JP2012221143A - Electric power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power supply in which cost can be reduced and an occupied area can be decreased.SOLUTION: A CPU power supply 140 is used along with an LED backlight circuit 116 for generating operation voltage of an LED 112 which is mounted on a vehicle and used as a backlight of an LCD module 110. The CPU power supply 140 includes: an electric power supply circuit 150 for generating constant output voltage from input voltage with permissible variation; a capacitor 160 charged by output voltage of the LED backlight circuit 116; a switch circuit 164 as an input voltage change-over circuit for supplying battery voltage to the electric power supply circuit 150 when the battery voltage is equal to or higher than a given value and supplying terminal voltage of the capacitor 160 to the electric power supply circuit 150 when the battery voltage becomes lower than the given value; and a detection IC 166.

Description

  The present invention relates to a power supply device that supplies a power supply voltage to a microcomputer or a CPU.

  2. Description of the Related Art Conventionally, a power supply circuit that holds a DC power supply voltage for a certain period of time when the power is off is known (see, for example, Patent Document 1). In this power supply circuit, a capacitor and a transistor are provided on the input side of the DC stabilized power supply circuit, and when the power is turned off, the transistor is turned off to increase the discharge time constant of the capacitor and delay the voltage drop. The output voltage of the circuit is maintained for a certain time. By maintaining this voltage, the microcomputer can perform a predetermined operation when the power is turned off.

Japanese Patent Laid-Open No. 7-14164 (page 1-2, FIG. 1-2)

  By the way, when considering an in-vehicle display product that includes a display device and its control unit and performs display based on a video signal input from another device, the minimum operation guaranteed voltage as the product is 9V, 6.5V. Until then, the communication function must be active. Assuming that the operating voltage of the microcomputer or CPU included in this product is 5 V, when the power supply circuit disclosed in Patent Document 1 is used, the capacitor provided on the input side of the DC stabilized power supply circuit is reduced from 6.5 V. Since the voltage difference until the voltage drops to 5V is only 1.5V, it is necessary to use a capacitor with a large capacitance when maintaining 5V, which is the output voltage of the DC stabilized power supply circuit, for a certain period of time, which increases the cost. In addition, there is a problem that the occupied area increases.

  The present invention has been created in view of such a point, and an object of the present invention is to provide a power supply device that can reduce the cost and the occupied area.

  In order to solve the above-described problem, a power supply device of the present invention is a power supply device used with a backlight circuit that is mounted on a vehicle and generates an operating voltage of a light emitting diode used as a backlight of a liquid crystal display device, A power supply circuit that generates a constant output voltage from an input voltage that is allowed to fluctuate, a capacitor that is charged by the output voltage of the backlight circuit, and a battery voltage that is supplied to the power supply circuit when the battery voltage exceeds a predetermined value. And an input voltage switching circuit for supplying the terminal voltage of the capacitor to the power supply circuit when the battery voltage becomes lower than a predetermined value. In particular, the backlight circuit described above generates an output voltage by boosting the battery voltage, and the input voltage is switched by the input voltage switching circuit within the allowable range of the input voltage fluctuation of the power supply circuit. To at least the output voltage of the backlight circuit.

  In general, the operating voltage of a light emitting diode used as a backlight of a liquid crystal display device mounted on a vehicle is higher than the battery voltage. Therefore, this high voltage is held in a capacitor, and the input voltage of the power circuit is reduced when the battery voltage drops. As a result, it is possible to lengthen the time for the input voltage to drop to a voltage at which the power supply circuit becomes inoperable. In other words, the capacitance of the capacitor required to guarantee the normal operation of the power supply circuit for a certain time when the battery voltage drops can be greatly reduced. In particular, since the capacitance of capacitors and the cost and occupied area are almost proportional, the cost can be significantly reduced and the occupied area can be reduced even if additional circuits (input voltage switching circuit) are added. It becomes.

  The input voltage switching circuit described above includes a battery voltage detection circuit that detects the battery voltage, and a switch circuit that applies the terminal voltage of the capacitor to the power supply circuit when the battery voltage is lower than a predetermined value by the battery voltage detection circuit. It is desirable to provide. As a result, it is possible to reliably switch the input voltage when the battery voltage decreases and to maintain the normal operation of the power supply circuit.

  Also, it is desirable that a current backflow prevention element is inserted in each of the battery voltage supply path to the power supply circuit and the capacitor terminal voltage supply path to the power supply circuit. Thereby, the battery voltage and the terminal voltage of the capacitor can be selectively input to the power supply circuit.

It is a figure which shows the structure of the display apparatus of one Embodiment. It is a figure which shows the detailed structure of CPU power supply.

  Hereinafter, a display device according to an embodiment to which the present invention is applied will be described with reference to the drawings.

  FIG. 1 is a diagram illustrating a configuration of a display device according to an embodiment. A display device 100 shown in FIG. 1 is mounted on a vehicle and displays a video signal input from an external device (not shown). An LCD (liquid crystal display) module 110, an LCD power supply 114, an LED The backlight circuit 116, the video IC 120, the video IC power source 122, the input I / F (interface) 124, the CPU 130, the BUS I / F 132, the CPU power source 140, the coil 142, and the capacitor 144 are configured.

  The LCD module 110 incorporates an LED (light emitting diode) 112 as a backlight, and display control is performed using a plurality of drive voltages generated by the LCD power source 114.

  The LED backlight circuit 116 is an LED power source for driving the LED 112 and, for example, boosts 12V, which is a terminal voltage (battery voltage) of the battery 200, to 22V to generate an operating voltage of the LED 112. This 22V assumes the case where VF has six LED elements connected in series, and when the number of elements in series is different or the VF of the LED elements used is different, the value of this operating voltage Will also be changed.

  The video IC 120 controls the LCD module 110 to display a video corresponding to an input video signal input via the input I / F 124. The video IC power supply 122 receives a battery voltage and generates an operating voltage for the video IC 120. An input I / F (interface) 124 is connectable to an external device, receives a video signal input from the external device, and inputs it to the video IC.

  The CPU 130 controls operations of the entire display device 100, specifically, the LED backlight circuit 116, the video IC 120, the video IC power source 122, and the LCD power source 114. The CPU 130 can transmit and receive (communication) various signals to and from an external device via the BUS I / F 132. For example, an interrupt signal sent from the external device can be reflected in the control operation. It becomes.

  The CPU power supply 140 generates an operating voltage for the CPU 130. In the present embodiment, when the battery voltage is excessively lowered or disconnected, the CPU 130 saves the user adjustment information to an EEP-ROM (not shown) and prevents the LCD module 110 from being damaged. In order to prevent the occurrence of an unnatural afterimage, it is necessary to perform various controls such as compliance with the power-off sequence of the video IC and compliance with the off-sequence of the video IC. For this reason, the operating voltage (for example, 5V) supplied to the CPU 130 needs to be maintained for a certain period of time even when the battery voltage is excessively lowered or disconnected. Devised for maintenance. Note that an LC filter is formed by the coil 142 and the capacitor 144, and noise included in the terminal voltage of the battery 200 is reduced.

  FIG. 2 is a diagram showing a detailed configuration of the CPU power supply 140. As shown in FIG. 2, the CPU power supply 140 includes a power supply circuit 150, capacitors 152, 154 and 160, diodes 156, 162 and 170, a switch circuit (SW) 164, a detection IC 166 and a resistor 168.

  The power supply circuit 150 is a stabilized power supply circuit that generates an operating voltage of 5V to be supplied to the CPU 130, and has an input voltage of 5V or more in a predetermined range (for example, from 5V to 22V that is the output voltage of the LED backlight circuit 116). A constant voltage of 5V is generated when it fluctuates in the range. Smoothing capacitors 152 and 154 are connected to the input side and the output side of the power supply circuit 150.

  The diode 156 is a current backflow prevention element that cuts off between the input side of the power supply circuit 150 and the battery terminal side when the battery voltage is excessively decreased. The diode 156 is an LC filter formed by the coil 142 and the capacitor 144 and a power source. The anode is inserted between the circuit 150 and the input terminal of the power supply circuit 150 so that the anode is on the LC filter side.

  The capacitor 160 is connected to the output terminal of the LED backlight circuit 116 via a diode 162, and holds electric charge according to the output voltage (22V) of the LED backlight circuit 116. The capacitor 160 is for supplying an input voltage to the power supply circuit 150 in place of the battery 200 when the battery voltage drops, and has a capacitance of 100 μF, for example. The diode 162 is a current backflow prevention element that cuts off between the output side of the LED backlight circuit 116 and the capacitor 160 when the output voltage of the LED backlight circuit 116 decreases, and the cathode is the capacitor 160 between them. It is inserted to the side. The capacitor 118 provided on the output side of the LED backlight circuit 116 is for smoothing the output voltage of the LED backlight circuit 116.

  The switch circuit 164 has one end connected to the capacitor 160 and the other end connected to the input side of the power supply circuit 150 via a diode 170 as a current backflow prevention element. Switch circuit 164 is turned on when the battery voltage drops, and is turned off otherwise. The switch circuit 164 can be formed by an analog switch, FET, bipolar transistor, or the like, for example. The detection IC 166 detects the battery voltage, and turns on the switch circuit 164 when the battery voltage falls below a predetermined value (for example, 6.5 V). The detection IC 166 is operated by a voltage applied from the capacitor 160 side via the resistor 168, and a reliable operation when the battery voltage is reduced is ensured.

  The LCD module 110 described above is the liquid crystal display device in the claims, the LED backlight circuit 116 is the backlight circuit, the switch circuit 164, the detection IC 166, the diodes 156 and 170 are the input voltage switching circuit, and the detection IC 166 is the battery voltage. Each corresponds to a detection circuit.

  The CPU power supply 140 (power supply device) of the present embodiment has such a configuration, and the operation thereof will be described next.

(Normal operation)
When the battery voltage is normal at 6.5 V or higher, the switch circuit 164 is turned off. At this time, the capacitor 160 is charged by the output voltage of the LED backlight circuit 116, and the voltage across the capacitor 160 is maintained at substantially the same value as the output voltage (22V) of the LED backlight circuit 116 (in practice, The voltage is reduced by the forward voltage of the diode 162). The power supply circuit 150 generates a constant (5V) output voltage based on the battery voltage applied via the LC filter and the diode 156. This output voltage is applied to the CPU 130 and the BUS I / F 132 as an operating voltage.

(When voltage drops)
When the battery voltage drops below 6.5 V, the detection IC 166 detects this drop in battery voltage and turns on the switch circuit 164. Thereafter, the terminal voltage (both ends voltage) of the capacitor 160 is applied to the input side of the power supply circuit 150 via the diode 170. The power supply circuit 150 generates a constant (5 V) output voltage based on the terminal voltage of the capacitor 160 applied via the switch circuit 164. In particular, since the terminal voltage of the capacitor 160 maintains a high value of 20 V or more, which is the output voltage of the LED backlight circuit 116, immediately before the switch circuit 164 is turned on, the capacitor 160 has the terminal voltage after the switch circuit 164 is turned on. It is possible to lengthen the time until the terminal voltage drops to around 5 V where the power supply circuit 150 can operate normally.

  As described above, in the CPU power supply 140 according to the present embodiment, the high output voltage of the LED backlight circuit 116 is held in the capacitor 160 and used as the input voltage of the power supply circuit 150 when the battery voltage drops. However, it is possible to lengthen the time for the power supply circuit 150 to fall to a voltage at which it cannot operate. That is, the capacitance of the capacitor 160 required to guarantee normal operation of the power supply circuit 150 for a certain period of time when the battery voltage decreases (a certain operation time of the CPU 130 necessary for performing predetermined processing when the battery voltage decreases) is greatly increased. Can be made smaller. In particular, since the capacitance of the capacitor 160 and the cost and occupied area are substantially proportional to each other, the cost can be greatly reduced and the occupied area can be reduced even if the additional circuit such as the detection IC 166 is added. Become.

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation implementation is possible within the range of the summary of this invention. For example, in the above-described embodiment, the present invention is applied to the CPU power supply 140 provided in the display device 100. However, if the device uses an LED as the backlight of the LCD module, the output voltage of the LED backlight circuit is used. Therefore, the present invention can be widely applied to various devices other than the display device 100.

  In the above-described embodiment, the case where the CPU 130 is operated by the operating voltage generated by the power supply circuit 150 is considered. However, the present invention is also applied to the case where the operating time other than the CPU such as a microcomputer or a memory is extended. Can do.

  As described above, according to the present invention, the capacitance of the capacitor 160 required to guarantee the normal operation of the power supply circuit 150 for a certain period of time when the battery voltage drops can be greatly reduced. The occupied area can be reduced.

100 Display device 110 LCD module 112 LED
114 LCD power supply 116 LED backlight circuit 120 Video IC
122 Video IC power supply 124 Input I / F
130 CPU
132 BUS I / F
140 CPU power supply 142 Coil 144, 152, 154, 160 Capacitor 200 Battery 150 Power supply circuit 156, 162, 170 Diode 164 Switch circuit (SW)
166 Detection IC
168 resistance

Claims (4)

A power supply device used in conjunction with a backlight circuit that generates an operating voltage of a light emitting diode mounted on a vehicle and used as a backlight of a liquid crystal display device,
A power supply circuit that generates a constant output voltage from an input voltage that is allowed to fluctuate;
A capacitor charged by the output voltage of the backlight circuit;
An input voltage switching circuit that supplies the battery voltage to the power supply circuit when the battery voltage is equal to or higher than a predetermined value, and supplies the terminal voltage of the capacitor to the power supply circuit when the battery voltage becomes lower than a predetermined value. When,
A power supply apparatus comprising: In claim 1,
The backlight circuit boosts the battery voltage to generate an output voltage,
The allowable range of fluctuation of the input voltage of the power supply circuit includes at least from the predetermined value at which the input voltage is switched by the input voltage switching circuit to the output voltage of the backlight circuit. apparatus. In claim 1 or 2,
The input voltage switching circuit is
A battery voltage detection circuit for detecting the battery voltage;
A switch circuit that applies a terminal voltage of the capacitor to the power supply circuit when the battery voltage is lower than a predetermined value by the battery voltage detection circuit;
A power supply apparatus comprising: In claim 3,
A power supply device, wherein a current backflow prevention element is inserted in each of a battery voltage supply path to the power supply circuit and a terminal voltage supply path of the capacitor to the power supply circuit.

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