JP5462969B2 - LED power supply circuit and lighting apparatus using the same - Google Patents

Description

  The present invention relates to an LED power supply circuit having a DC-DC conversion circuit and a lighting fixture using the same.

  In recent years, the performance of LEDs has increased, and lighting fixtures using LEDs are in a state where they can be replaced with conventional light sources because of their long life. If the performance of LEDs further improves in the future, it will be adopted in the field of general-purpose lighting equipment. In addition, an LED power supply circuit using a DC-DC conversion circuit has been proposed to improve circuit efficiency.

  In Patent Document 1 (Japanese Patent Laid-Open No. 2008-130438), a commercial AC power supply is full-wave rectified by a diode bridge, and a DC voltage smoothed by a smoothing capacitor is converted into power by a DC-DC conversion circuit and supplied to an LED. A circuit is disclosed. Moreover, the structure which connected the circuit ground of the DC-DC conversion circuit to the instrument earth via the earth | ground capacitor | condenser is disclosed. However, detailed studies have not been made on optimizing the capacities of the smoothing capacitor and the grounding capacitor.

JP 2008-130438 A

  In an LED power supply circuit having a DC-DC conversion circuit, it is necessary to provide a noise filter in the power supply input portion so that switching noise does not leak to the input power supply line. It tends to increase. In order to reduce noise, it is conceivable to connect the circuit ground of the DC-DC conversion circuit to the instrument ground. However, as the capacity between the circuit ground and the appliance increases, the withstand capability against lightning surge voltage (common mode) decreases. Therefore, it is necessary to select a capacity so as to satisfy the lightning surge performance while suppressing the noise terminal voltage within the regulation range.

  The present invention has been made in view of the above points, and in an LED power supply circuit using a DC-DC conversion circuit, reduces high-frequency noise propagating to an input power supply line and improves lightning surge performance. Is an issue.

  In order to solve the above-mentioned problem, the invention of claim 1 is, as shown in FIG. 1, an input filter circuit including at least noise prevention capacitors C1 and C2 and a line filter LF, and an AC voltage connected to the input filter circuit. Bridge DB that performs full-wave rectification, a smoothing capacitor C3 that is connected to the output of the diode bridge DB and has a capacity of 1 μF or less that smoothes the pulsating voltage, and a DC-DC conversion circuit that is connected to both ends of the smoothing capacitor C3 (Here, a step-down chopper circuit) and an LED power supply circuit composed of an LED light-emitting unit 2 connected to the output of the DC-DC conversion circuit, between the input power supply lines between the line filter LF and the diode bridge DB Capacitors C11 and C12 are connected in series, and the capacitor C11 and C12 are connected between the midpoint of connection and the ground FG. Insert the capacitors C13, the total capacitance between the input power supply line and the earth FG is characterized in that which is set to be less than 1/200 of the smoothing capacitor C3.

  The invention of claim 2 is a lighting fixture in which the LED power circuit 4 according to claim 1 is housed in a metal case 7 (FIG. 7).

  According to the present invention, in an LED power supply circuit using a DC-DC conversion circuit, high-frequency noise propagating to an input power supply line is suppressed, and an applied voltage after rectification when a common mode lightning surge is applied is suppressed. -There exists an effect which can prevent destruction of the control circuit and LED of a DC conversion circuit.

It is a circuit diagram of Embodiment 1 of the present invention. It is a figure which shows the measurement result of the noise terminal voltage of the conventional LED power supply circuit. It is a figure which shows the measurement result of the noise terminal voltage of the LED power supply circuit of this invention. It is a figure which shows the measurement result of the lightning surge voltage of Embodiment 1 of this invention. It is a circuit diagram of Embodiment 2 of the present invention. It is a circuit diagram of Embodiment 3 of the present invention. It is sectional drawing of the lighting fixture of Embodiment 4 of this invention.

(Embodiment 1)
FIG. 1 is a circuit diagram of Embodiment 1 of the present invention. The AC input terminal of the diode bridge DB is connected to the commercial AC power source Vs via the line filter LF. A parallel circuit of a noise preventing capacitor C1 and a non-linear resistance element ZNR is connected to the power source side of the line filter LF. A noise prevention capacitor C2 is connected to the output end of the line filter LF. A series circuit of capacitors C11 and C12 (first and second capacitors) is connected in parallel to the noise preventing capacitor C2. The connection point between the capacitors C11 and C12 is connected to the ground FG via a capacitor C13 (third capacitor).

  A smoothing capacitor C3 is connected to the DC output terminal of the diode bridge DB. The smoothing capacitor C3 is a capacitor that smoothes the pulsating voltage at the DC output end of the diode bridge DB. The capacitance of the smoothing capacitor C3 is 1 μF or less.

  The negative electrode of the smoothing capacitor C3 is connected to the circuit ground G. The positive electrode of the smoothing capacitor C3 is connected to the anode side of the LED light emitting unit 2. One end of an inductor L1 is connected to the cathode side of the LED light emitting unit 2. The other end of the inductor L1 is connected to the anode of the diode D1. The cathode of the diode D <b> 1 is connected to the anode side of the LED light emitting unit 2. The anode of the diode D1 is connected to the drain electrode of the switching element Q1 made of MOSFET. A current detection resistor R1 is connected between the source electrode of the switching element Q1 and the circuit ground G. The non-ground side terminal of the current detection resistor R1 is connected to the detection terminal of the control unit 1. The gate electrode of the switching element Q1 is connected to the PWM signal output terminal of the control unit 1.

  The control unit 1 is a control IC for a switching power supply, and controls the on-time and off-time of the switching element Q1 while monitoring the current detected by the current detection resistor R1, so that the current flowing through the LED light-emitting unit 2 Is to control. When the switching element Q1 is on, a current flows through a path of the smoothing capacitor C3 → the LED light emitting unit 2 → the inductor L1 → the switching element Q1 → the current detection resistor R1 → the smoothing capacitor C3. At this time, the current flowing through the inductor L1 gradually increases, and electromagnetic energy is accumulated in the inductor L1. When the switching element Q1 is turned off, the electromagnetic energy accumulated in the inductor L1 is released through the path of the inductor L1, the diode D1, the LED light emitting unit 2, and the inductor L1. By repeating this operation at a high frequency, the average current flowing through the LED light emitting unit 2 is controlled to be a desired current.

  Since the switching element Q1 is switched at a frequency sufficiently higher than the frequency of the commercial AC power supply Vs, and the capacitance of the smoothing capacitor C3 is set to be as small as 1 μF or less (for example, 0.23 μF), the commercial AC power supply The input power factor from Vs increases. On the other hand, leakage of high frequency noise to the input power supply line becomes a problem. Therefore, the line filter LF and the noise prevention capacitors C1 and C2 are provided in the power supply input section to prevent leakage of high frequency noise to the input power supply line.

  Further, by connecting the input power supply line to the equipment ground FG at high frequency via the capacitors C11 to C13 connected in a Y-shape, the common mode high frequency noise applied between the ground and the input power supply line is reduced. Reduced. The appliance ground FG is electrically connected to a metal case that houses the power supply block, and the metal case is grounded.

  FIG. 2 shows the result of measuring the noise terminal voltage level when the capacitors C11 to C13 are not present, and FIG. 3 is the result of measuring the noise terminal voltage level when the capacitors C11 to C13 are present. In either case, the metal case that houses the power supply block is connected to the ground. The capacitance of each of the capacitors C11 to C13 was 220 pF, and the capacitance of the smoothing capacitor C3 was 0.23 μF.

  In FIG. 2 and FIG. 3, a line indicated by a straight line is a noise regulation line. In the case of FIG. 2 without the capacitors C11 to C13, there is a frequency band exceeding the noise regulation line. On the other hand, in the case of FIG. 3 having the capacitors C11 to C13, it can be seen that there is no frequency band exceeding the noise regulation line.

  Next, the result of measuring the lightning surge voltage after rectification by the diode bridge DB is shown in FIG. The horizontal axis represents the total capacitance value (pF) of the capacitors C11, C12, and C13, and the vertical axis represents the measurement result of the rectified surge voltage (V) when a common mode lightning surge (5 kV) is applied. The capacitance of the smoothing capacitor C3 was 0.23 μF.

  As shown in FIG. 4, it seems that the lightning surge voltage is dramatically improved when the total capacitance value of the grounding capacitors C11 to C13 is less than 300 to 500 pF, but the scale on the vertical axis is actually enlarged. Therefore, it can be said that it is within the range of measurement error (variation). The only thing that can be certainly said is that when the total capacitance value of the grounding capacitors C11 to C13 is in the range of several tens of pF to several thousand pF, the surge voltage after rectification increases as the total capacitance value of the grounding capacitors C11 to C13 increases. Can be said to be within the range of 900 to 1100V.

  As can be seen from the comparison between FIG. 2 and FIG. 3, when the total capacitance value of the grounding capacitors C11 to C13 increases, the noise terminal voltage decreases, but when it increases excessively, as shown in FIG. Will increase. Therefore, it can be said that the total capacitance value of the earthing capacitors C11 to C13 is preferably selected so that the lightning surge voltage is within the allowable range and the noise terminal voltage can be suppressed within the regulation range.

  When the capacity of the smoothing capacitor C3 is 1 μF or less (for example, 0.23 to 0.47 μF), the present inventors generally have a total capacity value of the capacitors C11 to C13 of 1/200 or less of the capacity value of the smoothing capacitor C3. If it is set to, the noise propagating to the input power line can be reduced within the restricted range while suppressing the lightning surge voltage (after rectification) within the range where there is no practical problem (around 1 kV). Obtained knowledge.

  In the present invention, the total capacitance value of the grounding capacitors C11 to C13 is not defined as an absolute value, but as a relative value with respect to the capacitance of the smoothing capacitor C3. The reason for this is that if the capacitance of the smoothing capacitor C3 is different, the impedance to the high frequency noise is different, so that the level of the high frequency noise superimposed on the input power supply line is changed, or the voltage after rectification is divided by the divided voltage with the grounding capacitors C11 to C13 This is because the possibility of the surge voltage level changing is taken into consideration. By defining the total capacitance value of the earthing capacitors C11 to C13 as a relative value with respect to the capacitance of the smoothing capacitor C3, it is possible to define the voltage division ratio with respect to the lightning surge voltage. it can.

(Embodiment 2)
FIG. 5 is a circuit diagram of Embodiment 2 of the present invention. The description of the same configuration as that of the first embodiment is omitted. In the present embodiment, the negative electrode of the DC output terminal of the diode bridge DB connected to the circuit ground G is connected to the appliance ground FG via a series circuit of capacitors C11 and C12. Also in this embodiment, when the capacitance of the smoothing capacitor C3 is 1 μF or less (for example, 0.23 to 0.47 μF), the total capacitance value of the capacitors C11 and C12 is approximately 1/200 or less of the capacitance value of the smoothing capacitor C3. If it is set to, the noise propagating to the input power line can be reduced within the regulation range while suppressing the lightning surge voltage.
(Embodiment 3)
FIG. 6 is a circuit diagram of Embodiment 3 of the present invention. In this embodiment, the configuration of the DC-DC conversion circuit in the first embodiment is a flyback converter circuit instead of the step-down chopper circuit. The configuration and operation of the flyback converter circuit are well known.

  When the switching element Q1 is on, a current flows through the path of the smoothing capacitor C3 → the primary winding of the transformer T1, the switching element Q1, the current detection resistor R1, and the smoothing capacitor C3. At this time, the current flowing through the primary winding of the transformer T1 gradually increases, and electromagnetic energy is accumulated in the transformer T1. When the switching element Q1 is turned off, the electromagnetic energy accumulated in the transformer T1 is released through the path of the secondary winding of the transformer T1, the diode D1, the LED light emitting unit 2, and the secondary winding of the transformer T1. By repeating this operation at a high frequency, the average current flowing through the LED light emitting unit 2 is controlled to be a desired current. Note that a capacitor C4 is connected in parallel with the LED light emitting unit 2 so that a current can be supplied to the LED light emitting unit 2 even when the diode D1 is in a cut-off state when the switching element Q1 is turned on.

  Also in this embodiment, when the capacitance of the smoothing capacitor C3 is 1 μF or less (for example, 0.23 to 0.47 μF), the total capacitance value of the capacitors C11 to C13 is approximately 1/200 or less of the capacitance value of the smoothing capacitor C3. If it is set to, the noise propagating to the input power line can be reduced within the regulation range while suppressing the lightning surge voltage.

Although not shown, also in the second embodiment, the configuration of the DC-DC conversion circuit may be a flyback converter circuit instead of the step-down chopper circuit.
(Embodiment 4)
FIG. 7 is a cross-sectional view of an LED lighting apparatus using the LED power supply circuit according to any one of Embodiments 1 to 3. The fixture housing 7 of the LED lighting fixture is embedded in the ceiling 9. The LED light emitting unit 2 and the power supply circuit unit 4 are built in the appliance housing 7. The instrument housing 7 is made of a metal cylinder that is open at the lower end, and the open end of the lower end is covered with a light diffusion plate 8. The LED light emission part 2 is arrange | positioned so that this light-diffusion plate 8 may be opposed. Reference numeral 21 denotes an LED mounting board on which the LEDs 2a to 2d of the LED light emitting unit 2 are mounted.

  Here, the LED light emitting unit 2 includes four LEDs 2a to 2d, and the LED 2a to LED 2d are connected in series from the anode to the cathode. When a positive voltage is applied to the anode side of the LED 2a and a negative voltage is applied to the cathode side of the LED 2d, each of the LEDs 2a to 2d emits light. When a voltage equal to or higher than the total of the forward voltages Vf of the LEDs 2a to 2d is applied, a light beam can be obtained from the LEDs according to the value of the flowing current. Since the forward voltage Vf is usually about 3.5 V, if four are connected in series, they can be lit at a DC voltage of 4 × 3.5 V or more.

  Reference numeral 41 denotes a power circuit board on which electronic components of the power circuit section 4 are mounted. The LED light emission part 2 is installed so that it may contact the heat sink 71 in the instrument housing | casing 7, and the heat | fever which LED2a-2d generate | occur | produces is released to the instrument housing | casing 7. FIG. Further, the LED light emitting unit 2 and the lighting circuit unit 4 are connected by a lead wire 5 through a hole provided in the heat radiating plate 71. The heat dissipation plate 71 is a metal plate such as an aluminum plate or a copper plate, and has both a heat dissipation effect and a shielding effect. The heat radiating plate 71 is electrically connected to the instrument housing 7 and grounded, but is a non-charging portion that is electrically separated from the plus side and the minus side of the lead wire 5.

2 LED light emitting unit DB Diode bridge LF Line filter C1, C2 Noise prevention capacitor C3 Smoothing capacitor C11 to C13 Earthing capacitor

Claims (2)

An input filter circuit including at least a noise prevention capacitor and a line filter;
A diode bridge connected to the input filter circuit for full-wave rectification of an AC voltage;
A smoothing capacitor connected to the output of the diode bridge and having a capacitance of 1 μF or less for smoothing the pulsating voltage;
A DC-DC conversion circuit connected to both ends of the smoothing capacitor;
An LED power supply circuit configured by an LED light emitting unit connected to an output of the DC-DC conversion circuit,
A first capacitor and a second capacitor are connected in series between input power lines between the line filter and the diode bridge, and between the connection midpoint of the first capacitor and the second capacitor and the ground. A third capacitor is inserted in the LED power supply circuit, and the total capacity between the input power supply line and the ground is set to 1/200 or less of the smoothing capacitor. A lighting fixture comprising the LED power supply circuit according to claim 1 housed in a metal case.

Images