JP5929457B2 - Power supply circuit and LED lighting device using the same - Google Patents

Description

  The present invention relates to a power supply circuit and an LED lighting device including the power supply circuit, and more particularly to a power supply circuit with enhanced measures against inrush current and an LED lighting device including the power supply circuit.

  FIG. 4 shows a conventional power supply circuit. The power supply circuit includes an AC-DC conversion circuit 1 that converts an AC power supply voltage into a DC voltage and charges the capacitor 15, and a current control circuit 3 that limits a current from the charging voltage of the capacitor 15 to the LED 5. The DC conversion circuit 1 includes an inrush current prevention circuit 2. The inrush current prevention circuit 2 prevents a large current from flowing as a charging current to the capacitor 15 when the AC power is turned on. If such a large current is not prevented, problems such as failure of components such as a rectifier circuit on the charging path of the capacitor 15 and blown fuse may occur in the power supply circuit. Problems such as switch contact welding, breaker disconnection, power supply voltage instability, and associated effects on other devices (sharing power supply) may occur (see, for example, Patent Documents 1 and 2).

  Regarding the inrush current prevention circuit 2, the transistor 22 is in an off state (non-conduction state) when the AC power is turned on, and an input current flows through the current limiting resistor 21. Accordingly, the capacitor 15 is charged while the inrush current is prevented. In the process, when the potential of the source side terminal of the transistor 22 rises, the gate driver 23 starts to operate. The gate driver 23 generates the gate voltage of the transistor 22 according to the time constant of the resistor 24 and the capacitor 25. When the gate-source voltage exceeds the threshold value, the transistor 22 is turned on (conductive state), and the current limiting resistor 21 is bypassed. Thereafter, the ON state of the transistor 22 is maintained by the gate-source voltage smoothed by the capacitor 25. As a result, it is possible to prevent an inrush current when the AC power source is turned on for the first time and to prevent a loss in the current limiting resistor 21 during the steady operation.

Japanese Patent No. 4249542 JP-A-11-289657

  However, in the above configuration, even when the AC power supply is instantaneously interrupted or when the AC power supply is turned off for a short time after being turned off, that is, even when the AC power supply is cut off for several milliseconds to several seconds, the capacitor 15 and If a certain voltage remains at 25, the power supply circuit continues the steady operation. In other words, even if the AC power supply voltage is temporarily interrupted, the voltage of the capacitor 25 is not completely discharged by the resistor 26 and the on state of the transistor 22 is maintained. On the other hand, the voltage of the capacitor 15 is discharged as a load current to the LED 5 by the operation of the current control circuit 3. As a result, depending on the AC power supply cut-off period, the voltage may remain in the capacitor 25 while the voltage of the capacitor 15 may be greatly reduced. When the AC power supply is restored in this state, a large current (that is, an inrush current) flows into the capacitor 15 with the current limiting resistor 21 bypassed by the transistor 22.

  Thus, if the inrush current at the time of AC power recovery flows into the capacitor 15 via the transistor 22, the transistor 22 may be damaged due to the large current. In addition, since the inrush current prevention circuit 2 does not perform its function, various problems due to the above-described inrush current may occur.

  Accordingly, the present invention provides a power supply circuit that can suppress an inrush current and protect an inrush current prevention circuit and avoid various problems caused by the inrush current even when the AC power supply is restored after being cut off for a short time. It is another object of the present invention to provide an LED lighting device using the same.

  A power supply circuit according to a first aspect of the present invention includes a DC conversion circuit that converts an input voltage into a rated output value and charges the first capacitor, and current control for generating a load current from the charging voltage of the first capacitor. A charge suppression circuit inserted in the charging path of the circuit and the first capacitor, having a current limiting state for limiting the input current and a current passing state for which the limitation is released, and during a predetermined period after the input voltage is cut off, A charging suppression circuit configured to maintain the passing state, and a discharge suppression circuit that reduces the load current and suppresses the discharge of the first capacitor when the charging voltage becomes equal to or lower than the set value are provided.

  As an example, the charge suppression circuit includes a resistor, a transistor, a driving unit that drives the transistor, and a second capacitor. A resistor is inserted in the charging path, the input terminal and output terminal of the transistor are connected to both terminals of the resistor, respectively, and the second capacitor is connected to hold the voltage between the control terminal and the output terminal of the transistor, and is driven The unit receives the input voltage and charges the second capacitor, and the input terminal and the output terminal are made conductive when the voltage of the second capacitor is equal to or higher than the threshold value.

  Here, the discharge suppression circuit may be configured to stop the operation of the current control circuit when the charging voltage becomes a set value or less.

  The set value is preferably 80% or more and 95% or less of the rated output value.

  According to a second aspect of the present invention, there is provided a power supply circuit according to the first aspect, an LED connected to an output end of a current control circuit of the power supply circuit, and a housing that includes the power supply circuit and has the LED attached thereto. LED lighting device.

It is a circuit block diagram of the power supply circuit by the Example of this invention. 1 is a diagram of an LED lighting device according to an embodiment of the present invention. It is a circuit block diagram of the power supply circuit by the modification of this invention. It is a circuit block diagram of the conventional power supply circuit.

Example.
FIG. 1 shows a circuit configuration diagram of a power supply circuit according to an embodiment of the present invention. The power supply circuit converts an AC power supply voltage into a direct current and charges the smoothing capacitor 15 with an AC-DC conversion circuit 1 (direct current conversion circuit), and current control for generating a load current to the LED 5 from the charged voltage of the capacitor 15 The circuit 3, the inrush current prevention circuit 2 (charge suppression circuit) inserted in the charging path of the capacitor 15, and the discharge suppression circuit that stops the current control circuit 3 and suppresses the discharge of the capacitor 15 when the charging voltage is lower than the set value. 4 is provided. In addition, in FIG. 1, although LED5 which consists of a single element as a load is shown in figure, LED5 is illustrated in the meaning including the structure by which a some LED element is connected in series.

  The AC-DC conversion circuit 1 includes a rectifier 11, a coil 12, a transistor 13, a diode 14, and a capacitor 15, and constitutes a boost chopper circuit. The transistor 13 is switching-controlled by the gate driving unit 16 and, for example, PWM-controlled in synchronization with the pulsating flow of the output of the rectifier 11. As a result, the AC power supply voltage (100 V, 200 V, etc.) is boosted to a rated output value (for example, about 400 V), and the capacitor 15 is charged.

  In this specification, “transistor” is described as including a field effect transistor (FET) and a so-called bipolar transistor. Therefore, in this application, the input terminal of a transistor is a drain terminal, a collector terminal, etc., the control terminal is a gate terminal, a base terminal, etc., and the output terminal is a source terminal, an emitter terminal, etc. is there.

  The inrush current prevention circuit 2 includes a current limiting resistor 21, a transistor 22, a gate drive unit 23 of the transistor 22, a resistor 24, a capacitor 25, and a resistor 26. When the AC power is turned on, the transistor 22 is in an off state (non-conducting state), and an input current flows through the current limiting resistor 21. Accordingly, the capacitor 15 is charged while the inrush current is prevented. In the process, when the potential of the source side terminal of the transistor 22 rises, the gate driver 23 starts to operate. The gate driver 23 generates the gate voltage of the transistor 22, and the gate-source voltage increases with the time constant of the resistor 24 and the capacitor 25. When the gate-source voltage exceeds the threshold value of the transistor 22, the transistor 22 is turned on (conductive state), and the current limiting resistor 21 is bypassed. Thereafter, the ON state of the transistor 22 is maintained by the gate-source voltage smoothed by the capacitor 25 regardless of the pulsating current of the AC power supply voltage. As a result, it is possible to prevent an inrush current when the AC power source is turned on for the first time and to prevent a loss in the current limiting resistor 21 during the steady operation.

  In other words, the inrush current prevention circuit 2 has a current limiting state in which the input current is limited when the transistor 22 is off, and a current passing state in which the current limitation is released when the transistor 22 is on. Then, the current limiting state is maintained during the charging period of the capacitor 25 after the input voltage is input, and the current passing state is entered after the charging period of the capacitor 25 elapses. On the other hand, the current passing state is maintained during the discharging period of the capacitor 25 after the input voltage is cut off, and the current limiting state is entered after the discharging period of the capacitor 25 has elapsed.

  The current control circuit 3 includes a transistor 31, a coil 32, a diode 33, and a capacitor 34, and constitutes a step-down chopper circuit. The transistor 31 is PWM-controlled by a gate drive unit 35 (for example, a gate drive IC), and is controlled so that the load current flowing through the LED 5 becomes a desired value. Specifically, when the transistor 31 is on, a current flows from the capacitor 15 to the transistor 31 → the coil 32 → the LED 5, and when the transistor 31 is off, the coil 32 → the LED 5 → the diode 33 based on the energy stored in the coil 32. Current flows through The gate driver 35 controls the on width of the transistor 31. In this embodiment, the operation of the gate drive unit 35 is active (steady operation) when the terminal A is high (open state) and is stopped when the terminal A is low (ground connection state). And

  The discharge suppression circuit 4 includes a detection unit including a resistor 41, a resistor 42, and a Zener diode 43, and a switching unit including a transistor 44, a resistor 45, a resistor 46, and a transistor 47. The detection unit detects the charging voltage of the capacitor 15, and the operation state of the switching unit is switched according to the detected charging voltage. For example, when the charging voltage of the capacitor 15 is the rated value (400 V) during steady operation, the transistor 44 is turned on, and thereby the transistor 47 is turned off. When the transistor 47 is off, the gate driving unit 35 (that is, the current control circuit 3) continues the steady operation as described above. On the other hand, when the charging voltage of the capacitor 15 becomes equal to or lower than the set value (360 V in this example) due to the decrease in the AC power supply voltage, the transistor 44 is turned off, and thereby the transistor 47 is turned on. When the transistor 47 is on, the gate drive unit 35 stops operating as described above, the transistor 31 is turned off, and the output of the current control circuit 3 is stopped.

  That is, when the AC power supply is temporarily cut off due to an instantaneous power failure or the like, the charging voltage of the capacitor 15 which was 400 V until then is discharged by the energization of the LED 5 by the current control circuit 3 and decreases to 360 V. When the charging voltage becomes 360 V or less, the operation of the gate driving unit 35 is stopped. Therefore, the current control circuit 3 is stopped and the charging voltage of the capacitor 15 is maintained at about 360V.

  On the other hand, if the voltage of the capacitor 25 of the inrush current prevention circuit 2 is maintained, the transistor 22 can be kept on. Here, assuming that the boost operation of the AC-DC conversion circuit 1 continues when the AC power is restored, the AC-DC conversion circuit 1 recovers about 40 V from about 360 V near the set value to 400 V of the rated output value. Therefore, the current flowing into the capacitor 15 is much smaller than the inrush current as in the prior art.

  The set value is determined in consideration of the boosting capability of the AC-DC conversion circuit 1 and the capacitance of the capacitor 15. The set value is preferably set to be equal to or lower than the lower limit value of the output error of the AC-DC conversion circuit 1, thereby preventing unnecessary operation of the discharge suppression circuit 4. Since this output error is determined by the specification of the gate drive IC used for the gate drive unit 16, for example, the set value is preferably about 95% or less of the rated output value. In order to further demonstrate the effects of the present invention, the set value is preferably about 80% or more of the rated output value. Accordingly, the set value is preferably about 80% to 95% of the rated output value, and most preferably about 90%. Note that if the voltage of the capacitor 15 becomes equal to or lower than the forward voltage (Vf) of the LED 5 when the AC power is cut off, the load current disappears, so the voltage of the capacitor 15 is not discharged any more, but the Vf of the LED 5 is significantly lower than the rated output value. In such a case, an inrush current may occur when the AC power is restored. Accordingly, it is desirable that the set value is higher than Vf of the LED 5.

  If the AC-DC conversion circuit 1 is in an inoperative state when AC power is restored, the voltage (360 V) of the capacitor 15 is higher than the peak voltage (141 V or 282 V) of the AC power voltage, and the diode 14 is turned off. The input current does not flow into the capacitor 15.

  In addition, when the AC power supply returns after a sufficient time has elapsed after being shut off (for example, when the shutoff period is several seconds or more), the voltage of the capacitor 25 of the inrush current prevention circuit 2 is discharged by the resistor 26. The transistor 22 is turned off. Therefore, the inrush current is prevented by the inrush current prevention circuit 2 regardless of the operations of the AC-DC conversion circuit 1, the current control circuit 3, and the discharge suppression circuit 4.

  Further, in a longer interruption period (for example, several minutes or more), the voltage of the capacitor 15 is preferably discharged by the resistors 41 and 42 and the resistors 45 and 46 in order to prevent a high voltage charged state for a long time. . As described above, the series resistance circuit of the resistors 41 and 42 constituting the detection unit and the series resistance circuit of the resistors 45 and 46 for generating the operating voltage of the switching unit have the remaining voltage of the capacitor 15 from a long-term viewpoint. It also functions as a discharge circuit. However, it is necessary to select the resistors 41, 42, 45, and 46 so that the voltage of the capacitor 15 stays in the vicinity of the set value for at least a period longer than the discharge period of the capacitor 25.

  Moreover, the discharge suppression circuit 4 can also be comprised with a microcomputer instead of the analog circuit which consists of resistance, a Zener diode, and a transistor. For example, a voltage detected by the resistors 41 and 42 may be input to the input port of the microcomputer, and a stop signal may be output from the output port to the gate driving unit 35 when the detected voltage becomes a predetermined value or less.

  In the above configuration, the configuration in which the operation of the current control circuit 3 is stopped when the detected charging voltage becomes equal to or lower than the set value is shown. However, the configuration in which the operation of the current control circuit 3 is not completely stopped may be employed. For example, the discharge suppression circuit 4 may operate the current control circuit 3 intermittently or operate the current control circuit 3 in a low output state (preferably the minimum output state) while the AC power supply is shut off. . For example, when the load is an LED, the LED blinks in the intermittent operation state and is dimmed in the low output state. In addition, when the load is a discharge lamp, blinking is not preferable from the viewpoint of the life of the discharge lamp and the like, and it is only necessary to perform dimming lighting by a low output operation instead of an intermittent operation. Thereby, the voltage of the capacitor 15 gradually decreases from the upper limit value of the set value toward the lower limit value.

  As described above, according to the power supply circuit of the present embodiment, even when the AC power supply is interrupted for a short time, the discharge suppression circuit 4 suppresses the discharge from the capacitor 15, thereby charging the capacitor 15 when the AC power supply is restored. The current can be reduced and the inrush current prevention circuit 2 can be protected. In addition to protecting the inrush current prevention circuit 2, circuit components such as the rectifier 11 and the diode 14 on the charging path of the capacitor 15 can be protected, and other various problems caused by the inrush current described above are avoided. can do.

  Here, the LED 5 is turned off by stopping the current control circuit 3 when the AC power supply is cut off. However, unlike the high pressure discharge lamp or the like, the LED does not require a special sequence (high voltage application, rise control, etc.) in relighting. Therefore, it is only necessary to restart the operation of the current control circuit 3 when the AC power is restored. Moreover, even if the LED 5 is turned off for almost the same time as the momentary power failure when the AC power supply is momentarily interrupted, there is almost no visual hindrance for the user. Therefore, there is no problem in turning off the LED 5 during the momentary power interruption of the AC power supply. In other words, the configuration of the power supply circuit of the present invention is particularly suitable for the LED lighting device.

  FIG. 2 shows a schematic configuration of an LED lighting device equipped with the above power supply circuit. The LED lighting device includes a power supply circuit 6 that is fed with power from an AC power supply via wirings L1 and L2, an LED 5 connected to an output end of the power supply circuit 6, and a housing 7 that encloses the power supply circuit 6. In FIG. 2, the power supply circuit 6 and the LED 5 are integrated, but the LED 5 may be separately provided from the power supply circuit 6 and the housing 7 via a cable.

  In this way, even when the AC power supply is momentarily interrupted or when the AC power supply is turned off for a short time after being turned off, a large current is prevented from flowing through the LED lighting device when the AC power supply is restored. Therefore, not only problems in the power supply circuit due to a large current when AC power is restored, that is, circuit component failure, fuse blown, but also problems outside the power supply circuit, that is, power switch contact welding, breaker disconnection, power supply voltage failure, etc. Stabilization and the accompanying influence on other devices (sharing power supply) are prevented.

Modified example.
In the above embodiment, a configuration including a current limiting resistor and a bypass transistor connected in parallel to the current limiting resistor is shown as the inrush current prevention circuit. FIG. 3 shows a circuit configuration diagram of this modification. The difference from the embodiment shown in FIG. 1 is that the inrush current prevention circuit 2 ′ is composed of a thermistor 27. Since the configuration other than the inrush current prevention circuit 2 'is the same as that of the above embodiment, the description thereof is omitted.

  The thermistor 27 is an NTC thermistor whose resistance value monotonously decreases with increasing temperature. Therefore, the thermistor 27 has a high resistance in a low temperature state immediately after the AC power supply is turned on, so that the input current to the capacitor 15 is limited. Here, when the AC power supply fails for a short time, the current does not flow to the thermistor 27 during the power failure, but the high temperature state is maintained, so that the resistance value of the thermistor 27 does not increase greatly.

  That is, the inrush current prevention circuit 2 ′, similarly to the inrush current prevention circuit 2, has a current limiting state in which the thermistor 27 limits the input current in a low temperature state and a current passing state in which the current limit is released in a high temperature state. Have. The current limit state is maintained during the temperature rise period of the thermistor 27 after the input voltage is turned on, and the current passing state is entered after the temperature rise period of the thermistor 27 has elapsed. On the other hand, the current passing state is maintained during the temperature drop period of the thermistor 27 after the input voltage is cut off, and the current limit state is entered after the temperature drop period of the thermistor 27 elapses. Therefore, assuming that the discharge suppression circuit 4 is not provided, an inrush current to the capacitor 15 occurs when the AC power is restored, as in the case of the prior art shown in FIG.

  Therefore, the power supply circuit of this modification also includes a discharge suppression circuit 4 that operates in the same manner as in the above embodiment when the AC power supply is stopped for a short time. The time required for the temperature of the thermistor 27 to decrease and the resistance value to be sufficiently high is longer than the time (time constant) in which the voltage of the capacitor 25 is discharged by the resistor 26 in the embodiment. Therefore, it is desirable to delay the discharge of the capacitor 15 by causing the discharge suppression circuit 4 to function until the inrush current prevention circuit 2 ′ recovers its function. In order to further delay the discharging of the capacitor 15 when the AC power supply is stopped, the resistance values of the resistors 41, 42, 45 and 46 may be set higher than those in the embodiment or set to a higher value. However, it is necessary to select the resistors 41, 42, 45, and 46 so that the voltage of the capacitor 15 stays near the set value for at least a period longer than the temperature decrease period of the thermistor 27.

  As described above, according to the power supply circuit of this modification, even when the AC power supply is interrupted for a short time, the discharge suppression circuit 4 suppresses the discharge from the capacitor 15, thereby charging the capacitor 15 when the AC power supply is restored. Can be reduced. Thereby, circuit components such as the rectifier 11 and the diode 14 on the charging path of the capacitor 15 can be protected, and various problems caused by the inrush current described above can be avoided.

In the above-described embodiments and modifications, the most preferred examples of the present invention have been shown. However, the present invention can be modified as follows.
For example, in the above-described embodiments and modifications, the input power supply is an AC power supply, but the present invention can also be applied to a DC power supply. In this case, the AC-DC conversion circuit 1 is replaced with a DC-DC conversion circuit having a known configuration.

  Moreover, in the said Example and modification, although the current limiting resistance 21 and the thermistor 27 of the inrush current control circuits 2 and 2 'were shown inserted into the high potential side of the charging path, the current limiting resistance 21 or the thermistor 27 is shown. May be inserted on the low potential side (ground line side) of the charging path. In other words, the inrush current suppressing circuit is not limited to the configuration shown in the embodiment or the modified example, and after the current flowing into the smoothing capacitor 15 is restricted when the AC power is turned on, the restriction is released with a predetermined time constant. Any charging suppression circuit may be used. In the above embodiment, the inrush current suppression circuit 2 is configured using the N-type transistor 22, but may be configured using a P-type transistor.

  Moreover, in the said Example and modification, although the current control circuit 3 was made into the step-down chopper circuit, the thing of other circuit formats, such as a flyback converter, may be sufficient. As the current control circuit 3, a step-down circuit, a step-up circuit, an AC conversion circuit, or the like can be applied depending on the load. For example, when the load is a discharge lamp for AC lighting such as a fluorescent lamp, the current control circuit 3 is a DC-AC conversion circuit such as a bridge circuit. That is, the current control circuit 3 according to the present invention only needs to discharge the charging voltage of the smoothing capacitor 15 to the load side by operating.

1. AC-DC conversion circuit (DC conversion circuit)
2, 2 '. Inrush current prevention circuit (charge suppression circuit)
3. 3. Current control circuit 4. Discharge suppression circuit LED (load)
6). 6. Power supply circuit Housing 15. Capacitor 21. Current limiting resistor 22. Transistor 23. Gate driver 24, 26. Resistance 25. Capacitor 27. Thermistors 41, 42, 45, 46. Resistance 43. Zener diodes 44, 47. Transistor

Claims (5)

The LED A power circuit to a load,
A DC conversion circuit that converts the input voltage into a rated output value and charges the first capacitor;
Current control circuit for generating a load current to the charging voltage or al the LED of the first capacitor,
A charge suppression circuit inserted in a charging path of the first capacitor, having a current limiting state for limiting an input current and a current passing state for releasing the limitation; charging inhibition circuit current passing state is configured to be maintained, and the charging voltage, stops the operation of the current control circuits to become less high set setpoint than the forward voltage Vf of the LED A power supply circuit comprising a discharge suppression circuit that suppresses discharge of the first capacitor.   2. The power supply circuit according to claim 1, wherein the charge suppression circuit includes a resistor, a transistor, a driving unit that drives the transistor, and a second capacitor, and the resistor is inserted into the charging path, and the input of the transistor A terminal and an output terminal are respectively connected to both terminals of the resistor, the second capacitor is connected to hold a voltage between the control terminal of the transistor and the output terminal, and the drive unit supplies the input voltage A power supply circuit configured to receive and charge the second capacitor and to conduct the input terminal and the output terminal when the voltage of the second capacitor is equal to or higher than a threshold value;   The power supply circuit according to claim 1, wherein the set value is 80% or more and 95% or less of the rated output value. A power supply circuit according to claim 1 or al 3 have shifted or claim, wherein the LED is mounted with enclosing said L ED connected to the output terminal of the current control circuit of the power supply circuit, and a power supply circuit LED lighting device provided with a housing. A power supply circuit having a discharge lamp as a load,
A DC conversion circuit that converts the input voltage into a rated output value and charges the first capacitor;
A current control circuit for generating a load current to the discharge lamp from a charging voltage of the first capacitor;
A charge suppression circuit inserted in a charging path of the first capacitor, having a current limiting state for limiting an input current and a current passing state for releasing the limitation; A charge suppression circuit configured to maintain a current passing state; and
A discharge suppression circuit that reduces the load current in the current control circuit when the charge voltage becomes a set value or less to dimm the discharge lamp and suppress the discharge of the first capacitor.
Power supply circuit with

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