JP3082873B2 - AC / DC converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC / DC converter for converting a commercial AC input power supply voltage into a stable DC output voltage, and more particularly to a high power factor AC / DC converter.

2. Description of the Related Art As an AC / DC converter which receives a commercial AC power supply and converts it into a DC voltage, there has conventionally been, for example, one shown in FIG. In the figure, the AC input voltage Ei
Rectifier circuit RC1, smoothing capacitor C1,
The AC input voltage Ei is obtained by an AC / DC converter composed of a field effect transistor Q1 as a switching element, a transformer Tr1, a transformer reset diode D4, an output rectifier diode D2, a flywheel diode D3, an output smoothing choke coil L2, and an output smoothing capacitor C2. Is converted to a stable DC output voltage Eo. However, such a conventional AC / DC converter has desirable characteristics with respect to the output DC voltage, but only when the waveform of the input current corresponds to the vicinity of the peak value of the input AC voltage as shown in FIG. Since it does not flow, the power factor is low, about 0.5 to 0.7. In order to improve the power factor, there is a method of inserting and connecting a sufficiently large choke coil to the rectifier circuit, but there is a disadvantage that the weight becomes large. In recent years, a method of electronically improving the power factor by providing a pre-converter for improving the power factor has been used in some cases. However, the number of components is increased, the size is increased, the price is high, and the mutual interference of the switching elements is caused. There was a problem of inviting.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a small, lightweight, and economical high power factor AC / DC converter circuit having a simple circuit configuration.

SUMMARY OF THE INVENTION In order to solve this problem, the present invention rectifies and smoothes an AC input voltage, and turns the rectified voltage on and off by a semiconductor switching element to provide a primary winding of a transformer. A high-frequency AC voltage is applied to the secondary winding, and a high-frequency AC voltage is rectified and smoothed to obtain a predetermined voltage. A high power factor AC / DC converter is proposed in which a boost choke coil and a diode are inserted, and a resonance capacitor is connected to a connection point between the boost choke coil and the diode and a connection point between the transformer and the switching element. Things.

FIG. 1 shows an AC / DC converter according to the present invention. As shown in Fig. 1, the configuration is such that a commercial AC power supply Ei is connected to the bridge type rectifier circuit via input terminals X1 and X2.
Connect to RC1. The DC output terminal of the rectifier circuit RC1 is supplied to a smoothing capacitor C1 via a choke coil L1 and a diode D1. The connection point between the choke coil L1 and the diode D1 is connected to the drain electrode of the field effect transistor Q1 via the capacitor C3, and its emitter is connected to the negative electrode of the capacitor C1. The gate terminal of the field-effect transistor Q1 is turned on and off at a high frequency of about 100 kHz by a control circuit U1 for a switching regulator. These parts are rectifier chopper circuits. That is, the input commercial AC power supply Ei (100V 50Hz) is
The current is rectified by 1 and the field effect transistor Q1 is repeatedly turned on and off at a high frequency of about 100 kHz via the choke coil L1 and the capacitor C3. Here, the choke coil L1 was selected to be about 500 μH, the capacitor C3 was selected to be 0.02 μF, and the capacitor C1 was selected to be 200 μF. First, when the field effect transistor Q1 is on, a current for charging the capacitor C3 flows from the choke coil L1. This current is determined by the voltage of capacitor C3
, And energy is accumulated in the choke coil L1 and the capacitor C3. Next, when the field effect transistor Q1 is turned off, the current energy stored in the choke coil L1 charges the capacitor C1 through the diode D1. Since the capacitance of the capacitor C1 is a sufficiently large value, the DC voltage Eb is kept almost constant in a steady state. Input AC current must be choke coil
Since the current passes through L1, the current is continuous. Next, the capacitor
The plus terminal of C1 is connected to the drain of field effect transistor Q1 via primary winding n1 of transformer Tr1. Transformer Tr
1 is connected to a smoothing capacitor C2 via a rectifying diode D2 and a smoothing choke coil L2, and is also connected to DC output terminals Y1 and Y2. The detection / comparison circuit DET1 is connected to the DC output terminals Y1 and Y2, and the output is connected to the detection input terminal of the control circuit U1 via the photocoupler Q2. Here, the detection / comparison circuit DET1 is a general circuit configured by adding an output current amplifier circuit and some auxiliary components to the Texas Instruments TL494 or equivalent, which is a widely used switching power supply integrated circuit, or an equivalent. is there. The detection / comparison circuit DET1 is composed of a resistor voltage divider and a constant voltage diode. And photocoupler Q2
Select a withstand voltage sufficient to insulate the commercial AC power supply Ei.
A diode D3 acting as a flywheel is connected between the other terminal of the secondary winding n2 of the transformer Tr1 and a connection point between the diode D2 and the choke coil L2. This part has a function called a so-called forward type converter and a reset function of the transformer Tr1 due to natural vibration of the capacitor C3 and the primary winding n1 of the transformer Tr1. When the field effect transistor Q1 is on, the electric charge stored in the capacitor C1 supplies power to the output terminal through the primary winding n1 of the transformer Tr1 and the subsequent circuits, and the field effect transistor Q1 is off. At this time, the energy of the current flowing in the primary winding n1 of the transformer Tr1 flows through the path of the capacitor C3 and the diode D1 to reset the transformer Tr1 and to reset the capacitor C3.
Is inverted. Next, the operation will be described in detail. It is assumed that the switching frequency of the field effect transistor Q1 is sufficiently high with respect to the frequency of the input AC power supply. Therefore, the input voltage is considered to be constant during one switching cycle, and the choke coil L1 is sufficiently large with respect to the switching frequency, so that it can be regarded as almost constant current. In addition, the exciting inductance of the transformer Tr1 is considerably smaller than L1, the turns ratio is 1: 1, and the output filter choke coil L2 is sufficiently large as a current source. Hereinafter, the description will be given by dividing into time sections T0, T1,..., T7 shown in FIG.

[Section T0-T1] When the field effect transistor Q1 is turned on at time T0, the current that has been flowing through the closed loop of Ei → L1 → C3 → n1 → C1 → Ei flows into the field effect transistor Q1. At the same time, the voltage Eb of the capacitor C1 is applied to the primary winding n1 of the transformer Tr1 to generate a voltage in the secondary winding n2, and all the current flowing in the choke coil L2 is commutated to the secondary winding n2. I do. Therefore, the current of the primary winding n1 of the transformer Tr1 becomes a step change of the current flowing through the diode D3 at the time T0 as shown in FIG. 2A, and then Eb / L0 (L0: the exciting inductance of the transformer Tr1). ). The current i1 flowing through the choke coil L1 is represented by Expression 1.

(Equation 1) In Equation 1, the desired value differs depending on the phase of the input voltage Ei. Jo increases as the input voltage Ei increases, and Vco decreases as the input voltage Ei increases. Therefore α is the input voltage
The higher the phase of Ei, the larger the AC input voltage becomes.
From 50 to 80 degrees from the peak to the peak. Also, T1 ~
The period of T2 is a period during which the capacitor C3 is charged up to the voltage Eb of the capacitor C1, and the charging is completed earlier when the input voltage is in the higher phase. Therefore, the period is longer when the input voltage is in the lower phase, and it takes about 5 to 1.5 μs. Become. Figure 2 shows the input current waveform.
The waveform becomes as shown in (b). The voltage of the capacitor C3 rises almost linearly as shown in FIG. The current of the field effect transistor Q1 is the sum of the current flowing through the winding n1 and the current flowing through the capacitor C3, as shown in FIG. The current flowing through the diode D3 flows into the secondary current In2 of the transformer Tr1, and becomes equal to the output current I0. Fig. 2 (e) shows the waveform.

[Section T1-T2] At time T1, when the voltage of the capacitor C3 becomes the voltage Eb of the capacitor C1, the voltage is clamped, and the choke coil is turned on.
The current of L1 flows into the capacitor C1 via the diode D1. Therefore, the current flowing through the field effect transistor Q1 loses the current flowing through the capacitor C1, but continues to rise with the slope of Eb / L0. In addition, a capacitor is used for output.
An output current I0 is supplied from C1 via a transformer. FIG.
(b) and (c) show the waveforms. At this time, the current i1 flowing through the choke coil L1 is expressed by Expression 2 assuming that the voltage of the capacitor C3 is constant.

(Equation 2) Since Eb is always higher than Ei, Ii decreases from Equation 2.
Further, the slope of the decrease becomes gentler as the input voltage Ei has a higher phase. This operation mode is based on the field effect transistor Q1.
Continue until turned off. The conduction period of the field-effect transistor Q1 is substantially constant unless the effective values of the load and the input voltage change, so that this period is longer when the phase of the input voltage is higher, and is approximately 0 to 3.5 μs.

[Section T2-T3] When the field-effect transistor Q1 is turned off at time T2, the exciting current flowing through the primary winding n1 becomes n1 → C3 → D1
→ It flows into the closed loop of n1. The voltage of the field effect transistor Q1 increases from zero according to the voltage of the capacitor C3. On the other hand, the current of the secondary winding n2 of the transformer Tr1 continues to flow even after the field-effect transistor Q1 is turned off because the voltage of the capacitor C3 of the primary winding n1 of the transformer Tr1 is applied. And
The current of the choke coil L1, which is the input current, continues to flow to the capacitor C1 while continuously decreasing, and is expressed as an extension of Equation 2. At this time, the current i3 flowing through the capacitor C3 is expressed by Expression 3.

(Equation 3) In Equation 3, since K30 is large, γ is approximately 70 degrees, and the change in i3 is small and considered to be almost constant. This operation mode is a period until the voltage of the capacitor C3 becomes zero, and is 1 μs or less.

[Section T3-T5] At time T3, when the voltage of the capacitor C3 becomes zero, the voltage of the primary coil n1 of the transformer Tr1 also becomes zero, the secondary current is cut off, and the current of the choke coil L2 is passed through the flywheel diode D3. Keep flowing. Therefore the transformer
The primary current In1 of Tr1 becomes Io at time T3 as shown in FIG.
And then the excitation inductance Lo and the capacitor
Free oscillation with C3 continues, and the voltage of capacitor C3 reverses and increases in the negative direction. The voltage of the field effect transistor Q1 keeps rising according to the voltage of the capacitor C3. At time T4, the current of the primary winding n1 reverses direction, the voltage of the capacitor C3 reaches a negative peak, and continues to oscillate until time T4 when the current becomes equal to the current of the choke coil L1. Therefore, the current flowing through the capacitor C3 at this time is a current obtained by adding Io to Equation 3. The time from time T3 to T4 is little influenced by the input voltage phase and is almost 2 μs or more. Since the time from T4 to T5 becomes longer as the input current becomes larger, it becomes longer as the phase of the input voltage becomes higher, and the difference is about 1 μs.

[Section T5-T6] At time T5, when the current of the choke coil L1 becomes smaller than the current of the primary winding n1, the diode D1 turns off,
A current flows through the closed loop of Ei → L1 → C3 → n1 → C1 → Ei. Since the choke coil L1 is sufficiently larger than the exciting inductance Lo, the rate of change of the primary winding current In1 decreases, the primary winding voltage decreases rapidly, and the voltage of the field effect transistor Q1 also decreases. The voltage of the capacitor C3 changes almost linearly. The current i1 flowing through the choke coil L1 at this time is expressed by Expression 4.

(Equation 4) Looking at the relationship between Ei and Vc50 in Equation 4, when Ei has a small voltage phase, the section from section T3 to T5 is short, and the expected value of Vc50 is negatively large (about -350 V). When Ei increases, the expected value of Vc50 becomes almost zero. Therefore, δ is about 50 degrees near zero of the input voltage Ei, and becomes almost zero as the input voltage Ei increases. Also,
Since L1 is larger than Lo, ω4 becomes smaller than that in the section T3 to T5, and the current changes gradually. The waveform of the input current Ii is as shown in FIG. The voltage of the field effect transistor Q1 is a value obtained by adding the voltage Eb of the capacitor C1 to the value obtained by differentiating Expression 4 and multiplying it by Lo, as shown in FIG.

[Section T6-T7] At time T6, when the voltage of the primary winding n1 of the transformer Tr1 becomes zero and the polarity is about to be reversed, the choke coil is activated.
The current of L2 is shunted to the diode D3 and the secondary winding n2. Therefore, the winding voltage is suppressed to zero, and the voltage of the field effect transistor Q1 is clamped by Eb. Since the winding voltage becomes zero, there is no change in the exciting current, and the choke coil L1
The current change due to the vibration of the capacitor C3 flows through each winding of the transformer Tr1 as a shunt of the current of the choke coil L2. The current i1 of the choke coil L1 is represented by Expression 5.

(Equation 5) At time T7, the field effect transistor Q1 is turned on again, and the operation from time T0 is repeated. FIG. 2 (g) shows the waveform of the current Ii flowing through the choke coil L1. The operation of one cycle of the high-frequency switching has been described above. Next, the input current of the commercial AC power supply Ei in one cycle will be described. The first half of this converter circuit constitutes a so-called boost chopper circuit.
The input current flows continuously over the entire range of the input voltage. In the section T0-T1, the input current stores energy in the choke coil L1 while charging the capacitor C3 to the voltage Eb of the capacitor C1 when the switch is turned on. After charging the capacitor C1 to Eb, the capacitor C1 is charged by the sum of the energy stored in L1 and the input voltage regardless of whether the switch is on or off. The input current in the section T0-T1 is the same if the voltage of C3 at the time of switch on is the same in the entire range of the input voltage, the amount of current integration is the same, but the initial value of the capacitor C3 is almost inversely proportional to the input voltage . This is because the point at time T5 (the point where the current of L1 equals the current of L0 and D1 cuts off) is
As the input voltage increases, the delay increases
This is because the voltage of C3 approaches zero. Therefore, the input current increase when the field effect transistor Q1 is turned on increases as the input voltage decreases. On the other hand, in the reset mode of the choke coil L1 in the section T1-T5, since the reset amount is determined by the difference voltage between the input voltage and the voltage of C1, the input current decreases as the input voltage decreases. Therefore, although the integral amount of the input current in one switching cycle is affected by the AC input voltage, if a simulation is performed for one cycle of the AC frequency, a waveform such as a DC component superimposed on a sine wave as shown in FIG. 3 is obtained. Becomes This waveform corresponds to a power factor of about 0.98. The output voltage of the forward-coupled converter is determined by the voltage applied to the primary winding n1 of the transformer Tr1 and the duty ratio within a range where the current of the filter choke coil L2 does not cut off. Therefore, the duty ratio control for compensating for the voltage fluctuation of the converter circuit is performed by the control circuit U1 so that the output voltage is kept constant with respect to the load fluctuation. In this converter circuit, the duty ratio control is performed so that the output voltage is kept constant by only one field effect transistor Q1 as a switching element. On the other hand, the field effect transistor Q1 is controlled at the same time ratio as the switching element of the chopper circuit against the fluctuation of the AC input voltage, but as a result, the internal circuits are controlled to maintain a stable DC output voltage . Note that the field effect transistor Q1 can be replaced with another switching element such as a bipolar transistor. Further, the polarity of each semiconductor switching element can be all reversed. Further, the above-described constants are merely examples, and may be any combination of the values of the constants such that the operation mode described above is obtained. A smoothing filter can be further added to the DC output circuit. The connection place of the detection / comparison circuit DET1 is not necessarily limited to the output terminal, and there is a method of connecting directly to both ends of a remote load. Alternatively, an output voltage can be detected by providing a winding for voltage detection in the transformer Tr1. Further, a plurality of secondary windings may be provided in the transformer Tr1, and a rectifying / smoothing circuit and an output terminal may be provided in each of the secondary windings.

Second Embodiment FIG. 4 shows a second embodiment of the present invention.
This embodiment has the same configuration as the embodiment shown in FIG.
The difference in the configuration is that the connection polarity of the transformer Tr1 is
, The secondary rectifier circuit is a half-wave rectifier circuit consisting of only the diode D2 and the capacitor C2, and the diode is connected in series with the primary winding n1 of the transformer Tr1.
D4 is provided with the illustrated polarity. The difference in configuration corresponds to the operation in which the part of the converter operation is replaced by a so-called forward type to a flyback type. The other points are common in obtaining a high power factor which is the object of the present invention. The operation will be described below while avoiding duplication. The waveforms of each part will be described separately for time sections T0, T1,..., T5 as shown in FIG.

[Section T0-T1] When the field effect transistor Q1 is turned on at time T0, the current that has flowed through the closed loop of Ei → L1 → D1 → C1 → Ei flows into the field effect transistor Q1 while charging the capacitor C3. At the same time, the primary winding of the transformer Tr1
The voltage Eb of the capacitor C1 is applied to n1.
As for the voltage polarity of n2, a voltage having a negative polarity with respect to the output voltage E0 is generated and cut off by the diode D2, so that no current flows on the secondary side. Therefore, at time T0, the exciting current starts to flow through the closed loop of C1, n1, D4, Q1, and C1 in the primary winding n1 of the transformer Tr1, and Eb / L0 (L0: transformer Tr1) as shown in FIG. (Excitation inductance). The current i1 flowing through the choke coil L1 is expressed by a mathematical expression having the same form as the aforementioned mathematical expression 1.
In Equation 1, the desired value differs depending on the phase of the input voltage Ei. Jo2 increases as the input voltage Ei increases, and Vco becomes almost constant regardless of the input voltage Ei. Therefore, α increases as the input voltage Ei has a higher phase, and is approximately 50 to 80 degrees from 0 to the peak of the AC input voltage. Also, T1
The period from T2 to T3 is a period during which the capacitor C3 is charged to the voltage Eb of the capacitor C1. The charging is completed earlier when the input voltage is in the higher phase, and is longer when the input voltage is in the lower phase, and is approximately 5 to 2.0 μs. become. The input current waveform is as shown in FIG. The voltage of the capacitor C3 rises almost linearly as shown in FIG. The current of the field effect transistor Q1 is the sum of the current flowing through the winding n1 and the current flowing through the capacitor C3, as shown in FIG. Since the secondary current In2 of the transformer Tr1 is cut off by the diode D2, it is zero in this section as shown in the waveform of FIG.

[Section T1-T2] At time T1, when the voltage of the capacitor C3 becomes the voltage Eb of the capacitor C1, the voltage is clamped, and the choke coil is turned on.
The current of L1 flows into the capacitor C1 via the diode D1. Therefore, the current flowing through the field effect transistor Q1 loses the current flowing through the capacitor C1, but continues to rise with the slope of Eb / L0. 5 (b) and 5 (c) show the waveforms. At this time, the current i1 flowing through the choke coil L1 is expressed by the above-mentioned formula 2 assuming that the voltage of the capacitor C3 is constant.
Since Eb is always higher than Ei, Ii decreases from Equation 2.
Further, the slope of the decrease becomes gentler as the input voltage Ei has a higher phase. This operation mode is based on the field effect transistor Q1.
Continue until turned off. The conduction period of the field-effect transistor Q1 is almost constant unless the effective values of the load and the input voltage are changed. Therefore, this period is longer when the phase of the input voltage is higher, and is approximately 0 to 3.0 μs.

[Section T2-T3] When the field-effect transistor Q1 is turned off at time T2, the exciting current flowing through the primary winding n1 becomes n1 → D4 → C3
→ It flows into the closed loop of D1 → n1. Field effect transistor Q1
Rises from zero according to the voltage of the capacitor C3. On the other hand, the current of the secondary winding n2 of the transformer Tr1 does not flow even after the field-effect transistor Q1 is turned off because the voltage of the capacitor C3 of the primary winding n1 of the transformer Tr1 is applied. Then, the current of the choke coil L1, which is the input current, continues to flow through the capacitor C1 while continuously decreasing.
Expressed as an extension of At this time, the current i3 flowing through the capacitor C3 is expressed by Expression 6.

(Equation 6) In Equation 6, since K30 is large, γ is approximately 70 degrees, and the change in i3 is small and considered to be almost constant. This operation mode is a period until the voltage of the capacitor C3 becomes zero, and is 1 μs or less.

[Section T3-T4] At time T3, when the voltage of the capacitor C3 becomes -Vo, the voltage of the primary winding n1 of the transformer Tr1 also becomes -Vo, and current starts to flow to the secondary winding n2. Then, the secondary winding voltage is clamped at the output voltage Eo, and the primary winding is also fixed at Eo. 1
When the secondary winding voltage becomes constant at Eo, the capacitor C3 is no longer charged. Therefore, the primary current In1 of the transformer Tr1 is as shown in FIG.
As shown in (2), it becomes zero at time T3, and the stored energy is commutated to the secondary winding n2. The secondary winding current In2 decreases with the slope of Eo / Lo as shown in FIG. The voltage of the field effect transistor Q1 is the sum of the voltage of the capacitor C3, the voltage of the primary winding n1, and the output voltage Eo. At time T4, the secondary winding n2
Current becomes zero, and all the energy stored in the magnetizing inductance of the transformer Tr1 is released. The current of the choke coil L1 continues to flow through the capacitor C1, which is an extension of Equation 2. The time from time T3 to T4 is determined by the value of the output current Io, and is about 4 μs at the maximum output current.

[Section T4-T5] This section is a period from when the secondary current becomes zero to when the field effect transistor Q1 is turned on next time. The current of the choke coil L1 is a period during which the capacitor C1 is charged.
At time T5, the field-effect transistor Q1 is turned on again, and the operation from time T0 is repeated. FIG. 5 (g) shows the waveform of the current Ii flowing through the choke coil L1. Hereinafter, if a simulation is performed for one cycle of the AC frequency according to the principle substantially the same as that described in the first embodiment, the commercial AC input current Ii
Is a waveform as shown in FIG. 3 in which a DC component is superimposed on a sine wave. This waveform corresponds to a power factor of about 0.98. Although the diode D4 in the second embodiment is not an essential component, it can be omitted. However, the diode D4 is effective for preferable operation. On the other hand, in the first embodiment, there is no component corresponding to the diode D4, but the basic operation does not change even if the corresponding component is included.

The present invention has the features described above,
A single switching element stabilizes the output voltage while improving the AC input current waveform.
It can be improved to about 98. Since there is only one switching element, there is no mutual interference as in the case where a conventional pre-converter is provided. Furthermore, due to the resonance action of the converter, the switching element performs zero volt switching, the capacitor for resonance plays the role of a lossless snubber, and the snubber circuit of the switching element becomes unnecessary. Further, the converter's resonance function plays a role of a reset circuit of the transformer, and the converter transformer does not need a reset winding and a reset diode. As described above, the AC / DC converter according to the present invention has a simple configuration and has effects of small size, light weight, high power factor, and high efficiency.

[Brief description of the drawings]

FIG. 1 is a diagram showing the configuration of a first embodiment of an AC / DC converter according to the present invention.

FIG. 2 is a waveform chart for explaining the operation of the first embodiment of the AC / DC converter according to the present invention.

FIG. 3 is an AC input current waveform diagram of the AC / DC converter according to the present invention.

FIG. 4 is a diagram illustrating a configuration of an AC / DC converter according to a second embodiment of the present invention;

FIG. 5 is a waveform chart for explaining the operation of the second embodiment of the AC / DC converter according to the present invention.

FIG. 6 is a diagram illustrating an example of a configuration of a conventional AC / DC converter.

FIG. 7 is an AC input current waveform diagram of a conventional AC / DC converter.

[Explanation of symbols]

 C1, C2, C3 ... capacitors D1, D2, D3, D4 ... diodes DET1 ... voltage divider Ei ... commercial AC power supply L1, L2 ... choke coil Q1 ... field effect transistor Q2 ... photocoupler RC1, RC2 ... rectifier circuit Tr1 ... transformer U1… Control circuit X1, X2… Input terminal Y1, Y2… Output terminal

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H02M ^7/ 00-7/40 H02M 3/28

Claims (4)

(57) [Claims] A bridge-type rectifier circuit comprising a pair of input terminals to be connected to a commercial AC power supply, a pair of AC input terminals, and a pair of DC output terminals, wherein the AC input terminals of the rectifier circuit are provided. Are connected to the pair of input terminals, a bridge-type rectifier circuit is connected to a DC output terminal of the bridge-type rectifier circuit, a choke coil, a diode, and a capacitor are connected in series with each other; A control circuit for generating an on / off drive signal having a frequency sufficiently higher than the frequency, and a switching element having a pair of main electrodes and a control terminal, wherein the control terminal is driven on / off by the control circuit; One end of the main electrode is connected to a connection point between the choke coil and the diode via a second capacitor, and the other end of the main electrode is connected to the capacitor. A transformer comprising a switching element connected to one end of a capacitor, and at least a primary winding and a secondary winding, wherein the primary winding is connected to a connection point between the capacitor and the diode and the switching element. An AC / D comprising a transformer connected between the main electrode of the transformer, a rectifier connected to a secondary winding of the transformer, and an output terminal connected to the rectifier.
C converter. 2. The AC / D converter according to claim 1, wherein the rectifier connected to the secondary winding of the transformer transmits energy corresponding to a time when the switching element is turned on.
C converter. 3. The AC / D according to claim 1, wherein the rectifier connected to the secondary winding of the transformer transmits energy corresponding to a time when the switching element is turned off.
C converter. 4. The transformer according to claim 1, wherein a diode is connected in series with a primary winding of the transformer.
Or the AC / DC converter according to claim 3.