KR102695182B1 - Power supply with improved ripple - Google Patents

Abstract

A power supply device with improved ripple is disclosed, which uses a film capacitor instead of an electrolytic capacitor. The disclosed power supply device includes a transformer, in which a switching unit is connected to a primary coil and an AC power is inducerized into a secondary main coil and a secondary auxiliary coil and outputted as a voltage supplied to the primary coil according to a switching operation of the switching unit, a DC voltage output unit including a first diode and a first capacitor, which are film capacitors connected to the secondary main coil, and which converts the output power of the transformer into a DC voltage through the first diode and the first capacitor and supplies the same to an output terminal, and a ripple improvement unit connected to the DC voltage output unit, the output terminal, and the secondary auxiliary coil and which improves a ripple component of a voltage output from the DC voltage output unit.

Description

Power supply with improved ripple

The present invention relates to a power supply device with improved ripple, and more specifically, to a power supply device with improved ripple even when using a film capacitor instead of an electrolytic capacitor.

SMPS stands for Switching Mode Power Supply, and refers to a power supply device that uses a switching operation. In such power supply devices, commercial power (e.g., AC) is converted into direct current (DC) through a power conversion circuit.

When converting commercial power (e.g., AC) to power, there are regulations that require power factor (PF) management in order to efficiently supply high-quality power, and a power factor correction circuit (PFC) must be installed to meet the regulations. At this time, the power factor correction circuit that is mainly used may be a circuit that rectifies AC and then switches the rectified voltage to tens to hundreds of KHz without using a DC link capacitor, and then uses a DC link capacitor. As a practical circuit, there is a PF-flyback method.

To create direct current, a rectifying diode and a smoothing electrolytic capacitor are required.

Here, the lifespan of electrolytic capacitors is reduced, the capacity is reduced, and eventually, it can cause product failure depending on the usage environment (especially the ambient temperature).

Accordingly, film capacitors are aimed at ensuring reliability in the usage environment, but since film capacitors have a smaller electrostatic capacity, which is the largest requirement for smoothing capacitors, compared to electrolytic capacitors, they have some limitations in being used for smoothing commercial power supplies. In other words, it is difficult to resolve ripple.

The matters described in the background technology above are intended to help understand the background of the invention and may include matters that are not publicly available prior art.

Prior art 1: Republic of Korea registered patent No. 10-0808874 (Ripple voltage improvement circuit and improvement method thereof) Prior art 2: Republic of Korea registered patent No. 10-1132188 (Ripple removal device for power circuit for LED lighting equipment)

The present invention has been proposed in consideration of the above-mentioned conventional circumstances, and its purpose is to provide a power supply device with improved ripple that can output high-quality DC power by reducing the ripple component even while using a film capacitor instead of an electrolytic capacitor.

In order to achieve the above object, a power supply device according to a preferred embodiment of the present invention comprises: a switching unit which performs an on/off switching operation according to a control signal; a transformer which is connected to a primary coil of the switching unit and induces and outputs AC power to a secondary main coil and a secondary auxiliary coil with a voltage supplied to the primary coil according to the switching operation of the switching unit; a DC voltage output unit which includes a first diode and a first condenser, which are film condensers, connected to the secondary main coil, and which converts the output power of the transformer into a DC voltage through the first diode and the first condenser and supplies the converted DC voltage to an output terminal; and a ripple improvement unit which is connected to the DC voltage output unit, the output terminal, and the secondary auxiliary coil, and improves a ripple component of a voltage output from the DC voltage output unit; wherein the ripple improvement unit comprises: a third diode and a fourth diode which are mutually connected between the output side of the DC voltage output unit and the output terminal; and a second capacitor having one electrode connected between the third diode and the fourth diode and the other electrode connected to one end of a secondary auxiliary coil of the transformer;

The above second capacitor may be a film capacitor.

The output side of the DC voltage output unit is connected to the output terminal via the second diode, the anode terminal of the third diode is connected to the first node between the output side of the DC voltage output unit and the second diode, the cathode terminal of the third diode is connected to the anode terminal of the fourth diode and one electrode of the second capacitor, and the cathode terminal of the fourth diode can be connected to the second node between the second diode and the output terminal.

When the power induced in the secondary auxiliary coil of the transformer becomes a first level voltage, the output voltage of the DC voltage output unit is branched by a predetermined value at the first node and charged to the second capacitor through the third diode, and when the power induced in the secondary auxiliary coil of the transformer becomes a second level voltage higher than the first level voltage, the second level voltage is combined with the voltage previously charged to the second capacitor and can be superimposed on the voltage output from the DC voltage output unit at the second node through the fourth diode.

According to an embodiment of the present invention, a third capacitor may be additionally included, one electrode of which is connected to the cathode terminal of the fourth diode and the other electrode is connected to the other terminal of the secondary-side auxiliary coil.

The above third capacitor may be a film capacitor.

The above switching unit may include a metal oxide semiconductor field effect transistor (MOSFET).

The above metal oxide semiconductor field effect transistor can receive the control signal through a gate terminal, have a source terminal grounded, and have a drain terminal connected to the primary coil.

The above control signal may be a pulse width modulation (PWM) control signal.

According to an embodiment of the present invention, a DC-DC converter may be additionally installed between the ripple improvement unit and the output terminal.

According to the present invention of this configuration, ripple can be eliminated or reduced through a ripple improvement circuit connected to the secondary side of the transformer even when a film capacitor is used instead of an electrolytic capacitor.

In this way, better quality DC power can be achieved by improving ripple (e.g., eliminating or reducing it).

If the DC power with improved ripple is passed through a DC-DC converter (buck-boost converter), it can be made into a more perfect DC power.

FIG. 1 is a circuit diagram of a power supply device with improved ripple according to an embodiment of the present invention.
Figure 2 is a drawing showing an example of the waveform of power output from the rectifier illustrated in Figure 1.
Figure 3 is a drawing showing an example of the waveform of power output from the switching unit illustrated in Figure 1.
Figure 4 is a drawing showing an example of the waveform of power output from the DC voltage output unit illustrated in Figure 1.
Figure 5 is a drawing showing an example of the waveform of power induced in the secondary auxiliary coil of the transformer illustrated in Figure 1.
FIG. 6 is a diagram showing an example of the waveform of power at the second node illustrated in FIG. 1.
FIG. 7 is a circuit diagram of a power supply device with improved ripple according to another embodiment of the present invention.
Figure 8 is a drawing for explaining the effect through the DC-DC converter shown in Figure 7.

The present invention may have various modifications and embodiments, and specific embodiments are illustrated in the drawings and described in detail.

However, this is not intended to limit the present invention to specific embodiments, but should be understood to include all modifications, equivalents, or substitutes included in the spirit and technical scope of the present invention.

The terminology used in this application is only used to describe specific embodiments and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this application, it should be understood that the terms "comprises" or "has" and the like are intended to specify the presence of a feature, number, step, operation, component, part or combination thereof described in the specification, but do not exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms defined in commonly used dictionaries, such as those defined in common usage, should be interpreted as having a meaning consistent with the meaning they have in the context of the relevant art, and shall not be interpreted in an idealized or overly formal sense unless expressly defined in this application.

Hereinafter, with reference to the attached drawings, a preferred embodiment of the present invention will be described in more detail. In order to facilitate an overall understanding in describing the present invention, the same reference numerals are used for the same components in the drawings, and redundant descriptions of the same components are omitted.

FIG. 1 is a circuit diagram of a power supply device with improved ripple according to an embodiment of the present invention, FIG. 2 is a diagram showing an example of a waveform of power output from a rectifier illustrated in FIG. 1, FIG. 3 is a diagram showing an example of a waveform of power output from a switching unit illustrated in FIG. 1, FIG. 4 is a diagram showing an example of a waveform of power output from a DC voltage output unit illustrated in FIG. 1, FIG. 5 is a diagram showing an example of a waveform of power induced in a secondary-side auxiliary coil of a transformer illustrated in FIG. 1, and FIG. 6 is a diagram showing an example of a waveform of power at a second node illustrated in FIG. 1.

A power supply device according to an embodiment of the present invention may include a rectifier (10), a switching unit (20), a transformer (30), a DC voltage output unit (40), and a ripple improvement unit (50).

The rectifier (10) can rectify the input commercial AC power.

For example, the rectifier (10) may include a bridge diode (10a).

The bridge diode (10a) is composed of four diodes connected together and can rectify the input commercial AC power.

The rectifier (10) may be installed between the input terminal (AC-L, AC-N) of the commercial AC power source and one end of the primary coil (30a) of the transformer (30). Accordingly, the rectifier (10) may output power (e.g., voltage) having a waveform as illustrated in Fig. 2. In Fig. 2, the X-axis may represent time (t), and the Y-axis may represent voltage or current.

That is, power having a waveform as exemplified in Fig. 2 can be applied to one end of the primary coil (30a) of the transformer (30).

A switching unit (20) is installed at the other end of the primary coil (30a) of the transformer (30).

For example, the switching unit (20) may include a switching element (Q) such as a MOSFET (Metal Oxide Semiconductor Field Effect Transistor).

The switching unit (20) receives a control signal in the form of PWM (Pulse Width Modulation) and can perform an on/off switching operation according to the received control signal (i.e., PWM control signal).

For example, if the switching element (Q) of the switching unit (20) is assumed to be an N-channel MOSFET, the gate terminal of the switching element (Q) is connected to the output terminal of a PWM IC (not shown) and can receive a PWM control signal with a predetermined duty ratio from the PWM IC. The source terminal of the switching element (Q) is grounded, and the drain terminal of the switching element (Q) can be connected to the other end of the primary coil (30a) of the transformer (30).

The switching element (Q) of the switching unit (20) can perform an on/off operation depending on the state of the PWM control signal applied to the gate terminal. That is, when the pulse signal of the PWM control signal is in the on state (e.g., high level), the switching element (Q) of the switching unit (20) will be conducted, and when the pulse signal of the PWM control signal is in the off state (e.g., low level), the switching element (Q) of the switching unit (20) will be blocked.

The switching unit (20) can cause the output power of the rectifier unit (10) to be conducted to the ground side connected to the source terminal through the primary coil (30a) of the transformer (30) only when the switching element (Q) is turned on.

Accordingly, the switching unit (20) can output power (e.g., voltage) having a waveform as illustrated in Fig. 3 according to the on/off switching operation of the switching element (Q). In Fig. 3, the X-axis can mean time (t), and the Y-axis can mean voltage or current.

Accordingly, the transformer (30) can induce and output AC power to the secondary main coil (30b) and the secondary auxiliary coil (30c) by the voltage supplied to the primary coil (30a) according to the switching operation of the switching unit (20).

According to an embodiment, the DC voltage output from the rectifier (10) can be chopped by turning on/off the switching element (Q) of the switching unit (20), and the energy can be transferred to the secondary side through the transformer (30).

As current is applied to the primary coil (30a) of the transformer (30), power induced in the secondary main coil (30b) of the transformer (30) is rectified and smoothed through the DC voltage output unit (40) and then applied to the output terminal (V_OUT). The power output from the output terminal (V_OUT) can be supplied as driving power to the load (not shown). Of course, the voltage output from the DC voltage output unit (40) can be branched by a predetermined amount and applied to the ripple improvement unit (50). In an embodiment of the present invention, the output terminal (V_OUT) may mean the output terminal of a power supply device.

Meanwhile, as current is applied to the primary coil (30a) of the transformer (30), the power induced in the secondary auxiliary coil (30c) of the transformer (30) is applied to the ripple improvement unit (50) and flows into the lowest point of the output voltage ripple of the DC voltage output unit (40), thereby reducing the ripple voltage.

The DC voltage output unit (40) can convert AC power output from the transformer (30) into a DC voltage and output it to the output terminal (V_OUT). Here, a predetermined load (e.g., a lamp) (not shown) can be connected to the output terminal (V_OUT).

The DC voltage output section (40) may include a first diode (D1) for rectification and a first capacitor (C1) for smoothing.

The anode terminal of the first diode (D1) is connected to one end of the secondary main coil (30b) of the transformer (30), and the cathode terminal of the first diode (D1) can be connected to the output terminal (V_OUT) via the second diode (D2). For example, the cathode terminal of the first diode (D1) can be connected to the anode terminal of the second diode (D2), and the cathode terminal of the second diode (D2) can be connected to the output terminal (V_OUT).

The first capacitor (C1) may be connected between the cathode terminal of the first diode (D1) and the other end of the secondary main coil (30b) of the transformer (30). For example, one electrode of the first capacitor (C1) may be connected to the cathode terminal of the first diode (D1) and the anode terminal of the second diode (D2), and the other electrode of the first capacitor (C1) may be connected to the other end of the secondary main coil (30b) of the transformer (30). In addition, the other end of the secondary main coil (30b) of the transformer (30) and the other electrode of the first capacitor (C1) may be connected to ground.

Since the power supply device according to an embodiment of the present invention outputs high-quality DC power by reducing or eliminating ripple components even while using a film capacitor, it is preferable that the first capacitor (C1) described above be composed of a film capacitor.

The DC voltage output unit (40) can output a predetermined DC voltage by rectifying the AC power output from the transformer (30) with the first diode (D1) and smoothing it with the first capacitor (C1). As a result, the DC voltage output unit (40) can output a DC voltage having a waveform as illustrated in Fig. 4. In Fig. 4, the X-axis can mean time (t), and the Y-axis can mean voltage or current.

At this time, the DC voltage output unit (40) will not output an ideal DC voltage, but will output a DC voltage that includes a noisy ripple voltage (e.g., a pulse voltage where 0 V exists).

The amount of ripple voltage in a power supply using the PWM method is proportional to the switching cycle, duty cycle, output voltage of the transformer (30), etc., and has a characteristic of being inversely proportional to the capacity of the first capacitor (C1).

In this way, the DC output voltage in the DC voltage output section (40) of the power supply using the PWM method inevitably includes a predetermined ripple voltage due to the characteristics of the switching cycle, duty cycle, and capacity of the first capacitor (C1).

If an excessive ripple voltage occurs in the output voltage from the DC voltage output section (40), the Vcc voltage of the IC (Integrated Circuit) in a digital circuit or analog circuit that uses the DC output voltage becomes unstable, and there is a problem that the driving voltage to a load such as a lamp becomes unstable.

Therefore, in devices sensitive to ripple voltage, the ripple voltage of the DC output voltage must be minimized.

Accordingly, the ripple improvement unit (50) can improve (eliminate or reduce) the ripple component of the voltage (e.g., DC voltage) output from the DC voltage output unit (40).

The ripple improvement unit (50) can be connected between the DC voltage output unit (40) and the output terminal (V_OUT) and to the secondary side auxiliary coil (30c) of the transformer (30).

For example, the ripple improvement unit (50) may include a second diode (D2), a third diode (D3), a fourth diode (D4), a second capacitor (C2), and a third capacitor (C3).

The anode terminal of the second diode (D2) is connected to the cathode terminal of the first diode (D1) and one electrode of the first capacitor (C1), and the cathode terminal of the second diode (D2) can be connected to the output terminal (V_OUT).

The anode terminal of the third diode (D3) may be connected to the first node (a) between the output side of the DC voltage output unit (40) and the output terminal (V_OUT). More specifically, the anode terminal of the third diode (D3) may be connected to the first node (a) between the output side of the DC voltage output unit (40) and the anode terminal of the second diode (D2). The cathode terminal of the third diode (D3) may be connected to the anode terminal of the fourth diode (D4) and one electrode of the second capacitor (C2).

The cathode terminal of the fourth diode (D4) can be connected to the second node (b) between the cathode terminal of the second diode (D2) and the output terminal (V_OUT).

The second capacitor (C2) may be connected to the third diode (D3), the fourth diode (D4) and one end of the secondary-side auxiliary coil (30c) of the transformer (30). For example, the second capacitor (C2) may have one electrode connected between the cathode terminal of the third diode (D3) and the anode terminal of the fourth diode (D4), and the other electrode connected to one end of the secondary-side auxiliary coil (30c) of the transformer (30).

The third capacitor (C3) may be connected to the fourth diode (D4), the second node (b), and the other end of the secondary-side auxiliary coil (30c) of the transformer (30). For example, the third capacitor (C3) may have one electrode connected to the cathode terminal of the fourth diode (D4) and the second node (b), and the other electrode connected to the other end of the secondary-side auxiliary coil (30c) of the transformer (30). In addition, the other electrode of the third capacitor (C3) and the other end of the secondary-side auxiliary coil (30c) of the transformer (30) may be connected to ground.

Meanwhile, power of a waveform as illustrated in FIG. 5 can be induced in the secondary auxiliary coil (30c) of the transformer (30), and the power induced in the secondary auxiliary coil (30c) of the transformer (30) (see FIG. 5) can be applied to the ripple improvement unit (50) described above. In FIG. 5, the X-axis can mean time (t), and the Y-axis can mean voltage or current.

When the ripple improvement unit (50) of the circuit configuration is used, during a half cycle of operation of the transformer (30) (e.g., when the switching element (Q) is turned off), the output voltage (see FIG. 4) of the DC voltage output unit (40) is branched by a predetermined amount at the first node (a) and charged to the second capacitor (C2) through the second diode (D3), and during the next half cycle of operation of the transformer (30) (e.g., when the switching element (Q) is turned on), the previous voltage (V1) charged to the second capacitor (C2) is combined with the power (e.g., voltage (V2)) induced in the secondary-side auxiliary coil (30c) of the transformer (30). The combined voltage (V1+V2) passes through the fourth diode (D4) and is charged to the third capacitor (C3). At this time, since the third diode (D3) prevents reverse voltage, the voltage combined in the second capacitor (C2) passes through the fourth diode (D4) and is charged in the third capacitor (C3).

Here, the voltage charged in the third capacitor (C3) may overlap with the output voltage from the DC voltage output unit (40) at the second node (b) (i.e., the voltage of the DC voltage output unit (40) of the first node (a) that has passed through the second diode (D2)). Here, as the voltage overlaps at the second node (b), a power source (e.g., DC voltage) having a waveform as exemplified in FIG. 6 may be generated at the second node (b). In FIG. 6, the X-axis may represent time (t), and the Y-axis may represent voltage or current. At this time, since the third diode (D3) prevents reverse voltage, the voltage discharged from the third capacitor (C3) may be applied to the second node (b).

As the output voltage of the DC voltage output unit (40) passes through the ripple improvement unit (50), the ripple component of the DC voltage is removed or reduced, so that a more stabilized DC voltage (i.e., a DC voltage with the ripple component removed or reduced) can be output to the output terminal (V_OUT).

In other words, the rectifier (10) rectifies commercial AC power and outputs power (e.g., voltage) having a waveform as exemplified in Fig. 2. The output voltage from the rectifier (10) is applied to the primary coil (30a) of the transformer (30), and the switching unit (20) connected to the primary coil (30a) of the transformer (30) outputs power (e.g., voltage) having a waveform as exemplified in Fig. 3 according to the on/off switching operation of the switching element (Q).

Accordingly, a predetermined power (e.g., voltage) is induced in the secondary main coil (30b) and the secondary auxiliary coil (30c) of the transformer (30). The power induced in the secondary main coil (30b) is applied to the DC voltage output unit (40), and the power induced in the secondary auxiliary coil (30c) is applied to the ripple improvement unit (50).

At this time, when the power (e.g., voltage (V2); see FIG. 5) induced in the secondary auxiliary coil (30c) of the transformer (30) becomes, for example, 0 V (i.e., voltage of the first level) (e.g., when the switching element (Q) is turned off), the third diode (D3) becomes conductive, and the output voltage (see FIG. 4) of the DC voltage output unit (40) is branched to a predetermined value at the first node (a) and charged to the second capacitor (C2) through the third diode (D3). At this time, the voltage charged to the second capacitor (C2) can be referred to as V1.

Then, when the power (see FIG. 5) induced in the secondary-side auxiliary coil (30c) of the transformer (30) becomes, for example, greater than 0 V (for example, when the power induced in the secondary-side auxiliary coil (30c) of the transformer (30) becomes approximately 20 V) (for example, when the switching element (Q) is turned on), the current voltage (V2) that becomes greater than 0 V is combined with the voltage (for example, V1) previously charged in the second capacitor (C2) and applied to the third capacitor (C3) through the fourth diode (D4). Accordingly, the third capacitor (C3) is charged with the combined voltage (i.e., voltage (V1) + voltage (V2)). Here, the voltage greater than 0 V is called a second-level voltage.

Thereafter, when the power (e.g., voltage (V2)) induced in the secondary auxiliary coil (30c) of the transformer (30) becomes, for example, 0 V, the third diode (D3) becomes conductive, and the output voltage (see FIG. 4) of the DC voltage output unit (40) is branched by a predetermined value at the first node (a) and charged to the second capacitor (C2) through the third diode (D3). At the same time, the voltage (i.e., voltage (V1) + voltage (V2)) charged to the third capacitor (C3) is applied to the second node (b) and overlaps with the voltage output from the DC voltage output unit (40) at the second node (b). By this overlap at the second node (b), a DC voltage having a waveform as exemplified in FIG. 6 is generated.

That is, when comparing the output voltage of the DC voltage output unit (40) (see FIG. 4) and the output voltage passing through the ripple improvement unit (50) (see FIG. 6), the output voltage passing through the ripple improvement unit (50) becomes a pulsating current without 0 V. Accordingly, it can be seen that the ripple component of the DC voltage is eliminated or reduced as the output voltage of the DC voltage output unit (40) passes through the ripple improvement unit (50).

Due to the charging and discharging of the second capacitor (C2) and the third capacitor (C3) according to the on/off of the switching element (Q) as described above, the ripple component of the DC voltage output from the DC voltage output unit (40) can be eliminated or reduced.

In other words, the ripple voltage of the voltage (e.g., DC voltage) output from the DC voltage output unit (40) can be made smaller through the ripple improvement unit (50). As a result, a more stable (high quality) driving power can be provided to the load side.

FIG. 7 is a circuit diagram of a power supply device with improved ripple according to another embodiment of the present invention, and FIG. 8 is a drawing for explaining the effect through the DC-DC converter illustrated in FIG. 7.

The only difference between Fig. 7 and Fig. 1 is that a DC-DC converter (60) is additionally included.

That is, since Fig. 7 is identical to the configuration of Fig. 1 except for the DC-DC converter (60), the same reference numerals are given to the same components in Fig. 7 as in Fig. 1 and a description thereof is omitted.

As the DC-DC converter (60) is added in this way, the input side of the DC-DC converter (60) can be V_OUT1 (V_OUT in FIG. 1), and the output side of the DC-DC converter (60) can be V_OUT2. Accordingly, the output side (i.e., V_OUT2) of the DC-DC converter (60) becomes the final output terminal of the power supply device with improved ripple according to another embodiment of the present invention.

For example, the DC-DC converter (60) may be a buck-boost converter that operates as a boost converter that boosts an input voltage when an input voltage lower than a predetermined reference voltage (Vref) is input, as in FIG. 8, and operates as a buck converter that steps down an input voltage when an input voltage higher than a predetermined reference voltage (Vref) is input.

A DC voltage with improved ripple (see Fig. 6) can already be obtained at the front end of the DC-DC converter (60), and this DC voltage with improved ripple is input to the DC-DC converter (60).

Accordingly, the DC-DC converter (60) boosts an input voltage that is lower than a predetermined reference voltage (Vref) and lowers an input voltage that is higher than a predetermined reference voltage (Vref), as shown in Fig. 8. Here, the reference voltage can be determined between the highest and lowest values of the input voltage.

Accordingly, the voltage output from the DC-DC converter (60) will be a DC voltage with little change in voltage over time (e.g., a DC voltage that maintains the level of a predetermined reference voltage) as illustrated in FIG. 8.

The above description is merely an illustrative description of the technical idea of the present invention, and those skilled in the art will appreciate that various modifications and variations may be made without departing from the essential characteristics of the present invention. Accordingly, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention but to explain it, and the scope of the technical idea of the present invention is not limited by these embodiments. The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within a scope equivalent thereto should be interpreted as being included in the scope of the rights of the present invention.

10: rectifier 20: switching unit
30: Transformer 40: DC voltage output section
50: Ripple Improvement Section 60: DC-DC Converter

Claims (10)

A switching unit that performs an on/off switching operation according to a control signal;
A transformer in which the switching unit is connected to the primary coil and which induces and outputs AC power to the secondary main coil and the secondary auxiliary coil according to the voltage supplied to the primary coil according to the switching operation of the switching unit;
A DC voltage output unit including a first diode and a first capacitor connected to the secondary main coil, and converting the output power of the transformer into a DC voltage through the first diode and the first capacitor and supplying the DC voltage to the output terminal; and
A ripple improvement unit is connected to the DC voltage output unit, the output terminal, and the secondary auxiliary coil, and improves the ripple component of the voltage output from the DC voltage output unit;
The above first capacitor is a film capacitor,
The above ripple improvement part is,
A third diode and a fourth diode interconnected between the output side of the DC voltage output unit and the output terminal; and
A second capacitor, wherein one electrode is connected between the third diode and the fourth diode and the other electrode is connected to one end of the secondary auxiliary coil of the transformer;
The output side of the above DC voltage output section is connected to the output terminal through the second diode,
The anode terminal of the third diode is connected to the first node between the output side of the DC voltage output unit and the second diode,
The cathode terminal of the third diode is connected to the anode terminal of the fourth diode and one electrode of the second capacitor,
The cathode terminal of the fourth diode is connected to the second node between the second diode and the output terminal.
Power supply unit. In paragraph 1,
The above second capacitor is a film capacitor.
Power supply unit. delete In paragraph 1,
When the power induced in the secondary auxiliary coil of the transformer reaches the first level of voltage, the output voltage of the DC voltage output section is branched to a predetermined value at the first node and charged to the second capacitor through the third diode.
When the power induced in the secondary auxiliary coil of the transformer becomes a second level voltage higher than the first level voltage, the second level voltage is combined with the voltage previously charged in the second capacitor and overlaps with the voltage output from the DC voltage output section at the second node through the fourth diode.
Power supply unit. In paragraph 1,
A third capacitor, further comprising: a third electrode connected to the cathode terminal of the fourth diode and the other electrode connected to the other terminal of the secondary auxiliary coil;
Power supply unit. In paragraph 5,
The above third capacitor is a film capacitor.
Power supply unit. In paragraph 1,
The above switching part,
Including a metal oxide semiconductor field effect transistor (MOSFET),
Power supply unit. In Article 7,
The above metal oxide semiconductor field effect transistor,
The above control signal is input to the gate terminal, the source terminal is grounded, and the drain terminal is connected to the primary coil.
Power supply unit. In paragraph 1,
The above control signal is a pulse width modulation (PWM) control signal.
Power supply unit. In paragraph 1,
A DC-DC converter is additionally installed between the above ripple improvement unit and the output terminal.
Power supply unit.

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