JPH037407A - Output circuit - Google Patents

Abstract

PURPOSE:To reduce the current consumption and to attain a stable circuit by connecting a resistor to a differential amplifier in place of a current source supplying its operating current to the differential amplifier circuit. CONSTITUTION:A differential amplifier circuit 6 to which a resistor R2 is connected in place of the use of a constant current source is employed for the output circuit. When a voltage at an output terminal 5 changes negatively (less than Vcc/2), an emitter level of transistors(TRs) Q2, Q3 is decreased and a voltage across the resistor R2 is increased and a circuit I2 flowing thereto is increased. Moreover, when the output is changed positively (more than Vcc/2), the emitter level of the TRs Q2, Q3 is increased and the current I2 is decreased. When the voltage at the output terminal 5 changes positively in this way (no large base current is required for a TR Q7), the current I2 is decreased. Then no undesired current flows, resulting in decreasing the current consumption and the differential amplifier circuit 3 is turned off through the decrease in the current I2 and the possibility of adverse effect such as oscillation of the differential amplifier circuit 3 on other circuits is precluded and the stability of the circuit is improved.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an output circuit for an operational amplifier.

[Conventional technology]

As this type of output circuit, there is a circuit shown in FIG. This circuit consists of an input transistor Ql whose base is connected to an input terminal 1, a differential amplifier circuit 3 consisting of transistors Q2 to Q5 controlled by the transistor Q1, and a constant current source 2, a constant current source 4, and the constant current source. 4. Differential amplifier circuit 3
It also includes output transistors Q6 and Q7 that operate in push-pull mode using the input transistor Q1, a diode D1 for adjusting idling current, and a resistor R1 for preventing saturation of the transistor Q2.

In this circuit, the differential amplifier circuit 3 and the output transistor Q7 are connected in a voltage follower manner, so that the base voltage of the transistor Q2 appears at the base of the transistor Q3, that is, at the output terminal 5.

[Problem to be solved by the invention]

Incidentally, in this circuit, the base current of the transistor Q7 is supplied from the constant current source 2, and this base current must be sufficient to supply the maximum sink current from the output terminal 5.

In other words, the current value of constant current source 2 must be at least a value that can supply this base current, but due to the nature of constant current sources, the current supplied from it is always a constant value current, and transistor Q7 The same applies even when the unit is not operating.

Therefore, when the transistor Q7 is not in its maximum suction operation, a wasteful current is supplied, which is uneconomical. Further, even when the output terminal 5 changes from the negative side (Vcc/2 or less) to the positive side (Vcc/2 or more), the differential amplifier circuit 3 continues to operate by the constant current source 2, so that oscillations etc. There was a risk of adverse effects.

The present invention has been made in view of these points, and its purpose is to provide an output circuit that reduces current consumption and achieves circuit stability.

[Means to solve the problem]

To this end, the present invention provides an output circuit including a negative output transistor that performs a push-pull operation in combination with a positive output transistor, and a differential amplifier circuit that configures a voltage follower circuit in combination with the negative output transistor. In,
A current source that supplies an operating current to the differential amplifier circuit was configured with a resistor.

Further, different resistors can be connected in series to the emitters of two differentially connected transistors connected to the current source of the differential amplifier circuit.

〔Example〕

Examples of the present invention will be described below. FIG. 1 is a diagram showing an output circuit of one embodiment. Components that are the same as those in FIG. 3 are given the same reference numerals. In this embodiment, a differential amplifier circuit 6 to which a resistor R2 is connected is used in place of the constant current source 2 in FIG. 3.

Therefore, when the voltage at the output terminal 5 changes to the negative side (below Vcc/2), the emitter potential of the transistors Q2 and Q3 decreases, the voltage across the resistor R2 increases, and the current I2 flowing therein increases.

Furthermore, when the output changes to the positive side (Vcc/2 or higher), the emitter potentials of the transistors Q2 and Q3 rise, and the current 2 decreases.

In this way, when the voltage at the output terminal 5 changes to the positive side (transistor Q7 does not require a large base current), the current I2 decreases, so unnecessary current does not flow, reducing current consumption. be able to. Also, this current 1
2 is reduced, the differential amplifier circuit 3 is turned off, and there is no possibility that the differential amplifier circuit 3 will have an adverse effect such as oscillation on other circuits, leading to improvement in the stability of the circuit.

Here, we will consider the reduction in current consumption. In the circuit shown in FIG. 3, the base current 11 required to drive the transistor Q7 to the maximum is the current I drawn from the output terminal 5 at that time. , the current amplification factor of transistor Q8 is h2o
Then, I*-In/hrE・=(1), and the current I of constant current source 2 is (current I of equation 11)
is set equal to m, which flows regardless of the output.

On the other hand, in the circuit of this embodiment, in order to have the same driving ability as the circuit of FIG.
As in 2), the same current as in equation 11 is required, but
This current flows only when the transistor Q7 is driven to the maximum.

Here, when comparing the current in steady state, the third
In the circuit shown in the figure, a current 11 always flows, but in the circuit of this embodiment, It = (Vcc-(Vstt +Vcc/2)
) /R2''' V cc/ 2 V mcs
...(3). vmtz is the base-emitter voltage of transistor Q3. Therefore, the required current ratio ΔI in steady state is ΔI = (to / )iri) (Vcc/
2V! lE3 )...(4), and the current decreases by this amount.

FIG. 2 is a diagram showing an output circuit of another embodiment.

This embodiment uses a differential amplifier circuit 7 in which other resistors R3 and R4 are connected in series between the emitters of transistors Q2 and Q3 and resistor R2.

According to this circuit, the gain of the differential amplifier circuit 7 is reduced, and further stabilization of the circuit can be achieved.

〔Effect of the invention〕

As described above, the present invention has the advantage that the operating current of the differential amplifier circuit changes depending on the output voltage, thereby reducing current consumption and stabilizing the circuit.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an output circuit according to one embodiment of the present invention, FIG. 2 is a circuit diagram of another embodiment, and FIG. 3 is a conventional circuit diagram. ■...Input terminal, 2... Constant current source, 3... Differential amplifier circuit, 4... Constant current source, 5... Output terminal, 6.7
...Differential amplifier circuit.

Claims (2)

[Claims] (1) In an output circuit including a negative output transistor that performs push-pull operation in combination with a positive output transistor, and a differential amplifier circuit that configures a voltage follower circuit in combination with the negative output transistor, An output circuit characterized in that a current source for supplying an operating current to the differential amplifier circuit is constituted by a resistor. (2) According to claim 1, each resistor is connected in series to the emitters of two differentially connected transistors connected to the current source of the differential amplifier circuit. Output circuit.