JP2554874Y2 - Transistor circuit - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bipolar transistor used in a drive circuit of a DC motor or the like, and more particularly, to stop the transition of the transistor from a saturated state to an active state and improve the collector loss during normal operation. Transistor circuit.

[0002]

If BACKGROUND ART using bipolar transistors in the driving or the like of the DC motor M, a single transistor circuit shown in FIG. 4, when the excess current flows through the motor lock or the load short-circuit or the like, transistor Tr I _C shown in FIG. 5 -V _CE
The characteristic shifts from the saturated state to the active state, and the collector loss sharply increases. The transistor Tr1 shown in FIG.
When the Darlington transistor circuit composed of Tr2, although it is possible to prevent the transition to an active state with excess current, V _BE component of the second transistor from the I _C over V _CE characteristic shown in FIG. 7 even during normal operation ( There is an added collector loss of about 0.6V). Therefore, depending on the use conditions of the DC motor M, a protection circuit for preventing excess current from flowing through the transistor or a radiator for reducing the collector loss of the transistor is provided.

[0003]

An invention is, however, its use operating range is narrowed by excessive current flowing when abnormalities such as when the motor locks or load short circuit in a single transistor circuit, also is added during normal operation by V _BE is a Darlington transistor circuit This is disadvantageous in heat dissipation design due to the collector loss. SUMMARY OF THE INVENTION An object of the present invention is to provide a transistor circuit having a wide operating range while reducing collector loss to facilitate heat radiation design.

[0004]

In order to achieve the above object, a transistor circuit according to the present invention has a collector connected in common and a second transistor connected to a base of a first transistor for controlling current to a load. The transistor is connected to the emitter and connected to one of the input terminals based on the voltage between the collector and the emitter of the Darlington transistor provided with the base of each transistor as an input terminal and driven. and a drive circuit, the drive circuit by an input terminal of the first transistor and the dynamic drive only Toranjita the first during normal operation, the set value a voltage between the collector and emitter of the first transistor is predetermined configuration so as to drive Darlington transistor is switched to the input terminal of the second transistor when exceeded A.

[0005]

When the operation start signal is input, the drive circuit cuts off the base current of the second transistor and performs driving only with the base current supplied from the input terminal of the first transistor. The load during normal operation is supplied with a collector current controlled by the input terminal of the first transistor, and is operated by a single transistor. In the event of an error such as motor lock or load short circuit,
When an excessive current flows through the first transistor, the base current of the first transistor is cut off when V _CE shown in FIG. 2 becomes V _CE1 , and the base current is supplied by switching to the input terminal of the second transistor. Then, the driving by the Darlington transistor is continued. Thus, the transition of the transistor to the active region can be avoided.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described. FIG. 1 shows the basic configuration of the transistor circuit of the present invention. The transistors Tr1 and Tr2 are Darlington-connected, and a DC motor M as a load is connected to the collector. The DC motor M is supplied with a current I _C controlled by a transistor from a DC power supply B, and performs a predetermined rotation operation. The base of the first transistor Tr1 is connected to the emitter of the second transistor Tr2, and further connected to a drive circuit 1 described later via a resistor R1. The base of the transistor Tr2 is connected to the drive circuit 1 via the resistor 2.

The drive circuit 1 starts operating under the condition of an input signal (Hi signal) from an input terminal, and the transistor T
r2, the base current _IB2 is cut, and the transistor Tr
Motor control is performed using only one base current _IB1 .
That is, the DC motor M is supplied with the collector current I _C controlled by the transistor Tr1 indicated by the solid line in FIG. 2, and the motor control during normal operation is performed by the single transistor.

[0008] abnormality such as a motor lock or a load short, when excessive current flows through the transistor Tr1, the transistor Tr1 is dotted region of the illustrated I _B1, i.e. shifts to the active state, the V _CE increases sharply collector The loss increases. In order to avoid this phenomenon, the base current I _B1 is cut off when V _CE becomes V _CE1 , the base current I _B2 is supplied to the first transistor Tr2, and the motor control by the Darlington transistor is continued. A base current I _B2 of the transistor Tr2 of the switching point a, is know from the collector current I _C1 for advance V _CE1, if V _CE1 is detected, the switching operation from the I _B1 of the base current to the I _B2 is Done instantly. When the transistor is switched to the Darlington transistor, I _B2 shown by a solid line in the drawing from the switching point a
Is supplied to the transistor Tr2. As described above, when an abnormality occurs, the motor is controlled by the Darlington transistor, and the transition of the transistor to the active state can be avoided.

FIG. 3 shows a specific example of the drive circuit. In the figure, when the Lo signal is input to the input terminal, Tr3 is in the OFF state. When Tr3 is OFF, Tr5 is OFF because Tr4 is also OFF because Tr6 is OFF. Tr5 is OFF
At this time, since no base current is supplied to Tr1,
In the F state, no current is supplied to the motor M, and the motor M is in a stopped state. Comparator 2 applies the set voltage V _CC to the + terminal,
Input the collector / emitter voltages V _CE of the Darlington transistors Tr1 and Tr2 to the terminals, and V _CE > V _CC
(= V _CE1 ), the comparator 2 outputs a Hi signal. However, since the Lo signal is output from the comparator 2 when Tr1 is in the OFF state,
7 is in an OFF state. Therefore, the Tr6 is also kept off by turning off the Tr7, so that the light emitting diode LED becomes inactive and does not emit light.

When a Hi signal is input to the input terminal and the transistor Tr3 is turned on, Tr4 is turned off while Tr6 is turned off, so that Tr5 is turned on and Tr5 is turned on.
Base current I to Tr1 through the emitter / collector
_B1 is supplied to turn on Tr1. When Tr1 is turned on, the motor M is supplied with current from the + B power supply and is started. V _{CE of} Tr1 is equal to or lower than the set voltage V _CC (V _CE ≦ V
_{In CC} ), since no Hi signal is output from the comparator 2, Tr7 is kept in the OFF state, and Tr2 is not supplied with the base current I _B2 (= 0) and is in the OFF state. Therefore, when V _CE is equal to or lower than V _CC , motor control is performed in a normal operation by the characteristics of the single transistor by Tr1 shown in FIG.

By the way, in the abnormal time, such as motor lock, load short-circuit, but the collector current I _C of Tr1 flows excessively, when V _CE is increased beyond the V _CE1 shown in Figure 2, the comparator 2 is V _CC <V _CE To output a Hi signal, and T
Turn on r7. Then, Tr2 and Tr6 are turned on. When Tr6 is turned ON, Tr4 is turned ON, and Tr5 is turned OFF due to an increase in the base potential. Thereby, the base current I to Tr1 through Tr5
The supply of _B1 (= 0) is stopped. However, at the same time Tr2
Is turned on, Tr1 is supplied with a base current through the collector / emitter of Tr2, and is kept in the ON state. Therefore, V _CE exceeds the V _CE1, the motor control abnormality performed by the characteristics of the Darlington transistor to operate by supplying the base current I _B2 in Tr2 shown in Fig. In order to notify this operation state, Tr6
When it becomes N, the light emitting diode LED is operated to display light.

[0012]

As described above, according to the present invention, the base of the first transistor of the Darlington transistor is used as an input terminal, and the input terminal is driven during normal operation, and V _CE exceeds the set value. In this case, the driving is switched by using the base portion of the second transistor as an input terminal,
Transistor transition to the active region is prevented, and thermal breakdown is less likely to occur.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a basic configuration of a transistor circuit of the present invention.

2 is a I _C over V _CE characteristic diagram for explaining the operation of the transistor circuit of the present invention.

FIG. 3 is a circuit diagram showing a specific example of a drive circuit.

FIG. 4 is a basic circuit diagram of a single transistor.

FIG. 5 is a graph showing I _C -V _CE characteristics of a single transistor.

FIG. 6 is a basic circuit diagram of a Darlington transistor.

FIG. 7 is an I _C -V _CE characteristic diagram of a Darlington transistor.

[Explanation of symbols]

 1 Drive circuit 2 Comparison circuit Tr1, Tr2 Darlington transistor LED LED

Claims (1)

(57) [Scope of request for utility model registration] 1. A collector section is commonly connected, an emitter section of a second transistor is connected to a base section of a first transistor for controlling current to a load, and a base section of each transistor is inputted. A Darlington transistor provided as a terminal, and a drive circuit that switches to one of the input terminals and drives based on a voltage between the collector and the emitter of the first transistor. the driven by the input terminal of the first transistor Toranjita only, the switching to the input terminal of the second transistor when exceeding a set value voltage between the collector and the emitter of the first transistor is predetermined Transistor circuit characterized by being driven by Darlington transistors