JPH0549254A - Switching power supply circuit - Google Patents

Abstract

PURPOSE:To suppress noise or deterioration of conversion efficiency due to non-zero-cross operation at the time of forward rectification of a voltage resonance converter, through simple circuitry, by a constitution wherein a reset circuit resets a delay inductance element every switching cycle. CONSTITUTION:A delay inductance(resonancer) 25 made of Co base amorphous magnetic alloy, for example, is connected between the output side of an inverter transformer 16 and a rectifying diode 22 in order to promote voltage resonance. A series circuit of a diode 26 and a resistor 27, i.e., a reset circuit, is connected between the output side of the delay inductance 25 and the inverter transformer 16. The reset circuit resets the inductance 25 every switching cycle and causes resonance operation positively. In other words, transition loss of the switching element 11 can be reduced using the secondary reverse voltage being induced in the inverter transformer 16 upon turn OFF of the switching element 11 which does not output power.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of non-zero cross operation which occurs in a voltage resonant converter. More specifically, the present invention relates to a switching power supply circuit including a delay inductance reset circuit for suppressing conversion efficiency deterioration and noise generation due to non-zero cross operation when forward rectifying a voltage resonance converter.

[0002]

2. Description of the Related Art In a switching power supply circuit in which the voltage waveform of a switching element is a rectangular wave mode, the switching loss (transition loss) between turn-on and turn-off of the switching element is proportional to the switching frequency. This is an obstacle to the miniaturization of switching power supplies. As a method of reducing these transition losses in principle, a resonant converter in which the voltage and current waveforms of switching elements cross zero has been proposed and put into practical use.
FIG. 5 shows the operation of the basic circuit and the switching element of this voltage resonance type converter.
Is a switching element composed of MOSFETs 12, 13
Is a capacitor, 14 is a body diode of the switching element 11, 15 is a VFM signal input terminal, 16 is an inverter transformer, and 17 and 18 are output terminals.

In the voltage resonance type converter shown in FIG. 5, the voltage waveform when the switching element 11 is off becomes sinusoidal due to the resonance capacitance Cr and the resonance inductance Lr as shown in FIG. 6, and the off time Toff is reduced. The input voltage Vin is fixed at the resonance frequency f ₀ . Therefore, the leakage inductance of the inverter transformer 16 is used as the resonance inductance Lr,
It is rational to use an output circuit that is a capacitor input type smoothing circuit using the flyback rectification method. However, in the flyback rectification method, the ripple current of the capacitor increases and the ripple voltage of the output increases, so as shown in FIG. I am using.

In the forward rectification method of FIG. 7, the voltage resonance of the switching element 11 resonates around the input voltage Vin, so that when the flyback voltage when the switching element 11 is off falls below the input voltage, power is output to the output side. Supply. Therefore, the output impedance seen from the voltage resonance type converter is lowered, and the voltage waveform of the switching element 11 is changed from the sine wave mode to the rectangular wave mode immediately before the switching element 11 is turned on as shown in FIG. 8, and the current of the switching element 11 is positive. It doesn't flow out from the zero cross on. For this reason, transition loss occurs, and the reliability of the switching power supply is significantly reduced due to the reduction of conversion efficiency and the increase of noise. In this case, the switching loss (transition loss) at turn-on is calculated by the following formula. Turn-on loss = 1/2 · C · V ² · f [W] where C = capacitance of the resonance capacitor V = voltage of the switching element 11 immediately before turning on f = switching frequency.

Therefore, in the voltage resonance type converter,
In order to avoid non-zero cross-on in the case of forward rectification, there is known a circuit in which a delay inductance (resonancer) 25 is inserted in series between the output of the inverter transformer 16 and the rectification diode 22 as shown in FIG. (For example, JP-A-3-135367). The voltage Vls between the other output terminal of the inverter / transformer 16 and the delay inductance 25, the current Iq ₁ of the switching element 11, and the voltage Vq ₁ between the switching elements 11 at this time are shown in FIG. By delaying the drop in impedance, voltage resonance operation during forward rectification is continued, and zero cross-on is achieved.

[0006]

However, the resetting of the delay inductance (resonancer) 25 depends on the reverse recovery time of the rectifying diode 22, and the residual magnetic flux density (Br) of the Co-based amorphous magnetic alloy is high. As shown in the BH curve of FIG. 11, a reliable reset is not performed in each cycle. Therefore, the voltage resonance operation is not continued even if the core volume of the delay inductance (resonancer) 25 is sufficiently large with respect to the product of the secondary tap voltage of the inverter transformer 16 and the delay time, and the conversion efficiency is improved. There was a problem that noise could not be reduced. It is an object of the present invention to suppress a decrease in conversion efficiency and generation of noise due to non-zero cross operation when forward rectifying a voltage resonance converter with a simple circuit configuration.

[0007]

SUMMARY OF THE INVENTION The present invention is an inverter
In a switching power supply using a voltage resonance operation in which a delay inductance made of a Co-based amorphous magnetic alloy is inserted in series between an output side of a transformer and a rectifying diode, the delay inductance element for promoting voltage resonance. Is provided for each switching cycle, and a reset circuit that ensures the voltage resonance operation by its action is provided.

[0008]

By using the secondary reverse voltage of the inverter transformer when the switching element that does not supply power to the output is off, the delay inductance (resonancer) can be reliably reset at each switching cycle, and switching The increase in transition loss of the device can be reduced.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a basic circuit of the present invention. In this FIG. 1, the cathode side of a diode 26 is connected to the output side of the delay inductance (resonancer) 25 shown in FIG. A resistor 27 is connected in series to the anode side of the, and the other end of the resistor 27 is connected to the other end of the inverter / transformer 16. In such a circuit configuration, when the switching element 11 is turned off, the reset current Il≈V is applied to the delay inductance (resonancer) 25 by the diode 26 and the resistor 27.
ns / R [A] is flown. At this time, the maximum reset current≈ (Vt−VF) ÷ R [A]. However, Vt = tap voltage of the transformer 16 VF = forward voltage drop of the diode 26 R = resistance value of the resistor 27.

The reset current required by the delay inductance needs to flow more than the coercive force (Hc) of the magnetic core used for the delay inductance in order to obtain a stable delay time. The specific reset current depends on the material and shape of the magnetic core, but is calculated by the following formula. Reset current = Hc × Le ÷ N [A] where Hc = coercive force of magnetic core Le = magnetic path length of magnetic core N = number of windings of coil.

In the circuit of FIG. 1, the reset current of the delay inductance (resonancer) 25 is determined by the secondary voltage Vns of the inverter / transformer 16 and the resistance value R of the series resistor 27, and the reset time is the switching element 1
When the output voltage is high, the loss of the resistor 27 increases because the reset current of the delay inductance (resonancer) 25 is constant. Therefore, as a method of reducing the control power by the reset current, as shown in FIG. 2, a control coil 28 is provided on the secondary side of the delay inductance (resonancer) 25, and a diode 26 and a resistor 27 are connected in series to the control coil 28. The circuit is connected to the secondary side of the inverter / transformer 16.

With such a circuit configuration,
The reset current is the delay inductance (resonance)
25 and the winding number ratio of the control coil 28 and the resistance 27, the resistance loss of the circuit of FIG. 1 can be reduced. At this time, the maximum reset current≈ {(Vt−VF) ÷ R} × (NLs
s ÷ NLsp) [A]. Here, NLss = the number of main windings of the delay inductance 25, and NLsp = the number of windings of the control coil 28 of the delay inductance 25.

A method for reducing the reset current and the reset time is a method in which the control coil 28 is not used for the delay inductance (resonancer) 25. As a simple circuit configuration having the same function, the resistance of the circuit of FIG. A circuit in which a capacitor 29 is connected to 27 in parallel to form a circuit configuration as shown in FIG. 3 and the charge time constant of the capacitor 29 is used for resetting is also possible. At this time, the maximum reset current≈ (Vt−VF) × C ÷ t [A].

On the other hand, as a means for reducing the reset current from the delay inductance side, it is effective to use a Co-based amorphous alloy having a high squareness ratio annealed in the magnetic field in the magnetic core. For example, Co containing a small amount of Fe
Since the -Fe-Si-B amorphous alloy has a magnetostriction of almost zero and a coercive force (Hc) that is extremely small, it can be reset with a small current. Further, in order to suppress heat generation of the magnetic core, it is preferable to select a composition having a small saturation magnetization (Bs) of the amorphous alloy. As a specific method for lowering the saturation magnetization (Bs), a method of reducing the total amount of Co + Fe while keeping the ratio of Co and Fe at zero magnetostriction, Mo, Nb, Ta, W, Cr, V, etc. There is a method of adding a small amount of 5 atomic% or less. In addition, the addition of Sn and Si in a small amount of 1 atomic% or less expands the appropriate range of annealing conditions and brings about favorable results in the magnetic core processing process.

The optimum specifications for the magnetic core for delay inductance are as follows. Squareness ratio: 0.98, Bs: 0.3T, Hc: 0.0
06Oe Composition: Co-Fe-Si-B-Mo-Sn amorphous alloy

[0016]

Since the present invention is constructed as described above,
The delay inductance (resonance) reset circuit can reset the delay inductance (resonancer) element at the time of forward output in the voltage resonance type converter at every switching cycle, and the reliable zero crossing of the switching element allows the high-power of the power supply circuit. It is intended to provide a stable and highly reliable switching power supply circuit capable of improving efficiency and reducing noise generation.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram of a first embodiment of a switching power supply circuit according to the present invention.

FIG. 2 is an electric circuit diagram of a second embodiment of a switching power supply circuit according to the present invention.

FIG. 3 is an electric circuit diagram of a third embodiment of a switching power supply circuit according to the present invention.

FIG. 4 is a BH curve of a delay inductance including a reset circuit.

FIG. 5 is a basic circuit diagram of a voltage resonance converter.

FIG. 6 is a basic operation waveform diagram of the voltage resonance type converter.

FIG. 7 is a circuit diagram of a forward method of a voltage resonance type converter.

FIG. 8 is a waveform diagram in FIG. 7.

FIG. 9 is a circuit diagram of a voltage resonance type converter having a delay inductance.

FIG. 10 is a waveform diagram in FIG.

FIG. 11 is a BH curve of delay inductance without a reset circuit.

[Explanation of symbols]

11 ... Switching element, 12 ... Capacitor, 13 ... Capacitor, 14 ... Body diode of switching element 11, 15 ... VFM signal input terminal, 16 ... Inverter transformer, 17 ... Output terminal, 18 ... Output terminal, 19
... Inductance, 20 ... Input terminal, 21 ... Input terminal,
22 ... Diode, 23 ... Diode, 24 ... Capacitor, 25 ... Delay inductance, 26 ... Diode, 2
7 ... Resistor, 28 ... Control coil, 29 ... Capacitor.

Claims (4)

[Claims] 1. A switching power supply using a voltage resonance operation in which a delay inductance made of a Co-based amorphous magnetic alloy is inserted in series between an output side of an inverter / transformer and a rectifying diode, thereby promoting voltage resonance. A switching power supply circuit comprising: a reset circuit that resets the delay inductance element for each switching cycle to ensure a voltage resonance operation by its action. 2. The switching power supply circuit according to claim 1, wherein the reset circuit has a series circuit of a diode and a resistor inserted between the output side of the delay inductance and the other end of the inverter transformer. 3. The switching power supply circuit according to claim 1, wherein the reset circuit is formed by inserting a series circuit of a control coil on the secondary side of the delay inductance, a diode, and a resistor between both ends on the output side of the inverter / transformer. .. 4. The switching power supply circuit according to claim 2, wherein the reset circuit further comprises a resistor and a capacitor connected in parallel.