JPH0469251A - Print head driving circuit - Google Patents

Abstract

PURPOSE:To prevent burnings of a switching element and a load coil by comparing a voltage to be applied to the load coil with an input signal. CONSTITUTION:An input IN1 and an input IN2 are both at 1 at non-driving time and are made to be at 0 at driving time, so that transistors TR1 and TR2 are both turned on and a coil L is energized. When the input IN1 is at 1, a collector of the transistor TR1 is almost an earth voltage so that 1 is given to one input of an exclusive-OR circuit EOR and 0 is given to other input and its output is at 1. Further, when the input IN1 is at 0, the collector of the transistor TR1 becomes almost a power +VD and a connecting point of a resistance R1 and a Zener diode ZD becomes a voltage which corresponds to 1, and the output of the exclusive-OR circuit EOR becomes 1 also at this time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a print head drive circuit, and particularly to a print head drive circuit that drives a print head coil serving as a load by turning on and off a semiconductor switching element.

[Conventional technology]

Conventionally, this type of print head drive circuit has a print head coil and at least one semiconductor switching element connected in series between a power supply and the earth, and turns the switching element on and off according to a printing input signal. This is often used.

[Problem to be solved by the invention]

The conventional print head drive circuit described above turns the switching element on and off according to the print input signal, so if the switching element turns on and then goes out due to a failure number of the switching element, the current will flow to the load. The problem is that the current continues to burn out, causing the coil to burn out or the switching element to burn out, resulting in a serious accident.

[Means to solve the problem]

The print head drive circuit of the present invention turns on and off the current in the coil of the print head serving as a load by means of a semiconductor switching element connected in series to this coil, and turns on the switching element. By detecting a mismatch between the state of the input signal and the voltage applied to the coil end at the time of inputting this input signal and outputting an alarm signal, the input signal also turns on the switching element connected to the power supply side of the coil. Since the voltage applied to the end of the coil is the terminal voltage of a Zener diode connected between the power supply side terminal of the coil and the ground via a resistor, the input signal is also applied to the power supply side of the coil. The output is the logical sum of the input signals that turn on the switching elements connected to the side and the ground side, respectively, and the voltage applied to the coil ends is the output signal of the photocoupler connected to both ends of the coil. Consisted of.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a circuit diagram of an embodiment of the present invention. In the embodiment shown in FIG. 1, a driving PNP resistor TR, a load coil L, and an NPN transistor TR2 are connected in series between the power source VD and the earth.
is controlled from the input INI via the inverter INVI and the NPN transistor TR, and the input INI
r or “0°.

, the transistor TR2 is controlled from the input IN2 via the inverter I N V 2, and the transistor TR2 is controlled from the input IN2 through the inverter I N
It is configured to be turned on when N2 is "0".

On the other hand, a resistor R1 and a Zener diode ZD whose Zener voltage is a high voltage at a logic level are connected in series between the transistor T R1 and the connection point between the coil and the ground.
, and the Zener diode ZD and the input IN are connected to each of the two inputs of the exclusive OR circuit EOR, and the output of the exclusive OR circuit EOR serves as the alarm output AL.

In the above configuration, normally, the input I N 1 and the input IN2 are both set to 1° when not driven, and are both set to "0" when driven, so that the transistor TR
, and TR2 are both turned on, energizing the coil. Also, when input IN and power (1"), transistor T
Since the voltage on the collector 4i of RI is low, "1" is given to one input of the exclusive OR circuit EOR, "O" is given to the other input, and its output becomes °1. Furthermore, when the input IN is "0", the collector of the transistor T Rl becomes approximately +VO, and the resistor R1
The connection point between and the Zener diode ZD becomes a voltage corresponding to 1", and the output of the exclusive OR circuit EOR is also 1" at this time.
” becomes.

FIG. 2 is a waveform diagram including the time of failure shown in FIG. 1, and shows the waveforms of the level of the input IN, the collector voltage of the transistor TR1, and the alarm output AL. The first half of the waveform diagram shows normal conditions,
The second half is transistor TR.

This shows the case when the button is turned on. At this time, even when the input IN1 becomes "1", the connection point between the resistor R and the Zener diode ZD is "1".

A considerable voltage will be generated, and the output of the exclusive OR circuit EOR will be 0.”
and outputs a warning. It is clear that in this embodiment, even when the transistor TR is turned off due to an open failure, the alarm output AL outputs 0°.

FIG. 3 is a circuit diagram of another embodiment of the invention.

The embodiment shown in Fig. 3 is the same as the embodiment shown in Fig. 1 and the coil L serving as the load.
The circuit of the drive section is the same, but as a fault detection circuit,
A photocoupler PC is connected to both ends of the coil L via a resistor R1.
Connect the input side of the resistor R between the power supply +VB and the earth.
2 and the output side of the photocoupler PC, and resistor R2.
Exclusive OR circuit FO connects the connection point with photocoupler PC.
It is used as one input of R. Also inputs IN1 and IN
The negative output of the logical sum of 2 is used as the other input of the exclusive OR circuit FOR, and its output is used as the alarm output AL.

Therefore, the driving of the coil L in the configuration of FIG. 3 is the same as in the case of FIG. 1.

FIG. 4 is a waveform diagram including the case of the failure shown in FIG. 3, and shows the waveforms of the input IN, the collector voltage of the transistor N2 and the transistor TR, the output of the photocoupler PC, and the alarm output AL. In this waveform diagram, the input N2 becomes "O" longer than the input IN, and when the transistor TR1 is turned on and the excess current flows to the load, the alarm output AL is output.
This shows the case where . The first half of the waveform diagram shows the normal state, and the second half shows the state when the transistor TR1 is turned on. The photocoupler PC outputs "0" when current flows through the coil. On the other hand, when either of the inputs IN1 and IN2 is "1", the output from the logical OR NOT circuit NOR is "'0", that is, both are "0".
”, it outputs “1” only when the input is
, and ■N2 are "0°", the photocoupler PC outputs, so "0" is never output from the exclusive OR circuit EOR. By the way, when the transistor TR is turned on and then turned off, when the input IN2 becomes "'0", a current always flows through the coil and the photocoupler PC outputs "
0" is output, so when the output of the OR NOT circuit NOH is "0" and current flows through the coil, "0" is output from the exclusive OR circuit FOR, and the alarm output AL is "0".
is output.

Note that in this embodiment, input IN is longer than input IN2.
In the case of 0'', whether the transistor TR2 is turned on or not is similarly detected.

〔Effect of the invention〕

As explained above, the present invention detects not only open failures but also closed failures of switching elements that apply voltage to the coils by comparing the voltage applied to the coil serving as a load and the input signal. Since an alarm signal can be output, there is an effect that burning out of the switching element and the load coil can be prevented.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of one embodiment of the present invention, Fig. 2 is a waveform diagram of the main points of operation in Fig. 1, Fig. 3 is a circuit diagram of another embodiment of the invention, Fig. 4 3 is a waveform diagram of the main points of the operation in FIG. 3. INl, IN2...Input, INVl, INV2...
Inverter, L...coil, NOR...OR NOT circuit, EOR...EXOR circuit, R,, R2...
Resistor, TRI, TR2, TR3-transistor, Z
D...Zena diode, PC...photocoupler, AL...alarm output. Figure 1

Claims (1)

[Claims] 1. In a print head drive circuit that turns on and off the current of a print head coil serving as a load using a semiconductor switching element connected in series to this coil, an input signal that turns on the switching element and this A print head drive circuit characterized in that when an input signal is input, a discrepancy in state with a voltage applied to a coil end is detected and an alarm signal is output. 2. The input signal according to claim 1 is an input signal that turns on a switching element connected to the power supply side of the coil, and the voltage applied to the end of the coil is connected to the ground from the power supply side terminal of the coil via a resistor. A print head drive circuit characterized in that the voltage at the terminals of a Zener diode provided therein. 3. The input signal according to claim 1 is a logical sum output of input signals that turn on each of the switching elements connected to the power supply side and the earth side of the coil, and the voltage applied to the end of the coil is A print head drive circuit characterized in that the output signal is a photocoupler connected to both ends.