JPH07203673A - Switching power supply - Google Patents

Abstract

PURPOSE:To reduce loss and noise of a switching power supply for feeding a load with DC power by turning a series circuit of a rectifier circuit connected with a main power supply and a choke ON/OFF through a switching element and then rectifying and smoothing the output from the series circuit. CONSTITUTION:The primary coil n1 of a transformer T1 is inserted in series with a switching element SW1 and the secondary coil n2 of the transformer T1 is connected with a series circuit of an auxiliary switching element SW2 and an auxiliary power supply. The auxiliary switching element SW2 is turned OFF before the main switching element SW1 is turned ON in order to discharge the parasitic capacitor of the main switching element or an equivalent capacitor upon turn OFF of the main switching element SW1 thus attaining the objects.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to reduction of switching loss and switching noise of a switching power supply device.

(2)

2. Description of the Related Art A switching power supply device, such as a step-up chopper, is composed of the respective parts shown in FIG. PS in the figure
1 is a main DC power supply, L1 is a choke, D1 is a diode, C1
Is a capacitor. SW1 is the main switching element,
For example, a FET transistor is used. Cs is the parasitic capacitance of SW1. This switching power supply device stores and releases energy in a choke L1 by switching the main switching element SW1 and outputs its output to a diode D.
1. The capacitor C1 rectifies and smoothes and outputs to the load.

[0003]

As is generally well known, a loss occurs when the main switching element SW1 is turned on and turned off. For example, when the main switching element is turned on, but just before the turn-on, the parasitic capacitance Cs is charged with a voltage substantially equal to the output voltage as shown in FIG. 6 (a). The charge of the parasitic capacitance Cs is shown in FIGS. 6 (b) and 6 (c).
As shown in, the main switching element SW1
Be discharged through. At this time, the energy stored in the parasitic capacitance Cs is consumed by the main switching element SW1 to reduce the conversion efficiency. In addition, the main switching element S
Immediately before the turn-on of W1, as shown in FIGS. 6 (d) and 6 (e), the load current is flowing in the diode D1,
In this state, SW1 turns on and a reverse voltage is applied to D1. Since the reverse voltage is applied while the forward current is flowing, the recovery current flows through D1 at this time, and there is a problem that a large amount of loss and noise are generated.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a switching power supply device which solves the above-mentioned problems of the prior art.

(3)

FIG. 1 is a circuit diagram for explaining the principle of the present invention, and the same reference numerals as those in FIG. 5 indicate the same parts. In the conventional switching power supply device described above with reference to FIG. 5, a transformer T1 is added in series to the main switch SW1, and a capacitor C2 serving as an auxiliary power supply and an auxiliary switching element SW2 are connected to the secondary side n2 of the transformer. This circuit is intended to achieve low loss and low noise by using the parasitic capacitance Cs and the parasitic rectifying element Ds of the main switching element SW1 formed by these additional circuits and FET transistors. D
When a switching element having no s or the like is used, elements corresponding to Ds and Cs are connected. When the recovery current of the parasitic rectifying element Ds becomes a problem, the rectifying element D2 is connected in series to the auxiliary switching element SW2 as shown in FIG. A high-speed rectifying element Ds2 is connected in parallel for use.

[0006]

The operation of the circuits shown in FIGS. 1 and 2 will be described with reference to FIG. First, when the main switching element SW1 is turned on at time t0 in FIG. 3, an input voltage is applied to the series circuit of the choke L1 and the transformer T1. At this time, since the auxiliary switching element SW2 is off, no current flows in the secondary side of the transformer T1. Therefore, the transformer T1 is equivalent to its exciting inductance and operates in the same manner as the boost chopper of FIG. When the main switching element SW1 is turned off at time t1, a flyback voltage is generated in the transformer T1 and the capacitor C2 is charged through the diode Ds2. The voltage of transformer T1 is capacitor C
It is clamped at a voltage of 2 and its current decreases linearly. At this time, the current of the choke L1 is supplied to the load through the diode D1. This operation is similar to that of the conventional boost chopper. The time when the current of the transformer T1 reaches zero is t2. At this time, since SW2 is in the off state, no current flows in the secondary side of the transformer. Therefore, the transformer (4) T1 becomes equivalent to its exciting inductance again, and starts to resonate with the capacitors Cs and Cs2. At this time, the resonance current flows through the routes of Cs, T1, D1 and C1 and the routes of Cs2, T1 and C2.

The time when the auxiliary switching element SW2 turns on is T3. The voltage of the capacitor C2 is applied to the transformer T1 and its current increases linearly. Time t
When the auxiliary switching element SW2 is turned on at 4, the current stops flowing to the secondary side of the transformer, the transformer T1 becomes equivalent to its exciting inductance, and starts to resonate with Cs. At this time, the resonance current is a rule of Cs, T1, D1, and C1.
To discharge Cs. By turning on the main switching element SW1 when the voltage of Cs reaches zero or reaches the minimum point, SW1 becomes zero voltage switching or soft switching, and the switching loss can be greatly reduced. It will be possible. At this time, the current of the diode D1 is close to zero as shown in FIG. 3 (f), and it is possible to reduce the recovery noise generated when the SW1 is turned on at the next time t0. is there. Regarding the diode current, zero current switching can be performed by adjusting the ON period of the auxiliary switching element. Next, examples of the present invention will be described.

[0008]

FIG. 4 is a circuit diagram of an embodiment of the present invention having a constant voltage control function. In the figure, PS1 is an AC power source, D1 to D5 are diodes, L1 is a choke, C1. , C2
Is a capacitor and T1 is a transformer. DV is an output voltage detection circuit, of which R2 and R3 are output voltage dividing resistors, A4 is an error amplifier, VR is an output voltage setting reference voltage source, and the output of the error amplifier A4 is a reference voltage. The error voltage between the output voltage and the output voltage is transmitted. PC is an optical coupler, R
Reference numeral 4 is a current limiting resistor, and A3 is a drive signal generation circuit for the switching element, which receives the error signal transmitted by the optical coupler PC and sends the drive signal (5) for the main switching element and the auxiliary switching element. A1 and A2 are driving circuits which play a role of driving Q1 and Q2. Q1 is an FET transistor which is a main switching element, CS is its parasitic capacitance, and DS is a parasitic rectifying element. Q2 is an FET transistor which is an auxiliary switching element, CS2 is its parasitic capacitance, and DS2 is a parasitic rectifying element.

[0009]

As is apparent from the above, according to the present invention, the zero voltage switching of the switching element, the diode.
It is possible to obtain a switching power supply device with low switching loss and low noise by achieving zero current switching of the battery, and to provide a highly efficient and low noise power supply suitable for fields such as communication circuits and computers. I can.

[Brief description of drawings]

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

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

FIG. 3 is an operation waveform diagram of the present invention.

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

FIG. 5 is a circuit diagram of a conventional circuit.

FIG. 6 is an operation waveform diagram of a conventional circuit.

[Explanation of symbols]

 A1 drive circuit A2 drive circuit (6) A3 drive signal generation circuit A4 error amplifier PS1 main power supply V1 control circuit power supply Vr1 reference voltage source T transformer SW1 switching element SW2 switching element C1 capacitor C2 capacitor CS capacitor CS2 capacitor D1 diode D2 diode -D D3 diode D4 diode D5 diode DS diode DS2 diode L1 choke PC optical coupler Q1 FET transistor Q2 FET transistor R1 resistor R2 resistor R3 resistor

Claims (3)

[Claims] 1. A rectifier circuit is connected to a main power source, and a series circuit of an output of the rectifier circuit, a first inductance, and a primary coil of a first transformer is turned on and off by a first switching element, and a primary circuit of the first transformer is connected. A series circuit of a first rectifying element and a first capacitor is connected in parallel to a series circuit of a coil and a first switching element, and a second capacitor and a second capacitor are connected to a secondary coil of the first transformer. In a switching power supply device that connects a series circuit of switching elements and supplies electric power to a load connected to both ends of the first capacitor, a parasitic rectifying element and a parasitic static element are used as the first switching element and the second switching element. Before the turn-on of the first switching element, using an element having an electric capacity or connecting an electric capacity with a rectifying element instead of the rectifying element. The switching power supply device is characterized in that when the second switching element is turned off, the charge of the parasitic capacitance of the first switching element or the capacitance connected in place of this is discharged. 2. The third rectifying element according to claim 1, wherein the second rectifying element is connected in series to the second switching element, and the second rectifying element and the second switching element are connected in parallel to a series circuit. The switching power supply device is characterized in that. 3. A switching power supply device according to claim 1, wherein a rectifying circuit connected to a main power supply is omitted.