JP2002272109A - Power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power supply, in which the variation in the output voltage level from a plurality of power supply circuits can be suppressed. SOLUTION: Each power supply circuit 1 in the power supply comprises a transformer 3, a switching transistor 4 connected with a primary winding T1 of the transformer 3, a primary control circuit 5 for turning on/off the switching transistor 4, a phototransistor 6a in a photocoupler 6 for switching the operation of the primary control circuit 5, a rectifying circuit 7 connected across a secondary winding T2 of the transformer 3, a light-emitting diode 6b in the photocoupler 6, a resistive element R1, and a diode D1 connected in series between the output terminal of the rectifying circuit 7 and the ground terminal, and a reference voltage source 2. Since the reference voltage source 2 is shared among a plurality of power supply circuits 1, secondary output voltage of each power supply circuit 1 can be controlled accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a power supply device for driving a load using a plurality of power supply circuits.

[0002]

2. Description of the Related Art A print head of an ink jet printer is provided with a large number of nozzles, and these nozzles eject ink at the same time in plurals. The drive voltage of the print head is higher than other electronic components and often exceeds 40V. On the other hand, a voltage of about 3 to 5 V is supplied to general electronic components. As described above, since the inkjet printer requires a plurality of types of DC voltages having different voltage levels,
Normally, a DC-DC converter or the like is used to convert the DC voltage level.

FIG. 3 is a circuit diagram of a conventional power supply device for an ink jet printer. The power supply device of FIG.
A switching transistor 4 connected to the primary winding of the transformer 3; a primary control circuit 5 for controlling on / off of the switching transistor 4; and a photocoupler for switching whether or not to operate the primary control circuit 5 6, a rectifier circuit 7 connected between the secondary windings of the transformer 3, and a light emitting diode in the photocoupler 6 connected in series between an output terminal of the rectifier circuit 7 and a ground terminal. 6b and a Zener diode 13.

In the power supply device shown in FIG. 3, when the output voltage on the secondary side falls below the reference voltage, the light emitting diode 6b emits light, the phototransistor 6a turns on, and the switching transistor 4 on the primary side turns on. Conversely, when the output voltage on the secondary side falls below the reference voltage, the switching transistor 4 on the primary side is turned off, and the output voltage on the secondary side decreases. By repeating such control, the output voltage on the secondary side is controlled to a substantially constant level.

[0005]

Since a print head is provided with a large number of nozzles, it is not appropriate to supply a power supply voltage to all the nozzles with only one power supply circuit.
Normally, multiple power supply circuits are connected in parallel in the power supply,
A plurality of nozzles are driven by the plurality of power supply circuits.

However, since a current detection resistor is connected to each power supply circuit, and a difference occurs in the amount of load due to manufacturing variations of the nozzles, the power supply voltage supplied from each power supply circuit to each nozzle is not constant. was there. If a difference occurs in the power supply voltage, the amount of ink ejected from the nozzles, the ejection speed, and the like are affected, so that print quality may be degraded.

SUMMARY OF THE INVENTION The present invention has been made in view of the foregoing, and an object of the present invention is to provide a power supply device capable of suppressing variations in voltage levels output from a plurality of power supply circuits. .

[0008]

In order to solve the above-mentioned problems, the present invention relates to a power supply apparatus having a plurality of power supply circuits connected in parallel, wherein a reference voltage for supplying a reference voltage to each of the plurality of power supply circuits is provided. A voltage source, each of the power supply circuits includes a transformer, a rectifier circuit connected between secondary windings of the transformer, and an output terminal of the rectifier circuit and a reference voltage terminal of the reference voltage source. Connected in series to
It has a light emitting diode, a resistance element, and a diode, and a switching element connected to a primary winding of the transformer, and the switching element is on / off controlled by a current flowing through the light emitting diode.

In the present invention, since the plurality of power supply circuits share the reference voltage source, the secondary output voltage of each power supply circuit can be accurately controlled.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a power supply device according to the present invention will be specifically described with reference to the drawings. FIG. 1 is a circuit diagram of one embodiment of a power supply device according to the present invention, and shows a configuration of a power supply device for an ink jet printer, for example. The power supply device of FIG. 1 has a plurality of power supply circuits 1 connected in parallel. The feature of the power supply device of FIG.
Is that the reference voltage source 2 is shared.

Each power supply circuit 1 in the power supply device shown in FIG. 1 includes a transformer 3, a switching transistor 4 connected to a primary winding T1 of the transformer 3, and a primary-side control for controlling on / off of the switching transistor 4. The circuit 5 and a phototransistor (photodiode) in the photocoupler 6 for switching whether or not to operate the primary side control circuit 5
6a, a rectifier circuit 7 connected between the secondary winding T2 of the transformer 3, and a light emitting diode 6 in the photocoupler 6 connected in series between the output terminal of the rectifier circuit 7 and the ground terminal.
b, resistance element R1, diode D1, and reference voltage source 2
And The reference voltage source 2 is shared by a plurality of power supply circuits 1 and is configured by connecting a plurality of zener diodes D1 in series.

Next, the operation of the power supply device shown in FIG. 1 will be described.
Since an AC voltage is applied to the primary winding T1 of the transformer 3, an induced electromotive force is generated in the secondary winding T2, and this electromotive force is converted into a DC voltage by the rectifier circuit 7. When the secondary output voltage falls below the reference voltage, a current flows through the light emitting diode 6b in the photocoupler 6, and the switching transistor 4 is turned on. When the secondary output voltage becomes equal to or higher than the reference voltage, the switching transistor 4 is turned off. By repeating such an operation, the secondary output voltage is controlled to a substantially constant voltage (for example, 42 volts).

The power supply device shown in FIG. 1 has a plurality of power supply circuits 1 connected in parallel.
Sharing. Therefore, the voltage at the connection point between the reference voltage source 2 and the diode D1 in each power supply circuit 1 becomes the same voltage. For this reason, the variation element of the secondary-side output voltage of each power supply circuit 1 is only the light emitting diode 6b, the resistance element R1, and the diode D1. Since all are passive elements, the voltage fluctuation is small. Therefore, the power supply device of FIG. 1 can control the secondary output voltage of each power supply circuit 1 to be substantially constant. Therefore, when driving a print head having a large number of nozzles, a substantially equal power supply voltage can be supplied to each nozzle,
Printing quality can be improved.

FIG. 1 shows an example in which two power supply circuits 1 are connected in parallel, but the number of power supply circuits 1 connected in parallel is not particularly limited. In the case of the present embodiment, the reference voltage source 2 is shared by all the power supply circuits 1 connected in parallel. As a result, the secondary output voltage of each power supply circuit 1 becomes substantially constant.
If one power supply circuit 1 drives too much load,
Problems such as a decrease in the output voltage of the power supply circuit 1 occur.
Therefore, it is desirable that the load amount driven by one power supply circuit 1 does not exceed a predetermined limit power value (for example, 240 VA). If it is necessary to drive a load exceeding this power value, it is desirable to increase the number of power supply circuits 1 and distribute the load among a plurality of power supply circuits 1 to drive the load.

As described above, in this embodiment, since the plurality of power supply circuits 1 share the reference voltage source 2, each power supply circuit 1
Can be accurately controlled. Therefore,
When a print head having a large number of nozzles is driven, substantially the same voltage can be supplied to each nozzle. Further, by sharing the reference voltage source 2, the number of components can be reduced, and the cost of components and the size of the power supply device can be reduced.

In the case of the power supply device shown in FIG. 1, the secondary output voltage is detected by the photocoupler 6, and when the secondary output voltage falls below the reference voltage, the light emitting diode 6b in the photocoupler 6 is caused to emit light. Accordingly, the switching transistor 4 is turned on. For this reason, there is a possibility that the switching transistor 4 is repeatedly turned on and off frequently, so that power consumption is increased and noise is increased.

Therefore, the power supply device shown in FIG. 2 is devised so that the switching transistor 4 is not frequently turned on and off. Each power supply circuit in the power supply device of FIG. 2 includes a photocoupler 8, a resistor R2, and a switching transistor 9, which are connected in series between an output terminal of a rectifier circuit 7 in each power supply circuit and a ground terminal. It has a voltage detection circuit 10 for detecting the side output voltage, and a switching control circuit 11 for controlling ON / OFF of the switching transistor 9. Further, a phototransistor 8a in the photocoupler 8 is connected to the primary side control circuit 5, and when the phototransistor 8a is turned on, the switching transistor 4 is turned on.

When the voltage detection circuit 10 detects that the secondary output voltage has become lower than a predetermined voltage (for example, 42 volts), the switching control circuit 11 turns on the switching transistor 9 for a predetermined period from that time. I do. When the switching transistor 9 is turned on, the light emitting diode 8b in the photocoupler 8 emits light, and the switching transistor 4 is turned on. The switching transistor 4 is continuously turned on for a predetermined period.

As described above, by performing the control as shown in FIG. 2, the switching transistor 4 does not repeatedly turn on and off, so that power consumption can be reduced and noise generated from the switching transistor 4 can be suppressed.

In the above-described embodiment, the power supply device for an ink jet printer has been described. However, the present invention is applicable to power supply devices for various electric appliances.

In the above embodiment, there is no particular limitation on the number of power supply circuits 1 connected in parallel. Power supply circuit 1
Is not necessarily the same as that shown in FIG. 1 or FIG. Further, FIG. 1 illustrates an example in which the secondary output voltages of the power supply circuits 1 are equal, but different power supply voltages may be output from the power supply circuits 1. In this case, the resistance element R1 connected to the light emitting diode 6b
And the number of diodes D1 may be adjusted.

[0022]

As described above in detail, according to the present invention, since a plurality of power supply circuits connected in parallel share a reference voltage source, the secondary output voltage of each power supply circuit can be accurately controlled. Thus, a desired voltage can be supplied to the load. In addition, by sharing the reference voltage source, the number of components can be reduced, the product cost can be reduced, and the power supply device can be downsized.

In particular, when a print head having a large number of nozzles is driven, substantially the same power supply voltage can be supplied to each nozzle, so that print quality can be improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment of a power supply device according to the present invention.

FIG. 2 is a circuit diagram in which reduction in power consumption and noise reduction are taken into consideration.

FIG. 3 is a circuit diagram of a power supply device for a conventional inkjet printer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Power supply circuit 2 Reference voltage source 3 Transformer 4 Switching transistor 5 Primary control circuit 6,8 Photocoupler 6a, 8a Phototransistor 6b, 8b Light emitting diode 7 Rectifier circuit

Claims (4)

[Claims] 1. A power supply device comprising a plurality of power supply circuits connected in parallel, comprising: a reference voltage source for supplying a reference voltage to each of the plurality of power supply circuits; each of the power supply circuits includes a transformer; A rectifier circuit connected between the secondary windings; a light emitting diode, a resistor, and a diode connected in series between an output terminal of the rectifier circuit and a reference voltage terminal of the reference voltage source; A switching element connected to a primary winding of a transformer, wherein the switching element is on / off controlled by a current flowing through the light emitting diode. 2. The secondary output voltage of the plurality of power supply circuits is:
The power supply device according to claim 1, wherein the power supply device is used to drive a nozzle of a print head. 3. A secondary output voltage of said plurality of power supply circuits is:
The power supply device according to claim 1, wherein the power supply devices are controlled so that voltage levels are equal to each other. 4. The power supply device according to claim 1, wherein output powers of said plurality of power supply circuits are controlled so as not to exceed a predetermined limit power value.