JPS6353952B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat-generating recording element drive circuit, and particularly to a circuit that reduces power consumption and prevents damage to the heat-generating recording element.

Portable electronic devices such as calculators use batteries as a power source, but in order to withstand long-term use, it is necessary to reduce power consumption as much as possible. Therefore,
The ICs and LSIs that make up the central processing units (hereinafter referred to as CPUs) of electronic devices have low power consumption.
CMOS type etc. are used. Furthermore, among such portable electronic devices, there is a high demand for those equipped with printers that leave records, and thermal printing machines are sometimes used because they generate low noise when printing.

Here, in a thermal printing machine, when printing characters on thermal paper, one segment of the thermal head, that is, one heat-generating recording element, has approximately 100
It is necessary to pass a current of mA, and approximately 100 mA is also required to drive the small step motor that moves the thermal head.
Therefore, in electronic equipment that prints output data using such a thermal printing machine, such as a printing calculator, in order to extend the battery usage time, various types of devices that drive each device of the thermal printing machine are used. It is necessary to reduce power consumption in amplifier circuits, constant voltage circuits, etc. as much as possible.

Figure 1 shows an example of the drive circuit for the thermal printing machine described above, where BAT is a battery connected to a constant voltage circuit REG as a CPU power supply source using a CMOS type with low power consumption. , constant voltage circuit
The constant voltage obtained from REG is amplified by the amplifier circuit AMP1~
It is supplied to AMPN and heat generating recording elements TH1 to THN.

Here, when a key on the keyboard (not shown) is pressed down, a high logic level print signal is output to any of the output terminals T1 to TN of the CPU in response to that operation. The signal is amplified by the amplifier circuit AMP1~
When amplified by AMPN and applied to the bases of transistors TR1 to TRN, transistors TR1 to
TRN is made conductive, and the heat-generating recording elements TH1 to THN are driven to generate heat.

Here, a current is constantly passed through the constant voltage circuit REG from the battery BAT via the transistor TRR1, and the voltage at the connection point of the resistors R1 and R2 and the reference voltage by the Zener diode _DZ , that is, the base voltage of the transistor TRR2. and the emitter voltage, and based on the comparison value, the transistor
TRR1 is controlled, thereby controlling the current flowing through transistor TRR1 to obtain a constant voltage. Therefore, even when the heat-generating recording elements TH1 to THN are not driven, power is always wasted.

Also, the amplifier circuits AMP1 to AMPN are always
Electric current is flowing, and power is wasted here as well. Note that the CPU is directly connected to the battery BAT, but this is because if the CPU is configured with a CMOS type, the permissible fluctuation range of the power supply voltage is wide, so it can operate normally without supplying a constant voltage. Because it does.

In addition, when external noise caused by some reason disrupts the operation of the CPU and modulates the output, and the output terminals T1 to TN reach a high logic level, current flows through the heat generating recording elements TH1 to THN. Not only does this result in unnecessary power consumption, but
The heat-generating recording elements TH1 to THN may continue to generate heat for a long time, making them susceptible to damage. Furthermore,
The conventional circuit also had the problem that if the transistors TR1 to TRN were damaged, the elements TH1 to THN continued to generate heat.

An object of the present invention is to provide a heat-generating recording element drive circuit which eliminates the above-mentioned drawbacks, suppresses wasteful power consumption at times other than the printing time, and protects the heat-generating recording element by generating heat only at the desired printing time. Our goal is to provide the following.

Hereinafter, the present invention will be explained in detail based on the drawings. In this case, the same reference numerals are given to the same parts as in FIG. 1, and the explanation thereof will be omitted.

FIG. 2 shows the first embodiment of the present invention, in which OG is
An OR circuit that outputs "1" when a signal to drive the heat generating recording elements TH to THN is output to any of the output terminals T1 to TN of the CPU, and TRS1 is interposed between the constant voltage circuit REG and the ground. It is a switching transistor equipped with a switch, and “1” is connected to the OR circuit OG.
It becomes conductive when there is an output of .

Under the above configuration, when the print signal "1" is output to the output terminal T1 of the CPU, the transistor TRS1 becomes conductive and the constant voltage circuit REG is grounded. That is, since the collector side of the transistor TRR1 of the constant voltage circuit REG whose details are shown in FIG.
Applied to THN. At the same time, the amplifier circuit AMP1
A print signal is supplied to the transistor TR1 via the transistor TR1, and the transistor TR1 is driven. As a result, current flows only through the heat-generating recording element TH1 and heat is generated, thereby making it possible to perform printing.

In this way, only when a "1" signal is output to the output terminals T1 to TN of the CPU, the transistor TRS1 becomes conductive and current flows to the constant voltage circuit REG, which causes current to also flow to the amplifier circuits AMP1 to AMPN. The current flows and drives transistors TR1 to TRN. Thus, current flows through the heat-generating recording elements TH1-THN, causing them to generate heat, thereby performing printing. Therefore, according to this embodiment, wasteful power consumption of the battery at times other than the printing time can be prevented. Also, in the unlikely event that transistor TR1~
Even if the TRN is damaged, the transistor
TRS1 uses a heat-generating recording element at times other than the printing time.
Since no current flows through TH1 to THN, it is possible to prevent damage to the heat generating recording elements TH1 to THN.

FIG. 3 shows a second embodiment of the invention. R5 and C1 are a resistor and a capacitor, respectively, which constitute an integrating circuit. BU is a buffer for starting charging of the capacitor C1 from the battery BAT via the resistor R5. The integrating circuit is used as a timer circuit as described later. are doing. INV is Batsuhua BU
The inverter TRS2 inverts the output signal of
This is a transistor whose collector terminal is connected to the emitter side of the transistor TRS1 mentioned above, and the inverter INV is connected to the base terminal, and whose emitter terminal is grounded, and becomes conductive when the output of the inverter INV becomes "1".

Here, when the output signal from the CPU is “0”,
Since the output of the OR circuit OG is "0", the output of the buffer BU is "0". At this time, the battery
Since the current flowing from BAT through resistor R5 is grounded through buffer BU, capacitor C
1 is not charged. This signal state is
INV becomes "1" and drives the transistor TRS2, but since the transistor TRS1 is not driven, no current flows through the constant voltage circuit REG.

For example, if a key on the keyboard is operated and "1" is output to the output terminal T1 of the CPU, the output of the buffer BU becomes "1" and the battery
Charging of capacitor C1 from BAT starts.
At the same time, transistor TRS1 conducts and while capacitor C1 is being charged, transistor
Since TRS2 is in the driving state, the constant voltage circuit REG
As a result, a constant voltage is supplied from the constant voltage circuit REG to the heating recording element TH1, so that the element
TH1 generates heat and printing is performed.

Next, after a certain period of time has passed since charging of the capacitor C1 started, the voltage across the capacitor C1 exceeds the threshold of the inverter INV, so the output of the inverter INV becomes "0".
As a result, the transistor TRS2 enters the cut-off state.
Since the transistor TRS2 is cut off, no current flows to the constant voltage circuit REG even if the transistor TRS1 is driven. That is,
Even if "1" continues to be output to the output terminals T1 to TN of the CPU, after a certain period of time,
Since the supply of current from the battery BAT to the constant voltage circuit REG is stopped, wasteful power consumption can be prevented and damage to the elements TH1 to THN can be prevented. Moreover, here, when the output from the CPU becomes "0", the output of the buffer BU becomes "0", this signal is inverted by the inverter INV and becomes "1", and the transistor TRS2 becomes in the driving state.

Note that the time constant of the above-mentioned timer circuit is set as follows. That is, in order to operate one heat generating recording element TH1 to THN, for example, approximately
Since it is necessary to flow a current of 100 mA for approximately 10 msec, the capacitance of capacitor C1 in the timer circuit must be adjusted so that the transistor TRS2 does not shut off at the desired printing time and the supply of current from the battery BAT to the constant voltage circuit REG is not stopped. shall be determined.

As explained above, according to the present invention, current is caused to flow through the constant voltage circuit only when the output terminal of the central processing unit is at a high logic level, and a constant voltage is applied to the amplifier circuit for driving the heat generating recording element and the heat generating recording element. Since the recording element was made to generate heat by supplying it to
For the constant voltage circuit and the amplifier circuit for driving the recording element,
There is no need to constantly supply current, reducing battery power consumption. Further, even if the transistor that selects the heat-generating recording element is damaged, power is not continued to be supplied to the element as in the conventional case, and damage to the heat-generating recording element can be prevented.

In addition, by providing a timer circuit as shown in Figure 3, even if the CPU malfunctions due to external noise such as static electricity and continues to output "1" to its output terminal, it can be After the time has elapsed, the supply of current to the constant voltage circuit REG is cut off, and at the same time, the supply of power to the heat-generating recording element is also cut off, making it possible to suppress wasteful power consumption.

Furthermore, even if the transistors TR1 to TRN are destroyed or "1" continues to be output to the output terminal of the CPU, and power continues to be supplied to the recording element for a long time, the above-mentioned timer circuit allows Since the heat-generating recording element is made to generate heat for a period of time, the heat-generating recording element can also be protected.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of a conventional heat-generating recording element drive circuit, FIG. 2 is a circuit diagram showing an embodiment of the heat-generating recording element drive circuit of the present invention, and FIG. 3 is a circuit diagram showing another example of the heat-generating recording element drive circuit of the present invention. FIG. BAT...battery, CPU...central processing unit,
AMP1~AMPN...Amplification circuit, _DZ ...Zena diode, TH1~THN...Heat-generating recording element,
TR1～TRN, TRS1, TRS2, TRR1,
TRR2...transistor, OG...OR circuit,
BU...Battle, C1...Capacitor, INV...
...Inverter, REG... Constant voltage circuit, R1~R
6...Resistance, T1~TN...Output terminal.

Claims (1)

[Claims] 1. A constant voltage circuit that is supplied with power from a power source to obtain a constant voltage, and drives a heat-generating recording element in response to a signal output to an output terminal of a central processing unit;
In the heat-generating recording element driving circuit which supplies power from the constant voltage circuit to the driven heat-generating recording element to cause the heat-generating recording element to generate heat, the constant voltage circuit is grounded through a switching means;
The switching means is closed in response to the signal, power is supplied from the power supply to the constant voltage circuit to obtain a constant voltage, and power is supplied to the driven heat generating recording element. A heat-generating recording element drive circuit. 2. In the circuit described in claim 1,
a timer circuit, and after a signal is generated at the output terminal of the central processing unit, when a predetermined period of time has elapsed by the timer circuit, the constant is output from the power supply regardless of the state of the signal. 1. A heat generating recording element drive circuit characterized in that power supply to a voltage circuit is stopped.