JP4636442B2 - Pulse control device - Google Patents

Description

  The present invention relates to a pulse control device that performs, for example, PWM (Pulse Width Modulation) control on an output pulse.

Generally, in a switching power supply device or the like, a pulse output signal is supplied to a switching element to perform a switching operation, thereby extracting desired output power from input power and supplying it to a load. For controlling the switching operation, a pulse control device such as a PWM control IC is widely used in order to stabilize the output voltage. This pulse control device performs well-known pulse control such as PWM control on a pulse drive signal as an output pulse so that a stable output can be obtained based on a feedback signal of output power (output voltage , output current). Do.

  In recent years, various standards relating to so-called electromagnetic interference (EMI) have been established in which electromagnetic waves generated by the operation of electric / electronic devices impede the operation of other nearby devices. There is a strong demand for the noise level to satisfy a specified value defined in the EMI standard.

  However, in the conventional pulse control device, even if the pulse width is changed by PWM control, the frequency of the output pulse is normally constant, and the frequency noise level at the nth harmonic (n is an arbitrary integer) of the pulse frequency is There was a tendency to be higher than other frequency bands. FIG. 7 shows a frequency noise level n times the switching frequency fsw in a conventional fixed frequency switching power supply. The average level within the selection width Bw of the receiver is measured as the amount of noise. As described above, in the conventional pulse control device, a noise level peak appears at n times the fundamental frequency fsw, and there is a possibility that the noise level becomes equal to or more than the specified value.

As means for solving this problem, a spread spectrum method as disclosed in Patent Document 1 is widely known. In the spread spectrum method, a clock signal oscillated at a reference frequency is frequency-modulated with a predetermined frequency width to disperse frequency noise and attenuate the peak of the frequency noise level.
JP 2002-246900 A

However, heretofore, in this spread spectrum method, specific frequency determination means and calculation methods for effectively attenuating the frequency noise level to a level satisfying the EMI standard have not been established. .

  In view of the above problems, an object of the present invention is to provide a pulse control device capable of obtaining a constant attenuation with respect to a basic frequency noise level of a fixed frequency system.

  According to the first aspect of the present invention, carrier wave generating means for generating a carrier wave having a fundamental frequency fsw, frequency sweep wave generating means for generating a frequency sweep wave, and pulse generation for generating an output pulse based on the carrier wave The carrier wave generating means changes the frequency of the carrier wave in a range of a predetermined frequency spread width Δf according to the frequency sweep wave. To do.

In this way, the frequency of the carrier wave, and thus the output pulse, changes and disperses in the range of the frequency spread width Δf, and the power density of the frequency noise can be reduced.

  In the pulse control device according to claim 2 of the present invention, the frequency sweep wave is a triangular wave.

  In this way, the frequency of the carrier wave and thus the output pulse changes linearly, and the frequency noise level can be averagely dispersed within the range of the frequency spread width Δf.

  According to claim 1 of the present invention, it is possible to provide a pulse control device capable of obtaining a constant attenuation with respect to the basic frequency noise level of the fixed frequency system.

  According to claim 2 of the present invention, the frequency noise level can be attenuated more effectively.

  Hereinafter, preferred embodiments of a pulse control device according to the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a circuit diagram showing a circuit configuration of a forward converter as an example of a general switching power supply. A rectifier circuit 3 composed of, for example, a diode bridge as a rectifier is connected to both ends of the commercial power source 2 corresponding to the AC power source, and the AC power source voltage from the commercial power source 2 is rectified to form a PFC circuit (power factor correction circuit) at the subsequent stage. ) 4 is supplied. As is well known, the PFC circuit 4 connects a series circuit of a choke coil 5 and a drain-source of a switching element 6 such as a MOSFET to the output terminal of the rectifier circuit 3 and also includes a rectifier diode 7 and an electrolytic capacitor, for example. A series circuit with the capacitor 8 is connected between both ends of the switching element 6, that is, between the drain and source. The switching element 6 performs a switching operation by a pulsed drive voltage supplied from a PFC controller 9 connected to a gate as a drive terminal.

  When the switching element 6 is on, excitation energy is stored in the choke coil 5 by the full-wave rectified DC voltage from the rectifier circuit 3, and when the switching element 6 is off, the excitation energy stored in the choke coil 5 is stored. Energy is superimposed on the input voltage Vi generated between the output terminals of the rectifier circuit 3, and a voltage higher than the input side of the PFC circuit 4 is generated between both ends of the capacitor 8. The PFC controller 9 monitors the voltage Vc across the capacitor 8 and switches the switching element 6 so that the voltage Vc across the capacitor becomes constant, so that the input current waveform taken in via the choke coil 5 is converted into the commercial power supply. Approaching the sinusoidal voltage waveform from 2, the power factor is improved.

  Connected between both ends of the capacitor 8 is a series circuit composed of a primary winding 10a of the pulse transformer 10 and a drain-source of a main switching element 11 such as a MOSFET. Connected to the gate of the main switching element 11 is a PWM controller 12 that supplies a pulse drive signal for controlling the switching operation (ON / OFF operation) of the main switching element 11. In order to stabilize the output voltage Vo, the PWM controller 12 variably controls the pulse drive signal supplied to the main switching element 11 according to the fluctuation of the output voltage Vo, for example, by well-known PWM control. Details will be described later. Of course, the load current may be stabilized.

  The secondary winding 10b of the pulse transformer 10 includes a rectifying diode 13, a flywheel diode 14, a choke coil 15, and a smoothing capacitor 16 for rectifying and smoothing the induced voltage induced in the secondary winding 10b. A rectifying / smoothing circuit consisting of More specifically, the anode of the rectifier diode 13 is connected to the dot side of the secondary winding 10b, the anode of the flywheel diode 14 is connected to the non-dot side of the secondary winding 10b, and the cathode of the rectifier diode 13 The cathode of the flywheel diode 14 is connected. A choke coil 15 and a smoothing capacitor 16 are connected in an inverted L shape between both ends of the flywheel diode 14, and a pair for supplying an output voltage Vo to a load (not shown) between both ends of the smoothing capacitor 16. Output terminals 17 and 17 are provided.

In the forward converter 1, the PWM controller 12 supplies a pulse drive signal to the gate of the main switching element 11 to cause the main switching element 11 to perform a switching operation, whereby the voltage Vc across the capacitor 8 is changed to the primary winding 10 a of the pulse transformer 10. Is intermittently applied. The voltage induced in the secondary winding 10b of the pulse transformer 10 is rectified and smoothed by the rectifier diode 13 , the flywheel diode 14 , the choke coil 15 and the smoothing capacitor 16, and the DC output voltage Vo between the output terminals 17 and 17 is obtained. Is output as A feedback circuit 20 is connected to the output terminals 17 and 17, and the feedback circuit 20 and the PWM controller 12 form a feedback loop that stabilizes the output voltage Vo.

  Hereinafter, the configuration of the PFC controller 9 and the PWM controller 12 as the pulse control device in this embodiment will be described in detail. The PFC controller 9 sweeps (sweeps) the switching frequency of the switching element 6 with a triangular wave that is a frequency sweep wave input from the PFC triangular wave oscillator 21 serving as a frequency sweep wave generating means, and changes the frequency. On the other hand, the PWM controller 12 sweeps (sweeps) the switching frequency of the main switching element 11 with a triangular wave which is a frequency sweep wave inputted from the DC / DC triangular wave oscillator 22 as a frequency sweep wave generating means, and changes the frequency. Since these have substantially the same configuration due to the similarity in function, only the configuration of the PWM controller 12 will be described for the sake of simplicity.

  The PWM controller 12 compares the carrier wave and a feedback signal from the feedback circuit 20 with a carrier wave oscillator 30 as a carrier wave generating means for generating a carrier wave having a constant fundamental frequency fsw, and compares the carrier wave with a feedback signal from the feedback circuit 20 to generate a pulsed PWM wave. For example, a comparator 31 corresponding to a pulse generating means including a comparator, and a gate drive circuit 32 for converting the PWM wave into the pulse drive signal and outputting the pulse drive signal to the gate of the main switching element 11.

  The carrier wave oscillator 30 is an oscillator that generates a carrier wave such as a triangular wave or a sawtooth wave, for example. In this embodiment, the carrier wave oscillator 30 has a function of a voltage controlled oscillator in which the oscillation frequency changes according to the control voltage. A triangular wave input from the / DC triangular wave oscillator 22 is used as a control voltage so that the frequency of the carrier wave changes according to the voltage level. The carrier wave generated here is compared with the feedback signal from the feedback circuit 20 by the comparator 31, and the PWM wave having a rectangular wave shape having a pulse width proportional to the portion of the carrier wave exceeding the voltage level of the feedback signal is compared. Is output from the device 31 to the gate drive circuit 32. The gate drive circuit 32 generates a pulse drive signal that satisfies the drive condition of the main switching element 11 from the PWM wave, and outputs it to the gate of the main switching element 11.

  Next, the circuit configuration of the DC / DC triangular wave oscillator 22 will be described with reference to FIG. The output circuit of the DC / DC triangular wave oscillator 22 is an open collector type in accordance with the input of the PWM controller 12.

  The DC / DC triangular wave oscillator 22 generates a triangular wave by switching an open collector output transistor 51 by an oscillation circuit using an operational amplifier 43 with a DC power supply 40 as an input power supply, and charging and discharging a capacitor 53. A series circuit of resistors 41 and 42 is connected between both poles of the DC power supply 40, and a connection point of the resistors 41 and 42 is connected to a non-inverting input terminal of the operational amplifier 43. An inverting input terminal of the operational amplifier 43 is grounded via a capacitor 46. The output terminal of the operational amplifier 43 is connected to a non-inverting input terminal via a resistor 44 and to an inverting input terminal to which one end of a capacitor 46 is connected via a resistor 45. The output terminal of the operational amplifier 43 is connected to the non-inverting input terminal of the operational amplifier 47. The operational amplifier 47 has an output terminal and an inverting input terminal directly connected. The output terminal of the operational amplifier 47 is connected to the base of the transistor 51 via a resistor 48, and this base is grounded via a parallel circuit of a resistor 49 and a capacitor 50. The emitter of the transistor 51 is grounded, and a series circuit of a resistor 52 and a capacitor 53 is connected between the collector and the emitter. A series circuit of resistors 54 and 55 is connected between both ends of the capacitor 53, and a connection point of the resistors 54 and 55 is connected to the carrier wave oscillator 30 constituting the PWM controller 12. The operational amplifiers 43 and 47 are single power supply products, and a DC power supply 40 is connected to a power supply input terminal as an operation power supply.

  The operational amplifier 43 is configured to operate as a hysteresis comparator. Immediately after the power is turned on, the input voltage of the DC power supply 40 is divided by the resistors 41 and 42 and input to the non-inverting input terminal of the operational amplifier 43, while the voltage of the capacitor 46 is 0 V, so No input. Thereafter, the capacitor 46 is charged through the resistor 45, and the voltage gradually increases. When the voltage of the capacitor 46 exceeds the H side threshold voltage higher than the input voltage of the non-inverting input terminal, the output of the operational amplifier 43 becomes L level, the capacitor 46 is discharged through the resistor 45, and the voltage gradually decreases. When the voltage of the capacitor 46 falls below the L side threshold voltage lower than the input voltage of the non-inverting input terminal, the output of the operational amplifier 43 becomes H level, the capacitor 46 is charged through the resistor 45, and the voltage gradually increases. By repeating such an operation periodically, the operational amplifier 43 outputs a periodic square wave, that is, a pulse wave.

  Since the operational amplifier 47 operates as a buffer with an amplification factor of 1, the output of the operational amplifier 43 appears at the output terminal of the operational amplifier 47 as it is, and a pulse wave is output to the base of the transistor 51. As a result, the transistor 51 performs a switching operation, and a triangular wave is generated by the charging time constant of the resistor 54 and the capacitor 53 and the discharging time constant of the resistor 52 and the capacitor 53 and is input to the carrier wave oscillator 30. The amplitude (voltage level width) of the triangular wave can be adjusted by changing the constants of the resistors 54 and 55.

  On the other hand, the circuit configuration of the PFC triangular wave oscillator 21 will be described with reference to FIG. Unlike the DC / DC triangular wave oscillator 22, the output circuit of the PFC triangular wave oscillator 21 is a constant current charging type in accordance with the input of the PFC controller 9, and injects a triangular wave into the input terminal of the PFC triangular wave oscillator 21.

  The PFC triangular wave oscillator 21 generates a triangular wave by an oscillation circuit using an operational amplifier 63 with a DC power supply 60 as an input power supply. A series circuit of resistors 61 and 62 is connected between both poles of the DC power supply 60, and a connection point of the resistors 61 and 62 is connected to a non-inverting input terminal of the operational amplifier 63. The output terminal of the operational amplifier 63 is connected to the non-inverting input terminal via the resistor 64 and is connected to the inverting input terminal via the resistor 65. The inverting input terminal side of the resistor 65 is grounded via a capacitor 67, and a series circuit of a capacitor 68, a resistor 69, and a resistor 70 is connected across the capacitor 67. A connection point between the resistors 69 and 70 is connected to the PFC controller 9. The operational amplifier 63 is a single power supply product, and a DC power supply 60 is connected to a power supply input terminal as an operation power supply.

  The operational amplifier 63 is configured to operate as a hysteresis comparator. Immediately after the power is turned on, the input voltage of the DC power supply 60 is divided by the resistors 61 and 62 and input to the non-inverting input terminal of the operational amplifier 63, while the voltage of the capacitor 67 is 0 V, so No input. Thereafter, the capacitor 67 is charged through the resistor 65, and the voltage gradually increases. When the voltage of the capacitor 67 exceeds the H side threshold voltage higher than the input voltage of the non-inverting input terminal, the output of the operational amplifier 63 becomes L level, the capacitor 67 is discharged through the resistor 65, and the voltage gradually decreases. When the voltage of the capacitor 67 falls below the L side threshold voltage lower than the input voltage of the non-inverting input terminal, the output of the operational amplifier 63 becomes H level, the capacitor 67 is charged through the resistor 65, and the voltage gradually increases. By repeating such an operation periodically, the operational amplifier 43 outputs a periodic square wave, that is, a pulse wave. At this time, since the charging / discharging voltage of the capacitor 67 periodically increases and decreases in a triangular wave shape due to the time constant of the resistor 65 and the capacitor 67, a triangular wave is generated by removing the DC component of the charging / discharging voltage by the capacitor 68, and the resistance It is input to the PFC controller 9 from the connection point of 69 and 70. The amplitude (voltage level width) of the triangular wave can be adjusted by changing the constants of the resistors 69 and 70.

  As described above, the PWM controller 12 uses the triangular wave input from the PFC triangular wave oscillator 21 to perform spectrum spread on the pulse drive signal (carrier wave) that determines the switching frequency of the main switching element 11. By the spread spectrum, the frequency noise in the nth harmonic of the carrier wave can be dispersed to attenuate the peak of the frequency noise level. When the frequency sweep wave is a triangular wave as in this embodiment, the switching frequency is swept linearly and average dispersion is possible, so that a large attenuation effect is obtained. Of course, the frequency sweep wave may be a sine wave, but there is a possibility that the frequency dispersion is dense and sparse, and there is a risk that the average dispersion cannot be achieved sufficiently. For this reason, the voltage level such as a triangular wave or a sawtooth wave is linear. Preferably, the waveform changes with time.

  FIG. 5 shows the movement of the noise level when a certain frequency is changed. The fundamental wave indicated by a dotted line in the figure represents the noise level at a fixed frequency, and the switching frequency is represented by a frequency spreading width Δf. When regularly diffused, the noise level waveform indicated by the solid line is obtained. As shown in the figure, when average dispersion is performed, an attenuation effect of D [dB] can be expected with respect to the frequency of the fundamental wave. At this time, the attenuation amount D is expressed by the following Equation 2.

なお、ｆswはキャリア波の周波数であり、ノイズレベルを減衰させたいｎ次高調波の周波数を減衰対象周波数ｆとするとｆ＝ｎ×ｆswで表される。また、測定周波数幅ＢwはＥＭＩ規格に定められた規定値を満足すべき周波数範囲である。

Note that fsw is the frequency of the carrier wave, and is expressed by f = n × fsw, where the frequency of the nth-order harmonic whose noise level is to be attenuated is the attenuation target frequency f. Further, the measurement frequency width Bw is a frequency range that should satisfy the specified value defined in the EMI standard.

  Here, a calculation example of the attenuation amount D is shown.

  As calculation conditions, the fundamental frequency fsw is set to 70 kHz, the frequency fluctuation width b is set to ± 7% (65.1 kHz to 74.9 kHz), and the selection width of the spectrum analyzer as a noise measuring device, that is, the measurement frequency width Bw is set to 9 kHz. Attenuation amount D1 at the fundamental wave (n = 1) is a value expressed by Equation 3.

また、基本波（ｎ＝3）での減衰量Ｄ3は数式４で示される値となる。

Further, the attenuation amount D3 at the fundamental wave (n = 3) is a value expressed by Equation 4.

上記減衰量Ｄの計算式から、以下の数式５に示すように、減衰対象周波数ｆにおける減衰量Ｄを得る為の周波数拡散幅Δｆの条件式を導出することができる。

From the calculation formula of the attenuation amount D, a conditional expression of the frequency spread width Δf for obtaining the attenuation amount D at the attenuation target frequency f can be derived as shown in the following Expression 5.

この周波数拡散幅Δｆの範囲でキャリア波の周波数が変化するように、例えばＤＣ／ＤＣ用三角波発振器22で生成される三角波の振幅やキャリア波発振器30の制御設定などを調節する。

For example, the amplitude of the triangular wave generated by the DC / DC triangular wave oscillator 22 and the control setting of the carrier wave oscillator 30 are adjusted so that the frequency of the carrier wave changes in the range of the frequency spread width Δf.

  Here, a calculation example of the frequency spread width Δf is shown.

  Consider a case in which the attenuation D at 210 kHz is reduced by 5 dB from the current level in a 70 kHz switching power supply. The frequency spread width Δf is a value expressed by Equation 6.

従って、キャリア波の周波数を65．255〜74．745kHzの範囲で変化させれば、210kHzでのノイズレベルが5dB減衰することになる。

Therefore, if the frequency of the carrier wave is changed in the range of 65.255 to 74.745 kHz, the noise level at 210 kHz is attenuated by 5 dB.

  FIG. 6 is a waveform diagram showing a gate waveform of the main switching element 11. In each voltage waveform shown in the figure, 80 is a pulse drive signal output from the PWM controller 12 to the gate of the main switching element 11, and 81 is an operational amplifier output of the operational amplifier 43 constituting the DC / DC triangular wave oscillator 22. 82 is a voltage across the capacitor 53 constituting the DC / DC triangular wave oscillator 22, that is, a frequency sweep wave. FIGS. 6B to 6D are waveform diagrams obtained by enlarging each part in FIG.

  Since the output voltage waveform 81 of the operational amplifier 43 can be said to be the base waveform of the transistor 51, the transistor 51 is turned on when the level is H and the frequency sweep wave 82 has a downward slope. Is turned off, and the frequency sweep wave 82 has an upward gradient. The pulse drive signal 80 has a remarkably higher frequency than the frequency sweep wave 82 corresponding to the control signal, and the frequency is swept as the frequency sweep wave 82 gradually increases. In FIG. 6B in which the portion (BOTTOM) where the voltage level of the frequency sweep wave 82 is the minimum is displayed in an enlarged manner, the frequency of the pulse drive signal 80 is 55.83 kHz and the portion where the voltage level of the frequency sweep wave 82 is intermediate (MIDDLE). 6 (c) in which the frequency of the pulse drive signal 80 is 51.88 kHz and the portion (TOP) where the voltage level of the frequency sweep wave 82 is maximum is enlarged in FIG. 6 (d). The frequency of 80 is 50.00kHz.

As described above, the PFC controller 9 and the PWM controller 12 as the pulse control device of the present embodiment generate the carrier wave oscillator 30 as the carrier wave generating means for generating the carrier wave having the fundamental frequency fsw and the frequency sweep wave. A pulse control device comprising a PFC triangular wave oscillator 21 as a frequency sweep wave generating means , a DC / DC triangular wave oscillator 22, and a comparator 31 corresponding to a pulse generating means for generating an output pulse based on the carrier wave. Thus, the carrier wave oscillator 30 determines the frequency of the carrier wave according to Equation 7 according to the frequency sweep wave .

（Ｂwは測定周波数幅、Ｄは所望の減衰量、ｆは減衰対象周波数）
周波数拡散幅Δｆの範囲で変化させるものであることを特徴とする。

(Bw is the measurement frequency width, D is the desired attenuation, and f is the frequency to be attenuated)
It is characterized in that it is varied within the range of the frequency spread width Δf.

In this way, the frequency of the carrier wave, and thus the output pulse, changes and disperses in the range of the frequency spread width Δf, and the power density of the frequency noise can be reduced. Therefore, it is possible to provide a pulse control device capable of obtaining a constant attenuation with respect to the basic frequency noise level of the fixed frequency system.

  In the PFC controller 9 and the PWM controller 12 of this embodiment, the frequency sweep wave is a triangular wave.

  In this way, the frequency of the carrier wave and thus the output pulse changes linearly, and the frequency noise level can be averagely dispersed within the range of the frequency spread width Δf. Therefore, the frequency noise level can be attenuated more effectively.

  In addition, this invention is not limited to the said Example, It can change in the range which does not deviate from the meaning of this invention. The PFC controller 9 and the PFC triangular wave oscillator, or the PWM controller 12 and the DC / DC triangular wave oscillator can be configured with one component (one chip) using, for example, a microcomputer or a DSP (Digital Signal Processor), It can also be used for various electronic devices other than the switching power supply device.

It is a circuit diagram of the switching power supply device using the pulse control apparatus in the Example of this invention. It is a block diagram which shows a structure of a pulse control apparatus same as the above. It is a circuit diagram which shows the structure of the triangular wave oscillator of a pulse control apparatus same as the above. It is a circuit diagram which shows the structure of another triangular wave oscillator of a pulse control apparatus same as the above. It is explanatory drawing which shows the spread spectrum method performed with a pulse control apparatus same as the above. FIG. 4 is a waveform diagram showing the waveform of a pulse drive signal output from the pulse control device. It is explanatory drawing which shows the frequency noise level of the pulse control apparatus in a prior art example.

9 PFC controller (pulse controller)
12 PWM controller (pulse controller)
21 PFC triangular wave oscillator (frequency sweep wave generation means)
22 DC / DC triangular wave oscillator (frequency sweep wave generation means)
30 Carrier wave oscillator (carrier wave generation means)
31 Comparator (pulse generation means)

Claims (2)

Pulse control device comprising carrier wave generating means for generating a carrier wave having a fundamental frequency fsw, frequency sweep wave generating means for generating a frequency sweep wave, and pulse generating means for generating an output pulse based on the carrier wave Because
The carrier wave generating means changes the frequency of the carrier wave by sweeping with the frequency sweep wave ,
The frequency sweep wave generating means, the frequency of the carrier wave is determined by Equation 1

(Bw is a measurement frequency width that is a frequency range that should satisfy the specified value defined in the EMI standard , D is a desired attenuation, f is a frequency to be attenuated expressed by f = n × fsw, and n is to be attenuated. nth harmonic order )
A pulse control device characterized in that the frequency sweep wave is adjusted so as to change within a range of a frequency spread width Δf.   The pulse control device according to claim 1, wherein the frequency sweep wave is a triangular wave.

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