JP2008160934A - Power supply circuit and electronic equipment using the same - Google Patents

Power supply circuit and electronic equipment using the same Download PDF

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Publication number
JP2008160934A
JP2008160934A JP2006344575A JP2006344575A JP2008160934A JP 2008160934 A JP2008160934 A JP 2008160934A JP 2006344575 A JP2006344575 A JP 2006344575A JP 2006344575 A JP2006344575 A JP 2006344575A JP 2008160934 A JP2008160934 A JP 2008160934A
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voltage
power supply
circuit
supply circuit
overvoltage
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JP2006344575A
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Japanese (ja)
Inventor
Koichi Hanabusa
孝一 花房
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Sharp Corp
シャープ株式会社
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a power supply circuit which feeds power to an LED being an electric load, and can easily perform proper overvoltage protection processing adapted to the type of the load, and electronic equipment using the power supply circuit. <P>SOLUTION: The power supply circuit which feeds power to the electric load comprises an overvoltage protection circuit which controls an output voltage outputted to the load so as not to exceed a prescribed overvoltage detection level, and an adjusting means which adjusts the overvoltage detection level. The electronic equipment is provided with the power supply circuit. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a power supply circuit that supplies power to a load such as an LED, and an electronic device using the same.

  In recent years, the durability, luminous efficiency, and occupied area of liquid crystal display (LCD) illumination sources (backlights or frontlights) mounted on electronic devices such as mobile phones, PDAs (Personal Digital Assistants), and digital cameras For example, white light emitting diodes that are superior in view of the above have been used.

  This white light emitting diode requires a relatively high forward voltage, and a plurality of white light emitting diodes are used as an illumination source, which are connected in series to make the brightness of each white light emitting diode uniform. There are many cases. Therefore, driving a white light emitting diode as such an illumination source requires a higher DC voltage than a DC voltage from a battery built in the portable device.

  Further, along with video distribution to portable devices, portable devices equipped with a digital tuner are becoming widespread. However, a voltage source of about 30 V to 40 V is necessary, and a battery built in the portable device is required. A DC voltage higher than the DC voltage is required.

  As a circuit for driving a DC voltage higher than the DC voltage from such a battery, a boost type power supply circuit has been conventionally used. An example of a configuration diagram related to a conventional power supply circuit (LED driver circuit) is shown in FIG.

  In the power supply circuit shown in the figure, the magnitude of the output voltage output to the LED group as a load is detected and fed back. A drive circuit provided in the power supply circuit adjusts the supply voltage according to the detection result, thereby stabilizing the supply current. The power supply circuit is provided with an overvoltage protection circuit. A configuration diagram of this overvoltage protection circuit is shown in FIG.

The overvoltage protection circuit detects the voltage (output voltage Vout) on the upstream side of the LED group, and stops the operation of the drive circuit when this exceeds a predetermined voltage value (overvoltage detection level) (executes overvoltage protection processing) To do). This prevents overvoltage from being applied to the LED group and the capacitor.
JP-A-10-225110 JP 2006-211762 A

  As described above, the overvoltage protection circuit plays an important role in suppressing the occurrence of overvoltage, but an appropriate overvoltage detection level may vary depending on the load connected to the LED driver (power supply circuit). For example, in an example of an LED driver that supplies power to an LED, an appropriate overvoltage detection level varies depending on the number of LEDs connected in series.

The overvoltage detection level will be described more specifically with reference to the power supply circuit of FIG. When the forward voltage per LED is VF (LED), the number of LEDs is N, the voltage of the FB terminal (feedback terminal) is VFB, and the margin is Vα, the appropriate overvoltage detection level Vo is
Vo = VF × N + FB + Vα
It is represented by

  Also from this, the appropriate value of the overvoltage detection level that determines the timing at which the overvoltage protection process is performed varies depending on the number of LEDs. Therefore, for example, in a power supply circuit in which overvoltage protection functions properly when an LED group consisting of 10 LEDs is used as a load (appropriate overvoltage detection level is set), the LED group consisting of about 7 LEDs. Is connected as a load, the overvoltage detection level is too high. As a result, overvoltage protection may not function properly.

  Accordingly, in view of the above problems, the present invention supplies power to an LED as an electrical load, and a power supply circuit capable of easily realizing an appropriate overvoltage protection process according to the type of the load, and this An object is to provide an electronic device using such a power supply circuit.

  In order to achieve the above object, a power supply circuit according to the present invention is a power supply circuit that supplies power to an LED as an electrical load so that an output voltage output to the load does not exceed a predetermined overvoltage detection level. A configuration (first configuration) is provided that includes an overvoltage protection circuit to be controlled and an adjustment unit that adjusts the overvoltage detection level.

  According to this configuration, by providing the overvoltage protection circuit, it is possible to prevent the output voltage from becoming excessive as much as possible. Furthermore, since the adjusting means for adjusting the overvoltage detection level is provided, it is possible to appropriately perform overvoltage protection processing by making appropriate adjustment according to the type of LED. .

  In the first configuration, the overvoltage protection circuit receives the output voltage, divides the voltage, and outputs the voltage according to the voltage output from the voltage dividing circuit. A power control circuit that switches ON / OFF of the supply, and the adjustment unit may be configured to perform the adjustment (second configuration) by changing a voltage dividing ratio in the voltage dividing circuit.

  According to this configuration, it is possible to easily adjust the overvoltage detection level by changing the voltage dividing ratio in the voltage dividing circuit.

  The first or second configuration further includes an information acquisition unit that acquires information for adjusting the overvoltage detection level from the outside, and the adjustment unit is based on the information acquired by the information acquisition unit. Thus, a configuration for performing the adjustment (third configuration) may be employed. According to this configuration, the overvoltage detection level can be adjusted based on information from the outside (for example, designation by the user).

  The first or second configuration further includes a voltage detection unit that detects the output voltage, and the adjustment unit performs the adjustment based on a detection result by the voltage detection unit (fourth configuration). It is good. According to this configuration, the adjustment of the overvoltage detection level can be executed based on the status of the output voltage.

  In the first or second configuration, the adjustment unit includes an information acquisition unit that acquires information for adjusting the overvoltage detection level from the outside, and a voltage detection unit that detects the output voltage. The adjustment may be performed (fifth configuration) based on the information acquired by the information acquisition unit and the detection result of the voltage detection unit.

  According to this configuration, the overvoltage detection level can be adjusted based on both information from the outside and the status of the output voltage. As a result, it is possible to realize the adjustment of the overvoltage detection level more adapted to the needs.

  In any of the first to fifth configurations, an overvoltage detection unit that detects whether the output voltage exceeds an overvoltage detection level, and a signal output that outputs a signal corresponding to the detection result to the outside And a configuration (sixth configuration).

  According to this configuration, a signal regarding whether or not the output voltage exceeds the overvoltage detection level can be output to the outside. Therefore, for example, it is possible to provide an alarm device that performs acoustic output and generate a warning sound when the output voltage is an overvoltage.

  Further, in any of the first to sixth configurations, a configuration (seventh configuration) that is a step-up DC-DC converter circuit may be employed. In addition, if the electronic device has a configuration (eighth configuration) including the power supply circuit according to any one of the first to seventh configurations, an electronic device that can enjoy the advantages of the configuration can be realized. is there.

  As described above, according to the power supply circuit of the present invention, since the overvoltage protection circuit is provided, it is possible to prevent the output voltage from becoming excessive as much as possible. Furthermore, since the adjusting means for adjusting the overvoltage detection level is provided, the overvoltage protection processing can be appropriately performed by making an appropriate adjustment according to the type of the load (LED). It becomes possible.

  Embodiments of the present invention will be described below with reference to each of Examples 1 to 3.

[Example 1]
As Example 1 of the present invention, an LED driver circuit (power supply circuit) will be described below. First, the overall configuration of the LED driver circuit will be described with reference to FIG. The LED driver circuit includes a DC power source 1 such as a lithium ion battery, an input capacitor 2, a coil 3, a diode (rectifier element) 4, an output capacitor 5, an output current setting resistor Ro, and an IC that is integrated into a single package and energy for the coil 3. A step-up chopper regulator IC 6 and the like that perform the step-up operation by switching the accumulation / release of are arranged as shown in FIG. As a result, the LED driver circuit can function as a step-up DC-DC converter circuit.

  Between the downstream side of the diode 4 (upstream side of the output capacitor 5) and the upstream side of the output current setting resistor Ro, one or more white light emitting LEDs are connected in series as shown in FIG. The LED group 7 is connected. The LED driver circuit supplies power to the LED group 7 connected in this way.

  The negative terminal of the DC power source 1 is connected to the ground, and the positive terminal is connected to the ground via the input capacitor 2 and is connected to one end of the coil 3. The other end of the coil 3 is connected to the anode of the diode 4, and the cathode of the diode 4 is connected to the ground via the output capacitor 5. Further, an LED group 7 and an output current setting resistor Ro are connected in parallel with the output capacitor 5.

  The step-up chopper regulator IC 6 includes terminals such as a power supply terminal Vin, a power supply (ground side) terminal GND, an output voltage monitor terminal OVP, a feedback terminal FB, a control terminal CTRL, a switch terminal Vsw, and an alarm terminal ALARM as external connection terminals. It has. The power supply terminal Vin is connected to the positive terminal of the DC power supply 1, and the power supply terminal GND is connected to the ground. Thus, the boost chopper regulator IC 6 uses the DC power source 1 as its operating power source.

  The switch terminal Vsw is connected between the coil 3 and the diode 4, the output voltage monitor terminal OVP is connected to the cathode of the diode 4, and the feedback terminal FB is between the LED group 7 and the output current setting resistor Ro. It is connected. In addition, at the control terminal CTRL (ON / OFF terminal), when the input ON / OFF signal is OFF, the entire circuit is turned OFF by the ON / OFF circuit 18, so that the oscillation of the power transistor stops and the output voltage decreases. To do.

  Next, the internal configuration of the boost chopper regulator IC 6 will be described. As shown in FIG. 1, the step-up chopper regulator IC 6 includes a power transistor 11, an amplifier (adder) 12, a drive circuit 13, a current detection comparator 14, an oscillation circuit 15, an error amplifier 16, a PWM comparator 17, an ON / OFF circuit (operation). / Stop circuit) 18, an overvoltage protection circuit 19, a soft start circuit 20, and the like.

  The FET 11 has a drain connected to the switch terminal Vsw and a gate connected to the drive circuit 13. Similarly, the source is connected to the ground via a resistor R4. Both ends of the resistor R4 are connected to two input terminals of the current detection comparator 14, respectively, and the output of the current detection comparator 14 and one of the two outputs of the oscillation circuit 15 are added by the amplifier 12, and the PWM comparator 17 Is output to the non-inverting input terminal. The output side of the PWM comparator 17 and the other output side of the oscillation circuit 15 are connected to the drive circuit 13, respectively.

  The output side of the error amplifier 16 is connected to the inverting input terminal of the PWM comparator 17, and the inverting input terminal of the error amplifier 16 is connected to the feedback terminal FB. The outputs of the soft start circuit 20, the ON / OFF circuit 18, and the overvoltage protection circuit 19 are supplied to the drive circuit 13. Note that a brightness adjustment signal is supplied to the soft start circuit 20 and the ON / OFF circuit 18 via the control terminal CTRL. The overvoltage protection circuit 19 is supplied with the output voltage Vout via the output voltage monitor terminal OVP.

  Next, the operation content of the LED driver circuit will be described. The drive circuit 13 turns on / off the FET 11 to boost the input voltage from the DC power supply 1 and generate an output voltage across the output capacitor 5. That is, when the drive circuit 13 applies a predetermined gate voltage to the gate of the FET 11 and the FET 11 is on, current from the DC power source 1 flows through the coil 3 and energy is stored in the coil 3. When the drive circuit 13 does not apply a predetermined gate voltage to the gate of the FET 11 and the FET 11 is turned off, the stored energy is released to generate a counter electromotive force in the coil 3.

  The back electromotive force generated in the coil 3 is added to the input voltage of the DC power source 1 and charges the output capacitor 5 via the diode 4. Then, by repeating such a series of operations, a boosting operation is performed, and an output voltage Vout is generated across the output capacitor 5. By this output voltage Vout, an output current (Iout) flows through the LED group 7, and each LED emits light.

  A feedback voltage Vfb obtained by multiplying the current value of the output current Iout by the resistance value of the output current setting resistor Ro is supplied to the inverting input terminal of the error amplifier 16 via the feedback terminal FB. This voltage is compared with a reference voltage Vref supplied to the non-inverting input terminal of the error amplifier 16. Therefore, a voltage corresponding to the difference between the feedback voltage Vfb and the reference voltage Vref appears at the output of the error amplifier 16, and this voltage is supplied to the inverting input terminal of the PWM comparator 17.

  The signal input to the non-inverting input terminal of the PWM comparator 17 is obtained by adding the signal proportional to the current flowing through the resistor R4 when the FET 11 is turned on and the sawtooth wave signal from the oscillation circuit 15 by the amplifier 12. It is an amplified signal. That is, this signal is compared with the output voltage level of the error amplifier 16 supplied to the inverting input terminal of the PWM comparator 17.

  As a result, during a period in which the output voltage level from the error amplifier 16 is higher than the signal level from the addition amplifier 12, the PWM output of the PWM comparator 17 is at L (Low) level, and the output voltage level from the error amplifier 16 is the amplifier. During a period lower than the signal level from 12, the PWM output of the PWM comparator 17 is at the H (High) level.

  The drive circuit 13 receives the PWM output of the PWM comparator 17 and turns the FET 11 on / off with a duty corresponding to the PWM output. That is, the drive circuit 13 applies a predetermined gate voltage to the FET 11 to turn on the FET 11 when the PWM output of the PWM comparator 17 is at the H level and at the start of each cycle of the clock signal from the oscillation circuit 15. Let Then, when the PWM output of the PWM comparator 17 becomes L level, supply of the gate voltage to the FET 11 is stopped, and the FET 11 is turned off.

  When such on / off control of the FET 11 is performed, a boosting operation is performed so that the feedback voltage Vfb and the reference voltage Vref are equal. That is, the output current Iout is stabilized at a current value obtained by dividing the reference voltage Vref (= feedback voltage Vfb) by the resistance value of the output current setting resistor Ro. Further, the signal compared with the PWM comparator 17 is added with a signal corresponding to the current flowing through the resistor R4, that is, a signal corresponding to the current flowing through the coil 3 when the FET 11 is turned on. The peak current that flows through is limited.

  The overvoltage protection circuit 19 stops the operation of the drive circuit 13 when detecting that the output voltage Vout exceeds a predetermined overvoltage detection level. Thereby, an overvoltage exceeding the predetermined overvoltage detection level is prevented from being applied to the LED group 7 and the output capacitor 5 which are loads. Even when the LED driver circuit is used as a stabilized power source, the output voltage becomes higher than expected due to an assembly error or the like to prevent the FET from being destroyed. The detailed configuration of the overvoltage protection circuit 19 will be described again.

  The ON / OFF circuit 18 operates so as to turn off all circuits when the CTRL terminal is L, and consumes a low current (about 1 nA) when the CTRL terminal is turned off by an external signal. The soft start circuit 20 gradually increases the output voltage Vout by gradually changing the output duty of the drive circuit 13 at the start of the operation of the drive circuit 13.

  If the output voltage Vout is not gradually increased, an excessive charging current for charging flows from the DC power source 1 when the output capacitor 5 is not charged. For this reason, when the DC power source 1 is a lithium ion battery or the like, there is a problem that the battery is burdened and the battery voltage is lowered due to the excessive charging current, and the battery cannot be used up to the original end voltage.

  The detailed configuration of the overvoltage protection circuit 19 described above will be described with reference to FIG. As shown in the figure, the overvoltage protection circuit 19 includes an output voltage detection circuit 21, a voltage dividing circuit 22, a differential amplifier 24, an overvoltage detection unit 25, and the like. The voltage dividing circuit 22 is provided with a voltage dividing ratio switch 23.

  The output voltage detection circuit 21 detects the voltage output to the LED group 7, for example, by acquiring the voltage input from the OVP terminal. And according to this detection result, the control signal (for example, signal of several bits of H / L) for switching the voltage dividing ratio changeover switch 23 in the voltage dividing circuit 22 is outputted to the voltage dividing ratio changeover switch 23.

  The voltage dividing circuit 22 divides the voltage input via the OVP terminal, that is, the output voltage Vout on the upstream side of the LED group, using the resistor R1 and the combined resistor formed by any of R21 to R24. . This divided voltage is output to the differential amplifier 24 at the subsequent stage.

  Here, the resistance elements R21, R22, R23, and R24 are arranged so as to be connected in parallel to each other by a voltage dividing ratio changeover switch 23 configured by a relay or the like. An OVP terminal is connected to the upstream side of each of these resistors, and a resistor R1 and a differential amplifier 24 are connected to the downstream side. Thus, the voltage dividing ratio in the voltage dividing circuit 22 can be adjusted through the switching of the voltage dividing ratio changeover switch 23. As the voltage dividing circuit 22, several resistors may be inserted in parallel with the resistor R1, and control by a relay may be performed.

  The differential amplifier 24 receives the output of the voltage dividing circuit 22 and outputs a voltage corresponding to this voltage to the drive circuit 13. The drive circuit 13 is configured to stop the operation when the output of the differential amplifier 24 exceeds a predetermined value.

  The output voltage detection circuit 21 described above sets the voltage division ratio in the voltage dividing circuit 22 so that an appropriate overvoltage protection process according to the load (LED group 7) is realized. Various patterns can be adopted as the timing for setting the voltage division ratio. If this timing is set immediately after the start of driving of the LED driver, for example, the subsequent overvoltage protection processing can be made according to the load.

  Here, when the output voltage Vout is relatively small, the overvoltage detection level should also be set relatively small. Therefore, in this case, the output voltage detection circuit 21 makes the voltage dividing ratio in the voltage dividing circuit 22 small. Thereby, since the voltage output from the voltage dividing circuit 22 becomes larger, it is possible to reduce the substantial overvoltage detection level (even when the output voltage Vout is relatively small, it can be determined as an overvoltage).

  Conversely, when the output voltage Vout is also relatively large, the overvoltage detection level should be set to be relatively large. Therefore, in this case, the output voltage detection circuit 21 increases the voltage dividing ratio in the voltage dividing circuit 22. Thereby, since the voltage output from the voltage dividing circuit 22 becomes smaller, it is possible to increase the substantial overvoltage detection level (not to determine that it is an overvoltage until the output voltage Vout becomes relatively high). .

  With the above configuration, as described above, the overvoltage protection circuit 19 detects that the output voltage Vout has exceeded a predetermined overvoltage protection voltage, and stops the operation of the drive circuit 13. The overvoltage protection circuit 19 includes means for adjusting the overvoltage detection level according to the initial setting state of the load.

  Therefore, for example, an overvoltage protection process at an overvoltage detection level that is as appropriate as possible can be performed according to a use state in which the number of LED groups 7 connected in series is changed. As a result, it is possible to prevent an appropriate overvoltage protection process from being hindered as much as possible by changing the state of the load, and it is possible to avoid the destruction of the white light emitting diode or the like serving as the load.

  In the overvoltage protection circuit 19 described above, the output of the differential amplifier 24 is also used for executing a warning process. More specifically, the output of the differential amplifier 24 is transmitted to the overvoltage detection unit 25, and the overvoltage detection unit 25 determines whether the output voltage Vout is an overvoltage based on this output. Is done.

  When it is determined that there is an overvoltage, a signal (warning signal) indicating that is output to the ALARM terminal so that the warning signal can be taken out from the outside. In this way, for example, by providing a device (alarm device) that performs sound output or light emission when a warning signal is output, the user is in an abnormal situation (the output voltage Vout has become excessive). Can be notified.

[Example 2]
As a second embodiment of the present invention, an LED driver circuit (power supply circuit) will be similarly described below. Note that this embodiment is basically the same as the first embodiment except for the overvoltage protection circuit and its peripheral configuration, and thus a duplicate description is omitted.

  FIG. 3 shows a configuration diagram of the LED driver circuit of this embodiment. As shown in the figure, the LED driver circuit is provided with input terminals (P1 to P3) to which a signal (adjustment signal) for adjusting the overvoltage detection level is input from the outside. Each input terminal (P1 to P3) is connected to an overvoltage protection circuit 19. Although three input terminals are provided here, the number may be increased in order to improve the accuracy of overvoltage protection processing.

  A configuration diagram of the overvoltage protection circuit 19 is shown in FIG. In the overvoltage protection circuit 19, the switching state of the voltage dividing ratio changeover switch 23 is determined based on the adjustment signal input from the input terminals (P1 to P3). With this configuration, the LED drive circuit can adjust the voltage dividing ratio in the voltage dividing circuit 22 based on an adjustment signal acquired from the outside.

  Therefore, for example, if a user interface for a user to input an overvoltage detection level and a device that generates an adjustment signal according to this input and outputs it to the input terminals (P1 to P3) are provided, It is possible to adjust the voltage division ratio according to a user instruction. Therefore, for the user, for example, the overvoltage detection level can be set to a more appropriate state according to the type of load (LED group) connected to the LED drive circuit.

[Example 3]
As a third embodiment of the present invention, an LED driver circuit (power supply circuit) will be similarly described below. Since the present embodiment is basically the same configuration as the first embodiment except for the overvoltage protection circuit and its peripheral configuration, a duplicate description is omitted.

  FIG. 5 shows a configuration diagram of the LED driver circuit of this embodiment. As shown in the figure, the LED driver circuit is provided with input terminals (P1 to P3) to which a signal (adjustment signal) for adjusting the overvoltage detection level is input from the outside. Each input terminal (P1 to P3) is connected to an overvoltage protection circuit 19.

  A configuration diagram of the overvoltage protection circuit 19 is shown in FIG. The overvoltage protection circuit 19 includes an output voltage detection circuit 21 as in the case of the first embodiment. As a result, as in the first embodiment, an appropriate overvoltage detection level setting according to the load (LED group 7) is automatically realized through adjustment of the voltage dividing ratio in the voltage dividing circuit 22.

  Further, the above-described input terminals (P 1 to P 3) are connected to the output voltage detection circuit 21. As a result, the voltage dividing ratio changeover switch 23 can be switched through the output voltage detection circuit 21 by an adjustment signal input from the input terminals (P1 to P3).

  Thereby, any of the adjustment methods of the overvoltage detection level employed in the first and second embodiments described above can be selectively executed according to the situation. That is, when the adjustment signal is not input to the output voltage detection circuit 21, the overvoltage detection level is adjusted according to the detection result of the output voltage Vout, and conversely, when the adjustment signal is input, Based on this adjustment signal, the overvoltage detection level is adjusted. Therefore, it is possible to adjust the overvoltage detection level more flexibly according to the situation.

  In addition to the above, for example, the overvoltage detection level is always set based on the output voltage, while fine adjustment of the setting can be performed based on the adjustment signal (signal from the outside). You may do it. That is, both the status of the output voltage Vout and the adjustment signal can be simultaneously used as information for adjusting the overvoltage detection level.

[Summary]
As described above, in each of the embodiments of the present invention, in an LED driver circuit (power supply circuit) that supplies power to an LED that is an electrical load, the output voltage Vout output to the load is a predetermined overvoltage detection level. The overvoltage protection circuit 19 is controlled so as not to exceed. Furthermore, adjustment means (such as a voltage division ratio switch 23) for adjusting the overvoltage detection level is provided.

  Therefore, by providing the overvoltage protection circuit 19, it is possible to prevent the output voltage Vout from becoming excessive as much as possible. Furthermore, since an adjustment means for adjusting the overvoltage detection level is provided, by making an appropriate adjustment according to the type of load (LED), overvoltage protection processing (output voltage is excessive It is possible to appropriately carry out the processing to prevent the occurrence of this.

  The overvoltage protection circuit 19 receives the output voltage Vout, divides the voltage and outputs the voltage, and the power supply to the load is turned on according to the voltage output from the voltage dividing circuit 22. Power control circuits (differential amplifier 24, drive circuit 13, etc.) that switch / OFF are provided. The adjusting means for adjusting the overvoltage detection level is adjusted by changing the voltage dividing ratio in the voltage dividing circuit 22.

  In particular, the first embodiment includes a voltage detection unit (output voltage detection circuit 21) that detects the output voltage Vout, and adjusts the overvoltage detection level based on the detection result of the voltage detection unit. In the second embodiment, an information acquisition unit (such as the input terminals P1 to P3) that acquires information (adjustment signal) for adjusting the overvoltage detection level from the outside is provided. Based on the adjustment signal, the overvoltage detection level is adjusted. Adjustments are to be made.

  Further, the third embodiment includes both such an information acquisition unit and a voltage detection unit, and adjusts the overvoltage detection level based on the adjustment signal acquired by the information acquisition unit and the detection result by the voltage detection unit. It has become a thing.

  The LED driver circuit (power supply circuit) having the above configuration can be provided in an electronic device or the like. By doing so, overvoltage protection processing is more appropriately performed. Further, although the embodiments of the present invention have been described above, the scope of the present invention is not limited to these embodiments, and various modifications can be made without departing from the gist of the present invention.

  The present invention is useful in an LED driver that emits light from an LED.

It is a block diagram of the LED driver (power supply circuit) based on Example 1 of this invention. It is a block diagram of the overvoltage protection circuit based on Example 1 of this invention. It is a block diagram of the LED driver (power supply circuit) based on Example 2 of this invention. It is a block diagram of the overvoltage protection circuit based on Example 2 of this invention. It is a block diagram of the LED driver (power supply circuit) based on Example 2 of this invention. It is a block diagram of the overvoltage protection circuit based on Example 2 of this invention. It is a block diagram concerning an example of the conventional LED driver. It is a block diagram concerning an example of the conventional overvoltage protection circuit.

Explanation of symbols

1 DC power supply 2 Input capacitor 3 Coil 4 Diode 5 Output capacitor 6 Boost chopper regulator IC
7 LED group (electrical load)
11 FET
DESCRIPTION OF SYMBOLS 12 Amplifier 13 Drive circuit 14 Current detection comparator 15 Oscillation circuit 16 Error amplifier 17 PWM comparator 18 ON / OFF circuit 19 Overvoltage protection circuit 20 Soft start circuit 21 Output voltage detection circuit 22 Voltage dividing circuit 23 Voltage dividing ratio changeover switch 24 Differential amplifier 25 Overvoltage detection unit Ro Output current setting resistor R1, R4, R21 to R24 Resistance element

Claims (8)

  1. In a power supply circuit for supplying power to an LED as an electrical load,
    An overvoltage protection circuit for controlling the output voltage output to the load so as not to exceed a predetermined overvoltage detection level;
    Adjusting means for adjusting the overvoltage detection level;
    A power supply circuit comprising:
  2. The overvoltage protection circuit is:
    A voltage dividing circuit that receives the output voltage, divides the voltage, and outputs the divided voltage;
    A power control circuit that switches ON / OFF of the power supply according to the voltage output from the voltage dividing circuit,
    The adjusting means includes
    The power supply circuit according to claim 1, wherein the adjustment is performed by changing a voltage dividing ratio in the voltage dividing circuit.
  3. An information acquisition unit for acquiring information for adjusting the overvoltage detection level from the outside,
    The adjusting means includes
    The power supply circuit according to claim 1, wherein the adjustment is performed based on the information acquired by the information acquisition unit.
  4. A voltage detection unit for detecting the output voltage;
    The adjusting means includes
    The power supply circuit according to claim 1, wherein the adjustment is performed based on a detection result by the voltage detection unit.
  5. An information acquisition unit for acquiring information for adjusting the overvoltage detection level from outside;
    A voltage detection unit for detecting the output voltage,
    The adjusting means includes
    The power supply circuit according to claim 1, wherein the adjustment is performed based on the information acquired by the information acquisition unit and a detection result by the voltage detection unit.
  6. An overvoltage detector that detects whether the output voltage exceeds an overvoltage detection level; and
    A signal output unit for outputting a signal according to the detection result to the outside;
    The power supply circuit according to any one of claims 1 to 5, further comprising:
  7.   The power supply circuit according to claim 1, wherein the power supply circuit is a step-up DC-DC converter circuit.
  8.   An electronic apparatus comprising the power supply circuit according to claim 1.
JP2006344575A 2006-12-21 2006-12-21 Power supply circuit and electronic equipment using the same Pending JP2008160934A (en)

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2010263711A (en) * 2009-05-08 2010-11-18 Renesas Electronics Corp Input overvoltage protection circuit with soft start function
WO2011065536A1 (en) * 2009-11-30 2011-06-03 株式会社 東芝 Protective relay
JP2016115639A (en) * 2014-12-18 2016-06-23 三菱電機株式会社 Led lighting device and lighting fixture

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JP2010263711A (en) * 2009-05-08 2010-11-18 Renesas Electronics Corp Input overvoltage protection circuit with soft start function
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JP2011115004A (en) * 2009-11-30 2011-06-09 Toshiba Corp Protective relay
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JP2016115639A (en) * 2014-12-18 2016-06-23 三菱電機株式会社 Led lighting device and lighting fixture

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