JP4453900B2 - Switching power supply - Google Patents

Description

The present invention relates to a switching power supply apparatus having a circuit configuration for canceling a noise source voltage generated inside a circuit and reducing a noise component leaking to the outside.

  Conventionally, as a noise voltage canceling circuit of this type of switching power supply device, for example, there is one shown in FIG.

  In FIG. 9, this circuit operates as a forward converter. The primary side winding of the output transformer T11 is divided into two windings P11 and P21 having the same number of turns, and the secondary side winding is also divided into windings S11 and S21 having the same number of turns. The windings P11, P21, S11, and S21 are all wound around the same core and are magnetically coupled to each other.

  In the switching element TR11 using the MOS field effect transistor of the primary side circuit, the intermediate part of the primary side winding of the output transformer T11, that is, the drain terminal D of the switching element TR11 is wound on the winding P11, and the source terminal S is wound. It is connected to the line P21.

  The rectifier diode D11 on the forward side in the secondary circuit has an intermediate portion of the secondary winding of the output transformer T11, that is, a cathode terminal connected to the winding S11 and an anode terminal connected to the winding S21. The cathode terminal of the rectifier diode D21 on the flywheel side in the secondary circuit is connected to the secondary winding S11 and the choke coil L11 of the output transformer T11, and the anode terminal is the secondary winding S21 and the choke coil L21 of the output transformer T11. It is connected to the.

  The choke coils L11 and L21 are wound around the same core, are magnetically coupled to each other, and are wound in a winding direction in which the directions of magnetic flux generated by the currents flowing through the respective windings are the same. .

  The voltage generated in the primary windings P11 and P21 of the output transformer T11 due to the on / off operation of the switching element TR11 by the control IC 101 is in reverse phase, and the common mode noise generated between the ground terminal FG part is in reverse phase. It becomes.

Further, since the voltages generated in the choke coils L11 and L21 on the secondary circuit side are also in opposite phases, the common mode noises generated between the ground terminal FG and the phases are opposite to each other. For this reason, voltage oscillations generated by the on / off operation of the switching element TR11 on the primary side cancel each other and do not occur as common mode noise.

  However, in such a conventional switching power supply circuit configuration, the primary winding of the output transformer is divided into two, the switching element is connected between the windings, and the secondary winding is further connected. Since the structure is divided into two and the diode is connected between the windings, there is the following problem.

  First, as the number of pins necessary for the bobbin for connecting the winding of the output transformer, since the winding start and winding end of the windings P11, P21, S11, S21 are connected, at least 8 pins or more are required. As a result, the outer shape of the output transformer becomes large.

  Second, a pattern on the printed circuit board for wiring a switching element connected between the primary windings P11 and P21, and a forward rectifier diode connected between the secondary windings S11 and S21. Since power loss occurs due to the current flowing in the pattern on the printed circuit board for wiring, there is a problem that the conversion efficiency of the power supply device is lowered.

An object of this invention is to provide the switching power supply device which reduces a common mode noise component, without enlarging a transformer external shape.

  In order to achieve this object, the present invention is configured as follows.

  In the switching power supply device of the present invention, the first switching element is connected between the winding start side of the primary side winding of the output transformer and the plus side of the DC voltage source, and the primary side winding of the output transformer A primary circuit in which a second switching element is connected between the winding end side and the negative side of the DC voltage source, and an anode terminal of the first diode on the winding start side of the secondary winding of the transformer. The anode terminal of the second diode is connected to the winding end side of the secondary winding of the output transformer, the cathode terminal of the first diode and the second diode are connected, and the cathode terminal of the second diode Are connected to the winding start side of the first choke coil, the anode terminal of the second diode is connected to the winding end side of the second choke coil, and the winding end side of the first choke coil is connected to A secondary side circuit that is connected to the lath side output terminal, the winding start side of the second choke coil is connected to the negative side output terminal, and a capacitor is connected between the output terminals, and the first choke coil and the second choke The coils are characterized in that the same number of coils are wound around the same core in a direction in which the directions of magnetic fluxes generated by the currents flowing in the windings are the same, and are magnetically coupled.

  As described above, the switching power supply device of the present invention does not divide the primary side winding and the secondary side winding of the output transformer, and the first switching element and the second side at both ends of the primary side winding of the output transformer. By connecting each switching, a rectifying diode is connected to both ends of the secondary winding of the output transformer, and two choke coils coupled to each other are connected to both ends of the flywheel rectifying diode. The necessary number of pins is reduced to a minimum of 4 pins, the wiring pattern length required on the printed circuit board is shortened, and common mode noise is canceled.

  In another embodiment of the present invention, the winding start side and winding end side of the primary winding of the output transformer are connected in reverse, and the winding start side and winding end of the secondary winding are connected reversely. Anyway.

  As another embodiment of the present invention, the cathode terminal of the first diode and the winding end side of the secondary winding of the output transformer are connected, and the anode terminal of the first diode and the anode terminal of the second diode are connected. A circuit configuration in which the cathode terminal of the second diode and the winding start side of the secondary winding of the output transformer are connected may be employed.

  As another form of the present invention, a circuit configuration may be adopted in which the winding start side and winding end side of the first choke coil are connected in reverse and the winding start side and winding end side of the second choke coil are connected in reverse. .

  As another form of the present invention, the first and second diodes of the secondary circuit are made to correspond to the cathode side of the diode to the drain side of the field effect transistor and the anode side of the diode to the source side of the field effect transistor. Thus, the circuit configuration may be replaced with the first and second field effect transistors.

  Here, a field effect transistor or a bipolar transistor is used as the primary side switching element.

As another embodiment of the present invention, a circuit configuration in which a rectifying / smoothing circuit for rectifying an AC power supply is connected to the DC voltage source side, or a power configuration improving circuit is connected to the DC voltage source side may be used.

  According to the present invention, the primary and secondary windings of the output transformer are not divided, and the first switching element and the second switching are connected to both ends of the primary winding of the output transformer, respectively. The rectifier diode is connected to both ends of the secondary winding of the output transformer, and two choke coils coupled to each other are connected to both ends of the flywheel rectifier diode. The number of pins is reduced to a minimum of 4 pins, and the required wiring pattern length on the printed circuit board is shortened, thereby forming a noise source voltage canceling circuit without enlarging the transformer outline and reducing the common mode noise component. be able to.

As a result, the noise filter circuit connected to the inside of the power supply apparatus or the outside of the power supply apparatus can be reduced in size or omitted, and the apparatus can be reduced in size and cost.

  FIG. 1 is a circuit diagram showing an embodiment of a switching power supply device according to the present invention. First, the configuration will be described. The switching power supply circuit of the present invention includes a primary side circuit 1 and a secondary side circuit 2 and is configured to have an operation function as a forward converter.

  In the primary circuit 1, the output transformer T1 has a primary winding P1 and a secondary winding S1. The winding start sides of the windings P1 and S1 are indicated by “·”. A first switching element TR1 and a second switching element TR2 using field effect transistors are connected to the primary winding P1 of the output transformer T1.

  That is, the source terminal S of the first switching element TR1 is connected to the winding start side of the primary winding P1 of the output transformer T1, and the drain terminal D of the first switching element TR1 is connected to the positive voltage side of the DC voltage source 4. Connected to.

  The drain terminal of the second switching element TR2 is connected to the winding end side of the primary winding P1 of the output transformer T1, and the source terminal S of the second switching element TR2 is connected to the negative voltage side of the DC voltage source 4. To do. DC input terminals 3a and 3b are provided on the DC voltage source side. Further, a control IC 5 that performs on / off control of the first and second switching elements TR1 and TR2 is provided.

  Next, the secondary side circuit 2 will be described. The winding start side of the secondary winding S1 of the output transformer T1 is connected to the anode terminal of the first diode D1, and the winding end side of the secondary winding S1 is connected to the first winding. The anode terminals of two diodes D2 are connected, and the cathode terminals of the first and second diodes D1, D2 are connected in common.

  Subsequently, the common connection point on the cathode side of the first and second diodes D1 and D2 is connected to the winding start side of the first choke coil L1, and the anode terminal of the second diode D2 is connected to the second choke coil L2. Connect to the end of the winding. The winding end side of the first choke coil L1 is connected to the plus output terminal 6a, and the winding start side of the second choke coil L2 is connected to the minus output terminal 6b. A capacitor C1 is connected to both ends of the output terminals 6a and 6b.

  Here, the first choke coil L1 and the second choke coil L2 are wound around the same core in the same direction with the same number of turns and the direction of the magnetic flux generated by the currents flowing in the respective windings. The second choke coils L1 and L2 are in a magnetically coupled state.

  Further, the output terminals 6a and 6b are connected to the error amplification isolation unit 7, and this output is input to the control IC 5 to constitute a feedback circuit. The control IC 5 performs on / off control of the first and second switching elements TR1 and TR2 so as to eliminate the error of the output voltage detected by the error amplification isolation unit 7 with respect to the reference voltage.

  Next, the operation of the embodiment of FIG. 1 will be described. The circuit of the embodiment of FIG. 1 operates as a Ford converter. The first and second switching elements TR1 and TR2 provided in the primary circuit 1 are simultaneously turned on / off in the same phase by a control signal from the control IC 5.

  That is, the second switching element TR2 is also turned on when the first switching element TR1 is on, and the second switching element TR2 is also turned off when the first switching element TR1 is off.

  The secondary side circuit 2 forms a rectifying and smoothing circuit by the first and second diodes D1 and D2, the first and second choke coils L1 and L2, and the capacitor C1, and is fixed from the output terminals 6a and 6b. Supply DC voltage to the load side.

  In the forward converter, the ON / OFF operation of the first and second switching elements TR1 and TR2 causes the first and second switching elements TR1 and TR2 to be connected to the secondary side circuit 2 from the secondary winding S1. A rectangular wave voltage having a time width of the on-time is applied, and an average value of the rectangular wave voltage becomes a DC output voltage.

  Control for keeping the output voltage constant with respect to a change in load current by ON / OFF control of the first and second switching elements TR1 and TR2 is performed by the error amplification isolation unit 7 and the control IC 5.

  The voltage generated between the drain and the source by the on / off operation of the first and second switching elements TR1 and TR2 of the primary side circuit 1 is that the first and second switching elements TR1 and TR2 are on. Sometimes it drops to a voltage determined by the value of the on-resistance of the field effect transistor. Here, the on-resistance of the field effect transistor is sufficiently small and can be handled as almost 0 volts.

  On the other hand, when the first and second switching elements TR1 and TR2 are in the OFF state, the sum of the voltages generated in the DC voltage source 4 and the primary winding P1 of the output transformer T1 is the first and second switching elements TR1 and TR2. The voltage is divided and applied at the ratio of the drain-source capacitance in the off state of each field effect transistor of TR2.

  Since the field effect transistor used in the switching power supply device of the present invention that is normally manufactured uses the same manufacturing lot, the drain and source capacitance values of the first and second switching elements TR1 and TR2 are substantially the same. is there. Therefore, the voltages generated between the drains and the sources when the first and second switching elements TR1 and TR2 are turned off have substantially the same value.

  Therefore, the voltage generated between the drain and source of the first and second switching elements TR1 and TR2 has the same waveform in both the on period and the off period, and the common phase is generated between the ground terminal FG and the opposite phase. Mode noise is in opposite phase to each other.

  In the secondary circuit 2, the rectangular wave voltage applied from the secondary winding S1 of the output transformer T1 by the on / off operation of the first and second switching elements TR1, TR2 is the first and second choke coils. Although applied to L1 and L2, since the number of turns of the first and second choke coils L1 and L2 is the same, the value of the voltage applied to each is the same and has an opposite phase.

  As a result, the voltage oscillation in the circuit generated by the on / off operation of the first and second switching elements TR1 and TR2 is the voltage oscillation generated in the primary side circuit 1 and the voltage oscillation generated in the secondary side circuit 2. Since both are in opposite phases, common mode noise generated between the ground terminal FG part cancels out in opposite phases and does not appear as noise current leaking outside the power supply device.

  FIG. 2 is a circuit diagram showing another embodiment of the present invention. In this embodiment, the first and second switching elements TR1 and TR2 provided in the primary side circuit 1 in FIG. 1 are bipolar. The type transistors Q1 and Q2 are used, and the other configurations are the same.

  FIG. 3 is a circuit diagram showing another embodiment of the present invention, which is characterized in that the winding start and winding end are reversed for the primary side winding P1 and the secondary side winding S1 of the output transformer T1. . That is, in the embodiment of FIG. 1, the connection side with the first switching element TR1 side is started for the primary side winding P1 of the output transformer T1, but this is reversed in FIG. The winding end side of the primary winding P1 is connected to the first switching element TR1 side. Also, the diode D1 side of the secondary winding S1 of the output transformer T1 is reversed from the winding end side. Other configurations are the same as those of the embodiment of FIG.

  FIG. 4 is a circuit diagram showing another embodiment of the present invention, characterized in that the connection of the first and second diodes D1, D2 of the secondary side circuit is reversely connected to FIG. And That is, in the embodiment of FIG. 4, the cathode terminal of the first diode D1 is connected to the winding end side of the secondary winding S1 of the output transformer T1, and the anode terminal is connected to the cathode terminal of the second diode D2. And the cathode terminal of the second diode D2 is connected to the winding start side of the secondary winding S1 of the output transformer T1. Other configurations are the same as those of the embodiment of FIG.

  FIG. 5 is a circuit diagram showing another embodiment of the present invention. The winding start side and the winding end side of the first and second choke coils L1, L2 of the secondary side circuit 2 in the embodiment of FIG. It is characterized by being connected in reverse. Other configurations are the same as those of the embodiment of FIG.

  FIG. 6 is a circuit diagram showing another embodiment of the present invention, in which the first and second diodes D1, D2 of the secondary side circuit 2 in the embodiment of FIG. 1 are replaced with MOS field effect transistors, respectively. It is characterized by that.

  That is, in the embodiment of FIG. 6, the first field effect transistor FET1 and the second field effect transistor FET2 are connected to the secondary winding S1 of the output transformer T1 instead of the diodes D1 and D2. Yes.

  Here, in the field effect transistors FET1 and FET2, the drain terminal D corresponds to the cathode terminal of the diode, and the source terminal S corresponds to the anode terminal of the diode. Therefore, the winding start side of the secondary winding S1 in the output transformer T1 is connected to the source terminal S of the first field effect transistor FET1, and the winding end side of the secondary winding S1 is connected to the second field effect transistor FET2. Connected to the source terminal S, the drain terminals D of the first and second field effect transistors FET1, FET2 are connected in common.

  FIG. 7 is a circuit diagram showing another embodiment of the present invention, which is characterized in that a rectifying and smoothing circuit for connecting an AC power supply is provided instead of the DC voltage source 4 of the embodiment of FIG. In FIG. 7, the primary side circuit 1 and the secondary side circuit 2 are the same as those in the embodiment of FIG. 1, and a rectifying and smoothing circuit 8 is provided on the input side of the primary side circuit 1.

  The rectifying / smoothing circuit 8 is composed of AC input terminals 10a and 10b, a diode bridge 11 and a capacitor C2, and receives the supply of AC power from the AC power source 9 connected to the AC input terminals 10a and 10b and rectifies the diode bridge 11. Thereafter, the voltage is smoothed by the capacitor C <b> 2, and the DC voltage obtained thereby is input to the primary side circuit 1.

  FIG. 8 is a circuit diagram showing another embodiment of the present invention. In this embodiment, a power factor correction circuit 12 is provided instead of the DC voltage source 4 in the circuit of FIG. To do. The power factor correction circuit 12 constitutes a step-up chopper circuit, which is composed of a capacitor C3, a step-up choke coil L3, a switching element TR3, and a rectifying diode D3, and the switching element TR3 is switching-controlled by the control IC 13.

  A full-wave rectified voltage from the diode bridge 11 in the rectifying / smoothing circuit 8 of FIG. 7 provided in the preceding stage is input between the DC input terminals 3a and 3b. The control IC 13 performs on / off control of the switching element TR3 so that the peak current of the switching current is absorbed and the power factor becomes 1 when the average current is in phase with the full-wave rectified voltage. The primary side circuit 1 and the secondary side circuit 2 subsequent to the power factor correction circuit 12 are the same as those in the embodiment of FIG.

3 to 8, the first and second switching elements may be bipolar transistors Q1 and Q2 as shown in FIG. The present invention is not limited to the above-described embodiments, and includes appropriate modifications that do not impair the objects and advantages thereof.

A circuit diagram showing an embodiment of the present invention The circuit diagram which showed other embodiment of this invention which used the primary side switching element as the bipolar transistor. The circuit diagram which showed other embodiment of this invention which made the primary side coil | winding of the output transformer reverse polarity Circuit diagram showing another embodiment of the present invention in which the rectifier diode of the secondary side circuit is reversed and connected. Circuit diagram showing another embodiment of the present invention in which the winding start side and winding end side of the choke coil of the secondary side circuit are reversed and connected The circuit diagram which showed other embodiment of this invention which replaced the rectifier diode of the secondary side circuit with the field effect transistor The circuit diagram which showed other embodiment of this invention which provided the rectification smoothing circuit which connects alternating current power supply to the primary side circuit side The circuit diagram which showed other embodiment of this invention which provided the power factor improvement circuit in the primary side circuit side Circuit diagram of conventional switching power supply

Explanation of symbols

1: primary circuit 2: secondary circuit 3a, 3b: DC input terminal 4: DC voltage source 5: control IC
6a, 6b: Output terminal 7: Error amplification / isolation section 8: Rectification smoothing circuit 9: AC power supply 10a, 10b: AC input terminal 11: Diode bridge 12: Power factor correction circuit 13: Control IC
TR1: first switching element TR2: second switching element Q1: first bipolar transistor Q2: second bipolar transistor T1: output transformer P1: primary winding S1: secondary winding D1: First diode D2: second diode L1: first choke coil L2: second choke coils C1, C2, C3: capacitor FET1: first field effect transistor FET2: second field effect transistor

Claims (9)

A first switching element is connected between the winding start side of the primary winding of the output transformer and the positive side of the DC voltage source, and the winding end side of the primary winding of the output transformer and the DC voltage source A primary circuit in which a second switching element having substantially the same capacity as the first switching element is connected to the negative side of the first switching element ;
The anode terminal of the first diode is connected to the winding start side of the secondary winding of the transformer, and the anode terminal of the second diode is connected to the winding end side of the secondary winding of the output transformer. And the cathode terminal of the second diode are connected to each other, the cathode terminal of the second diode and the winding start side of the first choke coil are connected, and the anode terminal of the second diode and the winding end of the second choke coil are connected. The winding end side of the first choke coil is connected to the plus output terminal, the winding start side of the second choke coil is connected to the minus output terminal, and a capacitor is connected between the output terminals. The secondary circuit,
The switching power supply characterized in that the first choke coil and the second choke coil are magnetically coupled by winding the same number of cores in the same direction in the direction of the magnetic flux generated by the current flowing in each winding. apparatus.
A first switching element is connected between the winding end side of the primary winding of the output transformer and the positive side of the DC voltage source, and the winding start side of the primary winding of the output transformer and the DC voltage source A primary circuit in which a second switching element having substantially the same capacity as that of the first switching element is connected to the negative side of the first switching element ;
The anode terminal of the first diode is connected to the winding end side of the secondary winding of the transformer, and the anode terminal of the second diode is connected to the winding start side of the secondary winding of the output transformer. The cathode terminal of the second diode and the cathode terminal of the second diode are connected in common, the cathode terminal of the second diode and the winding start side of the first choke coil are connected, and the anode terminal of the second diode and the winding of the second choke coil are connected. The end side is connected, the winding end side of the first choke coil is connected to the plus side output terminal, the winding start side of the second choke coil is connected to the minus side output terminal, and a capacitor is connected between the output terminals A secondary circuit;
The switching power supply characterized in that the first choke coil and the second choke coil are magnetically coupled by winding the same number of cores in the same direction in the direction of the magnetic flux generated by the current flowing in each winding. apparatus.
A first switching element is connected between the winding start side of the primary winding of the output transformer and the positive side of the DC voltage source, and the winding end side of the primary winding of the output transformer and the DC voltage source A primary side circuit in which a second switching element having substantially the same capacity as the first switching element is connected to the negative side of the first switching element ;
The cathode terminal of the first diode is connected to the winding end side of the secondary winding of the transformer, and the cathode terminal of the second diode is connected to the winding start side of the secondary winding of the output transformer. The anode terminal of the second diode and the anode terminal of the second diode are connected in common, the cathode terminal of the second diode and the winding start side of the first choke coil are connected, and the anode terminal of the first diode and the winding of the second choke coil are connected. The end side is connected, the winding end side of the first choke coil is connected to the plus side output terminal, the winding start side of the second choke coil is connected to the minus side output terminal, and a capacitor is connected between the output terminals A secondary circuit;
The switching power supply characterized in that the first choke coil and the second choke coil are magnetically coupled by winding the same number of cores in the same direction in the direction of the magnetic flux generated by the current flowing in each winding. apparatus.
A first switching element is connected between the winding start side of the primary winding of the output transformer and the positive side of the DC voltage source, and the winding end side of the primary winding of the output transformer and the DC voltage source A primary side circuit in which a second switching element having substantially the same capacity as the first switching element is connected to the negative side of the first switching element ;
The anode terminal of the first diode is connected to the winding start side of the secondary winding of the transformer, and the anode terminal of the second diode is connected to the winding end side of the secondary winding of the output transformer. The cathode terminal of the second diode and the cathode terminal of the second diode are connected, the cathode terminal of the second diode and the winding end side of the first choke coil are connected, and the anode terminal of the second diode and the start of winding of the second choke coil The winding start side of the first choke coil is connected to the plus output terminal, the winding end side of the second choke coil is connected to the minus output terminal, and a capacitor is connected between the output terminals. The secondary circuit,
The switching power supply characterized in that the first choke coil and the second choke coil are magnetically coupled by winding the same number of cores in the same direction in the direction of the magnetic flux generated by the current flowing in each winding. apparatus.
A first switching element is connected between the winding start side of the primary winding of the output transformer and the positive side of the DC voltage source, and the winding end side of the primary winding of the output transformer and the DC voltage source A primary circuit in which a second switching element having substantially the same capacity as that of the first switching element is connected to the negative side of the first switching element ;
It said first field effect transistor of the source to the winding start side of the transformer secondary winding - scan terminals connected, the second field effect transistor of the source to the winding end side of the secondary winding of the output transformer - scan terminals are connected, the drain terminals of the first field effect transistor and a second field effect transistor are connected together, the winding start side of the drain terminal of the second field effect transistor and the first choke coil is connected, the 2 of the field effect transistor of the source - the winding end side of the scan terminals and the second choke coil is connected, the winding end side of the first choke coil is connected to the positive output terminal, the winding start side of the second choke coil A secondary circuit connected to the negative output terminal and having a capacitor connected between the output terminals;
The switching power supply characterized in that the first choke coil and the second choke coil are magnetically coupled by winding the same number of cores in the same direction in the direction of the magnetic flux generated by the current flowing in each winding. apparatus.
6. The switching power supply device according to claim 1, wherein the first and second switching elements of the primary side circuit are first and second field effect transistors, and the primary of the output transformer. The source terminal of the first field effect transistor is connected to the winding start side of the side winding, the drain terminal is connected to the plus side of the DC voltage source, and the first winding is connected to the winding end side of the primary winding of the output transformer. A switching power supply device comprising: a drain terminal of a second field effect transistor connected; and a source terminal connected to a negative side of a DC voltage source.
6. The switching power supply device according to claim 1, wherein the first and second switching elements of the primary circuit are first and second bipolar transistors, and the primary of the output transformer. The emitter terminal of the first bipolar transistor is connected to the winding start side of the side winding, the collector terminal is connected to the plus side of the DC voltage source, and the winding terminal is connected to the winding end side of the primary winding of the output transformer. A switching power supply device characterized in that the collector terminal of two bipolar transistors is connected and the emitter terminal is connected to the negative side of the DC voltage source.
8. The switching power supply device according to claim 1, wherein a rectifying / smoothing circuit for rectifying an AC power supply is connected to the DC voltage source side.
  8. The switching power supply device according to claim 1, wherein a power factor correction circuit is connected to the DC voltage source side.

Images