JP4329451B2 - Switching power supply - Google Patents

Description

  The present invention relates to a switching power supply device with high efficiency, small size, and low noise.

  FIG. 12 shows a circuit configuration diagram of a conventional two-converter switching power supply device including a power factor correction circuit and a converter circuit. The switching power supply device shown in FIG. 12 controls the full-wave rectification circuit B1 for full-wave rectification of the AC voltage of the AC power supply Vac1, and the full-wave rectification voltage from the full-wave rectification circuit B1 via the choke coil L1. A power factor improving circuit 50 that turns on / off the switch Q2 by a control signal from the circuit 101 and rectifies and smoothes it by a diode D2 and a capacitor C3 to obtain a DC voltage, and a DC voltage from the power factor improving circuit 50 is different from each other. And a converter circuit 60 for converting into a DC voltage.

  The control circuit 101 in the power factor correction circuit 50 controls the ON period of the switch Q2 so that the peak current flowing through the switch Q2 is proportional to the input voltage, and the switch Q2 is switched on after the choke coil L1 current becomes zero. Turn on. Specifically, the control circuit 101 compares the voltage across the resistor r3 that detects the current of the switch Q2 and the voltage obtained by dividing the input voltage (full-wave rectified voltage) by the resistor r1 and the resistor r2 (not shown). And an RS flip-flop (not shown) is operated by the output signal of the comparator to turn off the switch Q2. Thereby, the peak current of the switch Q2 is proportional to the input voltage. Further, the auxiliary winding 103 is added to the choke coil L1, and the control circuit 101 detects that the flyback voltage generated in the auxiliary winding 103 becomes zero and turns on the switch Q2. That is, the current flowing through the choke coil L1 starts from zero, reaches a peak on the sine wave envelope, and then returns to zero. Thereby, the input current (alternating current) flowing through the AC power supply Vac1 also becomes a sine wave current waveform following the AC voltage of the AC power supply Vac1, and the power factor is greatly improved.

  In addition, since the control circuit 101 performs on / off control of the switch Q2 based on the output voltage of the capacitor C3, the reference voltage, and the full-wave rectified voltage, the output voltage is kept constant.

  On the other hand, in the converter circuit 60, a main switch Q1 made of a MOSFET or the like is connected to the capacitor C3 via the primary winding 5a (number of turns n1) of the transformer T1, and both ends of the main switch Q1 are connected in series. A resistor R2 and a capacitor C2 are connected. The main switch Q1 is turned on / off by PWM control of the control circuit 102.

  Further, the primary winding 5a of the transformer T1 and the secondary winding 5b of the transformer T1 are wound so that opposite phase voltages are generated, and the secondary winding 5b (number of turns n2) of the transformer T1 is wound around the winding. A rectifying / smoothing circuit comprising a diode D1 and a capacitor C1 is connected. This rectifying / smoothing circuit rectifies and smoothes the voltage induced in the secondary winding 5b of the transformer T1 (on / off-controlled pulse voltage) and outputs a DC output to the load RL.

  The control circuit 102 includes an operational amplifier and a photocoupler (not shown). The operational amplifier compares the output voltage of the load RL with a reference voltage, and when the output voltage of the load RL becomes equal to or higher than the reference voltage, the main switch Control is performed so as to narrow the ON width of the pulse applied to Q1. That is, when the output voltage of the load RL becomes equal to or higher than the reference voltage, the output voltage is controlled to a constant voltage by narrowing the ON width of the pulse of the main switch Q1.

  Next, the operation of the converter circuit 60 will be described with reference to the timing chart shown in FIG. In FIG. 13, the voltage Q1v across the main switch Q1, the current Q1i flowing through the main switch Q1, the current n1i flowing through the primary winding 5a (number of turns n1) of the transformer T1, the current D1i flowing through the diode D1, and the main switch A Q1 control signal for ON / OFF control of Q1 is shown.

At time _{t 31,} the main switch Q1 is turned on by Q1 control signal, current Q1i is flowing through the main switch Q1 via the primary winding 5a of the transformer T1 from the capacitors C3. This current will linearly increase with time up to time t _32. Also, we continue to linearly increase with time until time _{t 32} as with current n1i also current Q1i flowing through the primary winding 5a.

In time _{t 32} from the time _{t 31,} the main switch Q1 side is the primary winding 5a - becomes the side, since the reversed phase to the primary winding 5a and the secondary winding 5b, the diode D1 Since the anode side is the-side, the current D1i does not flow through the diode D1.

Then, at time _{t 32,} the main switch Q1, the Q1 control signal, changes from the ON state to the OFF state. At this time, the excitation energy induced in the primary winding 5a of the transformer T1 and the excitation energy of the leakage inductance Lg (inductance not coupled to the secondary winding 5b) are stored in the capacitor C2 via the resistor R2. . For this reason, voltage resonance is caused by the leakage inductance Lg of the primary winding 5a of the transformer T1 and the capacitor C2, and the resonance waveform is ringed at the time of turn-off (change from the on state to the off state) as shown in FIG. A waveform RG (damped vibration waveform) is obtained.

If the value of the capacitor C2 and the value of the resistor R2 are adjusted to appropriate values, this ringing waveform can be made very small. Then, the ringing waveform RG is attenuated with the lapse of time by the resistors R2 becomes a constant value, the constant value continues until just before the time t _33. At time _{t 32} ~ time _{t 33,} since the main switch Q1 is off, current Q1i and current n1i becomes zero.

In time _{t 33} from the time _{t 32,} becomes the primary switch Q1 side is the positive side of the primary winding 5a, since the reversed phase with and the primary winding 5a and the secondary winding 5b, diode D1 Since the anode side becomes a positive side, a current D1i flows through the diode D1.

According to such a converter circuit 60, the circuit (C2, R2) is inserted at both ends of the main switch Q1, and the temporal change in the voltage of the main switch Q1 can be moderated, so that switching noise can be reduced. The surge voltage to the main switch Q1 due to the leakage inductance Lg of the transformer T1 can be suppressed.
JP 2001-157450 A (FIGS. 1 and 3)

  However, in this type of conventional switching power supply device, in order to comply with the harmonic regulation, the two-converter system of the power factor correction circuit 50 and the converter circuit 60 is used. For this reason, two control circuits (for power factor correction circuit and converter circuit) are required, and two switching circuits are also required.

  For this reason, the circuit is complicated and there are two switching portions, so noise and loss increase, which hinders miniaturization, low noise, and high efficiency.

  Further, in the conventional switching power supply device, since the charge charged in the capacitor C2 is consumed by the resistor R2, the loss increases. Since this loss is proportional to the capacitor capacity and the conversion frequency, if the capacitor capacity is increased for the purpose of noise suppression or the conversion frequency is increased for the purpose of miniaturization, the loss increases and the efficiency decreases. There was a drawback.

  A first object of the present invention is to provide a switching power supply device that can cope with harmonic regulation with a single converter and that achieves miniaturization, low noise, and high efficiency. A second object of the present invention is to provide a switching power supply device that enables zero voltage switching by using an auxiliary switch to achieve low noise and high efficiency.

The present invention has the following configuration in order to solve the above problems. The invention according to claim 1 is a switching power supply device that inputs alternating current, improves the power factor and outputs direct current, and is connected to the alternating current power supply to rectify the alternating voltage, and at both ends of the rectifying circuit A first series circuit in which the first reactor, the tertiary winding of the transformer, the primary winding of the transformer, and the main switch are connected in series; the tertiary winding of the transformer and the primary winding A second series circuit in which an auxiliary switch and a snubber capacitor are connected in series, and a third order of the transformer. A smoothing capacitor connected between a connection point between the winding and the primary winding and one end of the rectifier circuit; and a secondary winding of the transformer wound in a phase opposite to the primary winding for rectifying and smoothing the voltage generated in the rectifying and smoothing circuit, before A first parallel circuit is connected to both ends of the main switch, and a first diode and a first capacitor are connected in parallel, and is connected to both ends of the auxiliary switch, and a second diode and a second capacitor are connected in parallel. The second parallel circuit, the second reactor connected between the primary winding of the transformer and the second series circuit, the main switch and the auxiliary switch are alternately turned on / off, and the rectification is performed. A control circuit that controls the output voltage to a predetermined voltage by PWM-controlling the ON width of the main switch based on the output voltage of the smoothing circuit and a reference voltage, and the control circuit is configured to control whether the voltage of the main switch is After the zero voltage is reached, the first diode turns on the main switch during the conduction period, and after the auxiliary switch voltage becomes zero voltage, the second diode is turned on during the conduction period. And wherein the turning on the serial auxiliary switch.

In the invention of claim 2 , the first diode and the first capacitor are a parasitic diode and a parasitic capacitance of the main switch, and the second diode and the second capacitor are a parasitic diode and a parasitic capacitance of the auxiliary switch. It is characterized by being.

The invention according to claim 3 is characterized in that the first reactor and the second reactor are leakage inductances of the transformer.

5. The transformer according to claim 4 , wherein the transformer includes a core having a first leg, a second leg, and a third leg on which a magnetic circuit is formed, and the primary winding and the secondary winding are disposed on the first leg. And the third winding is wound around the second leg, and a gap is provided on the third leg.

The invention according to claim 5 is characterized in that the number of turns of the tertiary winding is equal to or greater than the number of turns of the primary winding, and the tertiary winding is wound in the same phase as the primary winding. And

7. The main switch according to claim 6 , further comprising an inrush current limiting resistor connected between the rectifier circuit and the smoothing capacitor and reducing an inrush current of the smoothing capacitor when the AC power supply is turned on. Is a normally-on type switch, and the control circuit turns off the main switch by the voltage generated in the inrush current limiting resistor when the AC power supply is turned on, and the smoothing capacitor is charged, A switching operation for turning on / off the main switch is started.

According to a seventh aspect of the present invention, the transformer further includes a quaternary winding, and has a normal operation power supply unit that supplies a voltage generated in the quaternary winding of the transformer to the control circuit.

The invention according to claim 8 has a semiconductor switch connected in parallel to the inrush current limiting resistor, and the control circuit turns on the semiconductor switch after starting the switching operation of the main switch. And

  ADVANTAGE OF THE INVENTION According to this invention, the switching power supply device which can respond to a harmonic regulation with one converter, and aims at size reduction, low noise, and high efficiency can be provided. In addition, it is possible to provide a switching power supply device that enables zero voltage switching by using an auxiliary switch to achieve low noise and high efficiency.

  In addition, since a transformer can be configured with one core and DC excitation can be canceled both when the main switch is on and off, a switching power supply device with a small size, high efficiency, and low noise can be provided.

  Embodiments of a switching power supply apparatus according to the present invention will be described below in detail with reference to the drawings.

  The switching power supply according to the first embodiment is a flyback switching power supply that inputs alternating current and outputs direct current, and can cope with harmonic regulation with a single converter, and can be downsized and reduced in noise. It is characterized by high efficiency.

  In addition, zero voltage switching can be performed by using an auxiliary switch to reduce noise and increase efficiency. That is, when the main switch is on, power is stored in a reactor connected to the tertiary winding, and when the main switch is off, power is supplied to the load via the secondary winding, and the smoothing capacitor is charged to charge the primary By storing the power stored in the reactor connected to the windings in the snubber capacitor and turning on the auxiliary switch, this power is returned to the output and zero voltage switching is achieved to achieve high efficiency and low noise. It is characterized by that.

  Further, the present invention is characterized in that the DC excitation of the transformer is reduced by constantly canceling the magnetomotive force of the current flowing through the winding of the transformer, thereby reducing the size of the transformer.

  FIG. 1 is a circuit configuration diagram of the switching power supply device according to the first embodiment. In the switching power supply device shown in FIG. 1, the full-wave rectifier circuit B1 is connected to the AC power supply Vac1, rectifies the AC voltage from the AC power supply Vac1, and outputs the rectified voltage to the positive output terminal P1 and the negative output terminal P2.

  At both ends of the full-wave rectifier circuit B1, a reactor L2 and a tertiary winding 5c (number of turns n3) of the transformer T, a reactor L3, a primary winding 5a (number of turns n1) of the transformer T, a switch Q1 (mainly) A series circuit with a switch) is connected. A diode D1 and a capacitor C1 (resonance capacitor) are connected in parallel to both ends of the switch Q1.

  One end of a switch Q2 (auxiliary switch) made of a MOSFET or the like is connected to a connection point between one end of the primary winding 5a of the transformer T and one end of the switch Q1, and a capacitor C3 (snubber capacitor) is connected to the other end of the switch Q2. And is connected to a connection point between the tertiary winding 5c of the transformer T and the reactor L3.

  A diode D2 and a capacitor C2 are connected in parallel across the switch Q2. A smoothing capacitor C4 is connected between the connection point between the tertiary winding 5c of the transformer T and the reactor L3 and the negative-side output terminal P2 of the full-wave rectifier circuit B1. The switches Q1, Q2 both have a period (dead time) in which they are turned off, and are alternately turned on / off by PWM control of the control circuit 10.

  The diode D1 and the capacitor C1 may be a parasitic diode and a parasitic capacitance of the switch Q1, and the diode D2 and the capacitor C2 may be a parasitic diode and a parasitic capacitance of the switch Q2. Further, the reactor L2 may be a leakage inductance between the windings of the transformer T, and the reactor L3 may be a leakage inductance between the windings of the transformer T.

  A secondary winding 5b (n2) of the transformer T is wound around the core of the transformer T so as to be tightly coupled to the primary winding 5a, and the primary winding 5a is wound around the core of the transformer T. A tertiary winding 5c (n3) of the transformer T is wound loosely. A rectifying / smoothing circuit including a diode D11 and a smoothing capacitor C11 is connected to both ends of the secondary winding 5b. The smoothing capacitor C11 outputs a direct current output to the load RL.

  Further, the number of turns of the tertiary winding 5c of the transformer T is equal to or greater than the number of turns of the primary winding 5a of the transformer T1. The secondary winding 5b of the transformer T is wound in an opposite phase to the primary winding 5a of the transformer T, and the tertiary winding 5c of the transformer T is wound in the same phase as the primary winding 5a of the transformer T. It has been turned.

  The control circuit 10 alternately performs on / off control of the switch Q1 and the switch Q2, and when the output voltage of the load RL becomes equal to or higher than the reference voltage, the ON width of the pulse applied to the switch Q1 is narrowed. Control is performed so as to widen the ON width of the pulse applied to Q2. That is, when the output voltage of the load RL becomes equal to or higher than the reference voltage, the output voltage is controlled to a constant voltage by narrowing the ON width of the pulse of the switch Q1.

  When the control circuit 10 turns on the switch Q1, the voltage of the switch Q1 becomes zero voltage due to resonance between the capacitor C1 connected in parallel with the switch Q1 and the leakage inductance between the windings of the transformer T. The switch Q1 is turned on during a predetermined period.

  Next, the operation of the switching power supply according to the first embodiment configured as described above will be described.

  FIG. 2 shows the input voltage Vi (AC voltage) of the AC power supply Vac1 and the input current Ii (AC current) flowing through the AC power supply Vac1. Details of each signal near the peak (P portion) of the input current Ii shown in FIG. 2 are shown in the timing chart of FIG.

  First, referring to the timing chart of FIG. 2, the operation of the input voltage and the input current, that is, the input current Ii has a waveform having a hump-like peak current near the peak of the sinusoidal current, Explain what can be done.

  First, when the switch Q1 is turned on, the electric charge stored in the smoothing capacitor C4 is discharged through the primary winding 5a of the transformer T, and energy is stored in the exciting inductance of the transformer T.

  At the same time, the AC voltage from the AC power supply Vac1 is rectified by the full-wave rectifier circuit B1, and the full-wave rectified voltage is output from the positive output terminal P1 and the negative output terminal P2. For this reason, the smoothing capacitor C4 is charged through the reactor L2 and the tertiary winding 5c of the transformer T by the full-wave rectified voltage rectified by the full-wave rectifier circuit B1.

  At this time, the voltage applied to the reactor L2 is the sum of the voltage of the tertiary winding 5c of the transformer T and the rectified voltage (| Vac1 |) of the input voltage, and the number of turns n1 and 3 of the primary winding 5a of the transformer T When the number of turns n3 of the next winding 5c is the same, | Vac1 | is obtained when the switch Q1 is turned on.

  For this reason, as shown in FIG. 2, an input current Ii proportional to the input voltage Vi flows. In the vicinity of the peak of the AC voltage, the current of the reactor L2 becomes continuous and increases. The energy stored in the reactor L2 is transmitted to the secondary winding 5b via the tertiary winding 5c of the transformer T when the switch Q1 is turned off and released to the output. For this reason, the peak (P part) of the input current Ii is suppressed.

  That is, the input current Ii has a waveform having a hump-like peak current near the peak of the sinusoidal current, the harmonics of the input current Ii are reduced, and a waveform satisfying the harmonic regulation can be obtained. That is, it is possible to cope with harmonic regulation with one converter.

  FIG. 3 is a diagram showing a class D determination waveform for determining a half-cycle waveform of the AC input current. A device with a special waveform AC input current in which the waveform of the half cycle of the AC input current enters at least 95% of the half cycle inside the thick solid line W1 in FIG. Is done. The limit value is based on the international standard IEC61000-3-2. As shown in FIG. 3 (b), the input current waveform of the embodiment is also inside the thick solid line W1 for at least 95% of the half cycle, and thus is regarded as a special waveform and the limit value is applied. The Moreover, since a high frequency can be suppressed by the low-pass filter by the reactor L2, the reactor L3, and the smoothing capacitor C4, a harmonic can be reduced significantly.

  Further, as apparent from FIG. 4, the input current becomes continuous, the high-frequency ripple is small, and the noise filter can be downsized.

  Next, detailed operations in the P section will be described with reference to the timing charts shown in FIGS. 4, 5, 6, and 8. FIG. 5 is a timing chart showing details of signals in the respective parts when the switch Q1 of the switching power supply according to the first embodiment is turned on. FIG. 6 is a timing chart showing details of signals in the respective portions when the switch Q1 of the switching power supply according to the first embodiment is turned off.

4 to 6, the voltage Q1v across the switch Q1, the current Q1i flowing through the switch Q1, the voltage Q2v across the switch Q2, the current Q2i flowing through the switch Q2, the input current flowing through the tertiary winding 5c. Ii, current I ₂ flowing through the diode D11 and flowing through the secondary winding 5b, a Q1 control signal (Q1g) for on / off control of the switch Q1, and a Q2 control signal (Q2g) for on / off control of the switch Q2 Show.

FIG. 8 is a timing chart of the current flowing in each winding of the transformer of the switching power supply device according to the first embodiment. In FIG. 8, a current (−Ii) which is the input current I ₃ flowing through the tertiary winding 5c and has the same magnitude as the input current Ii but having the opposite sign (−Ii), and the main winding current flowing through the primary winding 5a. I ₁ shows the output current I ₂ flowing through the secondary winding 5b. FIG. 8 shows a waveform when the number of turns of the primary winding 5a, the secondary winding 5b, and the tertiary winding 5c is the same.

At time _{t 1} (corresponding to time _t 11 _{~t 14),} when to turn on the switch Q1, a current flows Q1i in C4 → L3 → 5a → Q1 → C4. At the same time, a voltage is also generated in the tertiary winding 5c of the transformer T loosely coupled to the primary winding 5a, and the input current Ii flows and increases in B1->L2->5c->C4-> B1. . Input current I ₃ decreases. For this reason, while supplying electric power to the smoothing capacitor C4, electric power is stored in the reactor L2.

Then, at time _{t 2} (corresponding to time _t 21 _{~t 23),} when to turn off the switch Q1, because the current of the reactor L2 continues to flow, the voltage of the tertiary winding 5c is reversed, and at the same time the primary The voltage of the winding 5a and the voltage of the secondary winding 5b are also inverted. For this reason,
Since the energy stored in the reactor L2 is transmitted to the secondary winding 5b via the tertiary winding 5c of the transformer T, secondary winding and 5b current I ₂ begins to flow in the diode D11 is rendered conductive, the load Electric power is supplied to the RL and the smoothing capacitor C4 is charged.

Further, the voltage of the primary winding 5a is inverted in the transformer T, the energy stored in the reactor L3, at time _{t 23, L3 → 5a → D2} → C3 → L3 and current D2i flows through the capacitor C1 While charging, the capacitor C2 is discharged. After the discharge of the capacitor C2 is completed (the voltage Q2v of the switch Q2 becomes zero voltage), the capacitor C3 is charged via the diode D2. At time t ₂₃ the diode D2 in conduction and turn on the switch Q2, it is possible to achieve zero-voltage switching of the switch Q2.

After the charging of the capacitor C3 is completed, the electric charge charged in the capacitor C3 is discharged to the output through the switch Q2 and the primary winding 5a. At this time, the current Q2i flows in the switch Q2, with the current _{I 1} flows through the primary winding 5a, a current _{I 2} flows through the secondary winding 5b. Also, first voltage of winding 5a are clamped by the output voltage, current I ₁ is the resonance operation of the reactor L3 and the capacitor C3, flows sinusoidally (shown in FIG. 8, for example time t ₀ ~t ₁ waveform).

Therefore, so that the off period of the switch Q1 to a frequency lower than the frequency of the half period, setting the constant of the reactor L3 and the capacitor C3, a current I ₁ is positive when OFF switch Q2, current I ₁ continues and flows through L3->C4->C1->5a-> L3. For this reason, the capacitor C1 is discharged and the capacitor C2 is charged.

After the discharge of the capacitor C1 is completed (the voltage Q1v of the switch Q1 becomes zero voltage), the diode D1 becomes conductive. Into this period the diode D1 is conducting (for example, time t ₁₃ shown in FIG. _5), when to turn on the switch Q1, it is possible to achieve zero-voltage switching of the switch Q1.

  Since the output voltage is proportional to the energy of the reactor L2, the output voltage can be controlled by controlling the on / off duty of the switch Q1 by the control circuit 10.

A sum of current as can be seen from FIG. 8, a main winding current I ₁ and the output current I ₂ and the input current I ₃ in all of the timing, are substantially zero. That is, it can be seen that the DC magnetomotive force of the entire transformer T decreases, that is, the DC excitation component is substantially zero. Therefore, the gap of the transformer T is reduced, and a transformer having a large inductance can be easily manufactured. Further, since the DC excitation is substantially zero, the operating range of the magnetic flux can be expanded. Thereby, a transformer can be reduced in size. Further, if the number of turns n1 of the primary winding 5a and the number of turns n3 of the tertiary winding 5c are the same, the current can be substantially canceled out except for the excitation due to the gap.

  As described above, according to the switching power supply according to the first embodiment, the tertiary winding 5c is connected in series to the primary winding 5a of the transformer T, and the reactor L2 is connected in series to the tertiary winding 5c. Thus, by always canceling the magnetomotive force of the current flowing through the winding of the transformer T, the DC excitation of the transformer T can be reduced, and the transformer T can be downsized.

  Further, when the switch Q1 is turned on, power is stored in the reactor L2 connected to the tertiary winding 5c, and when the switch Q1 is turned off, power is supplied to the load RL via the secondary winding 5b, and a smoothing capacitor Charging C4, storing the power stored in the reactor L3 connected to the primary winding 5a in the snubber capacitor C3 and turning on the switch Q2, this power is returned to the output and zero voltage switching is performed. It can be achieved, and high efficiency and low noise can be achieved.

  FIG. 7 is a structural diagram of the transformer provided in the switching power supply according to the first embodiment. The transformer shown in FIG. 7 has a Japanese-shaped core 20, and a primary winding 5a and a primary winding 5a are tightly coupled to the central leg 20a of the core 20 on the primary winding 5a. The secondary winding 5b is wound. That is, the primary winding 5a and the secondary winding 5b are wound on the same leg to obtain a small leakage inductance. This leakage inductance is used as a substitute for the reactor L3.

  A tertiary winding 5c is wound around the side leg 20d, and a gap 20c is formed in the side leg 20b. A large leakage inductance is provided in the tertiary winding 5c and the primary winding 5a by the gap 20c, and this leakage inductance is substituted for the reactor L2.

  By using the leakage inductance for the reactors L2 and L3, all the windings can be constituted by one transformer T, so that the transformer T can be reduced in size.

  A gap 20e is also formed in the central leg 20a of the core of the transformer T. The gaps 20c and 20e are provided so that the electric charge stored in the smoothing capacitor C4 is supplied to the inductance (reactor L3) of the primary winding 5a in order to uniformly supply power to the load RL even in the valley of the AC input voltage. This is because the energy stored in the inductances (reactors L2 and L3) of both the primary winding 5a and the tertiary winding 5c is supplied to the load at the peak portion of the AC input voltage that is discharged to the storage load RL. . With this configuration, power can be supplied to the load RL even at the valley portion of the AC input voltage.

  Next, a switching power supply device according to a second embodiment will be described. In the switching power supply according to the first embodiment, a normally-off type MOS FET or the like is used as a switch. This normally-off type switch is a switch that is turned off when the power is turned off.

  On the other hand, normally-on type switches such as SIT (static induction transistor) are switches that are turned on when the power is turned off. This normally-on type switch has a high switching speed, a low on-resistance, and is an ideal element when used in a power conversion device such as a switching power supply, and can be expected to reduce switching loss and achieve high efficiency.

  However, in the normally-on type switching element, when the power is turned on, the switch is in an on state, so that the switch is short-circuited. For this reason, normally-on type switches cannot be activated and cannot be used for anything other than special purposes.

  Therefore, the switching power supply according to the second embodiment has the configuration of the switching power supply according to the first embodiment and uses a normally-on type switch for the switch Q1n. The configuration that eliminates the power-on problem by using the voltage due to the voltage drop of the inrush current limiting resistor inserted for the purpose of reducing the inrush current of the capacitor as the reverse bias voltage of the normally-on type switch. It is characterized by.

  FIG. 9 is a circuit configuration diagram showing a switching power supply according to the second embodiment. The switching power supply device shown in FIG. 9 has the configuration of the switching power supply device according to the first embodiment shown in FIG. 1, and includes a negative output terminal P2 of the full-wave rectifier circuit B1, a switch Q1n, a smoothing capacitor C4, and the like. The inrush current limiting resistor R1 is connected between these connection points.

  A normally-on type switch Q1n such as SIT is connected to the positive output terminal P1 of the full-wave rectifier circuit B1 via the reactor L2, the tertiary winding 5c of the transformer Tb, the reactor L3, and the primary winding 5a of the transformer Tb. The switch Q1n is connected and turned on / off by PWM control of the control circuit 11. The switch Q2 is a normally-off type switch.

  A switch S1 is connected to both ends of the inrush current limiting resistor R1. The switch S1 is a semiconductor switch such as a normally-off type MOSFET or BJT (bipolar junction transistor), and is ON-controlled by a short circuit signal from the control circuit 11.

  A starting power supply unit 12 including a capacitor C6, a resistor R2, and a diode D5 is connected to both ends of the inrush current limiting resistor R1. This starting power supply unit 12 takes out the voltage generated at both ends of the inrush current limiting resistor R1 and outputs the voltage across the capacitor C6 to the control circuit 11 in order to use it as a reverse bias voltage to the gate of the switch Q1n. Further, the charging voltage charged in the smoothing capacitor C4 is supplied to the control circuit 11.

  When the AC power supply Vac1 is turned on, the control circuit 11 is activated by the voltage supplied from the capacitor C6, outputs a reverse bias voltage from the terminal b to the gate of the switch Q1n as a control signal, and turns off the switch Q1n. This control signal is composed of, for example, a pulse signal of −15V and 0V, the switch Q1n is turned off by a voltage of −15V, and the switch Q1n is turned on by a voltage of 0V.

  After the charging of the smoothing capacitor C4 is completed, the control circuit 11 outputs a pulse signal of 0V and −15V as a control signal from the terminal b to the gate of the switch Q1n, and switches the switch Q1n. The control circuit 11 switches the switch Q1n and then outputs a short circuit signal to the gate of the switch S1 after a predetermined time has elapsed to turn on the switch S1.

  One end of the quaternary winding 5d (number of turns n4) provided in the transformer Tb is connected to one end of the switch Q1n, one end of the capacitor C7, and the control circuit 11, and the other end of the quaternary winding 5d is a diode. Connected to the cathode of D7, the anode of the diode D7 is connected to the other end of the capacitor C7 and the terminal c of the control circuit 11. The quaternary winding 5d, the diode D7, and the capacitor C7 constitute a normal operation power supply unit 13. The normal operation power supply unit 13 controls the voltage generated in the quaternary winding 5d via the diode D7 and the capacitor C7. 11 is supplied.

  Next, the operation of the switching power supply according to the second embodiment configured as described above will be described with reference to FIGS.

  In FIG. 11, Vac1 indicates the AC voltage of the AC power supply Vac1, the input current indicates the current flowing through the AC power supply Vac1, the R1 voltage indicates the voltage generated in the inrush current limiting resistor R1, and the C4 voltage is The voltage of the smoothing capacitor C4 indicates the voltage of the capacitor C6, the output voltage indicates the voltage of the capacitor C11, and the control signal is output from the terminal b of the control circuit 11 to the gate of the switch Q1n. Signals are shown.

First, at time _{t 0,} applying the AC power Vac1 (ON), the AC voltage of the AC power source Vac1 is full-wave rectified by the full-wave rectifier circuit B1. At this time, the normally-on type switch Q1n is in the on state, and the switch S1 is in the off state. For this reason, the voltage from the full-wave rectifier circuit B1 is applied to the inrush current limiting resistor R1 via the smoothing capacitor C4 ((1) in FIG. 10).

  The voltage generated in the inrush current limiting resistor R1 is stored in the capacitor C6 via the diode D5 and the resistor R2 ((2) in FIG. 10). Here, the terminal f side of the capacitor C6 has, for example, a zero potential, and the terminal g side of the capacitor C6 has, for example, a negative potential. For this reason, the voltage of the capacitor C6 becomes a negative voltage (reverse bias voltage) as shown in FIG. The negative voltage of the capacitor C6 is supplied to the control circuit 11 via the terminal a.

When the voltage of the capacitor C6 reaches the threshold voltage THL of the switch Q1n (time t _{1 in} FIG. 11), the control circuit 11 outputs a control signal of −15V from the terminal b to the gate of the switch Q1n. ((3) in FIG. 10). For this reason, the switch Q1n is turned off.

  Then, the smoothing capacitor C4 is charged by the voltage from the full-wave rectifier circuit B1 ((4) in FIG. 10), the voltage of the smoothing capacitor C4 rises, and the charging of the smoothing capacitor C4 is completed.

Then, at time _{t 2, the} control circuit 11 starts the switching operation. First, a control signal of 0V is output from the terminal b to the gate of the switch Q1n ((5) in FIG. 10). Therefore, when the switch Q1n is turned on, the current Q1i flows in the order of C4 → L3 → 5a → Q1 → C4 ((6) in FIG. 10).

  Also, a voltage is generated in the quaternary winding 5d that is electromagnetically coupled to the primary winding 5a of the transformer Tb, and the generated voltage is supplied to the control circuit 11 via the diode D7 and the capacitor C7 (FIG. (7) in 10). For this reason, since the control circuit 11 can continue the operation, the switching operation of the switch Q1n can be continuously performed.

Then, at time _{t 3,} and outputs from the terminal b of the control signal of -15V to the gate of the switch Q1n. Therefore, when off switch Q1n is a time t _3, to continue the current reactor L2 flows, tertiary winding 5c voltage is inverted, and at the same time the primary winding 5a of the voltage and the secondary winding 5b of the The voltage is also reversed. Thus, secondary winding and 5b the current I ₂ begins to flow, the diode D11 becomes conductive, power is supplied to the load RL, the smoothing capacitor C4 is charged.

Further, when the output from the control circuit 11 at time t ₃ the short signal to the switch S1, the switch S1 is turned on (in FIG. 10 (8)), both ends of the inrush current limiting resistor R1 is short-circuited. For this reason, the loss of the inrush current limiting resistor R1 can be reduced.

The time _{t 3} is about when the turning on the AC power Vac1 is set as the elapsed time from (time _{t 0),} for example, the time constant of the smoothing capacitor C4 and inrush current limiting resistor R1 (τ = C4 · R1) The time is set to 5 times or more. Thereafter, the switch Q1n repeats the switching operation by on / off. After the switch Q1n starts the switching operation, the switch Q1n and the switch Q2 perform the operations of the switches Q1 and Q2 of the switching power supply device according to the first embodiment shown in FIG. 1, that is, FIG. 4, FIG. The operation is similar to the operation according to the timing chart shown in FIG.

  As described above, according to the switching power supply device according to the second embodiment, the control circuit 11 turns off the switch Q1n by the voltage generated in the inrush current limiting resistor R1 when the AC power supply Vac1 is turned on. Since the switching operation for turning on / off the switch Q1n is started after C4 is charged, there is no problem when the power is turned on. Therefore, a normally-on type semiconductor switch can be used, and a switching power supply device with low loss, that is, a high efficiency can be provided.

  The switching power supply device of the present invention is applicable to a DC-DC conversion type power supply circuit and an AC-DC conversion type power supply circuit.

It is a circuit block diagram which shows the switching power supply device which concerns on 1st Embodiment. It is a timing chart of the signal of the input voltage and input current of the switching power supply concerning a 1st embodiment. It is a figure which shows the class D determination waveform for determining the waveform of the half cycle of alternating current input current. It is a detailed timing chart of the signal in the P section of the switching power supply device according to the first embodiment. It is a timing chart which shows the detail of the signal in each part at the time of turn-on of switch Q1 of the switching power supply device which concerns on 1st Embodiment. It is a timing chart which shows the detail of the signal in each part at the time of turn-off of switch Q1 of the switching power supply device which concerns on 1st Embodiment. 1 is a structural diagram of a transformer provided in a switching power supply device according to a first embodiment. It is a timing chart of the electric current which flows into each coil | winding of the transformer of the switching power supply device which concerns on 1st Embodiment. It is a circuit block diagram which shows the switching power supply device which concerns on 2nd Embodiment. It is a figure for demonstrating operation | movement of the switching power supply which concerns on 2nd Embodiment. It is a timing chart of the signal in each part of the switching power supply concerning a 2nd embodiment. It is a circuit block diagram which shows the conventional switching power supply device. It is a timing chart of the signal in each part of the conventional switching power supply device. It is a timing chart which shows the ringing waveform at the time of turn-off of the main switch in the conventional switching power supply device.

Explanation of symbols

Vdc1 DC power supply Vac1 AC power supply B1 Full-wave rectifier circuit 10, 11, 101, 102 Control circuit Q1, Q2, Q1n Switch RL Load
C1 to C3 Capacitor C4, C11 Smoothing capacitor S1 Switch T, Tb Transformer 5a Primary winding (n1)
5b Secondary winding (n2)
5c Tertiary winding (n3)
5d quaternary winding (n4)
12 Start-up power supply part 13 Normal operation power supply part D1, D2, D5, D7, D11 Diode L1-L3 Reactor

Claims (8)

A switching power supply that inputs alternating current, improves power factor and outputs direct current,
A rectifier circuit that rectifies the AC voltage by connecting to an AC power source;
A first series circuit connected to both ends of the rectifier circuit, wherein a first reactor, a tertiary winding of the transformer, a primary winding of the transformer, and a main switch are connected in series;
Connected between the connection point of the tertiary winding of the transformer and the primary winding and the connection point of the primary winding of the transformer and the main switch, and the auxiliary switch and the snubber capacitor are connected in series. A second series circuit,
A smoothing capacitor connected between a connection point between the tertiary winding and the primary winding of the transformer and one end of the rectifier circuit;
A rectifying / smoothing circuit for rectifying and smoothing a voltage generated in the secondary winding of the transformer wound in a phase opposite to that of the primary winding;
A first parallel circuit connected to both ends of the main switch and having a first diode and a first capacitor connected in parallel;
A second parallel circuit connected to both ends of the auxiliary switch and having a second diode and a second capacitor connected in parallel;
A second reactor connected between the primary winding of the transformer and the second series circuit;
The main switch and the auxiliary switch are alternately turned on / off, and the on-width of the main switch is PWM-controlled based on the output voltage of the rectifying and smoothing circuit and a reference voltage, thereby controlling the output voltage to a predetermined voltage. Control circuit,
The control circuit turns on the main switch while the first diode is in a conduction period after the voltage of the main switch becomes zero voltage, and after the voltage of the auxiliary switch becomes zero voltage, A switching power supply device, wherein the diode turns on the auxiliary switch during a conduction period. The first diode and the first capacitor are a parasitic diode and a parasitic capacitance of the main switch, and the second diode and the second capacitor are a parasitic diode and a parasitic capacitance of the auxiliary switch. The switching power supply device according to claim 1. 3. The switching power supply device according to claim 1, wherein the first reactor and the second reactor are leakage inductances of the transformer. The transformer includes a core having a first leg, a second leg, and a third leg on which a magnetic circuit is formed, the primary winding and the secondary winding are wound around the first leg, and the first leg 4. The switching power supply device according to claim 3, wherein the tertiary winding is wound around two legs, and a gap is provided on the third leg. The number of turns of the tertiary winding is equal to or greater than the number of turns of the primary winding, and the tertiary winding is wound in the same phase as the primary winding. Item 5. The switching power supply device according to any one of Items 4 to 4. An inrush current limiting resistor connected between the rectifier circuit and the smoothing capacitor and reducing the inrush current of the smoothing capacitor when the AC power supply is turned on;
  The main switch is a normally-on type switch,
  The control circuit turns off the main switch by a voltage generated in the inrush current limiting resistor when the AC power source is turned on, and turns on / off the main switch after the smoothing capacitor is charged The switching power supply device according to claim 1, wherein the switching power supply device is started. 7. The switching power supply device according to claim 6, wherein the transformer further includes a quaternary winding, and further includes a normal operation power supply unit that supplies a voltage generated in the quaternary winding of the transformer to the control circuit. Having a semiconductor switch connected in parallel to the inrush current limiting resistor;
  8. The switching power supply device according to claim 6, wherein the control circuit turns on the semiconductor switch after starting a switching operation of the main switch.

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