JPS60129816A - Output circuit - Google Patents

Abstract

PURPOSE:To reduce the power consumption of an output circuit at the time of a light load, by connecting the 1st and 2nd transistors with the load in the way of Darlington connection in which the 1st and 2nd transistors are positioned at the front and rear stages, respectively, and driving the 2nd transistor by means of the 3rd transistor. CONSTITUTION:At the starting time, the internal impedance of a motor is low and a large starting current is made to flow. At this time, the voltage between the collector and emitter of a starting transistor Q2 rises and another transistor Q1 is set to an active condition and, as a result, a base current is supplied to the transistor Q2 through the transistor Q1. Moreover, a fixed current is supplied from a transistor Q3 as the base current of the transistor Q2. That is to say, the transistor Q2 is driven by the transistors Q1 and Q3. When the motor becomes a normal condition, an output current Ic decreases and the transistor Q2 tends to become a saturated condition. As a result, the transistor Q1 also becomes a saturated condition and the transistor Q2 is driven by the transistor Q3 only. The collector-emitter voltage VCE of the transistor Q2 and the characteristic of the output current Ic correspond to the Area B of the figure.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application Field This invention relates to an output circuit used for driving a motor or the like.

(B) Prior art FIG. 1 is an explanatory diagram of a Darlington connection circuit which is a conventional output circuit, and FIG.
1c characteristic diagram is shown.

For example, if the load RL is a motor, the output current Ic changes as its value changes.

However, if the collector-emitter voltage VCE of transistor Q2 is VF 2 + VCEsat + (Fig. 2 17J
Point A) does not fall below. Here, VF is the forward voltage between the base and emitter of transistor Q2, VCEsa
t is the collector-emitter saturation voltage of transistor Q1. Therefore, the conventional output circuit has the disadvantage that the power consumption inside the circuit is relatively large when the load is light.

Furthermore, in an output circuit with a single transistor, the base current inevitably becomes large. Therefore, the ratio of circuit current to output current becomes large, resulting in poor efficiency.

(c) Purpose This invention has sufficient driving ability for large loads,
Another object of the present invention is to provide an output circuit that can reduce the power consumption of the circuit when the load is light.

B) Configuration The output circuit according to the present invention includes first, second, and third transistors, the first and third transistors are supplied with an input signal, and the first transistor and the second transistor are , are connected to the load through a Darlington connection arranged at the front stage and the rear stage, respectively, and the third transistor drives the second transistor.

(Po) Embodiment FIG. 3 is a circuit diagram showing the configuration of an embodiment of the output circuit according to the present invention, and FIG. 4 is a VCE-1 of the output circuit shown in FIG.
An Ic characteristic diagram is shown.

In FIG. 3, transistor Ql and transistor Q2
form a Darlington connection placed at the front stage and rear stage, respectively. The collector of the transistor [lL Q2 is connected to the power supply Vcc via the load RL, and the collector of the transistor Q2
The emitter of is grounded.

On the other hand, input signals are applied to the bases of transistor Q3 and transistor Q1 via resistors R1 and R2, respectively. Further, the collector of the transistor Q3 is connected to the power supply Vcc via a resistor R3, and the emitter is connected to the base of the transistor Q2.

Next, the operation of the embodiment having the above-described configuration will be explained.

For example, when driving a motor, the internal impedance of the motor is low at startup, and a large startup current flows. At this time, C of drive transistor Q2 whose load is the motor
The voltage across E increases, Ql becomes active, and Q2 becomes Q2.
The base current is supplied via l. Further, a constant current is simultaneously supplied from Q3 as the base current of Q2.

That is, transistor Q2 is driven by transistors Q1 and Q3. The VCE-1c characteristic at this time corresponds to region A in FIG. 4.

When the motor, which is the load, reaches a steady state, the output current c decreases, and Q2 tends to reach a saturated state. As a result, transistor Q1 is also saturated and transistor Q2 is driven only by transistor Q3.

Therefore, the collector-emitter voltage VCE of transistor Q2 becomes V CgsaL2. VCE at this time
The 1c characteristic corresponds to region B in FIG.

In addition, in the description of the above embodiment, transistors Q1 to Q
3 is an NPN) transistor as an example. However, it goes without saying that the present invention can produce similar effects even with PNP transistors.

(F) Effect The output circuit according to the present invention drives the base of the second transistor by the third transistor added according to the present invention even after the first transistor becomes saturated when the load is light. As a result, the collector-emitter voltage VCE of the second transistor can be made smaller than that of a conventional output circuit. Therefore, according to the present invention, the power consumption of the circuit can be reduced when the load is light. Therefore, the present invention is most suitable for driving a load such as a motor that requires a large current at startup but does not require much current to flow during steady state.

Further, according to the present invention, as described above, power consumption during full seating can be reduced, so temperature rise in the circuit can be suppressed. Therefore, it is convenient to realize the output circuit according to the present invention using an integrated circuit.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a Darlington connection circuit, which is a conventional output circuit, and FIG. 2 is an explanatory diagram of the Darlington connection circuit, which is a conventional output circuit.
1c characteristic diagram, FIG. 3 is a circuit diagram showing the configuration of an embodiment of the output circuit according to the present invention, and FIG. 4 shows a VCIE"Ic characteristic diagram of the output circuit shown in FIG. 3. 2, Q3...Transistor, RL...Load.Patent applicant: ROHM Co., Ltd., agent, patent attorney, Takaharu Ohnishi Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] (1) comprising a first, a second and a third transistor;
and a third transistor is provided with an input signal, and
An output characterized in that the first transistor and the second transistor are connected to a load in a Darlington connection arranged at a front stage and a rear stage, respectively, and the third transistor drives the second transistor. circuit.