JPS6240408Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a drive circuit for a solenoid plunger used for switching the operation of a tape recorder or the like.

In recent high-grade tape recorders called tape decks, the operation switching is generally performed by the suction operation of a solenoid plunger. In a tape recorder configured to switch operations by the suction operation of such a solenoid plunger, heat generation due to the holding current flowing through the solenoid coil poses a problem. Such a solenoid plunger has the property that the current required to hold the plunger in the attracted state is much smaller than the current at the start of attraction. As a method to solve the above-mentioned problem by utilizing such characteristics, two transistors are provided to drive the solenoid plunger, and when suction starts, the two transistors supply current to the solenoid coil, and after suction ends, one of the transistors supplies current to the solenoid coil. Generally, a transistor is used to supply current. Although this method can minimize the heat generation of the solenoid plunger, the problem is that the holding current is set taking into account fluctuations in the power supply voltage, so the amount of heat generated increases when the power supply voltage is high. There is.

The present invention has been developed in view of the above-mentioned points, and will be described in detail below with reference to the illustrated embodiments. In the figure, 1 is a solenoid coil constituting a solenoid plunger, 2 is a driving transistor whose collector is connected to the ground terminal A of the solenoid coil, and whose emitter is grounded. A bias is applied to the base to turn it into a conductive state. 4
is a power supply control transistor whose emitter is connected to the power supply terminal B of the solenoid coil 1 and whose collector is connected to a power supply, and a bias resistor 5 is connected between its base and collector. 6 is a Zener diode whose cathode is connected to the base of the power supply control transistor 4; 7 is a control transistor whose emitter is connected to the anode of the Zener diode 6 and whose collector is grounded; It is connected to the collector of the driving transistor 2 via a resistor 8. 9 is a capacitor connected between the base of the control transistor 7 and the ground and constitutes the delay circuit 10 with the resistor 8; 11 is the solenoid coil 1;
This is a diode connected in parallel to the solenoid coil 1, and has the function of absorbing the back electromotive force generated in the solenoid coil 1.

The drive circuit of the present invention is constructed as described above, and the operation of this circuit will now be described. In the non-operating state where the operating switch 3 is in the open state,
The driving transistor 2 is in a non-conducting state. In this state, the capacitor 9 constituting the delay circuit 10 is charged by the current flowing from the emitter of the power supply control transistor 4 through the solenoid coil 1 and the resistor 8, so that the control transistor 7 It is reverse biased by the charging voltage of , and is in a non-conducting state. In such a state, the charging current for the capacitor 9 flows through the solenoid coil 1, but since the current value is small, the plunger is not caused to perform a suction operation.

Next, a case will be described in which the operating switch 3 is closed in order to change the operation in such a state. When the operating switch 3 is closed, a bias current flows through the switch 3 to the base of the driving transistor 2, so that the driving transistor 2 is turned into a conductive state. When the drive transistor 2 is reversed to a conductive state, the potential of the ground terminal A of the solenoid coil 1 becomes the ground potential, so a drive current flows from the emitter of the power supply control transistor 4 to the solenoid coil 1, causing the plunger to perform a suction operation. It will be done. Further, when the driving transistor 2 is inverted to the conductive state, the control transistor 7 is inverted to the conductive state, but the inversion operation is delayed by a predetermined time by the delay circuit 10 . When a predetermined period of time has elapsed after the solenoid plunger was caused to perform a suction operation, the control transistor 7 is reversed to a conductive state, and the Zener diode 6 is brought into a conductive state. Therefore, in such a state, the base potential of the power supply control transistor 4 is made constant by the Zener diode 6, so the voltage applied to the solenoid coil 1 from the emitter of the power supply control transistor 4 becomes a constant voltage. . As is clear from this operation, when the solenoid plunger starts suction due to conduction of the drive transistor 2 as the operation switch 3 is closed, a high voltage is applied to the power supply terminal B of the solenoid coil 1 from the emitter of the power supply control transistor 4. When a voltage is applied and the suction operation is completed after a predetermined period of time has elapsed, the Zener diode 6 is conductive, so that the emitter of the power supply control transistor 4 is applied to the power supply terminal B of the solenoid coil 1 at a lower and constant voltage than when the suction starts. A voltage is applied. Therefore, at the start of suction, a high voltage is applied to the power supply terminal B of the solenoid coil 1, so a large current flows through the solenoid coil 1, and the suction force necessary to suction the plunger can be obtained, and the suction operation can also be performed. After completion, a constant low voltage is applied, so the current flowing through the solenoid coil 1 becomes small, and heat generation due to the holding current can be suppressed. Furthermore, after the suction operation of the solenoid plunger is completed, the plunger is suctioned and held by a constant voltage power source, so that it is not affected by fluctuations in the power supply voltage.

As explained above, since the plunger drive circuit of the present invention applies a high voltage to the solenoid coil when the plunger starts suction, a large suction force can be obtained and the suction operation can be performed reliably. In addition, after the plunger has completed its suction operation, a low, constant voltage is applied to the solenoid coil, making it possible to set the holding current to the minimum value without being affected by fluctuations in the power supply voltage. The present invention can minimize heat generation due to holding current. In addition, the present invention makes the Zener diode, which acts to supply constant voltage power to the solenoid coil, become conductive after the suction operation of the solenoid plunger is completed by making the base potential of the power supply control transistor constant voltage. This has the advantage that the suction operation of the solenoid plunger can be performed reliably without any wasted current flowing at the start of suction, which requires a large current. This is extremely effective when incorporated into equipment equipped with circuits.

[Brief explanation of the drawing]

The illustrated circuit is one embodiment of the solenoid plunger drive circuit of the present invention. Explanation of main drawing numbers, 1...Solenoid coil, 2
...Drive transistor, 4...Power supply control transistor, 6...Zener diode, 7...
...control transistor, 10 ...delay circuit.

Claims (1)

[Scope of utility model registration request] A collector-emitter path is connected between the ground terminal of the solenoid coil constituting the solenoid plunger and the ground, and a driving transistor that causes the solenoid plunger to perform a suction operation due to the conduction thereof, and between the power supply terminal of the solenoid coil and the power source. A power supply control transistor to which a collector-emitter path is connected and which controls power supply to the solenoid coil, a bias resistor connected to give a bias to the base of the power supply control transistor, and the drive transistor operate. a control transistor which is controlled and which is inverted to a conductive state after a predetermined time period set by a delay circuit after the driving transistor is inverted to a conductive state; a Zener diode that conducts when the transistor is in a conductive state and makes the base potential of the power supply control transistor a constant voltage; A solenoid plunger drive circuit characterized in that the Zener diode is made conductive by conducting, and a constant voltage power source is supplied to the solenoid coil by making the base potential of the power supply control transistor constant voltage.