JPS6245904Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device having various power supplies and a large number of excitation coils, such as a dot printer used as a terminal device of an information processing device. In devices without a power supply sequence, the power supply
The purpose is to prevent the excitation coil drive circuit (driver) from malfunctioning when turned on or off.

For example, in a dot printer, as shown in FIG. 1, the voltage _{V 1} of the power supply B 1 applied to the control circuit 1
and each load 3, 4, connected to the drive circuit 2.
There is a voltage V ₂ of the power supply B ₂ applied to 5. Loads 3, 4, and 5 include each printing pin of the printing head, a drive magnet, a space motor for reciprocating the carrier, a line feed motor, or a gap between the platen and the head in a passbook printing machine. Escape magnet etc. are connected.

In this case, the voltages V ₁ and V ₂ of the power supplies B ₁ and B ₂ require a certain amount of transient time to stabilize when they are turned on and off, so in the control circuit 1, the power supply voltage V ₁ is stabilized. Until then, the voltage at the output terminal for the drive circuit 2 is unstable, and if the drive voltage V ₂ is applied to the drive circuit 2 during that time,
Loads 3, 4, and 5 may malfunction.

Therefore, in general, the power supply circuit performs sequence control, and as shown in FIG. 2, when the power is turned on, the voltage V ₁ applied to the control circuit 1 is stabilized at T ₁
At time _T2 after the time T2, the voltage _V2 is applied to the drive circuit 2, and when the power is cut off, the drive voltage _V2
The control circuit voltage at time T ₄ after time T ₃ when the
It is controlled to shut off V ₁ .

However, when a power supply circuit is equipped with a sequence control function, the cost inevitably increases, so recently, there have been an increasing number of power supply devices that omit the sequence control function. Therefore, the control circuit voltage V ₁
If the drive voltage V ₂ is applied to the drive circuit 2 before the control circuit voltage V 1 is stabilized, or the drive voltage V ₂ may remain even after the control circuit voltage V ₁ is cut off, this may cause malfunction. Therefore, in such a case, it is necessary to take measures to prevent malfunctions on the printer side, and conventionally, for example, a circuit as shown in FIG. 3 has been adopted. In this figure, the drive circuit 6
A pull-up power supply _V3 is applied from the power supply B3 to the base of each transistor 7, 8, and ₉ through resistors 10, 11, and 12, and each transistor 7, 8, and 9
maintain in the operating area. That is, when a logic "L" signal is input to the inverter 14 in the control circuit 13, it is inverted by the inverter 14, and its output signal becomes "H". Therefore, the current due to the pull-up voltage _V3 cannot flow into the inverter 14, but flows through the resistor 10, the base and emitter of the transistor 7, and then to the ground. As a result, conduction is established between the collector and emitter of the transistor 7, and the drive voltage
A current due to V ₄ flows into the load 15 and drives the load. Conversely, when the input of the inverter 14 is logic "H", its output is inverted and becomes "L", the pull-up voltage _V3 is connected via the resistor 10 and the inverter 14, and the base voltage of the transistor 7 is extremely low. becomes a small value, and the transistor 7 enters the cut-off state. Therefore, no drive current flows through the load 15, and the load is not driven.

16 is a voltage abnormality detection circuit, and control circuit 13
The power supply voltage _V5 of the control circuit 13 is compared with the reference voltage _V6 that guarantees normal operation of the control circuit 13, and if the control circuit power supply voltage _V5 is lower than the reference voltage _V6 , the transistor 17 in the detection circuit 16 is compared. conducts, and pull-up voltage is generated through each diode 18, 19, 20.
V ₃ is grounded. As a result, the base voltage of each transistor 7, 8, 9 of the drive circuit 6 becomes a very small value, and the operation of the drive circuit 6 is prohibited.
Therefore, even if the voltage V ₄ of the drive circuit 6 is applied before the power supply voltage V ₅ of the control circuit 13,
Malfunctions can be prevented. Note that when the control circuit voltage _V5 exceeds the reference voltage _V6 , the transistor 17 is cut off. Therefore, the bases between the transistors 7, 8, and 9 of the drive circuit 6 are insulated by the two diodes 18, 19, or 20 connected in opposite directions, and
can perform their own intermittent operation using signals from the control circuit 13 without mutual interference.

In such conventional driver protection circuits, the pull-up voltage V ₃ is not set to a single value, but has the advantage of being able to be set arbitrarily for each channel of the drive circuit, but as the number of drive channels increases, it is necessary to add diodes. This poses problems in terms of number of parts and cost.

The present invention aims to solve the above-mentioned drawbacks of a driver protection circuit that does not have a power supply sequence. A control signal is applied to an open-collector inverter 39 powered by a pull-up power supply V6, and the driving transistors 32,
33, 34.
a comparison circuit 24 which compares the pull-up power supply V6 with a reference voltage V8, a transistor 38 which is turned on and off by the output of the comparison circuit, and a circuit which connects the output of the transistor 38 with the base terminals of the drive transistors 32, 33, 34, wherein the driver protection circuit is configured so that when the voltage value of the pull-up power supply V6 exceeds the reference voltage, the transistor 38 is made conductive.

Next, an embodiment of the present invention will be described based on FIG. 21 is a voltage abnormality detection circuit, and resistor 2
2, a Zener diode 23 and a comparator 24. The power supply voltage V ₆ (for example, 5V) applied to the control circuit 26 is applied to the difference input terminal 25 of the comparator 24, and the sum input terminal 27
For example, loads 28, 29, 3, which correspond to printing pins and space motors in dot printers, etc.
From the voltage V ₇ (e.g. 24V) applied to 0 to the resistor 2
A reference voltage V ₈ (for example 4.75 V) stabilized by a Zener diode 23 is applied via V 2 .

On the other hand, transistors 32, 33, of the drive circuit 31,
The base of 34 is connected to a power supply B 6 of a pull-up voltage V ₆ common to the power supply voltage of the control circuit 26 through resistors 35 , 36 , 37 and a transistor 38 which is controlled intermittently by the output of the voltage abnormality detection circuit ₂₁ in series. It is connected.

Therefore, the drive voltage of the loads 28, 29, and 30 is applied before the power supply voltage _V6 applied to the control circuit 26.
If V ₇ is applied, a reference voltage V ₈ is created by the Zener diode 23 and applied to the sum input terminal 27 of the comparator 24 . However, since the voltage V ₆ to the control circuit 26 has not yet risen, the voltage at the differential input terminal 25 of the comparator 24
Since V ₆ is lower than the reference voltage V ₈ of the sum input terminal 27, the output voltage V ₉ of the comparator 24 is positive. Therefore, the base voltage of the PNP type transistor 38 becomes higher than the emitter voltage and is cut off, so that there is no conduction between the emitter and the collector.
Therefore, the transistors 32 and 3 of the drive circuit 31
The pull-up voltage V ₆ is not supplied to the bases of transistors 3 and 34, and even if the output signal of the control circuit 26 becomes logic "H" due to malfunction, the
2, 33, and 34 cannot conduct. Therefore the driving voltage
Even if V ₇ is applied, the load 28, 29, 30
Since no current flows through, the load is not driven, and malfunctions due to uncertain signals can be prevented.

In the above state, the power supply voltage V ₆ to the control circuit 26
increases and exceeds the reference voltage V ₈ set by the Zener diode 23 , the voltage V ₆ at the difference input terminal 25 becomes higher than the voltage V ₈ at the sum input terminal 27 of the comparator 24 . The output voltage of becomes negative, causing transistor 38 to conduct. Therefore, the drive circuit 31
A pull-up voltage _V6 is applied to the bases of the transistors 32, 33, and 34 through respective resistors 35, 36, and 37. As a result, the drive circuit 31
Now, if the output level of the inverter 39 in the control circuit 26 is set to logic "H",
The current due to the pull-up voltage _V6 is inverter 39
The transistor 38, the resistor 35,
It flows to ground through the base and emitter of transistor 32. If the voltage V ₆ is, for example, 5V, the base voltage of the transistor 32 becomes approximately 1.5V, and conduction occurs between the collector and emitter of the NPN transistor 32, and the current due to the drive voltage V ₇ flows to the load 28, and the load 28 is driven.

Further, when the output signal of the inverter 39 is logic "L", the current due to the voltage _V6 flows through the transistor 3.
8, flows to ground through the resistor 35 and inverter 39. Therefore, the base voltage of transistor 32 of drive circuit 31 is about 0.2V of the forward voltage in inverter 39, and transistor 32 is cut off. Therefore, no current flows through the load 28 and it does not operate. As described above, according to the present invention, malfunctions can be prevented as reliably as in a circuit having a power supply sequence.

Although this embodiment is an example of three channels with three loads, it is easy to further increase the number of channels. In that case, it is only necessary to insert one resistor between the collector of the transistor 38 and the base of the drive transistor of the additional channel.
Even if it becomes multi-channel, there is no risk of cost increase.

Further, in this embodiment, the power supply voltage V ₆ of the control circuit 26 is a single power supply, which is common to the pull-up voltage to the bases of the transistors 32, 33, and 34 of the drive circuit 31. Even in the case of a power supply, the power supply abnormality detection circuit 2
By making improvements to 1, the same operation as above can be obtained. FIG. 5 shows that the power supply of the control circuit 26 is a voltage
Voltage abnormality detection circuit 2 in case of two voltages V ₈ and V ₉
This is an example of 1. The voltage now applied to the control circuit 26
Let V ₈ and V ₉ be 12V and 5V, for example, and load 28.
If the voltage _V7 applied to 29 and 30 is 24V, the power supply
Zener diode 4 from B ₇ through resistor 40
1 to obtain a reference voltage V ₁₀ of 4.75V, which is commonly applied to sum input terminals 44 and 45 of comparators 42 and 43. On the other hand, when the voltage V ₈ of the power supply B ₈ exceeds the voltage that ensures normal operation of the control circuit, it is divided by the resistors 46 and 47 so that it becomes the reference voltage V ₁₁ or more, and the difference between the comparator 42 is applied to input terminal 48. If the voltage V ₈ exceeds the specified voltage,
When the voltage at terminal 48 becomes equal to _or higher than the reference voltage V11 at terminal 44, the output voltage of comparator 42 becomes negative, and the emitter of PNP transistor 49 becomes negative.
The collectors are made conductive and voltage V ₉ is applied to the differential input terminal 50 of the comparator 43 . Similarly to the above operation, when the voltage V ₉ of the power supply B ₉ becomes equal to or higher than the reference voltage V ₁₁ that ensures normal operation of the control circuit 26, the output of the comparator 43 becomes negative and is connected to the output side of the comparator 43. By connecting the emitter and collector of the PNP type transistor 51 and connecting the collector of the transistor 51 to the connection point 52 of the resistors 35, 36, and 37 in FIG. 4, a pull-up voltage V connected to the emitter of the transistor 51 is established. ₁₁ to resistor 35, 36, 3
7 to the bases of the transistors 32, 33, and 34 to enable the operation of the drive circuit 31.

As described above, according to the present invention, a switching element such as a transistor is inserted in series between the base of the transistor of the drive circuit and the power source that supplies the base voltage, and the transistor is Switching is performed by a voltage abnormality detection circuit that detects whether the control circuit has reached a specified voltage that allows it to operate accurately, and if the specified voltage has not been reached, operation is disabled by not supplying the base voltage of the transistor of the drive circuit. Malfunctions can be prevented. In order to increase the number of channels, it is sufficient to add one resistor per channel, and the number of components is smaller than that of the conventional system, and the number of channels can be increased at a very low cost.
In addition, the transistor 3 for the switching element described above
8 can be made smaller in capacity.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an excitation coil drive circuit in a dot printer, etc., Fig. 2 is a timing chart of sequence control, Fig. 3 is a diagram showing a conventional driver protection circuit, and Fig. 4 is a diagram of a driver protection circuit according to the present invention. FIG. 5 is a diagram showing another embodiment of the voltage abnormality detection circuit. In the figure, 21 is a voltage abnormality detection circuit, 26 is a control circuit, 28, 29, and 30 are loads (excitation coils), 31 is a drive circuit, and 32, 33, and 34 are transistors.

Claims (1)

[Claims for Utility Model Registration] A control signal is applied to the open-collect inverter 39 that uses the pull-up power supply V6 as a power source, and depending on the level of this control signal, the driving transistors 32, 33, 34 of the pull-up power supply V6 are
a comparator circuit 24 that compares the pull-up power supply V6 and the reference voltage V8 in a driver circuit that controls application/non-application to the base terminal of the transistors and turns on/off the driving transistors 32, 33, and 34; It consists of a transistor 38 whose on/off is controlled by the output of the comparison circuit, and a circuit connecting the output of the transistor 38 and the base terminals of the drive transistors 32, 33, and 34, and the voltage value of the pull-up power supply V6. A driver protection circuit characterized in that the circuit is configured such that the transistor 38 becomes conductive when the voltage exceeds a reference voltage.