Push-pull current amplifier

 

(57) Abstract:

The invention relates to electronics and can be used as a powerful output stage in the composition of the low frequency amplifier, DC, video amplifier, various transducers, measurement equipment, output or grooms cascades transmitting devices in the range up to 10 MHz. The invention consists in the use of operational amplifiers as key elements for direct control of one of the most powerful output transistors and direct control of the current in each moment of time in combination with an additional source of bipolar constant voltage, galvanically isolated bus mass for independent power operational amplifiers, which determines the high thermal stability of the device and Vysocany synthesis of current output bus, is proportional to input the amplified current. 2 Il.

The invention relates to the field of radio electronics and can be used as a powerful output stage in the composition of the low frequency amplifier, video amplifier, translators cable networks, amplifiers DC, powerful shapers dupo voltage), in the measuring apparatus, the output or grooms cascades transmitting devices in the range up to 10 MHz.

Known for a variety of circuit solutions, aimed at improving the linearity and thermal stability of powerful amplification stages. Consider a few of the devices that implement some of these solutions, which represent the main ways of combating the effects of temperature, adversely affecting the operation of the devices and sharply reducing their reliability, as well as the ways in amplifier linearization circuits and increase the fidelity of signal transmission.

The number of known amplifiers [1] the dynamic bias transistor output stages (Super A "JVC" Non Switching "Pioneer," New Class A "Technics'"), intended for use in high-quality loudspeaker systems, the circuitry of which is directed to the linearization of the signal at small currents of peace and respectively at increasing the efficiency of amplifying paths. However, the tests above cascades showed that the effect of dynamic bias significantly affects the stability of the quiescent current, without changing the linearity of the amplifier rated power and not improving A - implemented on 11 transistors.

Known amplifier [2], also designed for use in high-quality loudspeaker systems, the output stage which is a sequential three-stage emitter follower, which is performed according to the scheme of accelerated resorption of excess base charge mode AB. Heat setting is carried out thermocompensation chain, a work element is a bipolar transistor having thermal contact with a powerful output transistors. Schematic of the output stage linearizes the work grooms (controlled current generator) and increases the linearity of the amplifier as a whole, but has at least two drawbacks. The first one occurs when you change the volume level and is determined by the inertia thermocompensation chain - decreasing amplitude of the input signal with the nominal level 10-15 (and higher) dB increase dramatically harmonic and dynamic distortion amplifier while cools the work item thermocompensation circuit and restores the bias current of the output stage. The second drawback is determined by the high inertia of three-stage emitter follower and Zack the devices from secondary breakdown for example, in case of short circuit of the amplifier output mode high power.

It is known device [3] , designed for thermal stabilization powerful bipolar devices. The device can be used in push-pull output stages and consists of a schema of the bias current and the control transistor. Heat setting is carried out as follows: the control electrode of one of the most powerful output transistors connected to the circuit bias current, and also to the collector of the control transistor, which branches off of this current. Output transistor circuit bias current control transistor and a corresponding powerful output transistor have a thermal contact. When heating increases the current schema offset and the current through the control transistor, the change in current through the control transistor is greater than the change in the current schema offset, which causes the reduction current of the control electrode powerful output transistor. The disadvantages of this device are thermal inertia, economiccost due to increased pass-through current through the bias circuit and the control transistor in the mode of temperature compensation, as well as the complication of the configuration and design when ispolnitel with thermal stabilization. Its essential difference from the above devices is that controlled direct current output transistors, not temperature. Control is exercised by the voltage drop across the emitter resistors of powerful transistors with thermo-compensated technological amplifier error signal included in the negative feedback circuit of the corresponding output transistor. Thus is not only a high stability of the device, but also a good compensation arising nonlinear distortion. However, the described advantages are achieved by the complexity of the scheme and the use of a large number of discrete components, which is a disadvantage with this device.

Closest to the proposed invention is a device [5], presented in the form of an integrated circuit with a powerful output. The device can be divided into 4 functional units: input operational amplifiers with differential inputs; the read transistors; node processing power transistors of reading; powerful output transistors. Consider the operation of the device on the example of one of the shoulders. The current of the output transistor is controlled by a current input amplifier, the value of sopranista read and powerful output transistor is connected. In addition, these transistors have a thermal contact. Changing the current through the transistor is read into the processing unit, a signal is generated that as the control is passed to the input amplifier circuit local negative feedback. Thus thermal stabilization and compensation of nonlinearity of the device.

The disadvantage of the prototype is the indirectness of the control current of the output transistors, which, without compromising thermal stabilization, adversely affects the efficiency of compensation of nonlinear distortion. You can also note the temperature inertia and complexity of the design, configuration, and selection of the pairs of transistors in the if amplifier made from discrete components.

The technical result of the proposed push-pull current amplifier are increased reliability due to the high thermal stability and characteristics of circuit solutions, as well as high accuracy and fidelity of signal transmission due to its high linearity.

This technical result is achieved by the fact that in the known device, containing the first operational amplifier, the second operational amplifier, the first transistor the second transistor, the second power terminal of which is connected to the power bus of the source of negative supply voltage, inputs of the first stabilizing resistor connected between the output of the first operational amplifier and a control electrode of the first transistor, the second stabilizing resistor connected between the output of the second operational amplifier and a control electrode of the second transistor, the first equalizing resistor between the negative input of the first operational amplifier and the second power terminal of the first transistor, the second equalizing resistor connected between the inverse input of the second operational amplifier and the first power terminal of the second transistor, a bipolar source of constant voltage, galvanically isolated bus mass and connected to the corresponding power pins of the first and second operational amplifiers, the circuit of the series-connected first oscillator bias current, a first bias resistor, a second bias resistor and the second oscillator bias current, the input of which is connected to the positive pole of an additional source of bipolar constant voltage, and the output to the negative pole will complement erwou input bus amplifier, and the anode is connected to a not inverting input of the first operational amplifier and the output of the first oscillator bias current, the second blocking diode, the anode of which forms the second input bus of the amplifier, and a cathode connected simultaneously to the not inverting input of the second operational amplifier and the input of the second oscillator bias current, and a chain of series-connected first resistor-current sensor and the second resistor is a current sensor connected between the second power klemay of the first transistor and the first power terminal of the second transistor, and the midpoint of which is connected to the midpoint of an additional source of the bipolar DC voltage and the midpoint of the first and second bias resistors and forms the output bus of the amplifier.

The proposed push-pull current amplifier in the block diagram depicted in Fig.1.

The proposed device comprises a first transistor 1, the first power terminal 2 which is connected to the power bus of the source of positive supply voltage, the first operational amplifier 3, the output 4 is connected through a first stabilizing resistor 5 to the control electrode 6 of the first transistor 1 and inverse 1, the second transistor 10, the second power terminal 11 is connected to the power bus of the source of negative supply voltage, the second operational amplifier 12, the output 13 is connected via a second stabilizing resistor 14 to the control electrode 15 of the second transistor 10, and the negative input 16 is connected via a second equalizing resistor 17 to the first power terminal 18 of the second transistor 10, an additional source of the bipolar DC voltage 19, galvanically isolated bus mass and its poles connected to the respective power pins 20, 21 and 22, 23 of the first 3 and the second 12 operational amplifiers, circuit, consisting of series-connected first current generator offset 24, the first bias resistor 25, the second bias resistor 26 and the second current generator bias 27, connected by the entrance to the positive pole of an additional source of bipolar constant voltage 19 and the output to the negative pole of an additional source of the bipolar DC voltage 19, the first blocking diode 28, the cathode of which forms a first input bus of the amplifier to the terminal 29 and the anode is connected to a not inverting input 30 of the first operational Wuxi the second input bus of the amplifier to the terminal 32, and the cathode is also connected to a not inverting input 33 of the second operational amplifier 12 and the input of the second current generator bias 27, and a circuit consisting of series-connected first resistor-current sensor 34 and the second resistor is a current sensor 35 connected to the input to the second power terminal 9 of the first transistor 1, the output to the first power terminal 18 of the second transistor 10, and the midpoint of which is connected to the midpoint of the first bias resistor 25, the second bias resistor 26, the midpoint additional source bipolar DC voltage 19 and forms an output bus of the amplifier.

The operation of the device is as follows.

When power is supplied from the power and additional sources in the upper shoulder of the first generator bias current 24 will begin to produce some stable current, which will generate the first bias resistor 25 and the corresponding voltage drop. At the inputs 30, 7 of the first operational amplifier 3 will have a differential voltage which will cause increasing control signal at its output 4. The control signal will open the first transistor 1 up until the current through m will disappear active differential voltage at the inputs 30, 7 of the first operational amplifier 3. When this control signal at its output 4 will record the current through the first transistor 1 and will maintain it at a constant level in the absence of the input current through the first blocking diode 28. Similar processes will occur in the lower arm device.

Drift no-load current of the first 1 and 10 second transistors are very small and depends on the properties of the used operational amplifiers, as well as the stability of the first 24 and second 27 current generators offsets.

The operation of the device in the dynamic mode presents diagrams of currents and voltages (Fig. 2) some characteristic points when the input bipolar signal of rectangular shape. As the transistors 1, 10 was used in the field of MOS devices, the amplifier output is loaded by a resistor with a resistance of 1 Ohm, the amplifier was supplied by the input Converter voltage - current with the device to create the initial bias of the diodes 28, 31. The voltage of the power supply network 15 In source - 12th Century

In the time interval t1-t2 input the amplified current operates at terminal 29, while the lower shoulder remains the state with the specified quiescent current, the reference voltage at the first bias resistor 25 (Fig.2,b) the interval (t1-t2), which will lead to increase of the control voltage at the output 4 of the first operational amplifier 3 to this level (Fig.2, with the interval t1-t2) at which the current of the first transistor 1 reaches the value (Fig.2,d is the interval t1-t2) required to create the same voltage drop on the first current sensor 34 (Fig.2,e, the interval t1-t2), and the first bias resistor 25. Otherwise, the voltage on the first current sensor 34 will be controlled by the first operational amplifier 3 and, depending on the signal on the first bias resistor 25 to be mounted at an appropriate level by controlling the current of the first transistor 1. In the time interval t2-t3 similar processes take place in the lower arm at a constant condition of the upper. As a result, the current output bus device (Fig. 2,f interval t1-t3) will be an amplified K times the input current, where K is the ratio of nominal resistance of the first bias resistor 25 to the nominal resistance of the first current sensor 34 and, accordingly, the second bias resistor 26 to the second current sensor 35. In Fig. 2,g presents output voltage for a given workload in the time interval t1-t3.

Feasibility of the proposed two-stroke utilite model without pre-selection of elements at maximum load showed within days amplifier parameters were not changed by more than 5% from the initial values, and overload output bus power is not critical and do not require special fast-acting protection devices, enabling them to do conventional slow-acting fuses. However, the amplifier does not require careful installation, shielding, insensitive to external disturbances and runs from a small number of discrete components.

References

1. Tanaka S. New Biasing Circuit for Class B Operation. Journal of the Audio Engineering Society, vol. 29,1981, N 3, p. 148-152.

2. Sukhov N. USC high fidelity. Radio, 1989, No. 6, S. 55-57, N 7, S. 57-61.

3. Amplifier with temperature compensation, U.S. patent N 5177454, H 03 F 3/04.

4. Circuit that supplies bias to the power amplifier, the Japan patent, N 4-76245, H 03 F 1/30, 1/32, 3/30.

5. The amplifier. EP 0346011 A2, application N 89305546.7, priority 02.06.89 (prototype).

Push-pull current amplifier containing the first operational amplifier, the second operational amplifier, the first transistor, the first power terminal of which is connected to the power bus of the source of positive supply voltage, the second transistor, the second power terminal of which is connected to the power bus istochniki resistor, included between the output of the first operational amplifier and a control electrode of the first transistor, the second stabilizing resistor connected between the output of the second operational amplifier and a control electrode of the second transistor, the first equalizing resistor between the negative input of the first operational amplifier and the second power terminal of the first transistor, the second equalizing resistor connected between the inverse input of the second operational amplifier and the first power terminal of the second transistor, a bipolar source of constant voltage, galvanically isolated bus mass and connected to the corresponding power pins of the first and second operational amplifiers, the circuit of the series-connected first oscillator bias current, a first bias resistor, the second bias resistor and the second oscillator bias current, the input of which is connected to the positive pole of an additional source of bipolar constant voltage, and the output to the negative pole of an additional source bipolar constant voltage, the first blocking diode, the cathode of which forms a first input bus of the amplifier and the anode at the same time five, the second blocking diode, the anode of which forms the second input bus of the amplifier, and a cathode connected simultaneously to the not inverting input of the second operational amplifier and the input of the second oscillator bias current, and a chain of series-connected first resistor-current sensor and the second resistor is a current sensor connected between the second power terminal of the first transistor and the first power terminal of the second transistor, and the midpoint of which is connected to the midpoint of an additional source of the bipolar DC voltage and the midpoint of the first and second bias resistors and forms the output bus of the amplifier.

 

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