JP2008312409A - Power supply device of electronic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power supply device capable of preventing smoking and ignition by suppressing an output voltage value even to comparatively small changes in an output current or an output voltage. <P>SOLUTION: On a secondary side of a switching power supply, the voltage at a point B on a transmission circuit in the vicinity of a load is monitored by a voltage detection circuit 20. When abnormality occurs, and the voltage at the point B is reduced, a voltage value input into a CPU 10 is reduced, and when the voltage value is detected to be equal to or lower than an abnormal threshold, a trigger signal is given to a low-voltage latch circuit 1. The low-voltage latch circuit 1 is put into a low-voltage supply state by this trigger signal, and this low-voltage state is given to the switching power supply. In the switching power supply, feedback processing is performed based on the given low-voltage state, and oscillation on a primary side is limited. As a result, the voltage value output from the secondary side is suppressed. Since the low-voltage latch circuit 1 continues to be operated even at this suppressed voltage value, the power supply is maintained while the low-voltage is supplied. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a power supply device for an electronic device, and more particularly to a power supply device that suppresses a DC voltage supplied to a secondary side when a relatively minor abnormality occurs.

  Conventionally, many power supply apparatuses that acquire a target DC voltage from a general-purpose AC voltage have been used. As such a power supply device, a switching power supply is generally used in order to obtain a stable DC voltage, and some have various functions so as to cope with a failure or the like.

  Patent Document 1 is a power supply device for an inkjet printer, and includes an overcurrent protection circuit that reduces a supply voltage when a load current on a secondary side rises above a predetermined value.

  Similarly, the power supply device of Patent Document 2 includes an overcurrent protection circuit that reduces the supply voltage when the load current on the secondary side rises above a predetermined value.

  Patent Document 3 is a power supply device for an antenna that detects an overcurrent on the secondary side and turns off the power supply circuit.

The power supply device of Patent Document 4 detects the output voltage on the secondary side, and controls the output to be stopped by the pull-up circuit on the primary side when this voltage value is detected.
Japanese Patent Application Laid-Open No. 2004-216771 Japanese Patent Laid-Open No. 11-46480 JP 2006-54833 A JP 2002-287575 A

  In each of the above-described conventional power supply devices, in order to detect an overcurrent without causing a false detection with the maximum current during normal operation, it is common to set the threshold of the overcurrent drawn from the power transformer to about twice the maximum current. Is. However, a short circuit after passing through a certain amount of resistance or circuit on the secondary side does not always result in a current value more than twice the maximum current in normal operation. Could not respond.

  Therefore, an object of the present invention is to reduce the output voltage value against a relatively small change in the output current or a change in the output voltage consisting of a minute circuit short circuit or the like, and an electronic device that can prevent smoke and fire. It is to provide a power supply device.

  The present invention provides a power transformer for outputting a general-purpose AC power supply voltage supplied from the primary side to each functional unit from the secondary side to a DC voltage having a target voltage value, and a secondary side corresponding to the target voltage value of the power transformer. The present invention relates to a power supply apparatus for an electronic device, which includes a feedback control unit that generates a feedback signal from the primary side to the primary side and controls oscillation of a power transformer on the primary side. In this power supply apparatus, target voltage monitoring means is installed on the secondary side of the power transformer. The target voltage monitoring means monitors the voltage value of the DC voltage, and outputs an abnormality detection signal when it detects that the voltage value is equal to or less than a preset abnormality threshold value. In addition, the power supply device includes voltage suppression control means for outputting a feedback signal from the feedback control unit that generates a DC voltage having a voltage value low enough to enable the operation of the target voltage monitoring means based on the abnormality detection signal. Prepare. At this time, the voltage suppression control means is configured by a latch circuit including a transistor that operates based on the abnormality detection signal.

  In this configuration, during normal operation, a control signal corresponding to the target voltage value is supplied to the primary side of the power transformer by the feedback control unit, and a stable DC voltage is output from the secondary side. On the other hand, when an abnormality occurs, control is performed by the abnormality detection signal so that the voltage suppression control unit generates a feedback signal that causes the secondary side voltage to decrease with respect to the primary side of the power transformer with respect to the feedback control unit. At this time, since the voltage suppression control means is realized by a simple structure of a latch circuit including a transistor, the voltage suppression control is performed without performing complicated control.

  In addition, the power supply device for an electronic device according to the present invention includes notification means for driving a low-voltage DC voltage generated based on the abnormality detection signal as a drive power supply.

  In this configuration, when an abnormal state occurs and the electronic device cannot perform normal operation, the abnormal state can be notified, and the user can easily and reliably recognize the abnormal state by this notification.

  In addition, the notification means of the power supply device of the electronic apparatus according to the present invention is a light emitting diode. In this configuration, the light emitting diode having a low driving voltage is used as the notification means, so that even when the voltage after suppression during abnormality is as low as about 3 V, the light emission notification can be reliably performed.

  According to the present invention, voltage suppression control at the time of abnormality can be performed by a simple circuit having a latch circuit. In other words, without using the over-current protection circuit that is more complicated and requires a large over-current for the operation shown in the conventional example, voltage suppression at the time of abnormality can be easily performed, and a relatively light short circuit Etc. can also be detected for voltage control. As a result, it is possible to prevent smoke and fire due to a relatively light short.

  A power supply device for an electronic apparatus according to a first embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 shows a schematic configuration of the electronic apparatus of the present embodiment.

  The electronic device shown in the present embodiment includes functional units A to D that receive a voltage supply from a general AC power source and are driven by a DC voltage, and the functional units A to D include a DC motor or the like. is there. In the present embodiment, there are four functional units A to D, but the number is not limited to this. This electronic device includes the above-described functional units A to D, a switching power supply, a DC-DC converter, regulators E and F, a CPU 10, a low voltage latch circuit 1, and a voltage detection circuit 20.

  Functional units A and B and a DC-DC converter are connected to the secondary side of the switching power supply via a predetermined circuit network, and a DC voltage having a predetermined voltage value (for example, 30 V) from the secondary side of the switching power supply. Is normally supplied as the target voltage. The functional units A and B normally operate with this normal target voltage. The DC-DC converter steps down the voltage on the secondary side of the switching power supply (for example, steps down from 30 V to 5 V) and supplies it to the functional unit C and the regulator E. The functional unit C normally operates with the stepped-down DC voltage. The regulator E rectifies the step-down voltage and supplies it to the functional unit D and the regulator F. The functional unit D normally operates with the rectified step-down voltage. The regulator F further rectifies the rectified step-down voltage and provides it to the CPU 10. The CPU 10 normally operates stably by the voltage rectified with high accuracy.

  For example, as illustrated in FIG. 1, the voltage detection circuit 20 detects a supply voltage to the functional unit A and supplies the detected voltage to the CPU 10. When the CPU 10 detects that the detection result of the voltage detection circuit 20 is abnormal, it outputs a trigger signal to the low voltage latch circuit 1. The low voltage latch circuit 1 latches to an extremely low voltage based on the trigger signal, and the latched extremely low voltage is applied to the switching power supply. The switching power supply reduces the output voltage on the secondary side of the switching power supply according to the extremely low voltage.

Next, a more specific circuit configuration and processing when an abnormality is detected will be described.
FIG. 2 is a circuit diagram showing the main configuration of the switching power supply device of this embodiment and the connection relationship with the CPU 10, the low voltage latch circuit 1, and the voltage detection circuit 20.
A transformer coil T11 is provided on the primary side of the power supply transformer TR of the switching power supply, and a transformer coil T21 is provided on the secondary side.

  Both ends of the transformer coil T11 of the power transformer TR are connected to connection terminals at both ends of the AC power supply Vin via a diode bridge DB which is a rectifier circuit. A series circuit of a switch element Q0 and a resistor R0 is connected between one end of the transformer coil T11 and the diode bridge DB, and a connection point between the diode bridge DB and the resistor R0 is a ground. It is connected to the. The switch element Q0 performs switching control based on an output signal from a photocoupler described later.

  The anode of the diode D1 is connected to one end of the transformer coil T21, and the other end of the transformer coil T21 is connected to the ground. The cathode of the diode D1 is connected to a load corresponding to the functional unit shown in FIG. 1 through a predetermined network. The cathode of the diode D1 is grounded via the capacitor C1. The cathode of the diode D1 is connected to the light emitting diode of the photocoupler PC. The light generated from the light emitting diode of the photocoupler PC is received by the phototransistor, and a control signal corresponding to the amount of received light is given to the switch element Q0.

  In addition, a series circuit including a resistor R3 and a resistor R4 is connected to the cathode of the diode D1, and the end of the series circuit opposite to the diode D1 is grounded. The base of the transistor Tr0 is connected to the connection point between the resistors R3 and R4, and the emitter of the transistor Tr0 is grounded via a Zener diode. The collector of the transistor Tr0 is connected to the light emitting diode of the photocoupler PC through the resistor R1, and is connected to the low voltage latch circuit 1 through the resistor R5.

  Further, a branch is made between the cathode of the diode D1 and the light emitting diode of the photocoupler PC, and a resistor R2 is connected. The resistor R2 is connected to a connection point A between the emitter of the transistor Tr0 and the Zener diode.

  A voltage detection circuit 20 is connected to a predetermined point B on the voltage supply line near the load. The voltage detection circuit 20 includes resistors R6 and R7 connected in series between a predetermined point B and the ground, a connection point between the resistors R6 and R7, and a resistor R8 connected between the CPU 10. Prepare. With such a configuration, the voltage detection circuit 20 detects the DC voltage value at the predetermined point B, that is, the DC voltage value in the vicinity of the load supplied to the load, and supplies it to the CPU 10.

  The low voltage latch circuit 1 that is a feature of the present invention includes transistors Tr11 and Tr12, resistors R11 and R12, and a capacitor C10. The transistor Tr11 is an NPN transistor, the base is connected to the CPU 10, and the emitter is grounded. The base of the transistor Tr11 is connected to the ground through the capacitor C10, and is connected to the collector of the transistor Tr12, which is a PNP transistor, through the resistor R12. The collector of the transistor Tr11 is connected to the base of the transistor Tr12, and is connected to the resistor R5 of the switching power supply via the resistor R11. The emitter of the transistor Tr12 is connected to the resistor R5 side in the resistor R11.

  With such a circuit configuration, when a trigger signal having a predetermined voltage value is input from the CPU 10, the transistor Tr11 is turned on, the base of the transistor Tr12 is grounded, and the transistor Tr12 is turned on. As a result, the resistor The low voltage latch circuit 1 side of R5 is approximately 0V (approximately 0.6V due to transistor offset).

In the above configuration, the secondary side of the switching power supply is suppressed to a low voltage during detection as described above.
When some circuit leak occurs and the voltage at point B on the transmission circuit near the load decreases (for example, about 20% in voltage value), the voltage value output from the voltage detection circuit 20 to the CPU 10 also decreases. . The CPU 10 outputs a trigger signal to the low voltage latch circuit 1 when detecting that the input voltage value is equal to or less than a preset abnormality threshold value (for example, the voltage value is about 20% of the normal voltage value). The low voltage latch circuit 1 supplies an extremely low voltage to the switching power supply by the circuit operation described above. The supply of this extremely low voltage changes the current value fed back to the primary side via the follower coupler PC, and the primary side oscillation is limited by the switch element Q0. As a result, the voltage value output to the secondary side is reduced to, for example, about 10% of the normally supplied voltage value. At this time, since the voltage value output from the secondary side is not completely 0 V, the voltage detection circuit 20 and the CPU 10 can continuously detect the low voltage state and supply it to the low voltage latch circuit 1. . As a result, the low voltage suppression state can be continuously maintained due to the occurrence of an abnormality, and smoke and fire can be prevented at the load. In this case, as a main configuration, suppression control can be performed by a latch circuit having a simple configuration including two transistors, two resistors, and one capacitor.

Next, a power supply device for an electronic apparatus according to a second embodiment will be described with reference to FIG.
FIG. 3 is a circuit diagram showing the main configuration of the switching power supply device of the present embodiment and the connection relationship between the CPU 10, the low voltage latch circuit 1, the voltage detection circuit 20, and the notification circuit 30.
The power supply device of this embodiment is obtained by adding a notification circuit 30 to the first embodiment.

  The notification circuit 30 has the same configuration as the low voltage latch circuit 1, and the transistors Tr11 and Tr12 of the low voltage latch circuit 1 correspond to the transistors Tr31 and Tr32 of the notification circuit 30, respectively. The resistors R11 and R12 of the low voltage latch circuit 1 correspond to the resistors R31 and R32 of the notification circuit 30, and the capacitor C10 of the low voltage latch circuit 1 corresponds to the capacitor C30 of the notification circuit 30.

  The resistor 31 of the notification circuit 30 corresponding to the resistor R11 of the low voltage latch circuit 1 is connected to the cathode of the light emitting diode, and the anode of the light emitting diode is connected to the point B on the transmission circuit near the load. .

  With this configuration, when an abnormal voltage is detected as described above, the cathode side of the light emitting diode of the notification circuit 30 becomes approximately 0 V, and the light emitting diode is turned on. Even if the output on the secondary side is reduced, the LED continues to light because the drive voltage of the light emitting diode itself is low. Thereby, generation | occurrence | production of abnormal voltage can be notified to a user. The notification circuit 30 is not limited to a light emitting diode, and a light emitting element or a sound emitting element driven at a low voltage can also be used.

It is a figure which shows schematic structure of the electronic device of embodiment of this invention. 1 is a circuit diagram illustrating a main configuration of a switching power supply device according to a first embodiment and a connection relationship between a CPU 10, a low voltage latch circuit 1, and a voltage detection circuit 20. FIG. It is a circuit diagram which shows the main structure of the switching power supply device of 2nd Embodiment, and the connection relationship with CPU10, the low voltage latch circuit 1, the voltage detection circuit 20, and the notification circuit 30.

Explanation of symbols

1-low voltage latch circuit, 10-CPU, 20-voltage detection circuit, 30-notification circuit

Claims (3)

A general-purpose AC power supply voltage supplied from the primary side, a power transformer that outputs a DC voltage of a target voltage value from the secondary side to each functional unit, and a secondary side to a primary side according to the target voltage value of the power transformer A feedback control unit that generates a feedback signal and controls oscillation of the power transformer on the primary side,
A target voltage monitoring unit that is installed on the secondary side of the power transformer, monitors the voltage value of the DC voltage, and outputs an abnormality detection signal when detecting that the voltage value is equal to or lower than a preset abnormality threshold value; ,
Based on the abnormality detection signal, the latch circuit includes a transistor that operates based on the abnormality detection signal, and generates a DC voltage having a voltage value that is low enough to allow the target voltage monitoring unit to operate. Voltage suppression control means for performing control to output a feedback signal from the feedback control unit;
A power supply device for electronic equipment.   The power supply device for an electronic device according to claim 1, further comprising a notification unit configured to drive the low-voltage DC voltage generated based on the abnormality detection signal as a drive power supply.   The electronic apparatus power supply device according to claim 2, wherein the notification unit is a light emitting diode.

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