JPH10243652A - Complex converter circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To get a small scale complex converter circuit by providing a complex converter circuit with a switching controller which controls the switching of switching elements contained in two converter circuits so that the output voltage may come to a fixed value. SOLUTION: The on-widths t of the switching element Q1 of a converter circuit 10 on the former stage and the switching element Q2 of a converter circuit 20 at the latter stage are controlled at the same time with a PWM control circuit 60. The roughly constant voltage being the output of the converter circuit 10 at the former stage is supplied to the converter circuit 20 at the latter stage prior to supply to load. The voltage control at this time is performed, using PWM control method, and the difference of starting voltage between the switching elements Q1 and Q2 can be adjusted by the potential division using resistors. This way, the converter circuit where the former stage is a back boost type converter, and the latter stage is a forward type converter is controlled with a switch controller, thus a complex converter small in circuit scale can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a composite converter circuit.

[0002]

2. Description of the Related Art Conventionally, a circuit for converting an AC input voltage into a DC constant voltage has a function of rectifying an AC, connecting a capacitor, converting the current by switching, and obtaining a stable DC voltage. .

FIG. 12 is a diagram showing a first configuration example of a conventional circuit. In the figure, 1 is an AC power supply, and 2 is a rectifier circuit for rectifying the AC power supply voltage. In the rectifier circuit 2 shown in the figure, a bridge rectifier circuit using four diodes is used. The rectifier circuit 2 does not need to be a bridge rectifier circuit, and other rectifier circuits such as a half-wave rectifier circuit and a full-wave rectifier circuit can be used. Reference numeral 10 denotes a buck-boost converter which is a first converter circuit receiving the output of the rectifier circuit 2, and reference numeral 20 denotes a forward converter which is a second converter circuit which receives the output of the first converter circuit 10.

The buck-boost converter 10 includes a field effect transistor (FET) Q1 for directly switching the output of the rectifier circuit 2, a choke coil L1 for storing energy, a rectifier diode D1, a smoothing capacitor C1, and an FET Q1. PWM control unit 1 for providing a switching control signal as a pulse width modulation (PWM) signal
1 is comprised.

The output of the FET Q1 is connected to a choke coil L1.
And the capacitor C1 are connected, and a diode D1 is connected between the choke coil L1 and the other end of the capacitor C1. The smoothing circuit is constituted by the choke coil L1 and the capacitor C1.

On the other hand, the forward converter 20 includes a field effect transistor (FET) Q2 for switching the output of the buck-boost converter 10, a power conversion transformer T, full-wave rectifier diodes D2 and D3, a choke coil L2, and a smoothing device. And a PWM control unit 21 that supplies a switching control signal to the FET Q2 as a pulse width modulation (PWM) signal. A smoothing circuit is configured by the choke coil L2 and the capacitor C2. The operation of the circuit thus configured will be described as follows.

(Operation of Buck-Boost Type Converter 10) The AC voltage of the AC power supply 1 enters the rectifier circuit 2 and is rectified to DC. Q1 turns on / off the output of the rectifier circuit 2 at a predetermined duty. PWM at the gate of Q1
A switching control signal having a cycle T and a pulse width t is applied from the control unit 11, and Q1 repeats a conduction state and a cutoff state. While the Q1 is in a conduction state, a DC voltage is applied from the rectifier circuit 2 to the choke coil L1. Is applied, and energy is stored in the choke coil L1.

Also, while Q1 is in the cutoff state,
The energy stored in the choke coil L1 is released to the capacitor C1 via the diode D1. As a result, a DC voltage _Vc1 as shown below is generated at both ends of the capacitor C1.

V _c1 = E _i × D / (1−D) (1) where E _i is the output DC voltage of the rectifier circuit 2 and D is the duty of Q1 (= t / T).

The PWM control unit 11 controls the switching of Q1 so that the voltage applied to the capacitor C1 becomes a predetermined value. As a result, the output of the buck-boost converter 10 becomes a DC voltage having a constant value as shown in Expression (1).

(Operation of Forward Converter 20) On the other hand, in the forward converter 20, a switching control signal having a period T and a pulse width t is applied from the PWM control section 21 to the gate of Q2, and Q2 is turned on. Repeat the blocking state. While Q2 is conducting, capacitor C1 of buck-boost converter 10
Is output via diodes D2 and D3 on the secondary side of the power conversion transformer T.

As a result, a DC voltage _Vc2 as shown below is generated at both ends of the capacitor C2. _{V c2 = V c1 × D =} (E i × D / (1-D)) × D = E i × D 2 / (1-D) (2) at this time, the DC voltage V _c2 is PWM controller 21 , And the PWM control section 21 controls the switching of Q2 such that the DC voltage _Vc2 becomes a predetermined value.
As a result, the DC voltage has a constant value. This DC voltage V _c2
Becomes the output voltage Vo of the power supply circuit, and power is supplied to the load R.

FIG. 13 shows an operation waveform example of each part at this time.
FIG. V_Q1Is the voltage across Q1, I_Q1Is Q1
Current flowing through_L1Is the electric current flowing through the choke coil L1.
Flow, I _D1Is the current flowing through the diode D1,_C1Is conde
The voltage across the sensor C1, V_Q2Are heels at both ends of Q2
Voltage, I_Q2Is the current flowing through Q2, I_D2Is the diode D
2, the current flowing through I_D3Is the current flowing through the diode D3,
I_L2Is the current flowing through the choke coil L2, V_C2Is conde
This is the voltage (output voltage) applied across the sensor C2.

Here, the reason why the voltage V _Q2 applied to both ends of _{Q 2} has a step will be described. Now, for simplicity,
Description will be made with a simplified circuit as shown in FIG. FETQ
The voltage V _Q2 of second ends, the current I _Q2 flowing through Q2 is in FIG. (A), it is assumed as (b), the the V _Q2 can stepped as indicated by hatching. In order to explain the reason for this step, an exciting current flowing through the winding of the power conversion transformer T will be considered.

The energy generated in the power conversion transformer T is supplied as a current to the transformer secondary when the FET Q2 is on. Since FETQ2 voltage is generated in the opposite direction to the primary side of the transformer is in the off, current flows I _c as shown in FIG. (C) the transformer primary winding and the transformer reset circuit (series circuit of a resistor and a diode) . This current I _c is the excitation current, the characteristics of the transformer T, transformer T Always energy on / off switching FETQ2 is not reset is saturated. As a result, the characteristics of the coil are not satisfied.

Therefore, the transformer T is reset by continuously supplying an exciting current (reset current). That is, the voltage of the transformer T becomes as shown in (d). The state where the transformer T is reset is a stepped portion shown in FIG. In other words, the voltage of the transformer T is as shown in (d), and no current flows in the 0 V portion (step portion). In FIG. 12, the transformer reset circuit is omitted.

FIG. 15 is a diagram showing a second configuration example of the conventional circuit. The same components as those in FIG. 12 are denoted by the same reference numerals. In this configuration example, the converter circuit includes a buck-boost converter 10 and a buck-boost converter 30.

In FIG. 1, reference numeral 1 denotes an AC power supply, and reference numeral 2 denotes a rectifier circuit for rectifying the AC power supply voltage. In the rectifier circuit 2 shown in the figure, a bridge rectifier circuit using four diodes is used. Reference numeral 10 denotes a buck-boost converter which is a first converter circuit receiving the output of the rectifier circuit 2.
Is a buck-boost converter which is a second converter circuit receiving the output of the first converter circuit 10.

The buck-boost converter 10 includes a field effect transistor (FET) Q1 for directly switching the output of the rectifier circuit 2, a choke coil L1 for storing energy, a rectifier diode D1, a smoothing capacitor C1, and an FET Q1. PWM control unit 1 for providing a switching control signal as a pulse width modulation (PWM) signal
1 is comprised. This buck-boost converter 10 is a buck-boost converter 1 shown in FIG.
This is the same circuit as 0.

The output of the FET Q1 is connected to a choke coil L1.
And the capacitor C1 are connected, and a diode D1 is connected between the choke coil L1 and the other end of the capacitor C1. The smoothing circuit is constituted by the choke coil L1 and the capacitor C1.

On the other hand, the buck-boost converter 30
A field effect transistor (FET) Q2 for switching the output of the buck-boost converter 10, a power conversion transformer T, a rectifying diode D4, a smoothing capacitor C2, and a switching control signal for the FET Q2 are pulse width modulated (PWM) signals. PWM control unit 31 given as
It is composed of

In the buck-boost converter 30, the coil of the power conversion transformer T is
, And the diode D4 is connected to the front-stage converter 10
, And the capacitor C2 is connected to the front-stage converter 10
Of the capacitor C1. The operation of the circuit thus configured will be described as follows.

(Operation of Buck-Boost Converter 10) The operation of the buck-boost converter 10 is shown in FIG.
2 is the same as the circuit shown in FIG. Then, a DC voltage V _c1 represented by the equation (1) is generated in the capacitor C1. (Operation of Buck-Boost Converter 30) Since 30 is also a buck-boost converter, its operation is the same as that of the buck-boost converter 10 in the preceding stage.
That is, a DC voltage _Vc2 as shown below is generated at both ends of the capacitor C2. (1) With reference to _{formula, V c2 = V c1 × D} / (1-D) = (E i × D / (1-D)) × D / (1-D) = E i × D 2 / (1-D) ² (3) This DC voltage V _c2 becomes the output voltage Vo of the power supply circuit, and supplies power to the load R.

At this time, the output voltage Vo is changed by the PWM control unit 3
The PWM control unit 31 controls the switching of Q2 so that the output voltage becomes a predetermined value. As a result, the output voltage becomes a constant value.

FIG. 16 shows an example of the operation waveform of each part at this time.
FIG. V_Q1Is the voltage across Q1, I_Q1Is Q1
Current flowing through_L1Is the electric current flowing through the choke coil L1.
Flow, I _D1Is the current flowing through the diode D1,_C1Is conde
The voltage across the sensor C1, V_Q2Are heels at both ends of Q2
Voltage, I_Q2Is the current flowing through Q2, I_D4Is the diode D
4, the current flowing through V_C2Is applied to both ends of the capacitor C2
Voltage (output voltage).

In the case of the buck-boost converter 30,
There is no step in the voltage V _Q2 applied to both ends of _Q2 . The reason is that when Q2 is off, the exciting current is supplied to the secondary side as energy, so that the power conversion transformer T is reset.

[0027]

In the above-described conventional composite converter circuit (AC / DC converter), the switching element and the switching control section are provided in a single set, so that the economy of the composite converter circuit is impaired. There is a risk.

Also, since the difference between the conversion frequencies of the converter circuit of the preceding stage and the converter circuit of the following stage is within several kHz, a beat (a phenomenon in which the output ripple increases) due to the difference between the transmission frequencies occurs, and May have an adverse effect on the side of the device that uses. Therefore,
As a countermeasure against the beat, the difference between the conversion frequencies of the converter circuits at the preceding and subsequent stages is increased to prevent the beat.

The present invention has been made in view of such a problem, and has as its object to provide a composite converter circuit having a small circuit scale.

[0030]

[Means for Solving the Problems]

(1) FIG. 1 is a principle block diagram of the present invention. In FIG, 4 is a DC power supply voltage E _i obtained by rectifying an AC power source, 40 is a first for switching an output of the DC power source 4
Is a second converter circuit for switching the output of the first converter 40. The output voltage Vo is obtained from the output of the second converter circuit 50, and the output is connected to the load 5. Reference numeral 60 denotes the first converter circuit 40 and the second converter circuit 5
This is a switching control unit that performs common switching control of the switching elements of 0.

In the first converter circuit 40, 41
Is a switching element for switching the output of the DC power supply 4, and 42 is a smoothing circuit for smoothing the DC voltage switched by the switching element 41. Switching element 4
1 is turned on / off by the switching control unit 60.

In the second converter circuit 50, 51
Is a switching element for switching the output of the first converter 40, T is a power conversion transformer connected to the switching element 51, 52 is a rectifier circuit connected to the secondary side of the power conversion transformer T, 53 is the rectifier circuit 52 Is a smoothing circuit for smoothing the output. The switching element 51 is
On / off of the switching control section 60 is controlled. The switching control unit 60 monitors the output voltage Vo, and controls the switching elements 41 and 51 to be on / off simultaneously so that the output voltage Vo becomes a constant value. 5 is a load of the power supply circuit.

According to the configuration of the present invention, the switching elements 41 and 51 of the two converter circuits 40 and 50 are controlled by the single switching control unit 60, so that a composite converter circuit having a small circuit scale can be provided.

(2) In this case, a buck-boost converter is used as the first converter circuit 40, and a forward converter is used as the second converter circuit 50, and the switching elements in these converter circuits are controlled by the switching controller 60. It is characterized by:

According to the configuration of the present invention, a converter circuit whose front stage is a buck-boost type converter and whose rear stage is a forward type converter is controlled by a common switching control unit, thereby providing a composite converter circuit having a small circuit scale. can do.

(3) Also, a buck-boost converter is used as the converter circuit 40 in the preceding stage, and a buck-boost converter is used as the converter circuit 50 in the subsequent stage, and the switching elements in these converter circuits are controlled by the switching control unit 60. It is characterized by:

According to the configuration of the present invention, the converter circuit whose front stage is a buck-boost converter and whose rear stage is a buck-boost converter is controlled by the common switching control unit, so that a composite converter circuit having a small circuit scale can be realized. Can be provided.

(4) An FET is used as the switching element, and the FET in the converter circuit 40 in the preceding stage is provided with an inrush current suppressing function. According to the configuration of the present invention, the F
By controlling the gate voltage of the ET, it is possible to increase the on-resistance and to provide an inrush current suppressing function.

(5) The output voltage is detected using a winding wound around a power conversion transformer. According to the configuration of the present invention, by providing another winding in the power conversion transformer T, the output voltage can be detected without using the output of the converter circuit 50 in the subsequent stage.

(6) Further, the output voltage is detected by voltage detection means provided in the primary circuit of the power conversion transformer. According to the configuration of the present invention, the output voltage can be detected without using the output of the subsequent converter circuit 50.

[0041]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 2 is a circuit diagram showing a first embodiment of the present invention. 1 and 12 are denoted by the same reference numerals. The buck-boost converter 10 of FIG. 12 is used as the first converter circuit 40, and the forward converter 20 of FIG. 12 is used as the second converter circuit 50. Therefore, the configurations of the buck-boost converter 10 and the forward converter 20 are the same as those in FIG. 1
Is an AC power supply, and 2 is a bridge rectifier circuit for rectifying the output voltage of the AC power supply 1. 5 is a load of the power supply circuit.

Q1 is a switching element provided in the buck-boost converter 10, and Q2 is a switching element provided in the forward converter 20.
The switching control unit 60 includes a pulse width modulation (PW
M), a buck-boost converter 10 and a forward converter 20 are used.
Control at the same time.

The output of the PWM control circuit 60 is applied to the switching element Q1 of the buck-boost converter 10 via the resistor R1, and the output of the PWM control circuit 60 is connected to the switching element Q2 of the forward converter 20 by the resistor R2. Is applied through. Since the primary side and the secondary side of the power conversion transformer T are insulated, PWM
The control circuit 60 drives the switching elements Q1 and Q2 in a floating state. For this reason, in the PWM control circuit 60, a photocoupler is used and the primary side and the secondary side are coupled so that the primary side and the secondary side can be operated even in a floating state. When the switching elements Q1 and Q2 are driven in a state other than the floating state, it is necessary to connect the primary side and the secondary side of the power conversion transformer T in common.

The PWM control circuit 60 is a general pulse width control circuit, and compares a reference voltage with an actual output voltage.
The present invention controls the on / off time of the switching elements Q1 and Q2. In the present invention, the former converter circuit and the latter converter circuit are controlled by separate PWM control units. 60. The operation of the circuit thus configured will be described as follows.

(Operation of Buck-Boost Converter 10) The AC voltage of the AC power supply 1 enters the rectifier circuit 2 and is rectified to DC. Q1 turns on / off the output of the rectifier circuit 2 at a predetermined duty. PWM at the gate of Q1
A switching control signal having a period T and a pulse width t is applied from the control circuit 60, and Q1 repeats a conductive state and a cutoff state. While the Q1 is in a conductive state, the DC voltage is supplied from the rectifier circuit 2 to the choke coil L1. Is applied, and energy is stored in the choke coil L1.

Also, while Q1 is in the cutoff state,
The energy stored in the choke coil L1 is released to the capacitor C1 via the diode D1. As a result, a DC voltage _Vc1 as shown in equation (1) is generated at both ends of the capacitor C1, and the capacitor C1 becomes a constant voltage source.

The PWM control circuit 60 controls the switching of Q1 so that the voltage applied to the capacitor C1 becomes a predetermined value. As a result, the output of the buck-boost converter 10 becomes a DC voltage having a constant value as shown in Expression (1).

(Operation of Forward Converter 20) On the other hand, in the forward converter 20, a switching control signal having a cycle T and a pulse width t is applied to the gate of Q2 from the PWM control circuit 60, and Q2 is turned on. Repeat the blocking state. While Q2 is conducting, the voltage generated across the capacitor C1 of the buck-boost converter is output via the diodes D2 and D3 on the secondary side of the power conversion transformer T.

As a result, a DC voltage _Vc2 as shown in equation (2) is generated at both ends of the capacitor C2. This DC voltage _Vc2 becomes the output voltage Vo of the power supply circuit. At this time, the output voltage _Vc2 is monitored by the PWM control circuit 60, and the PWM control circuit 60 controls the switching of Q2 so that the output voltage becomes a predetermined value. As a result,
The output voltage has a constant value.

That is, in this embodiment, the PWM control circuit 60 simultaneously controls the ON width t of the switching element Q1 of the preceding converter circuit 10 and the switching element Q2 of the following converter circuit 20. A substantially constant voltage, which is the output of the converter circuit 10 in the preceding stage, is supplied to the output by the switching element Q2 in the subsequent stage. The voltage control at this time uses a PWM control method, and the switching element Q
The difference between the starting voltages of Q1 and Q2 can be adjusted by the voltage division of the resistor.

FIG. 3 is a diagram showing an example of the operation waveform of each part of the first embodiment. V _Q1 is the voltage across Q1;
I _Q1 is a current flowing through Q1, I _L1 is a current flowing through the choke coil L1, I _D1 is a current flowing through the diode D1, V _C1
Is a voltage applied to both ends of the capacitor C1, V _Q2 is a voltage applied to both ends of _Q2 , I _Q2 is a current flowing to Q2, I _D2 is a current flowing to the diode D2, I _D3 is a current flowing to the diode D3, and I _L2 is a choke coil. Current flowing through L2, V _C2
Is a voltage (output voltage) applied to both ends of the capacitor C2.

According to this embodiment, the converter circuit whose front stage is a buck-boost type converter and whose rear stage is a forward type converter is controlled by a common switching control unit, so that a composite converter circuit having a small circuit scale can be realized. Can be provided.

FIG. 4 is a circuit diagram showing a second embodiment of the present invention. 1 and 15 are denoted by the same reference numerals. As the first converter circuit 40,
The buck-boost converter 10 of FIG. 15 is used,
As the second converter circuit 50, the buck-boost converter 30 of FIG. 15 is used. Therefore, the configurations of the buck-boost converter 10 and the buck-boost converter 30 are the same as those in FIG. 1 is an AC power supply, and 2 is a bridge rectifier circuit for rectifying the output voltage of the AC power supply 1.

Q1 is a switching element provided in the buck-boost converter 10, and Q2 is a switching element provided in the buck-boost converter 30. As the switching control unit 60, a PWM control circuit 60 using pulse width modulation (PWM) is used, and controls the buck-boost converter 10 and the buck-boost converter 30 simultaneously. The operation of the circuit thus configured will be described as follows.

(Operation of Buck-Boost Converter 10) The operation of the buck-boost converter 10 is shown in FIG.
5 is the same as the circuit shown in FIG. Then, a DC voltage V _c1 represented by the equation (1) is generated in the capacitor C1.

(Operation of buck-boost converter 30) Since the buck-boost converter 30 is also a buck-boost converter, its operation is the same as that of the buck-boost converter 10 in the preceding stage. That is, at both ends of the capacitor C2, (3)
A DC voltage _Vc2 as shown in the equation is generated. This DC voltage V _c2 becomes the output voltage Vo of the power supply circuit, and supplies power to the load 5.

At this time, the output voltage _Vc2 is monitored by the PWM control circuit 60, and the PWM control circuit 60 controls the switching of Q2 so that the output voltage becomes a predetermined value. As a result, the output voltage becomes a constant value.

FIG. 5 is a diagram showing an example of the operation waveform of each part of the second embodiment. V _Q1 is the voltage across Q1;
I _Q1 is a current flowing through Q1, I _L1 is a current flowing through the choke coil L1, I _D1 is a current flowing through the diode D1, V _C1
Is the voltage across the capacitor C1, V _Q2 is the voltage across Q2, I _Q2 is the current flowing through Q2, I _D4 is the current flowing through the diode D4, V _C2 is the voltage across the capacitor C2 (output voltage). It is.

In the case of the buck-boost converter 30,
There is no step in the voltage V _Q2 applied to both ends of _Q2 . The reason is that when Q2 is off, the exciting current is supplied to the secondary side as energy, so that the power conversion transformer T is reset.

According to this embodiment, the converter circuit in which the front stage is a buck-boost converter and the rear stage is a buck-boost converter is controlled by the common switching control unit, so that the composite converter circuit having a small circuit scale is provided. Can be provided.

FIG. 6 is a circuit diagram showing a third embodiment of the present invention. The same components as those in FIG. 2 are denoted by the same reference numerals. In this embodiment, a field effect transistor (FE) is used as the switching elements Q1 and Q2 in FIG.
T) is shown. The former converter is a buck-boost converter, and the latter converter is a forward converter. The output voltage Vo is detected as a control voltage applied to the PWM control circuit 60.

According to this embodiment, the switching element Q1 in the preceding stage is constituted by an FET. Therefore, the gate voltage applied to the preceding switching element Q1 is changed to PWM.
By adjusting the amplitude of the control voltage from the control circuit 60, the on-resistance can be increased and the inrush current can be suppressed. The amplitude of the control voltage can be realized by, for example, resistance voltage division.

FIG. 7 is a circuit diagram showing a fourth embodiment of the present invention. 6 are denoted by the same reference numerals. In this embodiment, the power conversion transformer T
A first winding N1, a second winding N2, a third winding N3, and a fourth winding N4 are provided, and provided on the second winding N2 and the fourth winding N4. The converter circuit can generate _two output voltages Vo ₁ and Vo ₂ , and supplies power to each load 5. The first winding N1 is a buck-boost converter circuit, and the second to fourth windings are forward converter circuits.

On the fourth winding N4 side, D5 and D6 are rectifying diodes, L3 is a choke coil, and C3 is a capacitor. From this forward type converter, the second
Of the output Vo ₂ is obtained.

On the other hand, on the third winding N3 side, D6 and D7 are rectifier circuits, L4 is a choke coil, C4 is a capacitor, and R3 is a resistor. When the switching element Q2 is turned on / off, a high-frequency AC is generated in the second winding N2 to the fourth winding N4. The diode D
6, a DC voltage is obtained by a converter circuit including D7, a choke coil L4, and a capacitor C4. This DC voltage has a value proportional to the output voltage Vo.

Therefore, the output voltage can be detected without using the output of the subsequent converter circuit as the output of the power supply circuit. The DC output is P
It is provided to the WM control circuit 60. As a result, the PWM control circuit 60 switches the switching element Q of the preceding converter circuit.
1 and the ON width t of the switching element Q2 of the subsequent converter circuit are simultaneously controlled so that the output voltage is constant.

According to this embodiment, another winding is provided in the power conversion transformer T, and the output of this other winding is rectified and smoothed, so that the output voltage can be detected without using the output of the subsequent converter circuit. can do.

FIG. 8 is a circuit diagram showing a fifth embodiment of the present invention. The same components as those in FIG. 7 are denoted by the same reference numerals. In this embodiment, the power conversion transformer T
A first winding N1, a second winding N2, and a third winding N3 are provided, and two output voltages from a converter circuit provided on the second winding N2 and the third winding N3 are provided. Vo ₁ , V
o ₂ can be generated, and each load 5
Supply power to The first winding N1 is a buck-boost converter circuit, and the second and third windings are forward converter circuits. On the third winding N3 side,
D5 and D6 are rectifying diodes, L3 is a choke coil, and C3 is a capacitor.

On the other hand, the capacitor C1 of the primary converter
Are used as voltage detecting means. The monitoring voltage of the PWM control circuit 60 is extracted from the capacitor C1.

In a normal operating state, the output of the preceding converter circuit is proportional to the output of the following converter circuit. Therefore, the output of the preceding converter circuit is used instead of the output voltage of the power supply circuit. No problem. That is, the voltage _Vc1 applied to both ends of the capacitor C1 is proportional to the output voltage Vo of the subsequent converter circuit.
Therefore, the voltage V applied to both ends of the capacitor C1 is
Switching control can be performed using _c1 instead of the output voltage.

According to this embodiment, the output voltage can be detected without using the output of the subsequent converter circuit. FIG. 9 is a circuit diagram showing a sixth embodiment of the present invention. 4 and 6 are denoted by the same reference numerals. 5 illustrates a case where a field effect transistor (FET) is used as the switching elements Q1 and Q2 in FIG. In this embodiment, the first stage is a buck-boost converter, and the second stage is also a buck-boost converter. The output voltage Vo is detected as a control voltage applied to the PWM control circuit 60.

According to this embodiment, the switching element Q1 at the preceding stage is constituted by an FET. Therefore, the gate voltage applied to the preceding switching element Q1 is changed to PWM.
By adjusting the control voltage from the control circuit 60 by resistance division or the like, the on-resistance can be increased and the rush current can be suppressed.

FIG. 10 is a circuit diagram showing a seventh embodiment of the present invention. 7 and 9 are denoted by the same reference numerals. In this embodiment, the power conversion transformer T is provided with a first winding N1, a second winding N2, a third winding N3, and a fourth winding N4. Two output voltages Vo ₁ and Vo ₂ can be generated from a converter circuit provided on the line N2 and the fourth winding N4, and power is supplied to each load 5. The first winding N1 to the fourth winding are all buck-boost converter circuits.

On the fourth winding N4 side, D7 is a rectifying diode, and C5 is a capacitor. On the other hand, on the third winding N3 side, D8 is a rectifying diode, L5 is a choke coil, C6 is a capacitor, and R5 is a resistor.

When the switching element Q2 is turned on / off, a high-frequency alternating current is generated in the second winding N2 to the fourth winding N4. A DC voltage is generated from the high-frequency AC by a buck-boost converter including a diode D8, a choke coil L5, and a capacitor C6. This DC voltage has a value proportional to the output voltage Vo.

Therefore, the output voltage can be detected without using the output of the subsequent converter circuit as the output of the power supply circuit. The DC voltage is P instead of the output voltage.
It is provided to the WM control circuit 60. As a result, the PWM control circuit 60 switches the switching element Q of the preceding converter circuit.
1 and the ON width t of the switching element Q2 of the subsequent converter circuit are simultaneously controlled so that the output voltage is constant.

According to this embodiment, a separate winding is provided in the power conversion transformer T, and a DC voltage is obtained from the separate winding, so that the output voltage can be detected without using the output of the subsequent converter circuit. be able to.

FIG. 11 is a circuit diagram showing an eighth embodiment of the present invention. 8 and 10 are denoted by the same reference numerals. In this embodiment, the power conversion transformer T is provided with a first winding N1, a second winding N2, and a third winding N3, and the second winding N2 and the third winding N3 are provided. Two output voltages Vo ₁ and Vo ₂ can be generated from the converter circuit provided on the line N 3, and power is supplied to each load 5. The first winding N1 is a buck-boost converter circuit, and the second and third windings are also buck-boost converter circuits. Third winding N3
On the side, D7 is an ion and C5 is a capacitor.

On the other hand, the capacitor C1 of the primary converter
Are used as voltage detecting means. The monitoring voltage of the PWM control circuit 60 is extracted from the capacitor C1.

In a normal operating state, the output of the preceding converter circuit and the output of the following converter circuit are in a proportional relationship, so that the output of the preceding converter circuit is used instead of the output voltage of the power supply circuit. No problem. That is, the voltage _Vc1 applied to both ends of the capacitor C1 is proportional to the output voltage Vo of the subsequent converter circuit.
Therefore, the voltage V applied to both ends of the capacitor C1 is
Switching control can be performed using _c1 instead of the output voltage.

According to this embodiment, the output voltage can be detected without using the output of the subsequent converter circuit.

[0082]

As described in detail above, according to the present invention, (1) a DC voltage is input to a circuit formed by connecting two converter circuits in series, and the output of the subsequent converter circuit is output. In the composite converter circuit as the output, by providing a switching control unit that performs switching control on the switching elements included in the two converter circuits so that the output voltage becomes a constant value, the switching elements of the two converter circuits are reduced. Since control is performed by one switching control unit, a composite converter circuit having a small circuit scale can be provided.

(2) In this case, a buck-boost converter is used as a preceding converter circuit, a forward converter is used as a subsequent converter circuit, and switching elements in these converter circuits are controlled by the switching control unit. By controlling the converter circuit in which the front stage is a buck-boost converter and the rear stage is a forward converter by a common switching control unit, a composite converter circuit having a small circuit scale can be provided.

(3) A buck-boost converter is used as a converter circuit in the preceding stage, a buck-boost converter is used as a converter circuit in the subsequent stage, and the switching elements in these converter circuits are controlled by the switching control unit. By controlling the converter circuit in which the first stage is a buck-boost converter and the second stage is a buck-boost converter by a common switching control unit, a composite converter circuit with a small circuit scale can be provided.

(4) Further, by using an FET as the switching element and giving an inrush current suppressing function to the FET in the converter circuit in the preceding stage, the gate voltage of the FET in the converter circuit in the preceding stage is controlled, thereby The on-resistance can be increased and an inrush current suppressing function can be provided.

(5) Further, by detecting the output voltage using the winding wound around the power conversion transformer, another winding is provided in the power conversion transformer, and the output voltage can be detected without using the output of the subsequent converter circuit. Can be detected.

(6) Further, the output voltage is detected by the voltage detection means provided in the primary circuit of the power conversion transformer, so that the output voltage can be detected without using the output of the converter circuit at the subsequent stage. it can.

As described above, according to the present invention, a composite converter circuit having a small circuit scale can be provided, and the practical effect is great.

[Brief description of the drawings]

FIG. 1 is a principle block diagram of the present invention.

FIG. 2 is a circuit diagram showing a first embodiment of the present invention.

FIG. 3 is a diagram showing operation waveforms of each unit according to the first embodiment.

FIG. 4 is a circuit diagram showing a second embodiment of the present invention.

FIG. 5 is a diagram illustrating operation waveforms of respective units according to the second embodiment.

FIG. 6 is a circuit diagram showing a third embodiment of the present invention.

FIG. 7 is a circuit diagram showing a fourth embodiment of the present invention.

FIG. 8 is a circuit diagram showing a fifth embodiment of the present invention.

FIG. 9 is a circuit diagram showing a sixth embodiment of the present invention.

FIG. 10 is a circuit diagram showing a seventh embodiment of the present invention.

FIG. 11 is a circuit diagram showing an eighth embodiment of the present invention.

FIG. 12 is a diagram illustrating a first configuration example of a conventional circuit.

FIG. 13 is a diagram showing operation waveforms of respective units of the first configuration example of the conventional circuit.

14 is an explanatory view of the can step on VQ _2.

FIG. 15 is a diagram illustrating a second configuration example of the conventional circuit.

FIG. 16 is a diagram showing operation waveforms of each unit of the second configuration example of the conventional circuit.

[Explanation of symbols]

 Reference Signs List 4 DC power supply 5 Load 40 First converter circuit 41 Switching element 42 Smoothing circuit 50 Second converter circuit 51 Switching element 60 Switching controller

Claims (6)

[Claims] 1. A composite converter circuit in which a DC voltage is input to a circuit formed by connecting a pre-stage and a post-stage converter circuit in series and an output of the post-stage converter circuit is used as an output. And a switching control unit for commonly performing switching control on the switching elements included in the control unit so that the output voltage becomes a constant value. 2. A buck-boost converter is used as a preceding converter circuit, a forward converter is used as a subsequent converter circuit, and switching elements in these converter circuits are controlled by the switching control unit. 2. The composite converter circuit according to 1. 3. A buck-boost converter is used as a first-stage converter circuit, and a buck-boost converter is used as a second-stage converter circuit, and switching elements in these converter circuits are controlled by the switching control unit. Item 7. The composite converter circuit according to Item 1. 4. The composite converter circuit according to claim 2, wherein an FET is used as said switching element, and an inrush current suppressing function is provided to an FET in a converter circuit at a preceding stage. 5. The composite converter circuit according to claim 1, wherein output voltage detection is performed using a winding wound around a power conversion transformer. 6. The composite converter circuit according to claim 1, wherein the output voltage is detected by voltage detection means provided in a primary circuit of the power conversion transformer.