1. Power Amplifier Basic Circuit Characteristics
2. Improvement of Basic Circuit of the Power Amplifier
Connected to power, measure BG1 of the collector to emitter voltage drop Uce, regulation allows Uce equal to 200K potential E/2-0.6; in the total supply voltage of 32V, when, BG1 static Uce should be equal to 15.4V(0.1V). Then measured the actual 200K potentiometer in which the resistance value, replace the fixed resistor with resistance potentiometer replacement, and then measuring BG1 static Uce should 15.4V(0.2V) within. To determine the static Uce good BG1 again after small to large BG4 and BG5 adjust R5 so that the quiescent operating current of 15mA. For insurance purposes, R8 and R9 can be for access into 100Ω/2W resistors, R8 and R9 on the first measurement of the static voltage drop should be 1.5V.
Disconnect the power supply, measuring the actual resistance of R5 in which adjustable resistor values, resistor R5 into the same fixed resistors, removed earlier from the output side are connected to the power supply at both ends of 1k/2W divider resistors. Re-connect power, R8 and R9 on the measurement of the static voltage drop should be maintained at between 1.2V ~ 1.8V. Measuring the output level should be the midpoint between the 16V(0.5V). The C1 input capacitance signal input terminal and the earth floating disconnected, measure the voltage drop R8 and R9, C1 encounter with the screwdriver when the input voltage on R8 and R9 dropped significantly larger. And then replace the 0.3Ω resistors R8 and R9, connected to the horn Lyrics. Connected to the power due to C0 charge, midpoint voltage of the output needs to rise slowly from zero, which produced only a slight impact on sound. When the hands touch the C1 input speaker will issue a "woo" the exchange of sound. The C1 input and ground (negative power supply side) short circuit, speakers should not sound, the actual will be issued by a slight background of white noise or very low voice communication hum.
As shown in Figure 2 complementary symmetry power amplifier improvement type OTL circuit, there is a clear disadvantage is that the input signal DC level than the midpoint of the output voltage is lower 2V ~ 3V, not in the public use and transistor op amp IC components, the high cost of the 20th century, early 80s, it has very good power amplifier using a single power supply practical circuit. The mid-20th century, 80, op amp IC, starting, people began to use pre-op amp IC to serve as a very great and inspiring.
A typical circuit shown in Figure 3 due to op amp IC do not need to adjust the static working point, as long as BG2 ~ BG5 adjust R5 so that the quiescent operating current of 10mA ~ 20mA can be. Note that, although the op amp IC do not need to adjust the quiescent point, but in BG2 ~ BG5 in a cut-off state, from R8, R9, and BG3, BG5 emission knot is wizard-pass will be the negative input of op amp IC is set to high, transport, Z IC output is low, then fired through the BG3 junction to the negative input of op amp IC is set to low, the output of op amp IC turning into a high, resulting in the output variable of the low-frequency oscillation state can not provide a stable The reference to the midpoint level.
In this situation, adjust the BG2 ~ BG5 quiescent operating current, op amp IC output is high when the regulator R5 is invalid; while IC op amp output to '0 BG5 can not turn to regulate the R5 can only BG2, BG3 , BG4 to enter the work area, BG2 actually only played the role of the diode by BG4, and BG2 the current direct all poured into the op amp IC output, resulting in BG2, and op amp IC damage due to over-current! (I have to hand at that time owned by a few domestic op amp IC and a dozen medium-power three pipes all the damage, but also failed to adjust the quiescent operating 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 in follower mode output stability level of the mid-point of reference, in this state, adjust R5 so that BG2 ~ BG5 the quiescent operating current of 15mA, the R5 resistance into the same fixed resistor confirm BG2 ~ BG5 quiescent operating current of 10mA ~ 20mA in between, and then the negative op amp IC input and output end to end open, the feedback resistor R6 access circuits.
Figure 4 that is, after the improved circuit, BG1 launch junction threshold voltage and BG2, BG3, BG4 the threshold voltage with temperature change, itself, can play a role in temperature compensation. In order to reduce the output of op amp IC quiescent operating current in the output of op amp IC gifts added to the ground side of the shunt resistor R10. With the shunt resistor, the adjustment of BG2 ~ BG5 quiescent operating current can not access the first op-amp IC, directly from one of R7, R8, and R10 divider out the approximate mid-point of reference level. Start with 0 to large adjust R5 so that BG2 ~ BG5 quiescent operating current of 10mA ~ 20mA in between, and then access to op amp IC, the circuit that is able to work properly.
In addition, the output of op amp IC 1 1k current-limiting resistor in series R15, can guarantee the output op amp IC is '0 BG5 will not enter the cut-off state.
In addition, the output DC level input signal DC level strict consensus, which makes the use of positive and negative dual power supply OCL power amplifier become a reality. Otherwise, the result of the output DC level and power level of the mid-point difference between the large, will lead to a good speaker does not work properly.
Said that they going to, not that people do not know how to design power amplifiers, but by the device of choice constraints, in different historical periods can only use the appropriate design of the circuit. In the 20th century, the late '80s, people began to more easily find properties matching using the same transistor. Due to differential amplification circuit can be extremely quiescent current and accurate design parameters for a given, do not adjust the differential amplifier tubes with a quiescent current. The circuit in Figure 5 the case of the use of 32V power, pre-differential amplifier tubes with a static current of 0.51mA ~ 0.52mA, as long as the first adjust R12 so that BG1 collector to ground terminal of the voltage dropped to 15.4V, and then adjust R5 so that BG2 ~ BG5 quiescent operating current can be between at 10mA ~ 20mA.
Connected to power, adjust R12 so that the first BG1 collector to ground terminal voltage reduced 15.4V0.2V, and then adjust R5 so that BG2 ~ BG5 the quiescent operating current of 15mA. For insurance purposes, the first R8 and R9 for access into the 100Ω/2W resistors R8 and R9 on the measurement of the static voltage drop should be 1.5V. Disconnect the power supply, measuring adjustable resistor R5 and R12 in which the resistance of the actual value of their fixed resistance into the same resistance. Connected to power, R8 and R9 on the measurement of the static voltage drop should be maintained at between 1.2V ~ 1.8V. Measuring the output level should be the midpoint between the 16V0.3V. Disconnect the power, the BG6, BG0 base Qudiao between the connection wires to the negative feedback resistor R10 access to the circuit. Re-connect power, R8 and R9 on the measurement of the static voltage drop should be maintained at between 1.2V ~ 1.8V. Measuring the output level should be 16V0.2V the mid-point between the difference in charge current magnification the greater the output DC level and signal the smaller the difference between the input DC level. C1 touch with the screwdriver when the input voltage on R8 and R9 dropped significantly larger. And then replace the 0.3Ω resistors R8 and R9, connected to the horn Lyrics. When connected to the power output of the midpoint voltage of the need to rise slowly from zero, which produced only a slight impact on sound. 2 seconds later, the hands touch the C1 input Speaker will issue a "woo" the exchange of sound. The C1 input and ground (negative power supply side) short circuit, speakers should not sound, the actual will be issued by a slight background of white noise or very low voice communication hum.
3. The Improvement of the Power Amplifier Circuit Useful
Figure 6 is to use a typical constant current source power amplifier circuit, in which: 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 be 0.5mA each of the quiescent operating current; which provides a constant current of 2mA, and inspire a very BG5 quiescent operating current of 2mA equal, so that the static Q amplifier output voltage is entirely by the mid-point resistance of the same partial pressure of R13 and R14 set out, are not so large deviation from E / 2. R14 series at the bottom on the D1 is a composite pipe to compensate for the threshold voltage drop above the bottom of a single complementary than the threshold voltage drop across the tube over a PN junction voltage drop, ensuring the same from the resistance voltage divider R13 and R14 determine the midpoint voltage out of more accurate.
Stimulate the quiescent operating current is very BG5 has been on a 1V drop from the R4 and R12 resistance 200Ω identified as 2mA, also do not adjust. Therefore, in the regulation of BG7 ~ BG10 quiescent operating current when the first non-access BG4 and BG5, directly in the R13 and R14 divider out of the mid-point reference voltage and provide 0.4mA ~ 1.1mA of bias current to the BG6 working conditions, Starting from the smallest zero resistance BG7 ~ BG10 adjust R10 so that the quiescent operating current of 15 mA can be. Then replaced by a fixed resistor R10, will BG4 and BG5 access to the circuit board, amplifier immediately work properly. Although the existence of discrete element parameters, which may cause a very real incentive BG5 quiescent operating current and BG4 a small amount of difference between the current source current, differential amplification most will be the output terminal Q of the steady-state voltage deviation from the midpoint of the actual situation of automatically change the static BG1 operating current, so that the actual BG5 quiescent operating current and BG4 constant source current exactly equal. Of course, the actual quiescent operating current BG5 automatically adjusted, the differential amplification extremely quiescent operating current does not allow any one of them significantly reduced too much.
In accordance with Figure 6 in the component parameters, as long as you can make BG5 change 0.1mA quiescent operating current change 1mA, sufficient to achieve the right BG5 quiescent operating current adjustment.
A better approach is to introduce mirror circuit, using the upper and lower symmetrical differential current-mode driver to enlarge the back of the work of complementary symmetry power amplifier tubes. Figure 7 that is used to enlarge the upper and lower symmetrical differential current-mode power amplifier to inspire a very practical circuit, due to higher output power in order to avoid overload damage to the device, circuit added to limit the maximum output current protection. Which, BG4 and BG5 constitute a mirror circuit operating current Ic5 can BG5 and BG4 operating current Ic4 remain completely equal, then the drive BG6.
Achieved by BG6, BG7 constitute the upper and lower symmetrical differential current amplification method. In this way, you can ensure that in the last half-wave signals need to stimulate greater drive current when a very, BG6 also simultaneously be able to export more to the posterior pole of the drive current power amplifier tube. To achieve the same purpose, people can also be taken in parallel and then a pair of complementary symmetrical front differential amplifier, which it has realized BG6 drive. However, the mirror circuit components requirements have not pre-high differential amplifier, using two pairs of differential pre-amplifier and the circuit can not increase any performance, no need to spend the cost of using the kind of awkward. Way to adjust the circuit shown in Figure 6 the use of the same constant current source power amplifier circuit.
This makes the low frequency limit of 20kHz treble amplification transistor capacity than 2kHz Alto amplification of our ability to make low, thus leading to the open-loop state, treble and tenor of the current magnification is no longer remain the same. The closed-loop negative feedback to maintain the same throughout the audio sampling magnification does not change the current mixed-signal inside pitch magnification than the tenor current situation of the low magnification, so that mixed-signal inside the treble actually higher than alto's lower magnification. Therefore, the use of high-frequency high-power transistor limit will enable mixed-signal inside Treble current magnification magnification than the tenor current decline was less.
If you are using only reached the maximum frequency of 1MHz production of high-power transistor audio power amplifier, will feel more than treble 8kHz component is seriously insufficient. Therefore, the foreign manufacturer of electronic components, has been 90 years in the 20th century developed a superior audio performance, dedicated high-power transistor amplifier. Japan 3 3 Ken Ken pipe manufactured by well-known audio power amplifier is the first dedicated high-power transistors, but they are not Darlington require superior performance of the power to do the same before the driver is a very, but also give the driver the front pole of the Power to install heat-sink.
In fact, making use of high-power FET amplifier than the use of high-power transistor amplifier made more convenient. But require special attention to the fact, although the effect of pipe is voltage-controlled device, but the high power FET input gate and the source exists between the large junction capacitance can be achieved around 800P, and therefore the higher the status of the operating frequency to be provided under the same charge and discharge 5mA ~ 10mA drive current.
Channeling Alliance in front of the gate resistance will affect the input junction capacitance charging and discharging, as far as possible to take a small resistance. Figure 11 that is, the practical use of high-power FET amplifier circuit, due to some high-power FET gate voltage there is no built-in limit to protect voltage regulator tube, specially in the circuit by adding a limit-voltage protection voltage regulator tube. With no built-in limit-voltage protection regulator tube high-power FET, welding wire must be used to gate and source short-circuit, welding good power FET and current-limit-voltage protection regulator tube before the gate and the source short-circuit between the wires removed. Use of high-power FET amplifier design, debug mode with the use of high-power transistor amplifier design is identical.
4. Power Supply "High-Performance" for Power Amplifier
Identifying characteristics are always matching pipe, composite pipe can be used of course, the way to do input stage differential amplifier circuit, so that the output DC level and signal input DC level remained nearly the same, a difference of less than 0.02V, very consistent characteristic need a pair of tubes made of semiconductor materials, this is the op amp IC production process advantages. In short, the only way to change the OTL output OCL output mode, in the circuit design does not have any increase.
In fact, with work produced in class AB type power amplifier complementary symmetry there is a flaw, which is the last stage high-power amplifier tubes, static current is near the end zone, regardless of the use of high-power three tubes, or the use of high-power FET , in the end zone in the vicinity of the dynamic resistance were significantly higher than the linear dynamic resistance area should be large enough number, the actual can vary by several times to 10 times. Quiescent current is smaller, the greater the dynamic resistance. When the amplifier output voltage is zero when the speaker vibration basin will continue to be damped oscillation to stop. Voice coil moving in a magnetic field generated by currents will hinder the free vibration speaker vibration basin, if the amplifier in series with the voice coil resistance relatively large, it will cause voice coil moving in a magnetic field generated by currents decrease, reducing the role of resistance Nepal, vibration basin Vibration damping is not easy to stop down, the voice of a "dragging its feet" in divergence Shoubu Zhu situation. At the same time, the voice coil woofer speaker moving in a magnetic field induced currents produced by power amplifiers that can not be shorted out as much as possible, it would become alt prevent interference with the work unit loudspeaker drive signals. A better reason why the replay amplifier sound quality, mystery lies in the fact that it has a very low quiescent output impedance.
A power amplifier due to large, fever serious, should not be used under large operating voltage. To do this, you can use the high and low supply two sets of positive and negative manner on the final stage power amplifier tubes with current working status of implementation of the dynamic bias, so that amplifier output voltage amplitude is less than 4V when the high-power amplifier tubes with working in a current class status, the output amplitude is greater than 4V, when transformed to B status. As the rotation of working in the high-power current amplification tube is always in high-current mode of operation, the actual effect is the same way as the work of a purely A.
Dynamic bias is the result of each one and a half-wave output signal through the 4V reference value transform, require dynamic bias changing the speed limit must be more than 20KHz frequency output signal of at least 100 times higher, photoelectric conversion device isolation frequency response to be at least 1MHz, The diodes used must also be high-speed pipe. When the output signal voltage is less than 4V, the optical output transistor is cut-off state, two complementary high-power current amplification tubes were biased in the quiescent current of 1A to work, and when the output signal voltage exceeds 4V, the optical output transistor in the conduction state of two complementary high-power current amplification tube was biased at 10mA quiescent current at work. However, as the output signal voltage exceeds 4V, the current high-power amplifier tubes operating current must exceed 0.5A, 4Ω load must exceed 1A, is also equivalent to the CPI actually work. In the meantime, the output signal when the voltage is 6V or less, BG11, BG12 in the cut-off state, T3, T4 Darlington switch is also closed, T1, T2 two complementary high-power amplifier tubes with current low-voltage power supply from 8V. In the output signal voltage exceeds 6V, when, BG11, BG12 in the conduction state, T3, T4 Darlington switch also turns on, T1, T2 two complementary current amplification tubes replaced by high-power 30V high-voltage power supply, so that High-power current amplification tubes to reduce power consumption.
The specific way the same way as described above, first T1, T2 from the R11, R12 series set out quiescent current regulator out of 1A, then the appropriate allocation of both the actual resistance, so that when the R12 in the short-circuit T1, T2 of the quiescent current 2mA ~ 10mA. That is not completely closed, there is no need to transfer large.
In this way, matching power amplifier with dynamic offset the use of the CPI level of the two groups also have positive and negative power supply designed to power supply.