JP2011090901A - Power supply circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power supply circuit which can reduce the "flickering phenomenon" of a lamp, by reducing the "capacity of a capacitor necessary for noise prevention", while increasing the reducing effect of switching noise, and in which the need for an electrolytic capacitor which controls the rate of the lifetime of the power supply circuit is dispensed with. <P>SOLUTION: In the power supply circuit 10 supplies power to a lamp 16, by rectifying and lowering the AC voltage Vi received from a commercial power source 12 via a dimmer 14 of a phase-control type, a line filter 22 installed on the primary side of a rectifying and smoothing circuit 18 is constituted of a noise-preventing capacitor 40, that is installed in parallel with the rectifying and smoothing circuit 18 and a filter resistor 42, installed at least on one of a pair of power supply lines 44 between the rectifying and smoothing circuit 18 and the noise-preventing capacitor 40. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a power supply circuit including a noise prevention capacitor for reducing switching noise generated in a switching type step-down circuit.

  Light-emitting diodes (hereinafter referred to as “LEDs”), which have lower power consumption and longer life than conventional incandescent bulbs, are used as one of the energy-saving measures as consumers become more eco-conscious. The range is rapidly widening, and there is a growing need to use LEDs as an alternative to incandescent bulbs.

  However, since the LED operates at a “DC” voltage lower than the commercial voltage (for example, 60 Hz, 100 V), when the LED is turned on using the commercial voltage, the commercial voltage is stepped down and rectified (= converted into a DC voltage). ) Or a power supply circuit for rectifying and stepping down and supplying power to the LED is essential.

  As such a power supply circuit, one that rectifies an AC voltage from a commercial AC power supply and converts it into a DC voltage, and then steps down the DC voltage with a switching circuit and supplies it to the LED has been developed. (For example, patent document 1).

  As shown in FIG. 3, the power supply circuit 1 described in Patent Document 1 is supplied with an AC voltage supplied from a commercial AC power supply 2 and input via a phase control type dimmer 3 using a triac 3a. After rectifying and smoothing by a rectifying / smoothing circuit 4 having a diode bridge 4a and a smoothing capacitor 4b, the voltage is stepped down to a predetermined voltage by a step-down chopper circuit 5 using a switching element, and then an LED 6 (in Patent Document 1, A plurality of LEDs are connected in series in the forward direction).

  According to this power supply circuit 1, the AC voltage from the commercial AC power supply 2 is converted into a DC voltage by the rectifying / smoothing circuit 4, and then the voltage is stepped down to a voltage corresponding to the LED 6 by the step-down chopper circuit 5. By supplying, the LED 6 can be turned on.

  Here, in order to dim the LED 6 using the phase control type dimmer 3, the rectifying / smoothing circuit 4 needs to reduce the capacity of the smoothing capacitor 4b to a “pulsating” DC voltage. is there. This is because if the capacitance of the smoothing capacitor 4b is increased to a constant voltage DC, the change in the DC voltage after rectification and smoothing at the conduction angle 90 ° to 180 ° of the triac 3a is reduced, and the LED 6 can be dimmed. Because it disappears. Furthermore, because of the capacitor input circuit, the distortion of the input current waveform is large, the holding current of the triac 3a cannot be maintained, malfunction occurs, and flicker occurs.

JP 2004-296205 A

  When the switching element used in the step-down chopper circuit 5 of the power supply circuit 1 is operated, switching noise (high frequency noise) is generated from the switching element. Among the switching noises, the frequency is relatively low. Since switching noise in the frequency range (150 kHz to 1 MHz) is particularly easy to return to the commercial power supply side, the power supply circuit 1 has a noise prevention capacitor 7 attached to the primary side of the rectifying / smoothing circuit 4 as a countermeasure against this switching noise. Yes.

  However, although the noise prevention capacitor 7 is effective as a countermeasure against switching noise from the switching element as described above, on the other hand, the presence of the noise prevention capacitor 7 causes an alternating current flowing through the noise prevention capacitor 7 to be present. Becomes a phase advance current, and this phase advance current flows also to the dimmer 3, so that the triac 3 a used in the dimmer 3 may malfunction and cause the LED 6 to flicker.

  That is, the dimmer 3 dims the load of the LED 6 by changing the effective value of the commercial AC voltage supplied to the LED 6 by controlling the phase angle (ignition phase angle) at which the triac 3a is turned on by the phase control signal. The TRIAC 3a operates so that, after the phase control signal is turned on, the TRIAC 3a is turned off by the characteristics of the TRIAC itself when the current value to be passed becomes equal to or lower than the holding current value. Therefore, when the phase advance current flows through the dimmer 3, if the commercial AC voltage is already flowing through the triac 3a at the timing of 0V, the triac 3a cannot be turned off, In some cases, the triac 3a may remain on until the current becomes zero over a half cycle.

  Moreover, since the phase advance current becomes 0 A before the timing when the commercial AC voltage becomes 0 V, the triac 3 a may be turned off at an early timing. In general, since a plurality of power supply circuits 1 are connected in parallel to one dimmer 3, a plurality of noise prevention capacitors 7 included in the power supply circuit 1 are also connected in parallel. The phase current increases, and the possibility that the triac 3a malfunctions further increases.

  By the way, the rectifying / smoothing circuit 4 of the power supply circuit 1 is provided with a smoothing capacitor 4b for smoothing the voltage rectified by the diode bridge 4a, in addition to the noise preventing capacitor 7, and this smoothing capacitor 4b. Has the effect of reducing switching noise, similar to the noise prevention capacitor 7.

  Therefore, it is conceivable to solve the above-described problem of the phase advance current by setting the capacity of the smoothing capacitor 4b to be large and reducing the capacity of the noise prevention capacitor 7. However, in this case, another problem arises. Will occur.

  That is, if the capacity of the smoothing capacitor 4b is set large, the alternating voltage rectified by the rectifying / smoothing circuit 4 becomes a constant direct current, and the dimming of the LED 6 using the phase control type dimmer 3 is controlled. There was a risk of being unable to do so.

  In addition, as the smoothing capacitor 4b having a large capacity, it is common to use an electrolytic capacitor that is easy to make because of its structure, and the electrolytic capacitor has a life-dependence due to temperature. The life of the electrolytic capacitor may become the rate limiting factor of the life of the power supply circuit 1.

  Further, if the capacitance of the noise prevention capacitor 7 and the smoothing capacitor 4b (that is, the capacitance of the capacitor used in the entire power supply circuit 1) is large, the input power factor of the power supply circuit 1 is lowered, and the input current is reduced accordingly. There was also a problem that it had to be increased.

  The present invention has been developed in view of such problems of the prior art. Therefore, the main problem of the present invention is to reduce the capacitance of the capacitor for noise prevention and the capacitance of the smoothing capacitor at the same time by reducing the capacitance of the capacitor necessary for reducing the switching noise in the entire power supply circuit. As a result, it is possible to reduce the possibility of a “flickering phenomenon” in the LED 6 due to the malfunction of the triac of the dimmer due to the phase advance current, and the AC voltage rectified and smoothed by the rectifying / smoothing circuit becomes a constant voltage DC. Therefore, dimming is not possible, and it is possible to avoid the use of electrolytic capacitors that limit the life of the power supply circuit by using a small-capacity film capacitor with good temperature characteristics as a smoothing capacitor. A power supply circuit capable of avoiding a decrease in input power factor is also provided. A.

The invention described in claim 1 is “a power supply circuit 10 that rectifies and steps down an AC voltage Vi received from a commercial AC power supply 12 via a phase control dimmer 14 and supplies power to the lamp 16.
A rectifying / smoothing circuit 18 having a rectifying circuit 26 and a smoothing capacitor 28 that rectifies and smoothes the AC voltage Vi into a pulsating DC voltage Vdc;
A switching step-down circuit 20 for stepping down the DC voltage Vdc;
A line filter 22 provided on the primary side of the rectifying / smoothing circuit 18;
The line filter 22 is for noise prevention, which is attached in parallel to the rectifying / smoothing circuit 18 between a pair of power supply lines 44 that electrically connect the rectifying / smoothing circuit 18 and the commercial AC power supply 12. A capacitor 40;
Between the rectifying / smoothing circuit 18 and the noise preventing capacitor 40, the power supply circuit 10 "includes a filter resistor 42 attached to at least one of the pair of power supply lines 44.

  The power supply circuit 10 of the present invention includes a line filter 22 to prevent switching noise due to switching operation of the switching step-down voltage circuit 20, and the line filter 22 rectifies and rectifies between a pair of power supply lines 44. A noise preventing capacitor 40 attached in parallel to the smoothing circuit 18, and a filter resistor 42 attached to at least one of the pair of power supply lines 44 between the rectifying / smoothing circuit 18 and the noise preventing capacitor 40. have.

  The inventors have added the filter resistor 42 to the noise preventing capacitor 40 to form the line filter 22, whereby the power supply circuit 10 as a whole is compared with the conventional power supply circuit 1 that does not include the filter resistor 42. It has been found that the effect of reducing the switching noise in the low frequency region can be enhanced while keeping the capacitance of the capacitor required for reducing the switching noise low.

  A specific experimental result using the power supply circuit 10 having the line filter 22 composed of the noise prevention capacitor 40 and the filter resistor 42 will be described. The capacitance of the noise prevention capacitor 40 is set to 0.1 μF, and the smoothing capacitor When the embodiment is configured by setting the capacitance of 28 to 0.1 μF and the resistance value of the filter resistor 42 to 22Ω, as shown in FIG. 2, the capacitance of the noise preventing capacitor 7 is set to 0.1 μF. In the conventional example in which the smoothing capacitor 4b has a capacitance of 0.1 μF and no filter resistor (= 0Ω), the voltage level of the switching noise at the entrance of the power supply circuit 1 is 50 to 60 dBμV in the band near 150 to 500 kHz. In contrast, in the embodiment, the voltage level of switching noise in the same band is 35 to 40 dBμV. Thus, it can be seen that the switching noise reduction effect in the low frequency range is extremely high.

  If, in the power supply circuit 1 of the conventional example, the capacitance of the capacitor that contributes to the reduction of switching noise is increased to obtain the switching noise reduction effect of the above-described embodiment level, the noise preventing capacitor 7 or the smoothing capacitor 4b The capacitance must be set to 1 μF or more. In this case, the “flicker phenomenon” (when the capacitance of the noise prevention capacitor 7 is increased) or “the state where the dimming cannot be performed” (the capacitance of the smoothing capacitor 4b is set to be smaller). If the value is increased, the input power factor will decrease.

The cut-off frequency f ₀ of the line filter 22 composed of the noise prevention capacitor 40 and the filter resistor 42 is f ₀ [Hz] = 1 / (2π × “capacitance value [F] of the noise prevention capacitor 40”. it is possible to calculate in × "resistance of the filter resistor 42 [Omega]"), in the above embodiment, the cut-off frequency _{f 0 is, f 0 = 1 / (2π} × 0.1 × 10 -6 × 22) ≈72,000 Hz = 72 kHz, and it can be seen that switching noise higher than 72 kHz (including low frequency range (150 kHz to 1 MHz)) can be reduced.

  Further, in the case of the power supply circuit 1 of the conventional example, the input power factor to the power supply circuit 1 is 63%, whereas in the case of the power supply circuit 10 of the present invention, the input power factor to the power supply circuit 10 is 69%. It was found that the power factor was improved by reducing the capacitor capacity of the power supply circuit 10 as a whole.

The invention described in claim 2 relates to the power supply circuit 10 of claim 1, wherein “the minimum frequency of switching noise to be reduced is f _min [Hz], and the capacitance value of the noise prevention capacitor 40 is C [F]. The resistance value R [Ω] of the filter resistor 42 satisfies the expression 1 ”, and the expression 1 is as follows.
R> 1 / (2π × f _min × C) Formula 1

The present invention sets the lower limit value of the filter resistor 42 used in the line filter 22. According to the present invention, various standards (the standards that are applied according to the place of use and usage) in which the frequency of noise to be reduced are determined. For example, in the CISPR standard, the frequency range is 150 kHz to 30 MHz. In the case of electrical appliances, the minimum frequency f _min [Hz] of switching noise to be reduced is set on the basis of the frequency of 526.5 kHz to 30 MHz, and the triac 46 of the dimmer 14 is set. When the capacitance value C [F] of the noise preventing capacitor 40 is set so as not to have an influence, the resistance value of the filter resistor 42 satisfies the above-described expression 1, and thus the set minimum frequency f _min [Hz] or more. Switching noise can be reduced.

  According to the power supply circuit of the present invention, it is possible to reduce the capacitance of the capacitor necessary for reducing the switching noise in the entire power supply circuit by enhancing the effect of reducing the switching noise generated from the switching step-down voltage circuit. A power supply circuit that can reduce the possibility of “flickering”, can prevent dimming of the lamp, can avoid the use of electrolytic capacitors, and can also avoid a decrease in input power factor. Could be provided.

It is a figure which shows the power supply circuit of this invention. It is a graph which shows the reduction effect of the switching noise in the Example of this invention, and a prior art example. It is a figure which shows the power supply circuit of a prior art.

  Hereinafter, a power supply circuit 10 to which the present invention is applied will be described with reference to the drawings. FIG. 1 is a diagram showing a power supply circuit 10 of the present embodiment, and FIG. 2 is a graph showing switching noise reduction effects in the embodiment and the conventional example.

  The power supply circuit 10 is a circuit that rectifies the AC voltage Vi received from the commercial AC power supply 12 via the phase control type dimmer 14, steps down the voltage, and supplies the voltage to the lamp 16. And a step-down circuit 20 and a line filter 22. In this embodiment, the lamp 16 in which two LEDs are connected in series in the forward direction is used. However, the lamp 16 is not limited to this, for example, a halogen lamp that is lit with a DC voltage of 12 V, etc. Any type and number of light sources can be used as long as they are lit with a voltage obtained by rectifying and stepping down a commercial AC voltage.

  As described above, the rectification / smoothing circuit 18 is a circuit that rectifies and smoothes the alternating voltage Vi received through the phase control type dimmer 14 into a pulsating direct current voltage Vdc. A full-wave rectified AC voltage Vi is converted into a pulsating DC voltage, and the rectifier circuit (full-bridge circuit) 26 composed of four diodes 24a to 24d is connected in parallel on the secondary side of the rectifier circuit 26. And a smoothing capacitor 28. Although the utilization efficiency of the AC voltage Vi supplied from the commercial AC power supply 12 is deteriorated, a half-wave rectifier circuit can be used instead of the full-wave rectifier circuit.

  The smoothing capacitor 28 is a capacitor that smoothes the pulsating DC voltage supplied from the rectifier circuit 26 and reduces switching noise in cooperation with the line filter 22. In the power supply circuit 10 in the present embodiment, as will be described later, the capacity of the capacitor required for reducing the switching noise can be made smaller than that of the conventional one, so that the capacity of the smoothing capacitor 28 is small. For example, a film capacitor having good temperature characteristics can be used.

  The step-down circuit 20 is a circuit that is attached in parallel to the secondary side of the rectifying / smoothing circuit 18 and that steps down the DC voltage of the pulsating current that has been rectified and smoothed by the rectifying / smoothing circuit 18. A field effect transistor) 30, a high-speed diode 32, and an FET switching unit 35 including a current-limiting inductance 34, a current detection resistor 36, an internal oscillator for switching operation, and the switching FET 30 of the FET switching unit 35 And a PWM (pulse width control) circuit 38 for on / off control. For example, a Supertex LED driver IC “HV9910” is used as the PWM circuit 38.

  The step-down circuit 20 detects the lighting current of the lamp 16 with a current detection resistor 36 as a sense voltage (sense voltage of the current detection resistor 36 = lighting current × resistance value of the current detection resistor 36), and the sense voltage In response to the pulse width signal output from the PWM circuit 38, the FET switching unit 35 is switched, and the lighting current output from the FET switching unit 35 is controlled by the pulse width so that the lamp 16 is lit at a constant level. It is designed to supply current.

  The line filter 22 is provided on the primary side of the rectifying / smoothing circuit 18 and transmits the switching noise generated by the switching operation in the step-down circuit 20 to the upstream side (that is, the dimmer 14 or the commercial AC power supply 12 side). It has a role to prevent, and has a noise preventing capacitor 40 and a filter resistor 42.

  The noise preventing capacitor 40 is connected in parallel to the rectifying / smoothing circuit 18 between a pair of power supply lines 44 that electrically connect the rectifying / smoothing circuit 18 and the commercial AC power supply 12, that is, on the primary side of the rectifying / smoothing circuit 18. It is an attached capacitor. Any type of capacitor can be selected for use in the noise preventing capacitor 40. However, the capacitance of the noise preventing capacitor 40 of this embodiment may be small as in the smoothing capacitor 28 described above. For this reason, it is preferable to use a film capacitor having good temperature characteristics.

  The filter resistor 42 is a resistor attached to at least one of the pair of feed lines 44 (in this embodiment, the lower feed line 44 in the figure) between the rectifying / smoothing circuit 18 and the noise preventing capacitor 40. It is. Of course, between the rectifying / smoothing circuit 18 and the noise preventing capacitor 40, a filter resistor 42 may be attached to the other power supply line 44 (upper power supply line 44 in the figure), or the pair of power supply lines 44 You may attach to both.

The resistance value R [Ω] of the filter resistor 42 is expressed by the following [Equation 1] when the minimum frequency of switching noise to be reduced is f _min [Hz] and the capacitance value of the noise prevention capacitor 40 is C [F]. It is preferable to set so as to satisfy.
R> 1 / (2π × f _min × C) Formula 1

According to this, various standards for which the frequency of noise to be reduced is determined (standards applied according to the place of use and usage, for example, in the case of the CISPR standard, the frequency range is 150 kHz to 30 MHz. In the case of electrical appliances, the frequency is 526.5 kHz to 30 MHz.) Based on the above, the minimum frequency f _min [Hz] of switching noise to be reduced is set, and the triac 46 of the dimmer 14 is affected. When the capacitance value C [F] of the noise preventing capacitor 40 is set so as not to give a noise, the resistance value of the filter resistor 42 satisfies the above-described equation 1, so that the switching noise with the set minimum frequency f _min or more is generated. Can be reduced.

For example, when the minimum frequency f _min is 150 kHz and the capacitance of the noise prevention capacitor 40 is 0.1 μF, R> 1 / (2π × 0.1 × 10 ⁻⁶ × 150 × 10 ³ ) = 10.6Ω. Therefore, if the resistance value of the filter resistor 42 is 11Ω or more, switching noise of the minimum frequency or more can be reduced.

  The dimmer 14 (note that the dimmer 14 is not an element constituting the power supply circuit 10) is a phase control system using a triac 46, and a phase angle (ignition phase) at which the triac 46 is turned on. By controlling the angle) with the phase control signal, the effective value of the current supplied to the lamp 16 through the power supply circuit 10 is changed, and the lamp 16 is dimmed and controlled.

  When the AC voltage Vi from the commercial AC power supply 12 is supplied to such a power supply circuit 10 via the dimmer 14, the AC voltage Vi passes through the line filter 22 via the power supply line 44 and is rectified and smoothed. Introduced into the circuit 18. The AC voltage Vi introduced into the rectifying / smoothing circuit 18 is full-wave rectified and smoothed by the rectifying / smoothing circuit 18, and then attached to the secondary side of the rectifying / smoothing circuit 18 as a pulsating DC voltage Vdc. Is supplied to the step-down circuit 20. The step-down circuit 20 that has received the pulsating DC voltage Vdc supplied to the step-down circuit 20 supplies the lamp 16 with a constant lighting current that has been stepped down to a predetermined voltage (for example, several V to several tens of V).

  The line filter 22 in the power supply circuit 10 of this embodiment includes a noise prevention capacitor 40 and a filter resistor 42 attached to one of a pair of power supply lines 44, and includes a filter resistor. Compared with the conventional power supply circuit 1 that does not have the above, it is possible to extremely reduce the switching noise reduction effect in the low frequency range while keeping the capacitance of the noise preventing capacitor 40 low.

  This will be described using specific experimental results. Specific experimental results using the power supply circuit 10 having the line filter 22 including the noise preventing capacitor 40 and the filter resistor 42 will be described. When the embodiment is configured with the capacitance of the capacitor 40 set to 0.1 μF, the capacitance of the smoothing capacitor 28 set to 0.1 μF, and the resistance value of the filter resistor 42 set to 22Ω, as shown in FIG. In the conventional example in which the capacitance of the noise prevention capacitor 7 is 0.1 μF, the capacitance of the smoothing capacitor 4 b is 0.1 μF, and no filter resistance (= 0Ω), the power supply circuit 1 is used in a band near 150 to 500 kHz. In contrast to the voltage level of the switching noise at the inlet of 50 to 60 dBμV, in the embodiment, switching in the same band The voltage level of the noise has become a 35～40DBmyuV, the effect of reducing the switching noise of the low frequency region is extremely high seen.

  If, in the power supply circuit 1 of the conventional example, the capacitance of the capacitor that contributes to the reduction of switching noise is increased to obtain the switching noise reduction effect of the above-described embodiment level, the noise preventing capacitor 7 or the smoothing capacitor 4b The capacitance must be set to 1 μF or more. In this case, the “flicker phenomenon” (when the capacitance of the noise prevention capacitor 7 is increased) or “the state where the dimming cannot be performed” (the capacitance of the smoothing capacitor 4b is set to be smaller). If the value is increased, the input power factor will decrease.

The cut-off frequency f ₀ of the line filter 22 composed of the noise prevention capacitor 40 and the filter resistor 42 is f ₀ [Hz] = 1 / (2π × “capacitance value [F] of the noise prevention capacitor 40”. it is possible to calculate in × "resistance of the filter resistor 42 [Omega]"), in the above embodiment, the cut-off frequency _{f 0 is, f 0 = 1 / (2π} × 0.1 × 10 -6 × 22) ≈72,000 Hz = 72 kHz, and it can be seen that switching noise higher than 72 kHz (including low frequency range (150 kHz to 1 MHz)) is reduced.

  Further, in the case of the power supply circuit 1 of the conventional example, the input power factor to the power supply circuit 1 is 63%, whereas in the case of the power supply circuit 10 of the present invention, the input power factor to the power supply circuit 10 is 69%. It was found that the power factor was improved by reducing the capacitor capacity of the power supply circuit 10 as a whole.

Further, according to the calculation formula of the cut-off frequency f _0, by increasing the resistance value of the filter resistor 42, the value of the cut-off frequency f ₀ is small, but it becomes possible to reduce the switching noise of a lower frequency, When the resistance value of the filter resistor 42 is increased, power loss due to the filter resistor 42 increases, so it is not a good idea to increase the resistance value more than necessary. In this regard, in the case of the power supply circuit 10 that supplies power to the lamp 16 of about 5 W using LEDs, the input current is 0.1 A or less, and the resistance value of the filter resistor 42 is about 22Ω as in the above example, The power loss is 0.22 W or less and does not cause a particularly problematic loss.

DESCRIPTION OF SYMBOLS 10 ... Power supply circuit 12 ... Commercial alternating current power supply 14 ... Dimmer 16 ... Lamp 18 ... Rectification / smoothing circuit 20 ... Step-down circuit 22 ... Line filter 24 ... Diode 26 ... Rectification circuit 28 ... Smoothing capacitor 30 ... Switching FET
32 ... High-speed diode 34 ... Current-limiting inductance 35 ... FET switching unit 36 ... Current detection resistor 38 ... PWM circuit 40 ... Noise prevention capacitor 42 ... Filter resistor 44 ... Feed line 46 ... Triac

Claims (2)

A power supply circuit that rectifies and steps down an AC voltage received from a commercial AC power supply via a phase control type dimmer, and supplies the lamp to the lamp,
A rectifying / smoothing circuit having a rectifying circuit and a smoothing capacitor that rectifies and smoothes the AC voltage into a pulsating DC voltage;
A switching step-down circuit that steps down the DC voltage;
A line filter provided on the primary side of the rectifying and smoothing circuit,
The line filter includes a noise prevention capacitor attached in parallel to the rectification / smoothing circuit between a pair of power supply lines that electrically connect the rectification / smoothing circuit and the commercial AC power source,
A power supply circuit comprising: a filter resistor attached to at least one of the pair of power supply lines between the rectifying / smoothing circuit and the noise prevention capacitor. When the minimum frequency of the switching noise to be reduced is f _min [Hz] and the capacitance value of the noise prevention capacitor is C [F], the resistance value R [Ω] of the filter resistor satisfies Equation 1 below. The power supply circuit according to claim 1, wherein:
R> 1 / (2π × f _min × C) Formula 1

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