint voltage more accurate. Incentive very BG5 of quiescent current have the R4 and R12 on the resistance of 200Ω 1V drop defined as 2mA, also do not adjust. Therefore, in the regulation of BG7 ~ BG10 quiescent operating current when the first non-access BG4 and BG5, R13 and R14 directly in the partial pressure of the midpoint of the reference voltage and provide 0.4mA ~ 1.1mA of bias current to BG6 working conditions, Minimum initial adjustment by the zero resistance R10 to BG7 ~ BG10 static operating current 15 mA can be. Then replace the fixed resistor R10, to BG4 and BG5 access to the circuit board, amplifier to work immediately. Although the existence of discrete component parameters may be very real incentives to BG5 static current and BG4 a small amount of difference between the current source current, differential amplification most will output Q according to the static voltage deviation from the midpoint of the actual situation of the static automatic change BG1 operating current, so BG5 actual quiescent current and BG4 current source current exactly equal. Of course, BG5 actual quiescent current auto-adjustment, the differential amplification does not allow most of the quiescent current significantly reduce any of them too. The components in Figure ⑥ parameters, as long as the changes can make BG5 0.1mA quiescent operating current change 1mA, sufficient to achieve quiescent operating current adjustment BG5.

However, most current source limits the incentive can be provided in the cut-off state, the maximum current, improve the power supply voltage and output amplitude can not increase accordingly. Although the corresponding increase in the constant current source to increase the output current amplitude, but to encourage a very quiescent current will also increase accordingly, stability becomes worse. A better approach is to introduce mirror circuit, with the upper and lower symmetrical differential current mode driver behind the amplification of complementary symmetry power amplifier tubes work. Figure ⑦ that is used to enlarge the upper and lower symmetrical differential current mode power amplifier for a very practical motivation circuit, due to higher output power, to prevent overload damage to the device, circuit, add the maximum output current limit protection. Which, BG4 and BG5 constitute mirror circuit operating current Ic5 can BG5 work with BG4 current Ic4 remain exactly equal, then the drive BG6. Achieved by the BG6, BG7 constitute the upper and lower symmetrical differential current amplification mode. In this way, you can guarantee that in the last half-wave signals need incentives to provide greater drive current, very, BG6 can also synchronize the output after a larger drive current to the most power amplification. To achieve the same purpose, it can take longer parallel a pair of complementary symmetrical front differential amplifier, which will achieve BG6 drive. However, the requirements of the mirror circuit components without the high front differential amplifier, differential amplifier with two pairs of front and can not improve any performance of the entire circuit, no need to use that cost Ben Banfa spend. Adjustment method of the circuit shown in Figure ⑥ The power amplifier circuit using the same constant current source.

Power amplifier design using discrete components

Be considered from the principle of using the up and down method for symmetric differential current amplification circuit is no longer inspire great defect. However, the characteristics of high power transistors are not ideal, the output current to 1A or more, the current magnification 10 to 25, will make driving high-power transistors complementarity management must provide more than 200mA current to the posterior pole. Complementary power in itself, often more than 2W, severe fever, complementary management also need to install another radiator. In the electronic component manufacturers have developed to produce high-power Darlington's case, the switch has been made within the Darlington composite pipe for the final stage current amplifier tubes, can greatly reduce the output drive current complementary management requirements. SGS company as the TIP series of high-power Darlington transistor, the output current of 2A above, the current magnification can reach more than 500, which only need to provide complementary management 20mA drive current to the posterior pole of the following work, complementary control their own 0.2W power consumption to less. Need to modify the design parameters only based on the threshold voltage of Darlington transistor threshold voltage is equal to 2 ordinary times, to provide quiescent bias current shunt resistors R18, R19 double resistance in order to maintain control of quiescent current complementary does not change. At the same time complementary tube BG9, BG10 base-level voltage drop between the previous increase in the threshold voltage of an ordinary transistor, its quiescent current adjustment circuit means no impact.

As Darlington is not designed for audio power amplifier developed device, the operating frequency limit is not high. Upper frequency limit of ordinary high-power transistors only to 1MHz, the audio power amplifier developed for high-power transistor can only reach 10MHz, preferably no more than 100MHz. Although only the audio range 10Hz ~ 20kHz, but transistor current magnification and the frequency related to the upper limit of working frequencies, the current magnification will drop to 1 times. This makes the low frequency limit of the amplification transistor treble capacity of the 20kHz 2kHz Alto amplification capability than the lower, thus leading to the open-loop state, treble and tenor of the current no longer maintain the same magnification. The negative feedback loop to maintain the same throughout the audio sample rate does not change the current mixed-signal in pitch than the tenor current magnification and low magnification, thus enabling the mixed-signal in the treble the actual magnification than the lower midrange. Therefore, the use of high frequency power transistor cap, could treble the current mixed-signal in the current magnification ratio of Alto have fallen to less magnification. If only to 1MHz frequency limit production of high-power transistor audio power amplifier, will more than treble 8kHz was a serious shortage of components. Therefore, the foreign manufacturer of electronic components 90 in the 20th century, developed the superior performance of dedicated high-power transistor audio power amplifier. Sanken Sanken manufactured pipe is the first known specific high-power transistor audio power amplifiers, but they are not Darlington, requires superior performance in power to do the same before the great drive, and give the driver in front pole Power to install the radiator.

To the late 20th century, 80 people developed high-power FET higher performance. Any high-power FET frequency limit can reach 100MHz, but at first the lack of high-voltage high-power FET, manufacturers produce more than 40W power amplifier output power or to use high-power transistors. In fact, making use of high power FET amplifier using high-power transistors than the production of power amplifiers and more convenient. But requires special attention to the fact that although effect is voltage-controlled device control, but the input power FET gate and source junction capacitance between the larger, up to 800P or so, and therefore a higher frequency of state to be provided under the same charge and discharge 5mA ~ 10mA drive current. Channeling together before the gate affects the resistance of the input junction capacitance of the charge and discharge resistance as possible to take a small. Figure ⑨ is the practical use of high power FET amplifier circuit, as some of the power FET gate voltage is not built-in limit to protect regulator, specially in the circuit by adding a limited voltage protection regulator. No built-in voltage protection using the limited high-power FET regulator, welding wire must be used to gate and source short-circuit, good welding power protection FET and limited pressure regulator before the gate and the source short circuit between the wire removed. Using high-power FET amplifier design, debug, and use high-power mode power amplifier transistors designed exactly the same.

To note that the threshold voltage of power FET in between 2V ~ 3V, (manufactured by Samsung and more high-power FET threshold voltage to 2V), the actual power FET operating voltage should not exceed the maximum allowable half the value of voltage, maximum current peak should not exceed the allowable current of 2 / 3 can only work to ensure safe and reliable. This requirement is already higher than the requirements of the three machines much wider pipe, three tubes of the actual machine operating voltage not exceeding half the value of the maximum allowable voltage, while the three-machine control of maximum current peak can not exceed the maximum allowed current of 1 / 3 can only work. High-power FET is also a great advantage of a very good temperature stability from 25 ℃ ~ 125 ℃, almost exactly the same job characteristics. Therefore, when using high-power field effect transistor, the temperature of the radiator can also be correspondingly high to allow 90 ℃, while the transistors are still two of this breakdown may actually allow the temperature of the work should be limited to below 70 ℃.

4, using multiple high power amplifier power supply

Did not strictly control the output of the mid-point voltage value in the ideal conditions required under the PA can only use a single power supply, the midpoint of the floating power supply with automatic follow ways. As long as a sufficiently large capacity storage capacitance, the actual output capacity of OCL with the use of dual-power output mode no difference. The reason for using OCL output mode, in addition to face further power amplifier design with better performance, the greater practical significance is the use of positive and negative dual power supply mode can further reduce OCL output circuit background noise. In the pre-amplifier input stage with differential signal amplification circuit, output DC level has been with the DC level input signal to maintain almost the same, a difference of less than ± 0.2V. In this situation, the input signal DC level bias resistor connected to the midpoint potential of the positive and negative dual power supply, it can be a single power supply of the OTL output mode using positive and negative dual power supply into the OCL Output no longer automatically follow the float using the mid-point of power. In fact, do use the pre-signal IC op amp input stage can output DC level and DC level input signal to maintain almost the same, a difference of less than ± 0.02V, precisely because of the internal op amp IC is also used as input differential amplifier level, and generally the way the composite tube input stage differential amplifier circuit to do, so that flow into or out of IC positive and negative input quiescent current less than 0.1μA, the negative feedback resistor voltage drop has been lower than the static DC 0.01V. If the pairing has been found very characteristic pipe, composite pipe can be used of course, the way to do differential amplifier input stage, so that the output DC level and DC level input signal to maintain almost the same, a difference of less than ± 0.02V, features extremely the same need for a matching tube made of semiconductor materials, this is the op amp IC production process advantages. In short, the only way to change the OCL OTL output mode output in the circuit design does not have any increase. In fact, Class A and B work to produce complementary symmetry power amplifier there is a defect, which is the last stage high-power static current amplification is close to the cutoff position, regardless of high-power three tubes, or using high-power FET , in the end zone in the vicinity of the dynamic resistance is significantly higher than the linear area of dynamic resistance to big a lot, actually can be several times to 10 times. Quiescent current of the smaller, the greater the dynamic resistance. When the amplifier output voltage is zero, the horn will continue to damp vibration of pots to stop the vibration. Voice coil in a magnetic field generated by the current movement will hinder the free vibration speaker vibration basin, if the resistance amplifier in series with the voice coil larger, it will cause voice coil in a magnetic field generated by the current movement to reduce reduce the role of resistance Nepal, vibration basin Vibration damping is not easy to stop, the sound appears "muddy" the divergence Shoubu Zhu situation. At the same time, the speaker's voice coil woofer moving in a magnetic field generated by the induced current can not be shorted out power amplifier as much as possible, will be hampered alt work unit speaker drive signal interference. A good reason why the replay amplifier sound quality, secret is that it has very low output impedance of the static. However, Group A amplifier power consumption, heat seriously, should not be used in large supply voltage. To do this, you can use the high and low groups in the way of positive and negative power supply under the current power level on the last working state of implementation of the amplifier tubes dynamic bias, the amplifier output voltage range is less than 4V, the current high-power amplifier tubes work in a Class status, output rate greater than 4V, transformed into the B position. As the rotation of working in high-power current amplification is always work in the high current state, the actual effect of the work the same way with the Pure Class.

That is, high power Darlington transistor design using high-efficiency power amplifier A typical dynamic bias circuit, in order to achieve better dynamic offset, T1, T2 and down two high-power Darlington complementary pipe used in order to increase the threshold voltage bias circuit. Two complementary control parameters required exactly the same, the actual difference between the current magnification should not exceed 20%. Dynamic offset by a half-wave in each of the signal of 4V reference values change, the dynamic offset requirements by changing the speed limit must be more than 20KHz frequency output signal at least 100-fold, optical isolation transform the frequency response of the device at least to 1MHz, the diodes used must be high-speed pipe. When the output signal voltage is within ± 4V, the optical output transistor is off, the two complementary high-power current amplifier tubes are biased in the quiescent current of 1A to work, and when the output signal voltage exceeds ± 4V, the optical output transistor in-state, two complementary high-power current amplifier tubes are biased to work in the quiescent current of 10mA. However, the output signal voltage exceeds ± 4V, the power current amplifier tubes operating current must exceed 0.5A, 4Ω load must exceed 1A, the actual work is also equivalent to A. At the same time, the output signal when the voltage is within ± 6V, BG11, BG12 is off, T3, T4 Darlington switch is also closed, T1, T2 two complementary high-power current amplification is ± 8V supply low voltage power supply power. In the output signal when the voltage exceeds ± 6V, BG11, BG12 in conduction state, T3, T4 Darlington switch also turns on, T1, T2 two complementary high-power amplifier tubes replaced by the current high-voltage power supply ± 30V, High current amplification so that the power consumption.

Power amplifier design using discrete components

N groove and in the high-voltage power MOSFET P Erdaogou easy to buy the case, can use high-power field effect transistor to produce high-efficiency power amplifier A dynamic bias. Similarly, T1, T2 and down two high-power field effect transistor to be used complementary tube require two complementary control parameters the same, the actual difference between the current magnification should not exceed 20%. Work the use of dynamic bias, bias circuit to adjust the parameters slightly more complicated. Specific manner the same way as described above, first T1, T2 from the R11, R12 series identified in the 1A quiescent current regulator out, and then the actual resistance of the proper allocation of the two, so that when R12 is in short T1, T2 of the quiescent current 2mA ~ 10mA. That is not completely closed, did not need to transfer large.