JPS59156010A - Driver stage circuit of output amplifier - Google Patents

Abstract

PURPOSE:To decrease power consumption at non-signal when a power supply voltage is low and to prevent a chip size from being increased when the titled circuit is formed into a monolithic IC by constituting so that the same numbers of respective emitters of the 1st PNP and the 2nd NPN transistors (TR) of a driver stage are connected in parallel mutually. CONSTITUTION:The 1st and the 2nd diodes D1, D2 decide a bias current to the 2nd and the 3rd transistors(TR) Q2, Q3. A point connecting emitters of the 2nd and the 3rd TRs Q2, Q3 is connected to a reference voltage source Vref. A collector emitter voltage VCE of the 2nd TRQ2 of PNP type is small when a power supply voltage is low. Thus, a current amplification factor (hfe) is decreased. Then, plural numbers of the 2nd TRsQ2 are connected in parallel in order not to decrease the current amplification factor (hfe). There exists a relation in general that each base-emitter voltage VBE is equal when each collector current flowing to an NPN TR and a PNP TR is equal to each other.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a driver stage circuit for an output amplifier, and particularly to a driver stage circuit that reduces power consumption when the power supply voltage is low and when there is no signal, and which uses a monolithic IC. The present invention relates to a driver stage circuit for an audio output amplifier used at low voltages without increasing the chip size when formed.

[Prior art]

Generally, audio output amplifiers used at low voltages include:
There is something like the one shown in Figure 1. The operating principle will be explained below.

The audio signal is input to the operational amplifier 1. The output of the operational amplifier 1 is supplied to the base of the first transistor Q1 and amplified. The amplified signal is transmitted to the first . Second
diodes D1°D2 and the second. Third transistor Q
2, voltage-current conversion is performed by Q3.

Said 1st. The second diode DI, D2 is connected to the second diode DI, D2. 6th
It has the role of determining the magnitude of bias current flowing through transistors Q2 and Q5+.

Said 2nd. Third transistor Q2. The collector current of each of Q5 is 6th. Fourth diode D5. Flows to D4.

The third diode D3 is combined with a fourth transistor Q4;

A current mirror circuit is formed in combination with the fifth transistor Q5.

Therefore, the sixth diode D3 and the fourth transistor Q
4. The signal is current amplified by forming a current mirror circuit by combining the fourth diode D4 and the fifth transistor Q5.

In this case, generally the above-mentioned 4. Fifth transistor Q4jQ
5, to obtain high output.

A power transistor with a low saturation resistance, or a transistor with a low saturation resistance and several tens of transistors connected in parallel is used so that it can withstand large currents flowing.

Also, 5th. Fourth transistor Q5. The output of the connection point a between the collectors of Q4 is fed back to the operational amplifier 1 via the first resistor R1. The AC gain of this circuit is determined by the first resistor R1 and the second resistor connected between the input of the operational amplifier and the first resistor R1.
determined by resistance R2.

Also, the second. Third transistor Q2. The emitters of Q5 are connected to each other, and the connection point is clamped by a reference voltage source Vrtf that has sufficiently low impedance and has current supply capability.

FIG. 2 shows the signal waveform appearing at connection point C.

The part A of the waveform corresponds to the fifth transistor Q5.
second capacitor C2 and load resistance Rt.

It is created by the current flowing to ground through.

Further, a portion B is created by a current flowing through the load resistor l (L) via the second capacitor C2, the fourth transistor Q4, and the ground.

Therefore, in order to obtain a signal waveform of 7 parts, the following (
1) A current as shown in equation must be supplied to the reference voltage source Vrtj.

υA: Peak value ida of the l part of the signal waveform + 4th peak value when the signal shows a smoke waveform like the A part
Current flowing through diode D4 hjtQ5 r Current amplification factor je of fifth transistor Q5 Also, in order to obtain the signal waveform of part B, the following (
The current shown in equation 21 must be supplied from the reference voltage source Vrtf. At this time, the audio signal mentioned above is positive.

υB = peak value id5 of signal waveform part; 6th peak value when the signal shows a waveform like part B
Current hfgt2a flowing through diode D3: Current amplification factor hfe of fourth transistor Q4 However, when the power supply voltage is low, even if an attempt is made to obtain a wide amplitude near the power supply voltage Ycc at the above-mentioned connection point C,
Generally, the current amplification factor hfg of a monolithic PNP transistor, that is, the second transistor Q2 in FIG. 1, is low, even when the power supply voltage is low.

Since the collector-emitter voltage Vcg of the second transistor Q2 becomes small, the current amplification factor hfe at that time becomes considerably small.

Therefore, the amplitude of the B part of the output signal waveform is connected to the ground GND.
Even if you try to get it close to that, the current amplification factor hfg of the second transistor Q2 decreases.

There is a problem in that the current that should be supplied from the reference voltage source Vref is not supplied, and a large output signal cannot be extracted from the load resistor Rt.

Conventionally, as a solution to this problem, in order to prevent the current amplification factor hjt from decreasing even when the collector-emitter voltage Vcg of the second transistor Q2 is small, for example, as shown in FIG. the second transistor Q
It has been considered that N emitters of the third transistor Q3 are connected in parallel (five in the figure), and the same number of N emitters of the third transistor Q3 are connected in parallel.

However, first. Second diode D1. When D2 is 1 times the size, these collector currents are equal to a constant current of 10, whereas the 2nd. The collector currents of the fifth transistors Q2 and Q5 are eight times the constant current 1o, which causes a problem that the current increases when there is no signal and the power consumption increases.

On the other hand, as shown in FIG. 2nd diode D
1. D2 also has the second. Third transistor Q2. If the emitter size is increased 8 times as in Q3, the second . The current flowing through the sixth transistor is a constant current 1o, which is the same as in the case of the one-time size. however,
On the other hand, when forming a monolithic IC, problems arise in that the number of elements increases and the chip size increases.

[Purpose of the invention]

The object of the present invention is to eliminate the above-mentioned drawbacks and to obtain a large output when the source voltage is low without increasing the current when there is no signal.

Another object of the present invention is to provide a driver stage circuit for an output amplifier that does not increase the chip size when formed into a monolithic IC.

“Summary of the invention” In order to achieve the above object, the present invention provides a first NPN
The emitters of each of the PNP type transistor and the first PNP type transistor are connected to each other, and a second transistor having the same polarity as each of the transistors is connected to the base of each of the transistors; The emitters of the first PNP transistor and the second NPN transistor of the driver stage circuit of the output amplifier in which the emitters of the transistors are connected to each other are connected in parallel Mf in the same number. It has characteristics.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to one drawing.

FIG. 5 is a circuit diagram of an embodiment of the present invention.

In the figure, the same reference numerals as in Fig. 1.5.4 refer to the same or equivalent parts.

1st. Second diode D1. D2 is the second and sixth transistor Q2. The bias current of Q5 is determined. Said 2nd. The point where the terminals ε of the third transistors Q2 and Q3 are connected is connected to a reference voltage source Vrgf.

As mentioned above, when the power supply voltage is low, the collector-emitter voltage Vcg of the PNP type second transistor Q2
becomes smaller.

Therefore, the current amplification factor hfg decreases. Therefore, in order to prevent the current amplification factor bit from decreasing, a plurality of the second transistors Q2 are required.

Must be connected in parallel.

Generally, if the collector currents flowing through each of an NPN transistor and a PNP transistor are equal, the base-emitter voltage Vaε of each is equal, and this base-emitter voltage 1/aE is expressed by the following equation (3). Desired.

k; Portzmann coefficient T: temperature q: charge lc + collector current lS: base-emitter reverse saturation current Now, suppose that the second transistor Q2. N second diodes D2 are connected in parallel, and the first diodes D2 are connected in parallel. 11. The current flowing through the second diode DI, D2. Second. Assuming that the current flowing through the third transistor CI21<115 is 12, the voltage between the base and the terminal of each transistor is expressed by the following equation.

Based on the reference voltage source Vref.

Vsrtqs -Vazb2- Vagn1+Vszq
2=0. Therefore, solving this gives h = 12.

At this time, as is clear from FIG.

11: No 0 It is.

therefore.

No0 = No2 becomes.

As mentioned above, if the number of parallel emitters of the second transistor Q2 arranged oppositely shown in FIG. 5 is the same as the number of parallel emitters of the second diode D2, a constant current A current 12 equal to 0 flows through each.

〔Effect of the invention〕

The present invention, as described above, connects the emitters of the first NPN transistor and the first PNP transistor, and further connects the base of each of the transistors with a second transistor of the same polarity as each of the transistors. The number of emitters of each of the first PNP transistor and the second NPN transistor of the output amplifier driver stage circuit in which the transistors are connected and the terminals of the second transistors are connected to each other is the same number as each other. Since they are connected in parallel, there is no need to increase power consumption when there is no signal, and when forming a monolithic IC.

This has the advantage of not increasing the chip size.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a conventional audio output amplifier, Figure 2 is an output waveform diagram at connection point C in Figure 1, and Figures 6 and 4 are problems with the conventional audio output amplifier in Figure 1. FIG. 5 is a circuit diagram of an embodiment of the present invention. Dl...first diode. I) 2...Second diode. Q2...second transistor. Q3...Third transistor. β 4th country 5th share

Claims (1)

[Claims] (1) A first NPN transistor and a first PNP transistor whose emitters are connected to each other and whose connection point is connected to a reference voltage source, and whose base is connected to the base of the first NPN transistor. a second NP, N-type transistor through which a constant current flows into its collector, which is connected to and shorted to the base thereof, and whose base is connected to the base of the first PNP transistor and shorted to the base thereof; a second PNP transistor whose collector is connected to a signal source and whose emitter is connected to the emitter of the second NPN transistor, the output amplifier driver stage circuit comprising: a PNP type transistor and the second NPN
1. A driver stage circuit for an output amplifier, characterized in that the emitters of each type transistor are connected in parallel in equal numbers to each other.