JPH065387U - Switching power supply - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a switching power supply device that can achieve wide range of input voltage and stabilization of output voltage at the same time. [Configuration] A first transformer having a first primary winding and a first secondary winding, a second transformer having a second primary winding and a second secondary winding, the first primary winding and the second transformer The third switch S3 connecting the primary windings, the first switch S1, the second switch S2, and the direct current by rectifying and smoothing the switching signals induced in the first secondary winding and the second secondary winding. A rectifying / smoothing circuit that supplies a current, a pulse width control circuit that sends an on / off control signal that stabilizes the output voltage of the rectifying / smoothing circuit to the first to third switches, and first and second when the input voltage is high. And a voltage conversion ratio switching circuit that sends an off signal to the switch and sends an off signal to the third switch when the input voltage is low.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a switching power supply using a commercial AC power supply or the like as an input voltage source, and more particularly to an improvement capable of supplying a stable output voltage even if a wide input voltage range is allowed.

[0002]

[Prior art]

 FIG. 6 is a circuit diagram of a conventionally known flyback type switching power supply. The AC current sent from the commercial AC power supply is rectified and smoothed to obtain the input power supply Vin. A DC voltage is applied from the input power source Vin to the primary winding n1 of the transformer T 1, and it is turned on / off by the switching element S. Then, since a switching signal is induced in the secondary winding n2 of the transformer T, it is rectified by the diode D and smoothed by the capacitor C to supply the DC output voltage Vout to the load side. The primary winding n1 and the secondary winding n2 are wound in the direction in which the mutual inductance becomes negative, and the excitation energy stored in the transformer is sent to the load side when the switching element is off. At this time, if the winding ratio n (= n2 / n1) of the transformer T and the duty ratio D are used between the input voltage Vin and the output voltage Vout, the following relationship is established. Vout = Vin.D / [n. (1-D)] (1)

FIG. 7 is a circuit diagram of a forward type switching power supply device. An auxiliary winding n3 is wound in series with the primary winding n1 on the primary side of the transformer T, and is connected to a common connection point between the primary winding n1 and the switching element S via a diode D3. The anode terminal of the diode D1 is connected to the anode side of the secondary winding n2, the anode terminal of the diode D2 is connected to the cathode side of the secondary winding n2, and the cathode terminals of the diodes D1 and D2 are butted. And is connected to the smooth circuit of choke coil L and capacitor C.

In the forward type, the primary winding n1 and the secondary winding n2 are wound in the direction in which the mutual inductance is positive, and the excitation energy of the transformer is sent to the load side when the switching element is on. At this time, the relationship of the following equation is established between the input voltage Vin and the output voltage Vout. Vout = Vin · D / n (2)

[0005]

[Problems to be solved by the device]

 However, according to the conventional circuit, there is a proportional relationship between the input voltage Vin and the output voltage Vout as represented by the equations (1) and (2). It is necessary to reduce the ratio. In this case, for example, in a pulse width control circuit using a fixed switching frequency, the pulse on-time is shortened, but if the pulse width is shortened, the controllability is greatly reduced. On the contrary, if the input voltage becomes low, the duty ratio must be increased, but there was a limit to increase the duty ratio due to the relationship of exciting energy inflow and discharge. On the other hand, commercial AC power supplies coexist with 100V and 200V systems, and there was a demand for widening the input voltage in order to handle with a single switching power supply.

The present invention solves such a problem, and an object of the present invention is to provide a switching power supply device capable of achieving a wide input voltage and a stable output voltage at the same time.

[0007]

[Means for Solving the Problems]

 The present invention which achieves such an object is provided with a first primary winding to which a DC voltage is applied at one end, a first transformer having a first secondary winding, and a second transformer having one end connected to a primary side common. A second transformer having a primary winding, a second secondary winding, a third switch connecting the other end of the first primary winding and the other end of the second primary winding, and one end of the first primary winding The first switch, which is connected to the common connection point of the wire and the third switch, the other end of which is connected to the primary side common, and one end of which is connected to the DC voltage application end of the first primary winding and the other end Is a second switch connected to the common connection point of the second primary winding and the third switch, and the switching signal induced in the first secondary winding and the second secondary winding is rectified and smoothed to form a direct current. The rectifying and smoothing circuit that supplies the current to the load side and the output voltage of this rectifying and smoothing circuit are compared with the reference voltage, and the error signal An error amplifier for outputting the duty ratio, a pulse width control circuit for controlling the duty ratio in the direction in which the error signal is reduced, and sending an ON / OFF control signal to the first to third switches, and the first primary winding. Input the input voltage to be applied and send the OFF signal to the first and second switches when the input voltage is high and send the OFF signal to the third switch when the input voltage is low. And a switching circuit.

[0008]

[Action]

 If the first switch and the second switch are turned off and the current flowing in the primary winding is switched by the third switch, the conversion ratio of the output voltage to the input voltage becomes relatively small, which is suitable for high input voltage. There is. On the other hand, if the third switch is turned off and the current flowing through the primary winding is switched by the first switch and the second switch, the conversion ratio of the output voltage to the input voltage becomes relatively large, which is suitable for low input voltage. There is. Therefore, if the element in charge of switching is switched by the voltage conversion ratio switching circuit according to the input voltage, the fluctuation of the input voltage does not reach the duty ratio controlled by the pulse width control circuit, so the output voltage is reliably stabilized. You can do it.

[0009]

【Example】

 The present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of the present invention. In the figure, the first transformer T1 has a first primary winding n11 to which a DC voltage Vin is applied and a first secondary winding n12 at one end, and the mutual inductance is positive in the winding direction. It is rolled. The second transformer T2 has a second primary winding n21, one end of which is connected to the primary side common, and a second secondary winding n22. The winding direction is such that the mutual inductance is wound in the positive direction. There is. The third switch S3 connects the other end of the first primary winding n11 and the other end of the second primary winding n21, and a switching element such as an FET is used. The first switch S1 has one end connected to a common connection point between the first primary winding n11 and the third switch S3 and the other end connected to a primary side common, and a switching element such as FET is used. . The second switch S2 has one end connected to the DC voltage Vin application end of the first primary winding n11 and the other end connected to a common connection point between the second primary winding n21 and the third switch S3. A switching element such as a FET is used.

The rectifying / smoothing circuit 10 rectifies and smoothes the switching signal induced in the first secondary winding n12 and the second secondary winding n22 and supplies a direct current to the load side. The error amplifier 20 compares the output voltage Vout of the rectifying / smoothing circuit 10 with the reference voltage Vref and outputs an error signal. For example, a comparator is used. The pulse width control circuit 30 controls the duty ratio in the direction in which the error signal sent from the error amplifier 20 becomes smaller and sends an on / off control signal to the first to third switches S1 to S3. IC for use can be used. The voltage conversion ratio switching circuit 40 inputs the input voltage Vin applied to the first primary winding n11, and when the input voltage Vin is a high input voltage such as a 200V system, it is applied to the first and second switches S1 and S2. An off signal is sent. For example, when the input voltage is low such as 100 V system, the off signal is sent to the third switch S3. The OFF signal sent by the voltage conversion ratio switching circuit 40 has a higher priority than the ON / OFF control signal sent by the pulse width control circuit 30.

In the device configured as described above, when a high input voltage such as a 200 V system, an off signal is sent from the voltage conversion ratio switching circuit 40 to the first and second switches S1 and S2. A switching operation is performed by the third switch S3. Then, since the voltage of half the input voltage Vin is substantially applied to each primary winding n11, n21, the voltage of the switching signal induced in each secondary winding n12, n22 is also halved, and the output The voltage Vout also becomes low.

On the other hand, when the input voltage is low such as 100 V system, an off signal is sent from the voltage conversion ratio switching circuit 40 to the third switch S3, and the switching operation is performed by the first and second switches S1 and S2. To do. Then, since the input voltage Vin is substantially applied to each of the primary windings n11 and n21, the voltage of the switching signal induced in each of the secondary windings n12 and n22 also depends on the input voltage. The output voltage Vout also becomes high. Therefore, even if the input voltage fluctuates, the change of the duty ratio is small, so that the output voltage is stabilized.

FIG. 2 is an explanatory view of a second embodiment of the present invention, showing a flyback type switching power supply at a low input voltage. Since the input voltage is low, the voltage conversion ratio switching circuit 40 sends an OFF signal to the third switch S3, and the first and second switches S1 and S2 perform a switching operation by the ON / OFF control signal sent from the pulse width control circuit 30. To do. The rectifying and smoothing circuit 10 has a diode D4 having an anode terminal connected to the cathode side of the first secondary winding n12 and a diode D5 having an anode terminal connected to the cathode side of the second secondary winding n22. The cathode terminals of both diodes D4 and D5 are butted and connected to the capacitor C.

In the device thus configured, when the first and second switches S1 and S2 are driven in phase according to the on / off control signal sent from the pulse width control circuit 30, the above equation (1) is established. is doing. Vout = Vin.D / [n. (1-D)] (1)

FIG. 3 is an explanatory view of a third embodiment of the present invention, showing a flyback type switching power supply at a high input voltage. Since the input voltage is high, the voltage conversion ratio switching circuit 40 sends an OFF signal to the first and second switches S1 and S2, and the third switch S3 performs a switching operation by an ON / OFF control signal sent from the pulse width control circuit 30. To do. Then, the relationship of the following equation is established between the input voltage Vin and the output voltage Vout. Vout = VinD / [2n (1-D)] (3) This voltage conversion ratio is half the value based on the equation (1).

FIG. 4 is an explanatory view of a fourth embodiment of the present invention, showing a forward type switching power supply at a low and medium input voltage. Since the input voltage is medium to low, an off signal is sent from the voltage conversion ratio switching circuit 40 to the third switch S3, and the first and second switches S1 and S2 are switched by the on / off control signal sent from the pulse width control circuit 30. Take action. The rectifying / smoothing circuit 10 includes a diode D6 having an anode terminal connected to the anode side of the first secondary winding n12 and a diode D7 having an anode terminal connected to the anode side of the second secondary winding n22. The cathode terminals of both the diodes D6 and D7 are butted against each other, and further, the cathode terminals of the diode D8 are butted. The anode terminal of the diode D8 is connected to the common side of the first secondary winding n12 and the second secondary winding n22. The butted cathode terminals are connected to the capacitor C via the choukk coil L.

The in-phase / negative-phase switching circuit 35 inputs the on / off control signal output from the pulse width control circuit 30, and outputs a switching drive signal to the first and second switches S1 and S2. The switching follows the switching signal of the voltage conversion ratio switching circuit 40. The in-phase drive is performed for a medium input voltage, and the relationship of the above-mentioned equation (2) is established between the input voltage Vin and the output voltage Vout. Vout = Vin · D / n (2) In addition, the reverse phase drive is performed for a low input voltage, which has the property that the ripple current flowing in the choke coil L can be minimized, and the duty ratio D is 0.5 or less. Limited. In the reverse phase drive, the following relationship is established between the input voltage Vin and the output voltage Vout. Vout = 2Vin · D / n (4) The in-phase / negative-phase switching circuit 35 may be omitted, and only one of the in-phase drive and the anti-phase drive may be performed.

FIG. 5 is an explanatory view of a fifth embodiment of the present invention, showing a forward type switching power supply at a high input voltage. Since the input voltage is high, the voltage conversion ratio switching circuit 40 sends an OFF signal to the first and second switches S1 and S2, and the third switch S3 performs a switching operation according to an ON / OFF control signal sent from the pulse width control circuit 30. . Then, the relationship of the following equation is established between the input voltage Vin and the output voltage Vout. Vout = Vin.D / 2n (5) This voltage conversion ratio is half the value based on the equation (2), and is 1/4 based on the equation (4).

In the above embodiment, the case where the switches S1 to S3 are provided on the primary side of the transformer has been described, but similar effects can be obtained by providing the switches on the secondary side of the transformer.

[0020]

[Effect of device]

 As described above, according to the present invention, three switches are provided for the two transformers, and the switch that performs the switching operation is changed according to the level of the input voltage. Therefore, the pulse for stabilizing the output voltage is changed. The effect of the input voltage on the width control is reduced, and the wide range of the input voltage can be easily dealt with.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory view of a second embodiment of the present invention, showing a flyback type switching power supply at a low input voltage.

FIG. 3 is an explanatory diagram of a third embodiment of the present invention, showing a flyback type switching power supply at a high input voltage.

FIG. 4 is an explanatory diagram of a fourth embodiment of the present invention, showing a forward type switching power supply at a low input voltage.

FIG. 5 is an explanatory view of a fifth embodiment of the present invention, showing a forward type switching power supply at a high input voltage.

FIG. 6 is a circuit diagram of a conventionally known flyback type switching power supply.

FIG. 7 is a circuit diagram of a forward type switching power supply device.

[Explanation of symbols]

 S switch T transformer 20 error amplifier 30 pulse width control circuit 40 voltage conversion ratio switching circuit

Claims (1)

[Scope of utility model registration request] 1. A first transformer (T1) having a first primary winding to which a DC voltage is applied to one end and a first secondary winding, and a second primary winding having one end connected to a primary side common. And the second
A second transformer (T2) having a secondary winding, a third switch (S3) connecting the other end of the first primary winding and the other end of the second primary winding, and one end of the first primary winding And a third switch, a first switch (S1) having the other end connected to the primary side common, and one end connected to the DC voltage application end of the first primary winding, and the other end Is a second switch (S2) connected to a common connection point between the second primary winding and the third switch, and rectifies and smoothes the switching signals induced in the first secondary winding and the second secondary winding. A rectifying / smoothing circuit (10) that supplies a DC current to the load side, an error amplifier (20) that outputs an error signal by comparing the output voltage of this rectifying / smoothing circuit with a reference voltage, and this error signal becomes small. ON / OFF control of the first to third switches by controlling the duty ratio in the direction The pulse width control circuit (30) for sending the signal and the input voltage applied to the first primary winding are input, and when the input voltage is high, an off signal is sent to the first and second switches to set the low voltage. A switching power supply device comprising: a voltage conversion ratio switching circuit (40) which sends an off signal to the third switch when the input voltage is applied.