JPS59123207A - Magnet driving circuit for printer hammer - Google Patents

Abstract

PURPOSE:To suppress heat generation of power transistors and improve the stability of oscillation by a method wherein a positive feedback circuit is connected between a reference voltage supplying terminal of a differential amplifier which composes an oscillation circuit and a connection point of a transistor switch. CONSTITUTION:A positive feedback circuit 7 is connected between the collector of a power transistor 2 and the base of a transistor 41 of a differential amplifier 4. When a driving input IP is supplied to an input transistor 5, a driving current CI flows through a magnet coil 1 and the current CI is kept constant by the on- off operation of the transistor 2. When the transistor 2 is conductive, a feedback current FI, corresponding to the charge and discharge characteristics of a resistor 71 and a capacitor 72, is applied to the transistor 41 through the circuit 7 and is superposed on the current corresponding to the reference voltage and as a result, hysteresis is produced in the amplifier 4 and the frequency of the oscillation circuit is reduced. Accordingly, heat generation of the transistor 2 is suppressed and the switching speed of the transistors 41, 42 is increased and stability of the operation is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an improvement in an electromagnetic magnet drive circuit for driving a hammer in a foil printer.

[Technical background of the invention]

Conventionally, as this type of two-way system, there is a system using a chopper system as shown in FIG. 1, for example. In this Chodupa type circuit, a power transistor 2 is connected to a magnet coil I.
and a current detection resistor 3 for detecting the drive current of the magnet coil 1 are connected in series. and,
When the detection output of the current detection resistor 3 is led to the inverting input terminal of the differential amplifier 4 and the drive input signal IP is supplied to the input transistor 5 to the non-inverting input terminal of the differential amplifier 4 to make it conductive. The voltage obtained by the resistive voltage divider circuit 6 is supplied as the reference voltage Vref. The levels of these respective supply voltages are compared by a differential amplifier 4, and the comparison output controls the switching of the power transistor 2 described in 611. In other words, this circuit constitutes an oscillation circuit by a current detection resistor 3, a differential amplifier 4, and a τ resistor voltage divider circuit 6, and its oscillation output controls the power transistor 2 to drive the power flowing to the magnet coil 1. It is designed to keep the current constant.

[Problems with background technology]

However, such conventional circuits cannot perform stable switching operations unless an element with excellent switching characteristics is used as the power transistor 2, and since a high gain differential amplifier is used, the oscillation frequency is high. As a result, the power transistor 2 generates a large amount of heat, which has the drawback of adversely affecting surrounding circuits.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an electromagnetic magnetoresistive drive circuit for a printer hammer that can suppress heat generation of a power transistor by lowering the oscillation frequency and improve the stability of the oscillation operation.

[Summary of the invention]

In order to achieve the above object, the present invention provides a connection point between a reference voltage supply terminal of a differential amplifier constituting an oscillation circuit, a magneto-sotocoil, and a transistor switch for switching a drive current flow path of the magneto-sotocoil. A positive feedback circuit consisting of a resistor and a capacitor is connected between the two.

[Embodiments of the invention]

FIG. 2 is a circuit diagram of an electromagnetic magnet drive circuit according to an embodiment of the present invention, and the same parts as in FIG. 1 are given the same reference numerals and will be described.

The differential amplifier shown at 4 in the figure has transistors 41 and 42 paired with each other, and these transistors 41 and 42
The emitter is connected to a power supply output terminal (output voltage Vcc) via a resistor 43, and each collector is grounded via resistors 44, 45 and a resistor 4G. Then, the reference voltage Vref set by the resistor voltage divider circuit 6 is introduced into the base of the transistor 41, and the detection output of the current detection resistor 3 is applied to the transistor 41.
2, and a comparison output is supplied to the base of power transistor 2 from the connection point between 4 and resistor 45.

By the way, in the circuit of this embodiment, a positive feedback circuit 7 consisting of a series circuit of a resistor 7I and a capacitor 72 is connected between the collector of the power transistor 2 and the base of the transistor 41 of the differential amplifier 4. There is. This positive feedback circuit 7
, a portion of the drive current of the magnet coil I is positively fed back and superimposed on the current corresponding to the reference voltage Vref.

With such a configuration, when the driving power IP is supplied to the input transistor 5, the input transistor 5 becomes conductive and the reference voltage Vref set by each resistor 61, 62 of the resistor voltage divider circuit 6 becomes a differential voltage. It is supplied to the transistor 41 of the amplifier 4.

Then, the transistor 4I becomes conductive, and accordingly the power transistor 2 becomes conductive, and as a result, the magneto-sotocoil 11:IMA dynamic currents C and I flow. Then, this drive current CI increases by % IJn L, current detection resistor 3
When the voltage across the transistor 42 exceeds the reference voltage Vref as shown in FIG.
I becomes non-conductive, and as a result, transistor 2 becomes non-conductive. Therefore, the current C'I that had been flowing through the magnet coil 7 until then flows through the diode 8 and gradually decreases, causing the transistor 42 to become non-conductive. Thereafter, as long as the drive input IP is supplied to the input transistor 5, the above oscillation operation is repeated. Therefore, the driving current CI of the magnet coil I is kept constant by the on/off operation of the transistor 2. Here, the drive current CI of the magneto-sotocoil I is determined by changing the resistance values of the resistors 61, 6'2 and the current detection resistor 3 by R3°R, , R,
Then, it is expressed by .

By the way, in the circuit of this embodiment, when the transistor 2 becomes conductive, a feedback current Fl flows through the positive feedback circuit 7 to the transistor 4I according to the charging/discharging characteristics of the resistor 71 and the capacitor 72, as shown in FIG. . This feedback current FI is superimposed on the current corresponding to the reference voltage Vref, and as a result, hysteresis occurs in the differential amplifier 4 and the oscillation frequency of the oscillation circuit decreases. Therefore, the heat generated by the power transistor 2 is reduced, and as a result, the heat dissipation structure can be simplified, and the thermal influence on the peripheral circuits can be reduced to improve the characteristics. Furthermore, since the positive feedback current FI is superimposed on the basic current, the switching speed of the transistors 4I and 2 is increased. Therefore, the switching characteristics are improved and the operational stability is improved.

It should be noted that the present invention is not limited to the above embodiments (for example - NPN of each transistor).

The format of P N , l) may be determined in the opposite way. Also,
As an application example of the present invention, for example, the resistor 61°62 shown in FIG.
A circuit consisting of a series circuit of a resistor and a switching transistor is connected between the connection point of Accordingly, the magnitude of the current flowing through the magnetic coil I may be varied step by step. Furthermore, the current CI flowing through the magnet coil 1 is expressed as IRef1 because the current IRef flowing through the resistor 62 becomes VRef-RsIRef, and therefore the current CI flowing through the resistor 3 and the resistor 61 is expressed as It can be set by the ratio and reference current IRef.

〔Effect of the invention〕

As described in detail above, the present invention provides a connection point ( Second, connect a positive feedback circuit consisting of a resistor and a capacitor:

Therefore, according to the present invention, the oscillation frequency can be lowered to suppress the oscillation β of the power transistor, and the stability of the oscillation operation can be increased. It is possible to share the dynamic circuit with the car.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a conventional electromagnetic magnet and padding circuit, and Figure 2 is a diagram of a conventional electromagnetic magnet and a padding circuit.
1 path structure 5Q of electromagnetic magnet drive circuit in J
Figure 3 shows the working theory of the circuit shown in Figure 2.
FIG. 3 is a signal waveform diagram for 1...Magne, Sotocoil 22...i-1]r[)
Transistor, 3...Current detection resistor, 4...Differential one-way transistor, 5...Human transistor, 6 - Resistor voltage divider circuit-
7. Positive feedback circuit. Application fee j'! 1! Person Patent Attorney Takehiko Suzue 1st
Figure 2 Figure 3 Kazuo Wakasugi, Director General of the Japan Patent Office, 1984, 1983, Patent Application for Indication of Case. -231347 No. 2, Name of invention Electromagnetic magnet drive circuit for printer hammer 3, Relationship with the person making the amendment Patent applicant (356) Tokyo Electric Co., Ltd. 4, Agent 5, Spontaneous amendment 7, Same content of amendment ( 1) In the specification, page 4, line 12, "bias power supply output terminal (output voltage l Vcc) J" is corrected as [power supply terminal (voltage Vcc) J. (2) Specification, page 5, From the 5th line to the 6th line, the phrase ``of the drive current of the magnet coil 1'' is corrected to ``the voltage generated at the collector of the transistor 2''.

Claims (1)

[Claims] A transistor switch and a current detection resistor that detects the drive current of the magneto-sotocoil are connected in series to the magnet coil, and the detection output of this current detection resistor is level-compared with the drive human power pulse using a differential amplifier. In an electromagnetic drive circuit for a print hammer that performs oscillation operation by controlling the switching of a transistor switch, the connection point between the magnet coil and the transistor switch, and the input terminal of the drive human power pulse in the differential amplifier. 1. An electromagnetic magnet drive circuit for a printer, characterized in that a positive feedback circuit consisting of a resistor and a capacitor is connected between the magnets.