JPH1056774A - Power supply - Google Patents

Abstract

(57) [Summary] [PROBLEMS] A notebook personal computer that can use two power supplies, an AC adapter and a battery, has a wide power supply voltage fluctuation range, and it is difficult to ensure safety over all conditions with only a current fuse. It is. SOLUTION: A voltage 1 proportional to a period during which a switch element of a voltage control means built in the device is open and a voltage 2 proportional to a power supply voltage are constantly compared, and when the voltage 1 becomes lower than the voltage 2, Operation is stopped. [Effect] With this configuration, safety can be secured over the entire range of power supply voltage fluctuation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply, and more particularly to a power supply for lighting a discharge lamp for a liquid crystal backlight.

[0002]

2. Description of the Related Art A conventional power supply for lighting a discharge lamp is disclosed in, for example, Japanese Utility Model Application Laid-Open No. 5-80191, in which a tube current detected by a tube current detection circuit is provided to a voltage control means provided in a stage preceding the lighting circuit. Convert the value to voltage and feed it back,
The operation of the voltage control means is PWM-controlled so that the tube current flowing through the discharge lamp becomes constant. In the above prior art, even if the power supply voltage fluctuates, an operation is performed to keep the voltage supplied to the lighting circuit constant by controlling the open / close duty of the switch element provided in the voltage control means. Tube current flows.

[0003]

However, in the above-mentioned prior art, even if a part of the lighting circuit breaks down, the power consumption becomes larger than usual and the elements generate heat and the temperature becomes high, and the voltage becomes higher. Since the control means operates so as to keep the tube current constant, the control means continues to operate so as to output a constant tube current, that is, output power irrespective of heat generation of the element. As a result, the input power continues to operate in an abnormally high state, and in extreme cases, there is a risk of smoke and ignition.
In order to prevent such a situation, a current fuse or a thermal fuse is generally used. When a current exceeding a certain level flows, the current fuse is blown to prevent a further dangerous situation.

However, when the battery is used while charging the battery by connecting an AC adapter, such as a notebook personal computer, or when the battery is used when there is no outlet nearby, fluctuations in power supply voltage occur. The range varies over a wide range from 6V to 21V. The voltage control means operates so that the brightness of the backlight is constant even when the power supply voltage greatly changes.
That is, the operation is performed so that the power consumption becomes substantially constant. When the power supply voltage changes, since the product of the power supply voltage and the input current is power consumption, the power supply voltage and the input current change in an inverse relationship. Therefore, even if the rated value of the current fuse suitable for a certain power supply voltage condition is set, if the power supply voltage changes, the current fuse may not operate properly. In an extreme case, the current fuse may not operate even when the element is heated. That is, it is difficult to prevent the danger of smoking and the like in the entire range of the power supply voltage by using only the current fuse. .

[0005]

In order to solve the above problems, the present invention has the following configuration. As described above, the switching element of the voltage control means repeats the opening and closing operation,
In order to solve the above problem, there are provided means for generating a voltage 1 in proportion to the time ratio of opening of the switch element, and means for generating a voltage 2 in proportion to the power supply voltage. Is high, the determination circuit is provided for determining that it is normal, otherwise, it is determined that it is abnormal. The circuit operation is stopped when it is determined to be abnormal.

As described above, when the power supplied to the load of the voltage control means is constant, the ratio of the time during which the switch is closed in the opening and closing operation of the switch element is inversely related to the power supply voltage. is there. Therefore, the ratio of the time when the switch is open is proportional to the power supply voltage.
For this reason, the relationship between the voltage 1 proportional to the ratio of the time when the switch element is open and the voltage 2 proportional to the power supply voltage is also proportional. So when it is working properly,
It is set so that voltage value 1 is always higher than voltage value 2. If an abnormality occurs and the parts of the lighting circuit are heated and become dangerous, the power consumed by the lighting circuit increases. Therefore, the ratio of the time during which the switch element of the voltage control means is closed becomes larger than usual, and the voltage 1 proportional to the percentage of the time when the switch element is open becomes smaller. At this time, the voltage value 1 changes to a value lower than the voltage value 2, and it is possible to detect that an abnormality has occurred in the device.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of one embodiment of the present invention.
Is a DC power supply, 2 is a switching transistor, 3 is a choke coil, 4 is a resistor, 5 is a base resistance of the switching transistor 2, 6 is a diode, 7 is a transformer, 8 is a resonance capacitor, 9 and 10 are transistors, and 11 is a ballast capacitor. , 12 is a discharge lamp, 13 is a tube current detection circuit, 14 is an error amplifier, 15 is a reference voltage source, 16 is a feedback capacitor, 17 is a sawtooth wave generation circuit, 18 is a voltage comparator, and 19 is the base resistance of the transistor 20. , 21 is an inverter, 22 is a diode, 23 and 24 are resistors, 25 is a capacitor, 26, 27, 28 and 29 are dividing resistors of the power supply voltage of the DC power supply 1, 30 and 31 are voltage comparators, 32 is an OR circuit, 33 is a delay circuit, 34 is a latch circuit, 35 is a resistor, and 36 and 37 are constant voltage diodes.

The DC voltage output from the DC power supply 1 is chopped by the switching transistor 2, further smoothed by the choke coil 3, and input to the transformer 7 as a DC voltage corresponding to the duty of the switching transistor 2. A circuit composed of the transistors 9 and 10, the resonance capacitor 8, the resistor 35, and the transformer 7 is a so-called push-pull voltage resonance circuit, and a sine wave oscillation operation is performed at a frequency substantially determined by the inductance of the transformer 7 and the capacitance value of the resonance capacitor 8. I do. The DC voltage input to the transformer 7 is converted into an AC voltage according to the voltage value by the push-pull voltage resonance circuit. Further, this AC voltage is boosted to a secondary voltage according to the turn ratio of the transformer 7, applied to both ends of the discharge lamp 12 via the ballast capacitor 11, and the discharge lamp 12 is turned on. When the discharge lamp 12 is turned on, a tube current determined by the impedance of the ballast capacitor 11 and the secondary voltage of the transformer 7 flows through the discharge lamp 12.

A tube current flowing through the discharge lamp 12 is converted into a voltage value by a tube current detection circuit 13 and input to an error amplifier 14. The error amplifier 14 outputs to the voltage comparator 18 a voltage obtained by amplifying the difference between the voltage value corresponding to the input tube current and the voltage value of the reference voltage source 15. The voltage comparator 18 calculates this voltage,
The output voltage of the saw-tooth wave generator 17 is compared, and the comparison result is output.

The triangular waveform shown in FIG. 2A is the output voltage waveform of the sawtooth wave generator 17, and the solid straight line is the output voltage waveform of the error amplifier 14. FIG. 2B shows an output voltage waveform of the voltage comparator 18. The switching transistor 2 is turned on because the transistor 20 is turned on while the voltage is high, and the switching transistor 2 is turned off while the voltage is low. If the voltage of the DC power supply 1 increases, the voltage input to the transformer 7 also increases, so that the tube current flowing through the discharge lamp 12 increases. For this reason, FIG.
As shown by the broken straight line, the output voltage of the error amplifier 14 increases. For this reason, the high voltage period in the output voltage waveform of the voltage comparator 18 changes in the direction of shortening, so that the duty of the switching transistor 2 decreases, the voltage input to the transformer 7 is suppressed, and the current flowing through the discharge lamp 12 decreases. Be kept constant.

The waveform shown by the thick solid line in FIG. 2 (c) is shown by the solid line in FIG. 2 (b), that is, the output voltage waveform of the voltage comparator 18 when the power supply voltage is low is changed by the inverter 21. Is the inverted waveform. The waveform shown by the broken line in FIG. 2D is the waveform shown by the broken line in FIG.
That is, the output voltage waveform of the voltage comparator 18 when the power supply voltage is high is inverted by the inverter 21. Each of these outputs a high-level voltage value while the switching transistor 2 is off. FIG. 2 (c) and (d)
The solid and dashed waveforms of the diode 22 and the resistor 2
3 and 24, and the waveform rectified and smoothed by the capacitor 25,
It is the waveform shown by the thin solid line in FIG.2 (c) and (d).
That is, when the power supply voltage is low, the average voltage of the thin solid line is low, and when the power supply voltage is high, the average voltage of the thin solid line is high.

FIG. 3F is a graph showing the relationship between the power supply voltage and the average voltage of the thin solid line in a normal operation state. This voltage is input to voltage comparators 30 and 31. Next, the relationship between the voltage at the midpoint of the resistors 26 and 27 and the power supply voltage in the circuit diagram 1 and the relationship between the voltage at the midpoint of the resistors 28 and 29 and the power supply voltage are shown in FIGS. .

For example, when an abnormality occurs in the voltage resonance circuit and heat is generated, and the power consumption becomes larger than usual, the duty of the switching transistor 2 increases.
As a result, the time ratio of the switching transistor 2 being turned off decreases, so that the average voltage across the capacitor 25 decreases. Therefore, by setting the voltage level of FIG. 3 (g) to an appropriate level, it is possible to set the voltage level of FIG.
Becomes lower than the voltage level of (g),
The voltage comparator 31 is inverted to generate a high level output. Therefore, the OR circuit 32 also outputs a high-level voltage. Even when the discharge lamp is normal, the response may be delayed due to a phenomenon peculiar to the discharge lamp, such as a discharge delay at the time of starting, and the OR circuit is passed through the delay circuit 33 to prevent erroneous detection.
A high-level output signal of the circuit is latched by a latch circuit. When the latch circuit 34 latches the high-level signal, the output of the voltage comparator 18 is forcibly fixed to the low level, so that the operation of the switching transistor 2 is stopped in the off state, thereby ensuring safety.

If, for some reason, the power consumption of the voltage resonance circuit is reduced contrary to the above, the voltage comparator 3 is set to an appropriate value of the level shown in FIG.
0 is inverted and a high level signal is also output. Thereafter, the operation is the same as when the power consumption of the voltage resonance circuit is increased, and safety is ensured.

[0015]

As described above, according to the present invention, the abnormality of the device can be detected and the operation can be stopped with a simple circuit, so that a safe power supply device can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of one embodiment of the present invention.

FIG. 2 is an operation waveform diagram of one embodiment of the present invention.

FIG. 3 is an explanatory view of one embodiment of the present invention.

[Explanation of symbols]

2: switch transistor, 21: inverter, 2
2 Diodes, 23 and 24 resistors, 25 capacitors, 26, 27, 28 and 29 resistors 30 and 31 Voltage comparators, 36 and 37 diodes.

Continued on the front page (72) Inventor Motohiro Sugino 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside Hitachi Image Information System Co., Ltd.

Claims (4)

[Claims] A DC-DC converter having a DC power supply as a power supply and having at least one semiconductor switch; and a control circuit, wherein the control circuit outputs a PWM signal, and the PWM signal turns on the semiconductor switch. In the power supply device having a configuration in which the output voltage of the DC-DC converter is maintained at a predetermined voltage by performing / OFF operation, a constant low level voltage when the semiconductor switch is ON, and a constant high voltage when the semiconductor switch is OFF. A signal generating circuit for outputting a voltage of a level; comparing a voltage obtained by rectifying an output voltage of the signal generating circuit with a voltage value 1 obtained by dividing a voltage of the DC power supply by resistance, and rectifying an output voltage of the signal generating circuit; A power supply unit configured to stop the operation of the DC-DC converter when the applied voltage is equal to or less than the voltage value 1; 2. A signal generating circuit for outputting a constant low level voltage when the semiconductor switch is turned on and a constant high level voltage when the semiconductor switch is turned off, wherein the output voltage of the signal generating circuit is rectified. And a voltage value obtained by dividing the voltage of the DC power supply by resistance and a voltage value 2 having a resistance division ratio set so that the voltage value is higher than the voltage value 1. The output voltage of the signal generation circuit is When the rectified voltage is equal to or less than the voltage value 1 or equal to or more than the voltage value 2,
The power supply device according to claim 1, further comprising a configuration for stopping the operation of the DC-DC converter. 3. The power supply device according to claim 2, wherein a constant voltage element 1 or a constant voltage element 2 is connected in series with a resistor for giving said voltage value 1 or said voltage value 2. 4. A discharge lamp lighting device having a second semiconductor switch is connected to an output of the power supply device according to claim 1, and a discharge lamp is connected to an output of the discharge lamp lighting device. The operation of the DC-DC converter and the operation of the discharge lamp lighting device are performed after a certain period of time has elapsed after the rectified voltage of the output voltage of the signal generation circuit has become equal to or less than the voltage value 1 or equal to or more than the voltage value 2. A discharge lamp device characterized by being configured to be stopped.