JP2016019378A - Switching power supply circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a switching power supply circuit capable of reducing harmonic noises generated in switching while reducing disturbance of switching waveform.SOLUTION: The switching power supply circuit transforms a DC voltage applied to an input terminal to output the same to an output terminal. The switching power supply circuit includes: a first inductor element connecting across an input terminal and an output terminal being interposed by an input/output line; a switching element that performs switching operation to accumulate the electric power on an inductor element; a first diode that supplies the electric power accumulated on the first inductor element to the output terminal; and a noise reduction element which is connected to the first diode at the anode side.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a switching power supply circuit.

  A DC-DC converter circuit that boosts or lowers a DC voltage to a desired DC voltage uses a switching power supply that is small in size, generates little heat, and has good power conversion efficiency. The switching power supply circuit switches a semiconductor switch at high speed to convert a DC input voltage into a pulse wave, and then smoothes the pulse wave to obtain an arbitrary DC output voltage. Thereafter, the output voltage is compared with the reference voltage, and the error voltage is adjusted so as to be suppressed by the control circuit, and a desired voltage is output.

  However, the switching power supply circuit has a problem that harmonic noise having a pulse frequency as a fundamental wave is generated in the process of conversion to a pulse wave. Therefore, as a countermeasure against noise, a method in which the pulse wave is blunted by a capacitor and a snubber circuit is employed. (For example, patent document 1).

Japanese Patent Laid-Open No. 2014-054131

  The configuration of Patent Document 1 has a problem of heat generation and a decrease in conversion efficiency. In order to reduce harmonic noise, there is a measure to insert a ferrite bead inductor in series with the catch diode, but as a trade off, ripples are generated in the waveform due to the inductance component of the ferrite bead inductor, and in some cases the absolute value of the circuit element There was a problem of exceeding the maximum rating.

  Against the background of the above problems, an object of the present invention is to provide a switching power supply circuit that reduces harmonic noise generated in switching and reduces disturbance (ripple) of a switching waveform.

  A switching power supply circuit for solving the above-mentioned problems is a switching power supply circuit that transforms a DC voltage applied to an input terminal and outputs it to an output terminal, and is an input / output line connecting between the input terminal and the output terminal A first inductor element interposed between the first inductor element, a switching element that stores a power in the first inductor element by performing a switching operation, and a first diode that supplies power stored in the first inductor element to an output terminal; And a noise reduction element connected to the anode side of the first diode.

  With the above configuration, harmonic noise and switching waveform disturbance (ripple) generated during switching can be reduced.

The figure which shows the structure of the switching power supply circuit of this invention. The figure which shows the state of the electric current which flows into a 1st inductor element. The figure which shows the state of the harmonic noise in the waveform observation point P1. The figure which shows the state of the ripple in waveform observation point Q1. The figure which shows another example of a structure of the switching power supply circuit of this invention. The figure which shows the state of the ripple in waveform observation point Q2.

  As shown in FIG. 1, the switching power supply circuit 1 of the present invention is configured based on a known step-down switching power supply circuit. Note that details of the switching power supply circuit (both step-down type and step-up type) are described in a special article in the March 2005 issue of “Transistor Technology”.

  The configuration of FIG. 1 is “the switching element is interposed between the first inductor element and the input terminal in the line between the input and output, and the first diode is the input / output between the switching element and the first inductor element. The cathode side is connected between the input line and the reference potential line connecting the input reference terminal and the output reference terminal so that the cathode side is connected to the input / output line, and the noise reduction element is the first diode and the reference potential line And further includes a capacitor element interposed between the input / output line between the first inductor element and the output terminal and the reference potential line. With this configuration, in a so-called step-down chopper type switching power supply circuit, it is possible to reduce harmonic noise and switching waveform disturbance generated during switching.

  A transistor Tr1 (a switching element of the present invention) and a coil L1 (a first inductor element of the present invention), which is also called a choke coil, are inserted in an input / output line 8 that connects the input terminal 4 and the output terminal 6. The transistor Tr1 has a collector terminal C connected to the input terminal 4 side, an emitter terminal E connected to one end side of the coil L1, and a base terminal B connected to the control circuit 3. The control circuit 3 includes, for example, a well-known microcomputer, and switches the transistor Tr1 by well-known PWM control.

  The other end of the coil L1 is connected to the output terminal 6 and the positive side (positive electrode) of the capacitor C1 (capacitor element of the present invention). The negative side (negative electrode) of the capacitor C 1 is connected to a reference potential line 9 that connects the input reference terminal 5 and the output reference terminal 7.

Connected to the input / output line 8 between the transistor Tr1 and the coil L1 is a cathode side of a diode D1 (first diode of the present invention), also called a catch diode. A noise reduction element 10 is interposed between the anode terminal of the diode D1 and the reference potential line 9. The configuration of the noise reduction element 10 uses one of the following.
Includes only ferrite bead inductor L2 (second inductor element of the present invention) (excluding diode D2 from the configuration of FIG. 1). This configuration is “the noise reduction element includes the second inductor element”. With this configuration, harmonic noise generated during switching can be reduced.

A ferrite bead inductor L2 and a diode D2 (second diode of the present invention) connected in parallel to the ferrite bead inductor L2 are included (configuration in FIG. 1). The cathode side of the diode D2 is connected to the anode side of the diode D1, and the anode side of the diode D2 is connected to the reference potential line 9 side.

  The configuration described above is “the noise reduction element includes a second inductor element and a second diode connected in parallel to the second inductor element and having the cathode side connected to the anode side of the first diode”. With this configuration, by using the second inductor element, disturbance (ripple) of the output voltage waveform of the switching element, which occurs during switching, can be reduced by the second diode.

  The switching power supply circuit 1 turns on / off (switches) the transistor Tr1 with a DC voltage E1 (V) applied between the input terminal 4 and the input reference terminal 5 by the DC power supply 12 and a PWM signal from the control circuit 3. The collector-emitter voltage Vce1 is changed in a pulse shape. By changing the duty ratio of PWM, the current IL1 flowing through the coil L1 is changed, the current IL1 is smoothed by the capacitor C1, and an arbitrary DC output voltage Vout1 (V) (between the output terminal 6 and the output reference terminal 7). The applied voltage E1 (V) of the DC power supply 12 is lower).

  Specifically, as shown in FIG. 2, when the transistor Tr1 is turned on, Vce1 is about 0.6 (V). The current path is the DC power supply 12 to the transistor Tr1 to the coil L1 to the output terminal (path K1), and the current Ie1 flows through the coil L1 to store energy. After this, when the on-time determined by the PWM duty ratio has elapsed and the transistor Tr1 is turned off, Vce1 becomes substantially the same as the applied voltage E1 (V) of the DC power supply 12. The coil L1 tries to maintain the current (Ie1), generates an electromotive force by the energy stored in itself, and passes the current Id1 through the diode D1. Therefore, the current path is the diode D1 to the coil L1 to the output terminal (path K2). Therefore, IL1 which is the sum of Ie1 and Id1 flows through the coil L1. Note that the horizontal axis T in FIG. 2 indicates the passage of time.

  FIG. 3 shows an observation result of the waveform observation point P1 on the reference potential line 9 in the configuration of FIG. When the noise reduction element 10 is not inserted, at the waveform observation point P1, as shown in FIG. 3A, when the transistor Tr1 changes from the OFF state to the ON state (change point S of the current IL1 in FIG. 2), a diode Due to the recovery characteristic of D1, current flows instantaneously in the reverse bias direction, and noise N1 at the time of switching is observed. When the frequency at which the noise N1 is generated or a harmonic is close to the frequency used in the control of another device, the operation of the device may be affected.

  Therefore, if the noise reduction element 10 including only the ferrite bead inductor L2 is inserted, the current in the reverse bias direction can be reduced, so that the level of the noise N2 becomes smaller than the noise N1 as shown in FIG. The noise reduction effect by the ferrite bead inductor L2 is recognized.

  FIG. 4 shows an observation result of the voltage Vq1 generated at, for example, the waveform observation point Q1, which is the emitter terminal E of the transistor Tr1, in the configuration of FIG. When the noise reduction element 10 is not interposed, as shown in FIG. 4A, the transistor Tr1 changes from the on state to the off state, and Vq1 is changed from E1 (V), which is the applied voltage of the DC power supply 12, to 0 ( When changing to V), no abnormality is observed in the falling waveform of Vq1 (R1). On the other hand, when the noise reduction element 10 including only the ferrite bead inductor L2 is inserted, a ripple is generated in the waveform due to the inductance component of the ferrite bead inductor L2 at the fall of Vq1, as shown in FIG. 4B (R2). ).

  Therefore, when the diode D2 is connected in parallel to the ferrite bead inductor L2, a voltage higher than the forward voltage of the diode D2 is not generated at both ends of the ferrite bead inductor due to the forward characteristics of the diode D2, as shown in FIG. In addition, the ripple is reduced (R3). At this time, as shown in FIG. 3C, the noise N3 at the time of switching is substantially the same level as the noise N2, and the noise reduction effect is recognized also in this configuration.

  FIG. 5 shows another example of the switching power supply circuit of the present invention. The switching power supply circuit 2 is configured based on a known step-up switching power supply circuit. In addition, about the thing of the same structure as FIG. 1, the same code | symbol is provided and the detailed description here is omitted.

  The configuration of FIG. 5 is “the first diode is interposed between the first inductor element and the output terminal of the line between the input and output so that the cathode side faces the output terminal, and the switching element is the first inductor element. Between the input and output lines between the first diode and the reference potential line connecting the input reference terminal and the output reference terminal, and the noise reduction element is connected to the switching element of the input / output line. It is interposed between the connection point of the first inductor element and the first diode, and is interposed between the input / output line between the cathode side of the first diode and the output terminal, and the reference potential line. It further includes a capacitor element. With this configuration, in a so-called step-up chopper type switching power supply circuit, it is possible to reduce harmonic noise and switching waveform disturbance generated during switching.

  The input / output line 8 connecting the input terminal 4 and the output terminal 6 includes a coil L21 (first inductor element of the present invention), a noise reduction element 20, and a backflow prevention diode D21 (of the present invention). A first diode) is inserted. One end of the coil L <b> 21 is connected to the input terminal 4, and the other end is connected to the noise reduction element 20. One end of the noise reduction element 20 not connected to the coil L21 is connected to the anode side of the diode D21. The cathode side of the diode D21 is connected to the output terminal 6 side.

  Between the input / output line 8 between the coil L21 and the noise reduction element 20 and the reference potential line 9 connecting the input reference terminal 5 and the output reference terminal 7, the transistor Tr2 (the switching element of the present invention) Is inserted. The transistor Tr 2 has a collector terminal C connected to the input / output line 8, an emitter terminal E connected to the reference potential line 9, and a base terminal B connected to the control circuit 3. The control circuit 3 includes, for example, a well-known microcomputer, and switches the transistor Tr2 by well-known PWM control.

  A capacitor C2 (capacitor element of the present invention) is interposed between the input / output line 8 on the cathode side of the diode D21 and the reference potential line 9. The + side (positive electrode) of the capacitor C2 is connected to the input / output line 8. The negative side (negative electrode) of the capacitor C <b> 2 is connected to the reference potential line 9.

The configuration of the noise reduction element 20 is one of the following.
Only the ferrite bead inductor L22 (the second inductor element of the present invention) is included. This configuration is “the noise reduction element includes the second inductor element”. With this configuration, harmonic noise generated during switching can be reduced.

A ferrite bead inductor L22 and a diode D22 (second diode of the present invention) connected in parallel to the ferrite bead inductor L22 are included. The cathode side of the diode D22 is connected to the anode side of the diode D21. The anode side of the diode D22 is connected to the coil L21 side.

  The configuration described above is “the noise reduction element includes a second inductor element and a second diode connected in parallel to the second inductor element and having the cathode side connected to the anode side of the first diode”. With this configuration, by using the second inductor element, it is possible to reduce disturbance (ripple) in the output voltage waveform of the switching element that occurs during switching.

  The switching power supply circuit 2 turns on / off (switches) the transistor Tr2 with the DC voltage E1 (V) applied between the input terminal 4 and the input reference terminal 5 by the DC power supply 12 and the PWM signal from the control circuit 3. The collector-emitter voltage Vce2 is changed in pulses. The energy accumulated in the coil L21 is changed by changing the duty ratio of PWM. Then, by superimposing this energy on the applied voltage E1 (V) from the DC power supply 12 (step-up), an arbitrary DC output voltage Vout2 is output between the output terminal 6 and the output reference terminal 7.

  Specifically, when the transistor Tr2 is turned on, the current path becomes the coil L21 to the transistor Tr2 (path K21), the current Ie2 flows through the coil L21, and energy is stored.

  Thereafter, when the transistor Tr2 is turned off, the current path is from the coil L21 to the noise reduction element 20 to the diode D21 (path K22), and the coil L21 is caused by the energy accumulated in itself to maintain the current (Ie2). Electric power is generated and current Id2 is allowed to flow through diode D21. Therefore, IL2, which is the sum of Ie2 and Id2, flows through the coil L21. IL2 is smoothed by the capacitor C2, and Vout2 is output.

  In the configuration of FIG. 5, the relationship between Vce2, Ie2, Id2, and IL2 is the same as Vce1, Ie1, Id1, and IL1 of FIG. Therefore, when the noise reduction element 20 is not inserted, at the waveform observation point P2 on the reference potential line 9, as shown in FIG. 3A, the transistor Tr2 changes from the OFF state to the ON state (change in FIG. 2). Point S), current flows instantaneously in the reverse bias direction due to the recovery characteristic of the diode D21, and switching noise (hereinafter abbreviated as “noise”) N1 is observed. The noise level may be different from that in FIG.

  If the noise reduction element 20 including only the ferrite bead inductor L22 is inserted, the current in the reverse bias direction can be reduced. Therefore, as shown in FIG. 3B, the level of the noise N2 becomes smaller than the noise N1, and the ferrite The noise reduction effect by the bead inductor L22 is recognized.

  When the noise reduction element 20 is not inserted, for example, at the waveform observation point Q2, which is the collector terminal C of the transistor Tr2, the transistor Tr2 changes from the on state to the off state as shown in FIG. When the voltage changes from 0 (V) to E1 (V), which is the applied voltage of the DC power supply 12, no abnormality is observed in the rising waveform of the voltage Vq2 generated at Q2 (R21). On the other hand, when the noise reduction element 20 including only the ferrite bead inductor L22 is inserted, a ripple is generated in the waveform due to the inductance component of the ferrite bead inductor L22 at the rise of Vq2, as shown in FIG. 6B (R22). .

  Therefore, when the diode D22 is connected in parallel to the ferrite bead inductor L22, a voltage higher than the forward voltage of the diode D22 is not generated at both ends of the ferrite bead inductor due to the forward characteristics of the diode D22, as shown in FIG. In addition, the ripple of the waveform is reduced (R23). At this time, as shown in FIG. 3C, the switching noise N3 is substantially at the same level as the noise N2, and the noise reduction effect is recognized even in this configuration.

  Although the embodiments of the present invention have been described above, these are merely examples, and the present invention is not limited to these embodiments, and the knowledge of those skilled in the art can be used without departing from the spirit of the claims. Various modifications based on this are possible.

1, 2 Switching power supply circuit 4 Input terminal 5 Input reference terminal 6 Output terminal 7 Output reference terminal 8 Input-output line 9 Reference potential line 10, 20 Noise reduction element L2, L22 Ferrite bead inductor (second inductor element)
D2, D22 Diode (second diode)
Tr1, Tr2 transistors (switching elements)
L1, L21 Coil (first inductor element)
C1, C2 capacitors (capacitor elements)
D1, D21 Diode (first diode)

Claims (5)

A switching power supply circuit that transforms a DC voltage applied to an input terminal and outputs it to an output terminal,
A first inductor element interposed in an input / output line connecting between the input terminal and the output terminal;
A switching element for storing power in the first inductor element by performing a switching operation;
A first diode that supplies power stored in the first inductor element to the output terminal;
A noise reduction element connected to the anode side of the first diode;
A switching power supply circuit comprising:   The switching power supply circuit according to claim 1, wherein the noise reduction element includes a second inductor element. The noise reduction element is:
A second inductor element;
2. The switching power supply circuit according to claim 1, further comprising a second diode connected in parallel to the second inductor element and having a cathode side connected to an anode side of the first diode. The switching element is interposed between the first inductor element and the input terminal of the input / output line,
The first diode is connected between an input / output line between the switching element and the first inductor element and a reference potential line connecting an input reference terminal and an output reference terminal, and a cathode side is between the input / output. Interlaced to connect to the line,
The noise reduction element is interposed between the first diode and the reference potential line,
4. The capacitor element according to claim 1, further comprising a capacitor element interposed between an input / output line between the first inductor element and the output terminal and the reference potential line. 5. Switching power supply circuit. The first diode is interposed between the first inductor element and the output terminal in the line between the input and output so that a cathode side faces the output terminal,
The switching element is interposed between an input / output line between the first inductor element and the first diode and a reference potential line connecting the input reference terminal and the output reference terminal,
The noise reduction element is interposed between a connection point of the switching element and the first inductor element in the line between the input and output, and the first diode.
4. The capacitor element according to claim 1, further comprising a capacitor element interposed between an input / output line between a cathode side of the first diode and the output terminal, and the reference potential line. 5. The switching power supply circuit described.

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