JP7489939B2 - Switching Power Supply Unit - Google Patents

Description

The present invention relates to a switching power supply device equipped with a snubber circuit.

Figure 4 shows a conventional switching power supply 1C. In the switching power supply 1C, the AC input voltage input from the AC source E is full-wave rectified by a commercial bridge diode BD1, smoothed by a smoothing capacitor C11, converted to a DC voltage, and the converted DC voltage is switched by a switching element Q1 and applied to the primary winding N11 of the transformer T11. The switching element Q1 is PWM controlled in response to a drive signal from a drive circuit IC1.

When a voltage is applied to the primary winding N11 of the transformer T11, a voltage is induced in the secondary winding N12 of the transformer T11. The switching power supply device 1C rectifies the induced voltage in the secondary winding N12 with the diode D2 and smoothes it with the capacitor C2, converting it into a DC voltage (output voltage) and outputting it.

The switching power supply 1C has a clamp-type snubber circuit consisting of a resistor R1, a capacitor C1, and a diode D1 on the primary winding N11 side. The snubber circuit can reduce the spike voltage generated by the leakage inductance of the transformer T11 to an appropriate value when the switching element Q1 switches from on to off.

On the other hand, the switching power supply 1C has a problem in that the power factor on the input side is only about 0.5 to 0.55 because the pulsating voltage that is full-wave rectified by the bridge diode BD1 is directly smoothed by the smoothing capacitor C11.

As a switching power supply device that solves the above problem, for example, the one described in Patent Document 1 is known. Figure 5 shows a switching power supply device 1D described in Patent Document 1. The switching power supply device 1D includes a π-type noise filter 11, a first circuit A, and a second circuit B.

The first circuit A uses a rectifier circuit 12 to full-wave rectify the AC input voltage input through a noise filter 11 to generate a pulsating voltage, and switches the generated pulsating voltage with a switching element 13 to apply it to the primary winding N21 of the transformer T21. The second circuit B uses a bridge diode 15 to full-wave rectify the AC input voltage input through the noise filter 11, and switches the voltage smoothed by a capacitor 17 while limiting the current with a resistor 16 with the switching element 13 to apply it to the auxiliary winding N23 of the transformer T21.

In the switching power supply device 1D, the first circuit A is used during periods when the pulsating voltage is high, and the second circuit B is used during periods when the pulsating voltage is low, improving the power factor on the input side. However, in the switching power supply device 1D, there is a problem in that the resistor 16 that limits the current generates heat during periods when the pulsating voltage is low, resulting in power loss.

JP 2001-8449 A

The present invention was made in consideration of the above circumstances, and its objective is to provide a switching power supply device that can improve the power factor while suppressing the occurrence of power loss.

In order to solve the above problems, a switching power supply device according to the present invention comprises:
a voltage conversion circuit that converts an AC input voltage into a pulsating voltage;
a transformer having a primary winding and a secondary winding;
a first switching element that switches the pulsating voltage and applies it to the primary winding;
a clamp-type snubber circuit including a first resistor, a first capacitor, and a first diode, the snubber circuit being connected to both ends of the primary winding;
A switching power supply device comprising:
an auxiliary winding provided on the primary side of the transformer;
a second switching element that switches the charging voltage charged in the first capacitor and applies the voltage to the auxiliary winding;
a control unit that controls the first switching element and the second switching element;
Equipped with
The control unit is
The present invention is characterized in that the first switching element is driven during a first period in which the pulsating voltage is equal to or greater than a predetermined threshold, while the second switching element is driven during a second period in which the pulsating voltage is less than the predetermined threshold.

According to this configuration, in the first period when the pulsating voltage is equal to or greater than the predetermined threshold, the pulsating voltage is not directly smoothed, so the power factor is improved, and in the second period when the pulsating voltage is less than the predetermined threshold, the power factor is improved by switching the charging voltage charged in the first capacitor of the snubber circuit without using the pulsating voltage. In addition, according to this configuration, since there is no resistor that limits the current, power loss due to heat generation by the resistor can be avoided.

The switching power supply device is
a resistor voltage divider circuit for dividing the pulsating voltage to generate a divided voltage,
The control unit can be configured to determine whether the period is the first period or the second period by comparing the divided voltage with a preset voltage.

The switching power supply device is
a drive transformer or a high-side gate drive circuit;
A second diode;
Further equipped with
the control unit outputs a drive signal for driving the second switching element to a control terminal of the second switching element via the drive transformer or the high side gate drive circuit;
One end of the first capacitor may be connected to one end of the auxiliary winding via the second diode, and the other end of the auxiliary winding may be connected to the other end of the first capacitor via a current path of the second switching element.

The switching power supply device is
Further comprising a second diode and a third diode;
The first capacitor may be configured such that one end of the first capacitor is connected to one end of the auxiliary winding via the second diode, the other end of the auxiliary winding is connected to one end of a current path of the second switching element, and the other end of the current path of the second switching element is connected to the other end of the first capacitor via the third diode.

The present invention provides a switching power supply device that can improve the power factor while suppressing power loss.

1 is a circuit diagram of a switching power supply device according to a first embodiment. 11 is a diagram showing switching periods of first and second switching elements according to the magnitude relationship between a divided voltage and a set voltage; FIG. FIG. 7 is a circuit diagram of a switching power supply device according to a second embodiment. FIG. 1 is a circuit diagram of a conventional switching power supply device. 1 is a circuit diagram of a switching power supply device described in Patent Document 1.

Below, an embodiment of a switching power supply device according to the present invention will be described with reference to the attached drawings.

[First embodiment]
1 shows a switching power supply device 1A according to a first embodiment of the present invention. The switching power supply device 1A is a flyback converter.

The switching power supply device 1A includes a transformer T1, a bridge diode BD1, a snubber circuit 2, a DC circuit 3, a first switching element Q1, a second switching element Q2, an insulated drive transformer 4, a diode D3, a drive circuit 5, a resistive voltage divider circuit 6, and a control circuit 7. The drive circuit 5 and the control circuit 7 correspond to the "control unit" of the present invention.

The transformer T1 is an isolation transformer that includes a primary winding N1, a secondary winding N2, and a primary-side auxiliary winding N3. The primary winding N1 and the secondary winding N2 have coils wound in opposite directions. The auxiliary winding N3 and the secondary winding N2 also have coils wound in opposite directions. When a voltage is applied to the primary winding N1 or the auxiliary winding N3 of the transformer T1, a voltage is induced in the secondary winding N2.

The input terminal of the bridge diode BD1 is connected to the AC power source E. The high-potential output terminal of the bridge diode BD1 is connected to one end (black circle side) of the primary winding N1 of the transformer T1, and the other end of the primary winding N1 is connected to the low-potential output terminal of the bridge diode BD1 via the current path of the first switching element Q1. The bridge diode BD1 full-wave rectifies the AC input voltage supplied from the AC power source E, converts it to a pulsating voltage, and outputs it.

The snubber circuit 2 is a clamp-type snubber circuit consisting of a resistor R1, a capacitor C1, and a diode D1. The resistor R1 corresponds to the "first resistor" of the present invention, the capacitor C1 corresponds to the "first capacitor" of the present invention, and the diode D1 corresponds to the "first diode" of the present invention. The snubber circuit 2 is connected across the primary winding N1, and can reduce to an appropriate value the spike voltage generated by the leakage inductance of the transformer T1 when the first switching element Q1 switches from on to off.

The DC circuit 3 includes a diode D2 and a capacitor C2. The anode of the diode D2 is connected to the other end of the secondary winding N2 of the transformer T1, and the cathode is connected to one end (+ side) of the capacitor C2. The other end (- side) of the capacitor C2 is connected to one end (black circle side) of the secondary winding N2 of the transformer T1. The DC circuit 3 rectifies the induced voltage of the secondary winding N2 with the diode D2 and smoothes it with the capacitor C2, converting it into a DC voltage (output voltage) and outputting it.

The first switching element Q1 is composed of an FET (in this embodiment, an N-channel MOSFET). The first switching element Q1 has a gate connected to the first output terminal of the control circuit 7, a drain connected to the other end of the primary winding N1 and the anode of the diode D1, and a source connected to the low-potential output end of the bridge diode BD1. The first switching element Q1 switches the pulsating voltage output from the bridge diode BD1 and applies it to the primary winding N1.

The second switching element Q2 is composed of an FET (in this embodiment, an N-channel MOSFET). The second switching element Q2 has a gate connected to the second output terminal of the control circuit 7 via the drive transformer 4, a drain connected to the other end of the auxiliary winding N3, and a source connected to one end (black circle side) of the auxiliary winding N3 via a capacitor C1 and a diode D3. The second switching element Q2 switches the charging voltage charged in the capacitor C1 of the snubber circuit 2 and applies it to the auxiliary winding N3.

The drive transformer 4 ensures insulation between the control circuit 7 and the second switching element Q2. Note that instead of the drive transformer 4, an insulated high-side gate drive circuit (IC) capable of driving (turning on/off) the second switching element Q2 may be used.

Diode D3 corresponds to the "second diode" of the present invention, and has an anode connected to one end of capacitor C1 (the connection point between capacitor C1 and diode D1) and a cathode connected to one end of auxiliary winding N3. Diode D3 prevents capacitor C1 from being charged by the voltage induced in auxiliary winding N3 when first switching element Q1 is turned on.

The drive circuit 5 is a flyback converter control IC for performing PWM control, and outputs a PWM control signal (corresponding to the "drive signal" of the present invention) for driving the first switching element Q1 and the second switching element Q2 from an output terminal. The drive circuit 5 has, for example, a triangular wave oscillator and a feedback terminal (not shown) to which a feedback signal of the output voltage is input, and generates a PWM control signal by comparing the triangular wave voltage oscillated by the triangular wave oscillator with the terminal voltage of the feedback terminal.

The resistive voltage divider circuit 6 is composed of resistors R2 and R3 connected in series and is connected between the output terminals of the bridge diode BD1. The resistive voltage divider circuit 6 generates a divided voltage by dividing the pulsating voltage.

The control circuit 7 has a first input terminal to which the PWM control signal is input from the drive circuit 5, a second input terminal to which the divided voltage is input from the resistive voltage divider circuit 6, a first output terminal connected to the gate of the first switching element Q1, and a second output terminal connected to the gate of the second switching element Q2 via the drive transformer 4.

The control circuit 7 drives the first switching element Q1 during a first period when the pulsating voltage is equal to or greater than a predetermined threshold, and drives the second switching element Q2 during a second period when the pulsating voltage is less than the predetermined threshold. As shown in FIG. 2, the control circuit 7 compares the divided voltage with a preset voltage V1 to determine whether the period is the first period or the second period. The control circuit 7 determines the period when the divided voltage is equal to or greater than the preset voltage V1 as the first period, and determines the period when the divided voltage is less than the preset voltage V1 as the second period.

When the control circuit 7 determines that the first period is occurring, it outputs a PWM control signal to the first switching element Q1, but does not output a PWM control signal to the second switching element Q2. When the control circuit 7 determines that the second period is occurring, it outputs a PWM control signal to the second switching element Q2 via the drive transformer 4, but does not output a PWM control signal to the first switching element Q1. The drive transformer 4 can convert the PWM control signal input from the control circuit 7 into a voltage level that can drive (turn on/off) the second switching element Q2, and output it.

During the first period, the first switching element Q1 switches and applies the pulsating voltage to the primary winding N1. The capacitor C1 of the snubber circuit 2 smoothes the flyback voltage that occurs when the first switching element Q1 switches from on to off and the spike voltage that occurs in the leakage inductance of the transformer T1, but does not directly smooth the pulsating voltage. This improves the power factor during the first period.

During the second period, the second switching element Q2 switches the charging voltage stored in the capacitor C1 of the snubber circuit 2 and applies it to the auxiliary winding N3. The capacitor C1 has a capacitance that enables PWM control of the second switching element Q2 during the second period. In this way, the pulsating voltage is not switched during the second period, improving the power factor.

Furthermore, because the switching power supply unit 1A does not have a resistor that limits current, power loss due to heat generation can be avoided.

[Second embodiment]
3 shows a switching power supply 1B according to a second embodiment of the present invention. The switching power supply 1B is the same as the switching power supply 1A according to the first embodiment, except that the second switching element Q2 is driven without using a drive transformer 4 or a high-side gate drive circuit (IC).

The switching power supply 1B includes a diode D4, which corresponds to the "third diode" of the present invention. In the switching power supply 1B, one end of the capacitor C1 of the snubber circuit 2 (the connection point between the capacitor C1 and the diode D1) is connected to one end of the auxiliary winding N3 via the diode D3, and the other end of the auxiliary winding N3 is connected to the anode of the diode D4 via the current path (between the drain and source) of the second switching element Q2. The cathode of the diode D4 is connected to the other end of the capacitor C1.

The switching power supply device 1B has the above circuit configuration, and thus can drive the second switching element Q2 without using a drive transformer 4 or a high-side gate drive circuit (IC). This allows the switching power supply device 1B to be smaller in overall size than the switching power supply device 1A according to the first embodiment.

Furthermore, with the switching power supply device 1B, like the switching power supply device 1A according to the first embodiment, the power factor can be improved even with a one-converter configuration using a single transformer T1.

[Modification]
Although the embodiments of the switching power supply device according to the present invention have been described above, the present invention is not limited to the above-described embodiments.

The switching power supply device according to the present invention may include a voltage conversion circuit that converts an AC input voltage into a pulsating voltage, a transformer having a primary winding and a secondary winding, a first switching element that switches the pulsating voltage and applies it to the primary winding, a clamp-type snubber circuit consisting of a first resistor, a first capacitor, and a first diode and connected to both ends of the primary winding, an auxiliary winding provided on the primary side of the transformer, a second switching element that switches the charging voltage charged in the first capacitor and applies it to the auxiliary winding, and a control unit that controls the first switching element and the second switching element.

The control unit of the present invention can be configured as appropriate to drive the first switching element during a first period when the pulsating voltage is equal to or greater than a predetermined threshold, and drive the second switching element during a second period when the pulsating voltage is less than the predetermined threshold.

In the above embodiment, the drive circuit 5 and the control circuit 7 are configured separately, but they may also be configured as a single circuit.

In the above embodiment, a flyback converter was used as an example, but the present invention can also be applied to other types of switching power supply devices.

1A, 1B Switching power supply device 2 Snubber circuit 3 DC converter circuit 4 Drive transformer 5 Drive circuit 6 Resistive voltage divider circuit 7 Control circuit

Claims (4)

a voltage conversion circuit that converts an AC input voltage into a pulsating voltage;
a transformer having a primary winding and a secondary winding;
a first switching element that switches the pulsating voltage and applies it to the primary winding;
a clamp-type snubber circuit including a first resistor, a first capacitor, and a first diode, the snubber circuit being connected to both ends of the primary winding;
A switching power supply device comprising:
an auxiliary winding provided on a primary side of the transformer;
a second switching element that switches the charging voltage charged in the first capacitor and applies the voltage to the auxiliary winding;
a control unit that controls the first switching element and the second switching element;
Equipped with
The control unit is
a first switching element is driven during a first period in which the pulsating voltage is equal to or greater than a predetermined threshold, and a second switching element is driven during a second period in which the pulsating voltage is less than the predetermined threshold. a resistor voltage divider circuit for dividing the pulsating voltage to generate a divided voltage,
2. The switching power supply device according to claim 1, wherein the control unit determines whether the period is the first period or the second period by comparing the divided voltage with a preset voltage. a drive transformer or a high-side gate drive circuit;
A second diode;
Further equipped with
the control unit outputs a drive signal for driving the second switching element to a control terminal of the second switching element via the drive transformer or the high side gate drive circuit;
3. The switching power supply device according to claim 1, wherein one end of the first capacitor is connected to one end of the auxiliary winding via the second diode, and the other end of the auxiliary winding is connected to the other end of the first capacitor via a current path of the second switching element. Further comprising a second diode and a third diode;
3. The switching power supply device according to claim 1, wherein one end of the first capacitor is connected to one end of the auxiliary winding via the second diode, the other end of the auxiliary winding is connected to one end of a current path of the second switching element, and the other end of the current path of the second switching element is connected to the other end of the first capacitor via the third diode.

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