CN205489774U - Power supply unit and printer - Google Patents

Abstract

An object of the present invention is to provide a power supply device and a printer capable of appropriately supplying electric power even when a load current fluctuates greatly. For this purpose, in the AC converter (3) for supplying a DC current to a load based on an AC current, there are provided a plurality of power supply circuits having a voltage drop characteristic of an output voltage with respect to a load current supplied to a thermal printer (4), the power supply circuit When the current value of the load current is in a specific state, the voltage drop characteristic is switched.

Description

Power supply unit and printer

technical field

The utility model relates to a power supply device and a printer equipped with the power supply device.

Background technique

Conventionally, it is known that in a power supply device such as an AC converter for supplying electric power, the characteristic that the output voltage drops together with the output current, that is, the so-called "F" (curve with the output current on the horizontal axis and the output voltage on the vertical axis) is used. In the figure, the characteristic of a line similar to the character of the Japanese kana "フ" is drawn) "Drop characteristic to perform overcurrent protection technology (for example, refer to Patent Document 1)

However, in the case of a power supply device having a "F-shaped" drop characteristic, when the load fluctuates greatly, it may not be possible to supply appropriate power. For example, when a power supply device supplies power to a print head of a thermal printer, the number of heating elements to be energized by the print head varies greatly depending on the content to be printed. Therefore, the current flowing from the power supply unit to the load fluctuates greatly. For example, when many heating elements are energized, the voltage drops due to the characteristics of the power supply unit, and there is a possibility that power cannot be properly supplied to the print head.

Patent Document 1: JP Unexamined Publication No. 2005-160241

Utility model content

The present invention is made in view of the above circumstances, and an object of the present invention is to provide a power supply device and a printer capable of appropriately supplying electric power even when the load fluctuates greatly.

In order to achieve the above object, the power supply device of the present invention is characterized in that the power supply device is a power supply device for a printer that supplies a direct current to a load based on an alternating current, and has at least three A power supply circuit having a voltage drop characteristic of an output voltage of a load current, wherein the power supply circuit switches the voltage drop characteristic when a current value of the load current is in a specific state.

Thereby, even when the fluctuation of the load current is large, it is possible to supply appropriate electric power by switching the voltage drop characteristic.

In addition, the power supply device of the present invention is characterized in that the power supply circuit has a first voltage drop characteristic, a second voltage drop characteristic, and a third voltage drop characteristic, and the first voltage drop characteristic indicates In the output voltage drop characteristic, the second voltage drop characteristic represents a characteristic in which the output voltage drops with a gentler gradient than the first voltage drop characteristic as the load current increases, and the third The voltage drop characteristic indicates a characteristic in which the output voltage drops with a drop in the load current.

In addition, the power supply device of the present invention is characterized in that the power supply circuit switches from the first voltage drop characteristic to the second voltage drop characteristic as the load current increases, and switches to the second voltage drop characteristic as the load current decreases. is the third voltage drop characteristic.

Accordingly, appropriate electric power can be supplied, and overcurrent protection can be performed.

Furthermore, the power supply device of the present invention is characterized in that the power supply circuit includes: a detection unit that detects that the load current is in the specified state; and a switching unit that detects that the load current is in the specified state; As a result, the voltage drop characteristic is switched.

Accordingly, even when the load current fluctuates greatly, since the load current is detected and the voltage drop characteristic is switched, electric power can be appropriately supplied.

Furthermore, the power supply device of the present invention is characterized in that the detection unit switches the output when the current value of the load current reaches a specific current value, and the switching unit switches the output of the load current based on the output of the detection unit. The voltage drop characteristics described above.

Accordingly, electric power can be appropriately supplied even when the fluctuation of the load current is large.

In addition, the power supply device of the present invention is characterized in that the power supply circuit is a switch system including a switch circuit, and the switching unit switches the switch by setting the current value of the load current to a specific current value. The frequency of the circuit is varied to switch the voltage drop characteristic.

In addition, the power supply device of the present invention is characterized in that the power supply circuit has: a primary side circuit, which includes the switching circuit; and a secondary side circuit, which is coupled to the primary side circuit and supplies the DC current For the load, on the side of the secondary side circuit, a reference voltage circuit; a voltage dividing circuit for dividing the output voltage of the secondary side circuit; a comparison circuit for dividing the voltage A divided voltage of the circuit is compared with a reference voltage; and a feedback circuit that changes the frequency of the switching circuit based on a comparison result of the comparison circuit, and the switching section changes the divided voltage of the voltage dividing circuit by changes to switch the voltage drop characteristic.

Accordingly, it is possible to appropriately supply electric power by changing the reference voltage to switch the voltage drop characteristic.

Furthermore, the power supply device of the present invention is an AC converter type in which the power supply circuit is covered by a housing.

Accordingly, it is possible to adapt a power supply circuit having switching voltage drop characteristics to an AC converter.

In order to achieve the above object, the printer of the present invention is characterized in that it has: a printing head, which has a plurality of printing elements fixed in a direction intersecting with the conveying direction of the printing medium; The head supplies a direct current, the power supply circuit has at least three voltage drop characteristics with respect to the output voltage of the load current supplied to the printing head, and switches when the current value of the load current becomes a specific state. The voltage drop characteristic.

Thus, by switching the voltage drop characteristic of the power supply device, even when the load current flowing from the power supply device to the print head fluctuates greatly, it is possible to appropriately supply electric power to the print head. Therefore, even when the number of printing elements energized by the print head fluctuates greatly, high-quality printing can be performed on the printing medium.

Description of drawings

FIG. 1 is a diagram showing the configuration of a printing system according to a first embodiment.

FIG. 2 is a block diagram showing a schematic configuration of the thermal printer.

FIG. 3 is a graph showing voltage drop characteristics.

FIG. 4 is a diagram showing a timing chart of an AC converter.

FIG. 5 is a diagram showing a configuration of a thermal printer according to a second embodiment.

detailed description

first embodiment

FIG. 1 is a diagram showing the configuration of a printing system 1 . The printing system 1 shown in FIG. 1 includes a thermal printer 4, and an AC converter 3 (power supply device) that covers a power supply circuit with a frame. The power supply circuit is composed of a primary side circuit 3A and a primary side circuit 3A in order to supply power to the thermal printer 4. The secondary side circuit 3B is configured.

The AC converter 3 is connected to the commercial AC power supply 2 via a cable, for example, rectifies, smoothes, and converts the commercial AC power supply 2 of 100 volts, and supplies 24 volts of direct current to the thermal printer 4 via the cable. The AC adapter 3 is configured to be detachable from the thermal printer 4 via a connector.

The AC converter 3 performs overcurrent protection to protect the load so as not to output an overcurrent when an abnormality such as a short circuit or an overload occurs. For this overcurrent protection, it is conceivable to set the characteristics of the AC converter 3 to, for example, a characteristic in which the output voltage slowly decreases as the load current increases, that is, the so-called "ヘ" character (in which the output current is taken as the horizontal axis and the output voltage is taken as the horizontal axis). In the graph on the vertical axis, the characteristic of a line similar to the character "ヘ" in Japanese katakana characters)" drop characteristic (first voltage drop characteristic) is plotted. In addition, for example, a so-called "F-shape" drop characteristic (second and third voltage drop characteristics).

The thermal printer 4 conveys and prints an unillustrated heat-sensitive roll paper (printing medium) housed in a main body casing.

FIG. 2 is a block diagram showing a schematic configuration of the thermal printer 4 .

As shown in FIG. 2 , the thermal printer 4 includes a thermal line head 42 in which a large number of heating elements (printing elements) 41 are linearly arranged. The arrangement direction of the heating elements 41 in the line thermal head 42 is a direction perpendicular to the conveying direction of the heat-sensitive web. The line thermal head 42 is fixed. The thermal printer 4 applies heat to the printing surface of the heat-sensitive roll paper by energizing the heating element 41 of the line thermal head 42 to print characters, images, and the like. When the printing duty ratio is high such that many heating elements 41 are driven, a large load current flows instantaneously.

The thermal printer 4 includes a print head drive unit 43 that controls energization to the heating element 41 of the line thermal head 42 . Furthermore, the thermal printer 4 includes a conveyance roller (not shown) for conveying the heat-sensitive roll paper, and a conveyance motor 44 for driving the conveyance roller. The print head drive unit 43 and the conveyance motor 44 are connected to a power supply unit 45 , and are operated upon receiving power supply from the power supply unit 45 .

In addition, the print head drive unit 43 and the conveyance motor 44 are connected to the control unit 46 . The control unit 46 controls the print head driving unit 43 so as to energize each heating element 41 included in the line thermal head 42 . In addition, the control unit 46 controls the transport motor 44 so as to transport the heat-sensitive roll paper by transport rollers. While conveying the heat-sensitive web, the fixed line thermal head 42 is driven to print on the heat-sensitive web.

The power supply unit 45 is connected to the AC converter 3 and receives DC current from the AC converter 3 .

In the line thermal head 42 of the thermal printer 4 , the number of heating elements 41 to be energized varies depending on the content to be printed. As an index of the number of heating elements 41 to be energized, a printing duty ratio indicating the ratio of the set printable dots to the actually printed dots in a given printing area can be used.

For example, when the thermal printer 4 prints print data with a high printing duty ratio, since the number of the heating elements 41 that are energized among the heating elements 41 included in the line thermal head 42 is large, the AC The load current flowing from the converter 3 to the thermal printer 4 increases. In this case, if the characteristic of the AC converter 3 is the above-mentioned "ヘ-shaped" drop characteristic, the output voltage will drop as the load current increases. Furthermore, even when the load current exceeds the rated current, power may be supplied from the AC converter 3 to the thermal printer 4, and there is concern about whether overcurrent protection can be reliably realized.

On the other hand, in the above-mentioned example, in the case where the characteristic of the AC converter 3 is the above-mentioned "F-shaped" drop characteristic, when the load current increases to reach a specific current value, the "F-shaped" drop characteristic , the output voltage drops as the load current decreases. When the control unit 46 detects a drop in the supply voltage, it detects a low voltage error in order to prevent a malfunction, and when the supply voltage becomes lower, it may shut down the thermal printer 4 in some cases. That is, even if an abnormality such as a short circuit or an overload does not occur, the thermal printer 4 may stop or shut down due to an error. In addition, in general printers, in order to recover from low voltage errors and shutdowns, it is necessary to turn off/on the power switch, and the same applies to the thermal printer 4 .

Therefore, the AC converter 3 of the present embodiment has a "ヘ-shaped" drop characteristic and a "フ-shaped" drop characteristic as the voltage drop characteristic, and has a configuration for switching the voltage drop characteristic according to the load current.

The AC converter 3 shown in FIG. 1 is connected to a commercial AC power supply 2 to a primary side circuit 3A, and is connected to a thermal printer 4 to a secondary side circuit 3B. The AC converter 3 converts the input voltage Vin input from the commercial AC power supply 2 to the primary side circuit 3A into an output voltage Vout, and outputs the output voltage Vout to the thermal printer 4 .

Primary side circuit 3A includes rectification circuit S31 connected to commercial AC power supply 2 , electrolytic capacitor C31 , primary winding L1 of transformer TR, and switching circuit K11 . In the primary side circuit 3A, the input voltage Vin which is an AC voltage is rectified and smoothed by the rectification circuit S31 and the electrolytic capacitor C31. Furthermore, it is comprised as the switching type circuit which controls the voltage applied to the primary winding L1 by the switching operation of the switching circuit K11.

The switch circuit K11 includes a control IC (Integrated Circuit) 111 and a transistor Q1. In this embodiment, a FET is used as the transistor Q1. The control IC 111 has an output terminal connected to the gate of the transistor Q1. The control IC 111 changes the voltage input to the gate of the transistor Q1 based on the output of the photocoupler Pc described later. Specifically, the control IC 111 outputs a pulse voltage to the gate of the transistor Q1 to turn the transistor Q1 on and off, whereby the transistor Q1 performs a switching operation. The control IC 111 controls the on-off time of the transistor Q1 by controlling the pulse width based on the output of the photocoupler Pc.

The secondary side circuit 3B includes a secondary winding L2 which is a winding on the secondary side of the transformer TR, a rectifying element S32, and an electrolytic capacitor C32. When a voltage is applied to the primary winding L1 of the primary side circuit 3A, a voltage corresponding to the ratio of the number of windings of the primary winding L1 to the number of windings of the secondary winding L2 is induced in the secondary winding L2. The induced voltage of the secondary winding L2 is rectified and smoothed by the rectifying element S32 and the electrolytic capacitor C32 , and output to the thermal printer 4 .

Thus, when the voltage applied to the primary winding L1 changes due to the switching operation of the switching circuit K11, the voltage induced in the secondary winding L2 changes, and the output voltage Vout of the secondary side circuit 3B changes.

The secondary side circuit 3B includes a detection circuit K21 (detection unit) and a switching circuit K22 (switching unit) between the output terminal OUT and the output terminal GND.

The detection circuit K21 detects the output current output from the AC converter 3 to the thermal printer 4 , that is, the current value of the load current flowing to the load. The detection circuit K21 includes a resistor R1, a resistor R5, a resistor R6, and a comparator CU. One end of the resistor R1 is connected to the output terminal GND, and the other end is connected to the resistor R6. The resistor R6 and the resistor R5 are connected in series, and the resistor R5 is connected to the output terminal GND. That is, resistors R5, R6, and R1 are connected in series between the output terminal OUT and the output terminal GND.

Comparator CU is composed of an operational amplifier. The inverting input terminal (-) of the comparator CU is connected to the node P1 connecting the resistors R5 and R6, and the non-inverting input terminal (+) is connected to the output terminal GND. When the voltage detected by the inverting input terminal of the comparator CU is lower than the voltage detected by the non-inverting input terminal, the comparator CU inputs a signal of “High” level to a transistor Q2 described later. Also, when the voltage detected by the inverting input terminal is higher than the voltage detected by the non-inverting input terminal, the comparator CU inputs a signal of “Low” level to the transistor Q2.

The voltage detected by the inverting input terminal of comparator CU can be expressed by the following equation (1).

V(-)＝Vout/(R5+R6)···(1)

In the above formula, V(-) represents the voltage value of the voltage detected by the inverting input terminal. In addition, R5 represents the resistance value of the resistor R5, and R6 represents the resistance value of the resistor R5.

The voltage value of the voltage detected by the non-inverting input terminal of comparator CU can be represented by the following equation (2).

V(+)＝Iout×R1···(2)

In the above formula, V(+) represents the voltage value of the voltage detected by the non-inverting input terminal, and Iout represents the current value of the load current flowing to the load. In addition, R1 represents the resistance value of the resistor R1.

The switching circuit K22 includes a resistor R2, a resistor R3, a resistor R4, and a transistor Q2. The resistor R2 and the resistor R3 are connected in series, one end of the resistor R2 is connected to the output terminal OUT, and one end of the resistor R3 is connected to the output terminal GND via the resistor R1. One end of the resistor R4 is connected to the collector of the transistor Q2, and the other end of the resistor R4 is connected to the output terminal OUT. The emitter of transistor Q2 is connected to node P2 connecting resistor R2 and resistor R3. The output signal of the comparator CU is input to the base of the transistor Q2, and the transistor Q2 is turned off when the output signal of the comparator CU is "Low" level, and is turned on when the output signal of the comparator CU is "High" level. If the transistor Q2 is turned on, the resistor R2 and the resistor R4 are connected in parallel.

The shunt regulator SA (comparison circuit) internally includes a reference voltage circuit having a predetermined reference voltage such as 2.5 volts. A shunt regulator SA is connected at node P2. The shunt regulator SA is composed of an IC, for example. When the transistor Q2 is turned off, the voltage at the node P2 after the voltage at both ends of the secondary winding L2 is divided by the resistor R2 and the resistor R3 (hereinafter expressed as P2 voltage (output The divided voltage of the voltage Vout)) is compared with the reference voltage of the internal reference voltage circuit. Between the output of the shunt regulator SA and the output terminal OUT, the light emitting diode Dp of the photocoupler Pc (feedback circuit) is connected via a current limiting resistor.

When the P2 voltage exceeds the reference voltage, that is, when the output voltage Vout has risen, the shunt regulator SA flows current to the photocoupler Pc. Thereby, the light emitting diode Dp constituting the photocoupler Pc emits light. The light emitted from the light emitting diode Dp is received by the phototransistor Qp constituting the photocoupler Pc together with the light emitting diode Dp. Then, when the phototransistor Qp receives light, a feedback current flows between the collector and the emitter of the phototransistor Qp. Based on this feedback current, the control IC 111 controls the pulse output to the transistor Q1 so as to reduce the voltage applied to the primary winding L1, thereby reducing the output voltage Vout.

On the other hand, when the P2 voltage is lower than the reference voltage, that is, when the output voltage Vout has dropped, the shunt regulator SA does not allow current to flow to the photocoupler Pc. Therefore, no feedback current flows between the collector and the emitter of the phototransistor Qp. Accordingly, the control IC 111 controls the transistor Q1 to increase the voltage applied to the primary winding L1, thereby increasing the output voltage Vout.

In this way, the shunt regulator SA lowers the output voltage Vout when the P2 voltage exceeds the reference voltage, and raises the output voltage Vout when the P2 voltage is lower than the reference voltage. That is, the shunt regulator SA controls the output voltage Vout such that the P2 voltage is equal to the reference voltage. When the transistor Q2 is turned off, the resistor R2 and the resistor R3 are a voltage divider circuit for the output voltage Vout. The shunt regulator SA controls the current flowing to the light emitting diode Dp of the photocoupler Pc by controlling the P2 voltage, which is the divided voltage at this time, to be equal to the internal reference voltage of the internal reference voltage circuit. Therefore, the AC converter 3 can change the output voltage Vout through the voltage dividing circuit by the resistor R2 and the resistor R3, the shunt regulator SA, the photocoupler Pc, and the switch circuit K11. When the transistor Q2 is turned on, the resistors R2 and R4 connected in parallel, and the resistor R3 connected in series with them are the voltage divider circuit of the output voltage Vout, and the voltage of the node P2 between the resistor R2 and the resistor R4 and the resistor R3 is a voltage divider .

The divided voltage input to the shunt regulator SA differs depending on whether the transistor Q2 is turned on or off. As described above, the shunt regulator SA controls the output voltage Vout by controlling the P2 voltage to be equal to the internal reference voltage. When the transistor Q2 is turned off, the voltage of P2 is the voltage obtained by dividing the output voltage Vout by the resistor R1 , the resistor R2 and the resistor R3 . Hereinafter, for simplicity of description, the voltage across the resistors R2 and R3 connected in series will be referred to as the voltage Vout′. The voltage Vout' is a rectified and smoothed voltage induced by the secondary winding L2.

The output voltage is represented by equations (3) and (4) shown below.

Assuming that the voltage Vout' when the transistor Q2 is turned off is the voltage Vout1', the voltage Vout1' is expressed by the following equation (3).

Vout1'=Vref×(R2+R3)/R3···(3)

In the above formula, Vref represents the voltage value of the internal reference voltage of the shunt regulator SA, R2 represents the resistance value of the resistor R2, and R3 represents the resistance value of the resistor R3. In this embodiment, the output voltage Vout when the transistor Q2 is turned off is set to 24 volts, and the voltage Vout1' is determined by the output voltage Vout and the value of the resistor R1.

On the other hand, assuming that the voltage Vout' when the transistor Q2 is turned on is the voltage Vout2', the voltage Vout2' is expressed by the following equation (4). When the transistor Q2 is turned on, the voltage at the node P2 between the resistors R2 and R4 connected in parallel and the resistor R3 connected in series with them is a divided voltage of Vout.

Vout2'=Vref×((R2×R4/(R2+R4))+R3)/R3··(4)

In the above formula, R4 represents the resistance value of the resistor R4. In this embodiment, the output voltage Vout when the transistor Q2 is turned on is 20 volts, and the voltage Vout2' is determined by the output voltage Vout and the value of the resistor R1.

3 is a graph showing the voltage drop characteristic of the AC converter 3 , the vertical axis represents the voltage value of the voltage Vout′, and the horizontal axis represents the current value of the load current Iout flowing to the thermal printer 4 . In the figure, Ve' represents the voltage value of the voltage Vout' corresponding to the threshold value of the output voltage Vout at which the thermal printer 4 becomes a low-voltage error, and Ve'=17 volts in the present embodiment.

When the current flowing to the thermal printer 4 increases, the voltage Vout' falls, and the output voltage Vout falls accordingly (first voltage drop characteristic). The point at which the voltage Vout′ turns to drop is set as the voltage drop point O1, and the value of the load current Iout at the voltage drop point O1 is set as I1.

When the current value further increases, the voltage drop characteristic of the AC converter 3 switches. Let the point at which switching of the voltage drop characteristic occurs be a characteristic switching point O2, and let the current value of the load current Iout at the characteristic switching point O2 be I2. Furthermore, in FIG. 3 , the current value I3 represents the value of the load current Iout at the overcurrent protection point O3 at which the overcurrent protection is started in the AC converter 3 .

As shown in FIG. 3 , the AC converter 3 exhibits a "ヘ-shaped" drop characteristic in the region where the load current Iout is less than I2, and a "フ-shaped" drop characteristic when the load current Iout exceeds I2.

That is, when the load current Iout increases to exceed the current value I1, the AC converter 3 gradually drops the voltage Vout' from the voltage Vout1' at the voltage drop point O1 according to the "ヘ-shaped" drop characteristic.

If the load current Iout further increases to exceed I2, in the detection circuit K21 of the AC converter 3, the input voltage V(+) of the non-inverting input terminal of the comparator CU becomes larger than the input voltage V of the inverting input terminal. (-). Since the input voltage V(+)>input voltage V(-), the level of the signal output from the comparator CU to the base of the transistor Q2 becomes "High".

If it is described in detail, when the value of the load current Iout is greater than I2, the relationship between the input voltage V(+) and the input voltage V(-) is V(+)>V(-), the relationship of the following formula (5) established.

R1×Iout＞Vout/(R5+R6)···(5)

That is, when the current value of the load current Iout is I2, V(+)=V(-), and when the load current Iout is greater than I2, V(+)>V(-). Therefore, the signal output from the comparator CU to the transistor Q2 becomes "High" level.

In the switching circuit K22, when the input signal from the detection circuit K21 becomes "High" level, the transistor Q2 is switched from OFF to ON. Since the resistor R2 and the resistor R4 are connected in parallel by switching the transistor Q2 on, the voltage at the node P2 that is a divided voltage of the output voltage Vout changes. Thus, the shunt regulator SA controls the current flowing to the light-emitting diode Dp of the photocoupler Pc so that the P2 voltage is equal to the internal reference voltage, and is reflected in the feedback current to the control IC111 to control the pulse output to the transistor Q1. frequency, changing the output voltage Vout. The AC converter 3 performs constant voltage control through the shunt regulator SA so that the voltage becomes Vout2'. Taking this as an opportunity, the voltage drop characteristic was switched from the "ヘ" drop characteristic to the "フ" drop characteristic.

After the voltage drop characteristic is switched, that is, the current value of the load current Iout is between I2 and I3, the AC converter 3 suppresses the voltage drop (second voltage drop characteristic) according to the "F-shaped" drop characteristic, so that the voltage Vout' does not lower than Ve'. As shown in FIG. 3 , the second voltage drop characteristic drops with a gentler gradient than the first voltage drop characteristic.

In this way, by switching the voltage drop characteristic of the AC converter 3 to the "F-shaped" drop characteristic accompanying the increase in the load current Iout, it is possible to perform constant voltage control of the output voltage Vout so that the voltage Vout' is maintained at a voltage higher than Ve'. value. Therefore, even when the load current Iout flowing through the line thermal head 42 of the thermal printer 4 fluctuates greatly, power can be appropriately supplied to the thermal printer 4, and the low voltage of the thermal printer 4 can be prevented. errors or downtime.

Here, when the load power further increases and the current value of the load current Iout reaches I2, the AC converter 3 reduces the load current Iout and lowers the output voltage Vout according to the "F-shape" drop characteristic after switching (third voltage drop characteristics). Thus, overcurrent protection is performed.

In this way, when the transistor Q2 is turned on, the voltage drop characteristic of the AC converter 3 is switched from the "ヘ-shaped" drop characteristic to the "フ-shaped" drop characteristic. Through this switching, even when the load current Iout exceeds the current value within the normal printing range, overcurrent protection can be reliably executed.

Next, the operation of the AC converter 3 in the case of printing print data with a high print duty will be described. In the present embodiment, during printing of print data with a high print duty ratio, the load current Iout exceeding I1 at the voltage drop point O1 shown in FIG. 3 flows to the load.

FIG. 4 is a timing chart of the AC converter 3 when printing print data with a high print duty ratio. FIG. 4(A) is a timing chart of the output voltage Vout, and FIG. 4(B) is a timing chart of the load current Iout. In the figure, Vout1 is the value of the output voltage Vout when the transistor Q2 is off, and Vout2 is the value of the output voltage Vout when the transistor Q2 is on.

When the thermal printer 4 starts printing the print data with a high print duty ratio at time t1 , a large load current Iout flows from the AC converter 3 to the thermal printer 4 . The value of the load current Iout flowing at time t1 is larger than I1 at the voltage drop point O1 shown in FIG. 3 .

As the load current Iout increases at time t1, the AC converter 3 lowers the output voltage Vout according to the "ヘ-shaped" drop characteristic. At time t2, the voltage drop characteristic is switched from the "ヘ-shaped" drop characteristic to the "フ-shaped" drop characteristic. Accordingly, the voltage value of the output voltage Vout of the AC converter 3 is maintained at Vout2 after time t2.

As described above, the AC converter 3 controls the output voltage Vout so that the output voltage Vout does not fall below Ve according to the "F-shaped" drop characteristic after switching to the "F-shaped" drop characteristic. Here, Ve is the threshold value of the output voltage Vout at which the thermal printer 4 becomes a low voltage error. Therefore, even if the load current Iout flowing to the thermal printer 4 increases, it is possible to prevent a low voltage error, shutdown, etc. caused by a drop in the output voltage Vout supplied from the AC converter 3 to the thermal printer 4 .

In addition, when printing by the thermal printer 4 ends at time t3, the load current Iout flowing to the thermal printer 4 decreases. In the AC converter 3, as the load current Iout decreases, the transistor Q2 is turned off, and the voltage at the node P2, which is a divided voltage of the output voltage Vout, changes. Control the current flowing to the light-emitting diode Dp of the photocoupler Pc so that the P2 voltage is equal to the internal reference voltage, and reflect it in the feedback current to the control IC111 to control the frequency of the pulse output to the transistor Q1, and change the output voltage Vout. The shunt regulator SA restores the output voltage Vout of the AC converter 3 from Vout2 to Vout1 according to the change in the divided voltage, and outputs Vout1.

In this manner, the AC converter 3 can appropriately supply electric power even if the load on the thermal printer 4 increases by switching the voltage drop characteristic. Therefore, the thermal printer 4 can properly print even print data with a high print duty. In addition, the thermal printer 4 can stably perform printing without causing a low-voltage error or shutdown due to a drop in the supply voltage of the AC converter 3 . Also, as the thermal printer 4 finishes printing, the load current Iout decreases, and the output voltage Vout of the AC converter 3 automatically returns to Vout1, so that the power supply to the thermal printer 4 can be maintained in a stable state.

As described above, the AC converter 3 (power supply device) according to the present embodiment supplies a DC current to a load based on an AC current. The AC converter 3 includes a power supply circuit having a plurality of voltage drop characteristics of an output voltage with respect to a load current supplied to a load. The power supply circuit switches the voltage drop characteristic when the current value of the load current is in a specific state.

Accordingly, the AC converter 3 can appropriately supply electric power even when the load fluctuates greatly.

In addition, the power supply circuit of the AC converter 3 has a "ヘ-shaped" drop characteristic (first voltage drop characteristic) showing a characteristic in which the output voltage drops with an increase in the load current, and a slope that is gentler than (the first voltage drop characteristic) The "F-shaped" drop characteristic is composed of a characteristic (the second voltage drop characteristic) and a characteristic (the third voltage drop characteristic) that shows the output voltage drops with the drop of the load current.

As a result, the AC converter 3 can appropriately supply electric power and perform overcurrent protection by switching the voltage drop characteristic from the "ヘ-shaped" drop characteristic to the "f-shaped" drop characteristic.

Furthermore, the power supply circuit of the AC converter 3 includes a detection circuit K21 (detection unit) that detects that the load current is in a specific state, and a switching circuit K22 (switching unit) that switches the voltage drop characteristic based on the detection result of the detection circuit K21. ).

Thereby, even when the fluctuation of the load current is large, it is possible to supply appropriate electric power by detecting the load current and switching the voltage drop characteristic.

In addition, in the power supply circuit of the AC converter 3, the detection circuit K21 switches the output of the detection result when the current value of the load current reaches a specific current value, and the switching circuit K22 switches the voltage drop according to the output of the detection circuit K21. characteristic.

As described above, when the current value of the load current Iout is I2, the voltage drop characteristic is switched. By switching, constant voltage control is performed so that Vout2 is output. This Vout2 is set to a value higher than Ve which is the voltage value of the low voltage error. Thus, by switching the voltage drop characteristic at I2, even if the load current Iout increases, the AC converter 3 can appropriately supply power without causing a low voltage error or even a shutdown of the power supply.

In addition, the power supply circuit of the AC converter 3 is a switching system. The power supply circuit includes a primary-side circuit 3A including a switch circuit K11 , and a secondary-side circuit 3B coupled to the primary-side circuit 3A for supplying a DC current to a load. The secondary side circuit 3B includes a reference voltage circuit, a voltage divider circuit for dividing the output voltage Vout of the secondary side circuit 3B, and compares the divided voltage of the voltage divider circuit with the reference voltage of the internal reference voltage circuit. The shunt regulator SA (comparison circuit), and the photocoupler Pc (feedback circuit) that feeds back the comparison result of the shunt regulator SA to the switch circuit K11. The switching circuit K22 of the AC converter 3 changes the divided voltage by changing the combination of resistors constituting the voltage dividing circuit, thereby changing the switching frequency of the power supply and switching the voltage drop characteristic.

Thereby, by changing the reference voltage, the voltage drop characteristic can be switched from the "ヘ-shaped" drop characteristic to the "フ-shaped" drop characteristic, and appropriate electric power can be supplied.

In addition, the AC converter 3 is formed by covering the power supply circuit with a housing.

Accordingly, it is possible to adapt a power supply circuit that switches between the “ヘ-shaped” drop characteristic and the “フ-shaped” drop characteristic to the AC converter 3 .

2nd embodiment

FIG. 5 is a diagram showing a configuration of a thermal printer 4A according to a second embodiment to which the present invention is applied.

The thermal printer 4A is the same as the thermal printer 4 described in the above-mentioned first embodiment, and includes a line thermal head 42 having a heating element 41, a print head drive unit 43, a conveyance motor 44, a power supply unit 45, and a control unit. Part 46 of the printer.

The thermal printer 4A incorporates a power supply circuit 30 equivalent to the AC converter 3 described in the first embodiment. Like the AC converter 3 , the power supply circuit 30 includes a primary side circuit 3A and a secondary side circuit 3B, and outputs the DC current generated by the secondary side circuit 3B to the power supply unit 45 . The output voltage Vout and the load current Iout output from the secondary side circuit 3B to the power supply unit 45 vary in the same manner as the output voltage Vout and the load current Iout described in the first embodiment.

The thermal printer 4A is directly connected to the commercial AC power supply 2 , and the primary side circuit 3A of the power supply circuit 30 is connected to the commercial AC power supply 2 inside the thermal printer 4A.

A thermal printer 4A according to the second embodiment has an AC adapter 3 ( FIG. 1 ) externally connected to the thermal printer 4 ( FIG. 1 ) built in the printer. In this configuration, similarly to the above-described first embodiment, even when the load on the line thermal head 42 increases, it is possible to prevent a voltage drop that would cause a low-voltage error. Therefore, the thermal printer 4A can perform a printing operation stably regardless of the printing duty ratio of the content to be printed.

In addition, said each embodiment is only one form which shows this invention after all, It can deform|transform and apply arbitrarily within the range of this invention. For example, in the first embodiment, the power supply device is illustrated as the AC converter 3 , but it is not limited thereto, and other power supply devices may be used as long as the power supply device changes the output voltage Vout. In addition, for example, it may be a device that is connected to a plurality of printers and supplies power. In addition, thermal printers 4 and 4A may be connected to a host computer (not shown), and may print images or characters based on data input from the host computer. In this case, the configuration of the host and the configuration related to the connection between the thermal printers 4 and 4A and the host are arbitrary.

In addition, for example, in this embodiment, the load supplied with electric power from the AC converter 3 is illustrated as the thermal printer 4, but the present invention is not limited thereto. For example, the thermal printer 4 may be another printer such as an inkjet printer equipped with a line head that is fixed during printing. In addition, the load is not limited to a printer, but may be an electronic device or a motor having other functions, and the present invention can be applied as long as the load is supplied with power from the AC converter 3 . Furthermore, the circuit configurations shown in FIG. 1 and FIG. 5 are merely examples, and configuration changes such as replacing the illustrated circuit elements with ICs of the same number or different numbers are possible, and can be arbitrarily changed within the scope of the present invention. There is no doubt about making changes.

Claims (9)

1. A power supply device, characterized in that, The power supply unit is a power supply unit for a printer that supplies a direct current to a load based on an alternating current, The power supply device has a power supply circuit having at least three voltage drop characteristics of an output voltage with respect to a load current supplied to the load, The power supply circuit switches the voltage drop characteristic when the current value of the load current is in a specific state. 2. The power supply device according to claim 1, wherein: The power supply circuit has a first voltage drop characteristic, a second voltage drop characteristic, and a third voltage drop characteristic, the first voltage drop characteristic indicates a characteristic in which the output voltage drops with an increase in the load current, and the second The voltage drop characteristic indicates a characteristic in which the output voltage decreases with an increase in the load current at a gentler gradient than the first voltage drop characteristic, and the third voltage drop characteristic indicates a decrease in the output voltage with a decrease in the load current. characteristics of the output voltage drop. 3. The power supply device according to claim 2, wherein: The power supply circuit switches from the first voltage drop characteristic to the second voltage drop characteristic as the load current increases, and switches to the third voltage drop characteristic as the load current decreases. 4. The power supply device according to claim 1, wherein: The power supply circuit has: a detection unit that detects that the load current is in the specified state; and A switching unit that switches the voltage drop characteristic based on a detection result of the detection unit. 5. The power supply device according to claim 4, wherein: The detection unit switches the output when the current value of the load current reaches a specific current value, The switching unit switches the voltage drop characteristic based on the output of the detection unit. 6. The power supply device according to claim 4, wherein: The power supply circuit is a switching system including a switching circuit, and the switching unit switches the voltage drop characteristic by changing a frequency of the switching circuit when a current value of the load current becomes a specific current value. . 7. The power supply device according to claim 6, wherein: The power circuit has: a primary side circuit comprising said switching circuit; and a secondary circuit coupled to the primary circuit for supplying the direct current to the load, On the secondary side circuit side, there are: Reference voltage circuit; a voltage dividing circuit that divides the output voltage of the secondary side circuit; a comparison circuit that compares the divided voltage of the voltage dividing circuit with a reference voltage; and a feedback circuit that changes the frequency of the switching circuit based on a comparison result of the comparison circuit, The switching unit switches the voltage drop characteristic by changing the divided voltage of the voltage dividing circuit. 8. The power supply device according to claim 1, wherein: The power supply device is an AC converter type in which the power supply circuit is covered by a housing. 9. A printer, characterized in that it has: a printing head having a plurality of printing elements fixed in a direction crossing the transport direction of the printing medium; and a power supply circuit that supplies a direct current to the print head based on an alternating current, The power supply circuit has at least three voltage drop characteristics with respect to the output voltage of the load current supplied to the print head, and the voltage drop characteristics are switched when the current value of the load current is in a specific state. .