JPH0445303Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Field of Application] This invention relates to a switching circuit using Darlington-connected transistors to drive an electromagnetic device such as an electromagnetic switch.

[Conventional technology]

When an electronically driven electromagnetic switch is turned on, a large current is required to attract the moving iron piece from the electromagnetic device, so full voltage is applied to the coil, but a small current is sufficient to hold the moving iron piece in the attracted state. A chopper voltage is applied to the coil to reduce its average current, thereby saving energy and making the electromagnet device more compact. A switching circuit in which transistors are connected in a Darlington manner as shown in FIG. 2 is used to open and close such a power supply. In FIG. 2, a switching circuit 1 has the emitter of an input transistor 3 connected to the base of an output transistor 2, and the collectors of both transistors 2 and 3 connected through a diode 4 to form a Darlington circuit. A coil 5 of an electromagnetic device is connected in series to the output end OB of the switching circuit 1, and a series circuit of the output end OB of the switching circuit 1 and the coil 5 is connected to a DC power source 7. 6 is coil 5
This is a diode that is connected in parallel with the coil 5 and absorbs the reverse voltage of the coil 5. A diode 8 is connected between the base and emitter of the input transistor 3, and the base is connected to a DC power source 7 with a resistor 9 connected in series. The signal generator 10 is connected to the input terminal OA of the switching circuit 1, and the input terminal A is connected to the base of the input transistor 3 to control the switching circuit 1.

The operation of this switching circuit 1 will be explained with reference to the time chart of FIG. FIG. 3 shows changes in the input signal S, the coil current I _C , and the current I _T of the output transistor 2 with respect to time t.
When a continuous input signal S is input at time t ₁ , the current
I _C and current I _T begin to flow simultaneously and gradually increase. Then, at time _t2 , when the coil 5 absorbs a movable iron piece of the electromagnet device (not shown), both the current I _C and the current I _T decrease instantaneously due to the increase in the inductance of the coil 5, but they increase again and the current I _T becomes the input current. It becomes stable at the size of I _n . The input signal S changes from a continuous signal to a chopper signal at time _t3 . Therefore, the current I _T changes to a chopper current, but since the electromagnetic energy of the coil 5 flows to the diode 6 when the current I _T is cut off, the current I _C does not become a chopper current but gradually decreases to a constant level. Stabilizes at a holding current of _IH .
However, once the movable iron piece of the electromagnet device is attracted, it can be held with a small current, so the operation of the electromagnet device is not affected and power is saved. Generally, the holding current I _H is sufficient to be about 1/15 of the input current I _n .

[The problem that the idea attempts to solve]

By the way, when a transistor suddenly changes from a conducting state to a non-conducting state, there is an accumulation time, and this accumulation time becomes longer when the current when conducting is large.
A circuit in which the output transistor operates in saturation, such as the circuit shown in FIG. 2, has the disadvantage that it impedes high-speed operation of the switching circuit.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a Darlington connection switching circuit which has a short storage time while still retaining the advantages of the prior art described above.

[Means for solving problems]

To achieve the above object, the present invention provides an output transistor whose collector is connected to a coil of an electromagnetic device; a collector whose collector is commonly connected to the coil of the electromagnetic device with the collector of the output transistor;
In a Darlington-connected switching circuit comprising an input transistor having a base connected to a signal generator and an emitter connected to the base of the output transistor, the electromagnetic device is connected between the output transistor and the collector of the input transistor. A resistor is connected between the coil and the output transistor, and when the resistance value R of this resistor is VBE, the voltage between the base and emitter of the output transistor is _VBE , and the input current of the coil of the electromagnet device is _In , R=
It is characterized by setting V _BE /I _n .

[Effect]

Since the holding current of an electromagnet device can be as small as about 1/15 of the input current, and the storage time of the output transistor is shorter as the current is smaller, the electromagnet device should be A resistor is connected between the coil and the output transistor, and when the resistance value R of this resistor is VBE, the voltage between the base and emitter of the output transistor is _VBE , and the input current of the coil of the electromagnet device is _In , R= By setting V _BE /I _n , the output transistor is used in a saturated state when the electromagnetic device is turned on to reduce power loss, while the output transistor is used in a non-saturated state when the electromagnetic device is held, thereby reducing the output transistor. Shorten storage time.

〔Example〕

Next, one embodiment of the present invention will be described in detail based on FIG. Here, parts having the same functions as those in FIG. 2 are given the same reference numerals and their explanations will be omitted.

In FIG. 1, this embodiment differs from the conventional one in that the diode connected between the collector of the output transistor 2 and the collector of the input transistor 3 is replaced with a resistor 11. In addition, an input transistor 3 is connected to the base of the output transistor 2 to form a Darlington circuit, a series circuit of the output terminal OB of the switching circuit 1 and the coil 5 is connected to the power supply 7, and a signal generator 10 is connected to the input terminal of the switching circuit 1. The point connected to the end OA is the same as the conventional one. Further, since the operation of this switching circuit 1 is the same as that of the conventional one, the explanation thereof will be omitted.

Here, in both the conventional circuit and the circuit of this embodiment, it is assumed that the voltage V _OB at the output terminal OB, the input current I _n of the output transistor 2, and the holding current I _H are equal, and the resistor 1
1 is the resistance value R, and the input current is first calculated for both circuits.
Compare I _n . In FIG. 2, if the voltage drop V ₄ of the diode 4 and the base-emitter voltage V _BE of the output transistor 2 are equal, then the collector-emitter voltage V 2 of the output transistor 2 and the collector-emitter voltage V ₂ of the input transistor 3 are equal. Emitter voltage
V is equal to ₃ . However, voltage V ₃ is the saturation voltage. In addition, in FIG. 1, the voltage drop across the resistor 11
When I _n ·R is made equal to the voltage V _BE , that is, when the resistance value R is V _BE /I _n , the power consumption, or heat generation, of the output transistor 2 is the same in both the conventional circuit and the circuit of this embodiment.

Next, assuming that the current I _n of the output transistor 2 is reduced to 1/15 of the holding current I _H when the resistance value R is V _BE /I _n , the voltage V ₂ is V ₂ = V _OB − I _H・R=V _BE・14/15+V ₃ , and the circuit of this example has output transistor 2
Since the voltage V ₂ of the output transistor 2 is higher than that of the conventional circuit by the voltage V _BE ·14/15, and the voltage drop across the resistor 11 is close to zero, the voltage V ₂ of the output transistor 2 becomes high, resulting in a non-saturated state. It has already been stated that the smaller the current of the output transistor 2 (here, the holding current I _H ), the shorter the storage time, so the explanation will be omitted.

[Effect of idea]

As explained above, according to the present invention, the output transistor has a collector connected to a coil of an electromagnet device, the collector is connected to the coil of the electromagnet device in common with the collector of the output transistor,
A Darlington-connected switching circuit comprising an input transistor having a base connected to a signal generator and an emitter connected to the base of the output transistor, the switching circuit having a Darlington connection between the collectors of the output transistor and the input transistor, A resistor is connected between the coil and the output transistor, and when the resistance value R of this resistor is VBE, the voltage between the base and emitter of the output transistor is _VBE , and the input current of the coil of the electromagnet device is _In , R=
By setting V _BE /I _n , the power loss of the output transistor can be reduced to the same level as conventional devices by using the output transistor in a saturated state during the closing operation of the electromagnet device. By using the output transistor in a non-saturated state during the holding operation of the device, the accumulation time of the output transistor can be shortened, so the duty ratio of the pulse for supplying the holding current can be accurately controlled. This has the effect that it is possible to perform high-speed operation, and it is also possible to increase the frequency of the switching circuit.

[Brief explanation of drawings]

Fig. 1 is a wiring diagram of a Darlington connection switching circuit showing an embodiment of the present invention, Fig. 2 is a wiring diagram showing an example of a conventional Darlington connection switching circuit, and Fig. 3 shows the operation of Fig. 2. This is a time chart. 1... Switching circuit, 2... Output transistor, 3... Input transistor, 11... Resistor.

Claims (1)

[Scope of utility model registration request] an output transistor whose collector is connected to a coil of an electromagnetic device, whose collector is connected in common with the collector of said output transistor to the coil of the electromagnetic device, whose base is connected to a signal generator, and whose emitter is connected to the base of said output transistor; In the Darlington-connected switching circuit, a resistor is connected between the collectors of the output transistor and the input transistor and between the coil of the electromagnetic device and the output transistor, and the resistance value of the resistor is A Darlington connection switching circuit characterized in that R is set to R = V _BE /I _n , where V _BE is the voltage between the base and emitter of the output transistor, and I _n is the input current of the coil of the electromagnet device. .