JPH0974746A - Switching power supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a switching power supply device for reducing a switching loss and for reducing switching noise. SOLUTION: An input voltage is applied to a primary coil winding 4a of a transformer 4 via a switching element 5 which repeats on-and-off and a capacitor 6 and a diode 5a connected in parallel with the switching element 5 and an energy stored in the transformer 4 is supplied as an output voltage via a rectification smoothing means consisting of a field effect transistor 8 and a capacitor 9 by a secondary coil winding 4c of the transformer 4. Then, an output voltage obtained via the current smoothing means is applied to a secondary coil winding 4c of the transformer 4 via the field effect transistor 8, thus regenerating an energy stored in the transformer 4 to an input voltage via the primary coil winding 4a of the transformer 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply device for supplying a regulated DC voltage to industrial and consumer electronic devices.

[0002]

2. Description of the Related Art Conventionally, this type of switching power supply device has a structure as shown in FIG.

In FIG. 4, reference numeral 1 denotes a DC power supply which is formed by rectifying and smoothing a commercial AC power supply or is composed of a battery or the like. An input voltage is supplied to an input terminal 2-3 and a positive voltage is supplied to the input terminal 2. Connect and connect negative voltage to input terminal 3
Connected to Reference numeral 4 denotes a transformer, one end of the first primary winding 4a is connected to the input terminal 2 and the other end is connected to the input terminal 3 via the switching element 5, and one end of the secondary winding 4c is connected to the output terminal 13. The other end is connected to the rectifying / smoothing circuit 22, one end of the second primary winding 4b is connected to the input terminal 3, and the other end is connected to the synchronous oscillation control circuit 7.

The switching element 5 is turned on / off by an on / off signal of a synchronous oscillation control circuit 7 applied to a control terminal, and a DC input voltage is applied to or cut off from a first primary winding 4a of the transformer 4. Or 20 is a capacitor and 21 is a resistor. This capacitor 20 and resistor 2
The series circuit of 1 is connected to both ends of the switching element 5, and when the switching element 5 is turned off, the spike voltage generated by the leakage inductance of the first primary winding 4a and the secondary winding 4c of the transformer 4 is applied. It is a snubber that absorbs and protects the switching element 5.

The synchronous oscillation control circuit 7 changes the ON period of the switching element 5 in accordance with a signal from the error amplifier 10 via the insulation signal transmission means 15, and changes the ON period of the voltage of the second primary winding 4b of the transformer 4 to the OFF period. The operation is continued until the polarity is reversed, and the oscillation is continued by repeating this operation.

The rectifying / smoothing circuit 22 has an anode connected to one end of the secondary winding 4c of the transformer 4 and a cathode connected to the output terminal 12 and a rectifying diode 23 and an output terminal 12-1.
Consisting of a smoothing capacitor 24 connected in parallel between
The induced voltage in the secondary winding 4c of the transformer 4 is rectified and smoothed and output as an output voltage to the output terminal 12-13 to be supplied to the load 14 as DC power. 10 is an error amplifier and output terminal 1
The error between the output voltage between 2 and 13 and the reference voltage 11 is compared and amplified, and the signal is output to the synchronous oscillation control circuit 7 via the insulating signal transmission means 15.

The operation of the conventional example having the above configuration will be described below. The input voltage supplied from the DC power supply 1 connected between the input terminals 2-3 turns on the switching element 5 by the ON signal of the synchronous oscillation control circuit 7, and turns on the transformer 4 during the ON period.
Is applied to the first primary winding 4a, a primary current flows, a magnetic flux is generated in the transformer 4, and energy is accumulated. At this time, an induced voltage is generated in the secondary winding 4c of the transformer 4, but the voltage is applied in a direction in which the rectifier diode 23 is reversely biased.

Next, when the switching element 5 is turned off by the off signal of the synchronous oscillation control circuit 7, a flyback voltage is generated in the first primary winding 4a of the transformer 4, and at the same time, in the secondary winding 4c of the transformer 4. Since a flyback voltage is generated and a voltage is applied in a direction that forward biases the rectifier diode 23, energy is accumulated in the transformer 4 and is discharged as a secondary current via the secondary winding 4c of the transformer 4, and the smoothing capacitor 24 Output terminal 12-1
Supplied between 3

When all the energy stored in the transformer 4 is released, the flyback voltage of the first primary winding 4a and the secondary winding 4c of the transformer 4 disappears, which is determined by the inductance and distributed capacitance of each winding. Resonance voltage causes ringing and a similar voltage is generated in the second primary winding 4b of the transformer 4, and the polarity of the flyback voltage changes to the opposite polarity. This change in polarity is transmitted to the synchronous oscillation control circuit 7 to turn on the switching element 5 again. By repeating these operations, the output voltage is continuously supplied from between the output terminals 12-13.

Further, the operation of stably controlling the output voltage will be described with reference to FIG.

In FIG. 5, (a) shows the switching element 5
Shows the voltage waveform VDS at both ends, (b) shows the current waveform IDS flowing through the switching element 5, (c) shows the output waveform VG of the synchronous oscillation control circuit 7 to the switching element 5,
(D) shows the secondary current waveform Io flowing through the secondary winding 4c of the transformer 4, and the solid line shows the case where the impedance of the load 14 is low and the output current IOUT is flowing out from the output terminals 12-13 (at heavy load). The dotted line shows the operation waveform of each part when the impedance of the load 14 is high and the output current IOUT is flowing out (light load).

The output current IOUT is expressed by IOUT = 1 / 21 / Ls (Ns / Np) VINTON ² / T, and the output voltage VOUT is VOUT = (Ns / Np) VIN It is represented by TON / TOFF, and the switching frequency f is represented by f = 1 / (TON + TOFF) = 1 / T. Here, Ns is the secondary winding 4 of the transformer 4.
c is the number of windings of the transformer 4, Np is the number of windings of the first primary winding 4a of the transformer 4, and Ls is the secondary winding 4c of the transformer 4.
, Lp is an inductance value of the first primary winding 4a of the transformer 4, VIN is an input voltage value supplied from the DC power supply 1, TON is an ON period of the switching element 5, and TOFF is the off period of the switching element 5, and T is the oscillation period.

The output voltage VOUT is compared and amplified with the reference voltage 11 by the error amplifier 10 and is transmitted to the synchronous oscillation control circuit 7 through the insulating signal transmission means 15 to be transmitted to the switching element 5.
The ON period of the switching element 5 is controlled to be constant so as to control the ON period of the switching element 5, and the ON period of the switching element 5 is changed and kept constant due to the fluctuations of the output current IOUT and the input voltage VIN.

[0014]

In the conventional structure as described above, the voltage waveform and the current waveform applied when the switching element 5 is turned on and off are changed while crossing due to the inclination determined by the response speed of the switching element 5. Therefore, a large switching loss occurs, and if the switching loss is reduced by increasing the response speed of the switching element 5, the voltage waveform,
The current waveform is rapidly completed together with the switching noise and the voltage applied to the switching element 5 and the spike of the current waveform are increased, and the noise filter inserted in the input / output terminal is increased in size in order to prevent noise disturbance of the equipment. . -A switching element 5 having a rating higher than necessary is required. In order to solve this, if the capacitance of the capacitor 20 of the snubber circuit configured by connecting the capacitor 20 and the resistor 21 in series is increased to suppress the sudden change of the voltage waveform, The charging / discharging current becomes large, the loss of the resistor 21 becomes very large, and the charging / discharging current of the capacitor 20 flows when the switching element 5 is turned on, so that the spike current increases, the turn-on loss increases significantly, and the efficiency significantly deteriorates. . There was a problem such as.

The present invention is intended to solve such a problem, and an object of the present invention is to provide a switching power supply device capable of reducing switching loss, reducing switching noise, and downsizing. To do.

[0016]

In order to solve the above problems, the present invention provides a primary winding of a transformer through a switching element in which an input voltage repeatedly turns on and off, and a capacitor connected in parallel with the switching element. The energy stored in the transformer is supplied as an output voltage from the secondary winding of the transformer via a rectifying / smoothing means composed of a field effect transistor and a capacitor, and the output obtained via the rectifying / smoothing means. By applying a voltage to the secondary winding of the transformer via the field effect transistor, the energy stored in the transformer is regenerated to the input voltage via the primary winding of the transformer. .

[0017]

With the above structure, a part of the energy stored in the transformer during the ON period of the switching element is released as a secondary current to the output through the secondary winding during the OFF period. Storing as a secondary current in the opposite direction that flows in the secondary winding again in the transformer, discharging the capacitor connected in parallel with the switching element via the primary winding and regenerating it to the DC power supply, causing a spike when the switching element turns on. The current can be prevented from flowing and the capacitor can prevent a rapid rise of the voltage waveform when the switching element is turned off, thereby reducing the switching loss and the switching noise.

[0018]

Embodiments of the present invention will be described below with reference to FIGS.

FIG. 1 is a circuit diagram of a switching power supply device according to an embodiment of the present invention. In FIG. 1, the same components as those in FIG. 5 are designated by the same reference numerals and the description thereof will be omitted.
Reference numeral 1 is a DC power source, 2-3 is an input terminal, 4 is a transformer, 4a is a first primary winding, 4b is a second primary winding, and 4c is a secondary winding. 5 is a switching element, 7 is a synchronous oscillation control circuit, 9 is a smoothing capacitor, 10 is an error amplifier, 11 is a reference voltage, 12-13 is an output terminal, 14 is a load. Yes, 15 is an insulation signal transmission means.

Reference numeral 5a is a diode, and when the energy stored in the transformer 4 is regenerated to the DC power source 1 through the first primary winding 4a of the transformer 4, the transformer 4 is turned off even when the switching element 5 is turned off. First primary winding 4 of
It is connected in parallel with the switching element 5 so that the regenerative current of a can flow, the anode is the input terminal 3, the cathode is one end of the switching element 5 and the transformer 4.
Is connected to one end of the first primary winding 4a of
Is a capacitor, a flyback voltage is generated in the first primary winding 4a of the transformer 4 when the switching element 5 is turned off by the off signal of the synchronous oscillation control circuit 7, but the flyback voltage applied to the switching element 5 is rapidly completed. In order to suppress the rise and reduce the turn-off loss, the switching element 5 is connected in parallel, and 8 is an N-channel field effect transistor, and the energy of the transformer 4 stored in the ON period of the switching element 5 is stored in the switching element 5. After being discharged from the parasitic diode 8a to the smoothing capacitor 9 through the secondary winding 4c of the transformer 4 in the off period, the reverse recovery time of the parasitic diode 8a of the N-channel field effect transistor 8 from the smoothing capacitor 9 (hereinafter The secondary current in the reverse direction flows through the secondary winding 4c of the transformer 4 only during the reverse current period). And gate terminals are drain terminals connected to one end of the secondary winding 4c of the transformer 4 is an output terminal 1
2 and one end of the smoothing capacitor 9.

The operation of the above configuration will be described below.
The input voltage supplied from the DC power supply 1 connected between the input terminals 2-3 turns on the switching element 5 by the ON signal of the synchronous oscillation control circuit 7, and during the ON period, the first primary winding 4a of the transformer 4 is turned on. Is applied to the transformer 4, a primary current flows, a magnetic flux is generated in the transformer 4, and energy is accumulated. At this time, the induced voltage is generated in the secondary winding 4c of the transformer 4, but the winding of the transformer 4 is configured so that the voltage is applied in the direction of reverse biasing the parasitic diode 8a of the N-channel field effect transistor 8. The N-channel field effect transistor 8 is off because the gate terminal and the source terminal are short-circuited.

Next, when the switching element 5 is turned off by the off signal of the synchronous oscillation control circuit 7, a flyback voltage is generated in the first primary winding 4a of the transformer 4, but the rise of the flyback voltage is compared by the capacitor 6. The flyback voltage is generated in the secondary winding 4c of the transformer 4 at the same time as the turn-off loss is reduced by suppressing the sudden rise of the voltage applied to the switching element 5 and the N is generated.
Parasitic diode 8 of channel field effect transistor 8
Since a voltage is applied in the direction of forward biasing a, energy is accumulated in the transformer 4 and is discharged as a secondary current through the secondary winding 4c of the transformer 4, and the smoothing capacitor 9
Is supplied as an output voltage between the output terminals 12 and 13.

When all the energy accumulated in the transformer 4 is released and the secondary current emitted from the secondary winding 4c of the transformer 4 becomes zero, the smoothing is performed only for the reverse current period of the parasitic diode 8a of the N-channel field effect transistor 8. A secondary current flows in the opposite direction from the capacitor 9 toward the secondary winding 4c of the transformer 4, and a magnetic flux in the opposite direction is generated in the transformer 4 to accumulate energy. In this state, the regeneration of the induced voltage generated in each winding of the transformer 4 does not change and the voltage of the second primary winding 4b of the transformer 4 does not change, so that the synchronous oscillation control circuit 7 maintains the OFF period of the switching element 5. Let

After the reverse current period, the secondary current in the reverse direction is rapidly reduced, and the polarity of the induced voltage generated in each winding of the transformer 4 is inverted, so that the induced voltage generated in the secondary winding 4c of the transformer 4 is reversed. Reversely biases the parasitic diode 8a of the N-channel field effect transistor 8 and
The induced voltage generated in the primary winding 4a is generated in such a direction that the connection end with the capacitor 6 becomes a negative voltage and the connection end with the input terminal 2 becomes a positive voltage, and the electric charge already accumulated in the capacitor 6 is discharged. Direction, that is, the primary current flows in the direction in which the DC power supply 1 is charged, and the energy accumulated in the reverse current period is regenerated to the DC power supply 1.

By this operation, when the voltage across the capacitor 6 drops to zero voltage, the primary current continues to flow through the diode 5a until the energy stored in the reverse flow period is exhausted. This period is called the regeneration period. At this time, the regenerative of the induced voltage generated in the second primary winding 4b of the transformer 4 is also reversed, so that the synchronous oscillation control circuit 7 turns on the switching element 5, but the primary current does not change in operation regardless of which one flows. Absent. When the energy stored in the transformer 4 becomes zero, a primary current in the opposite direction to the above flows from the DC power supply 1 through the switching element 5 which is already turned on, and a magnetic flux is generated in the transformer 4 to store energy. Since the voltage across the capacitor 6 is already zero during the regeneration period, zero switching occurs when the switching element 5 is on, and no turn-on loss occurs.

By repeating the above operation, the output voltage is supplied from the output terminal 12-13 to the load 14.

Next, the operation of stably controlling the output voltage will be described with reference to FIG. In FIG. 2, (a) shows the voltage waveform VDS across the switching element 5, (b)
Shows the current waveform IDS flowing through the switching element 5 and the diode 5a, (c) shows the output waveform VG of the synchronous oscillation control circuit 7 to the switching element 5, and (d) flows through the secondary winding 4c of the transformer 4. Shows the secondary current waveform Io,
(E) shows the current waveform IC flowing through the capacitor 6. Furthermore, the solid line is the waveform of each part when the impedance of the load 14 is low and a large amount of output current IOUT is flowing out from the output terminal 12-13 (during heavy load), and the dotted line is the load 14
Shows the waveform of each part when the impedance is high and the output current IOUT is low and flows out (light load).

The output current IOUT is calculated as follows: IOUT = 1 / 2.1 / Ls. (Ns / Np) .VIN {TON. (TON
-T = ON)} / T, and the output voltage VOUT is VOUT = (Ns / Np) .VIN (TON-T'ON) / (TOFF
-T'OFF) and the switching frequency f is expressed as f = 1 / (TON + TOFF) = 1 / T. Here, Ns is the secondary winding 4 of the transformer 4.
c is the number of windings of the transformer 4, Np is the number of windings of the first primary winding 4a of the transformer 4, and Ls is the secondary winding 4c of the transformer 4.
, Lp is an inductance value of the first primary winding 4a of the transformer 4, VIN is an input voltage value supplied from the DC power supply 1, TON is an ON period of the switching element 5, and TOFF is the off period of the switching element 5, T'ON is the regeneration period, and T '
OFF is the backflow period, and T is the oscillation period.

The output voltage VOUT is compared and amplified with the reference voltage 11 by the error amplifier 10 and is transmitted to the synchronous oscillation control circuit 7 through the insulating signal transmission means 15 to be transmitted to the switching element 5.
The ON period of the switching element 5 is controlled to be constant so as to control the ON period of the switching element 5, and the ON period of the switching element 5 is changed and kept constant due to the fluctuations of the output current IOUT and the input voltage VIN.

The operation in which a reverse secondary current flows through the secondary winding 4c of the transformer 4 during the reverse recovery time of the parasitic diode 8a of the field effect transistor 8 will be described with reference to FIG.

FIG. 3 shows experimental data obtained by the present inventor in the circuit configuration of FIG. 1 of the embodiment of the present invention, and is the order in which the secondary winding 4c of the transformer 4 flowing through the field effect transistor 8 flows to the smoothing capacitor 9. Directional current Io and output current IO
The characteristics of the reverse current −Io flowing from the UT and the smoothing capacitor 9 to the secondary winding 4c of the transformer 4 are shown.

However, VIN = 130 [V], VOUT = 15
[V], Lp = 300 [μH], Ls = 15 [μH], and the field effect transistor 8 is 2SK10 in FIG.
18 (Fuji Electric Co., Ltd.), FIG. 3 (b) shows IRFP450
It is a characteristic view of (INTERNATIONAL RECTIFIER).

As is apparent from FIG. 3, when the output current IOUT flows, that is, when the forward current Io flows, the reverse current −Io always flows. This is due to the reverse recovery time of the parasitic diode 8c of the field effect transistor 8.

Further, since the value of the reverse current −Io is substantially constant above a certain output current IOUT, that is, the forward current Io, the output voltage VOUT is switched by the fluctuations of the output current IOUT and the input voltage VIN as described above. The ON period of the device 5 changes and is kept constant.

Further, since the value of the reverse current −Io decreases at a certain output current IOUT, that is, at a certain forward current Io or less, the zero crossing switching of the switching element 5 may not occur as described above, but the output voltage VOUT becomes ,
The error amplifier 10 compares and amplifies with the reference voltage 11 and transmits it to the synchronous oscillation control circuit 7 through the insulation signal transmission means 15 and controls it to be constant to control the ON period of the switching element 5. Voltage VIN
Also, the ON period of the switching element 5 changes and is kept constant due to the fluctuation of. In this case, the output power of the switching power supply device is small, and loss and noise are not a problem.

As described above, the secondary winding 4c of the transformer 4
Since the reverse recovery time characteristic of the parasitic diode 8a of the field effect transistor 8 is used as a means for flowing a secondary current in the reverse direction, the field effect transistor 8 is sufficiently reversed like the reverse recovery time characteristic of the parasitic diode 8a. It is clear that the same effect can be obtained as a rectifying device having a recovery time, especially as a PN junction diode.

Further, in order to suppress the surge voltage value and switching noise applied to the switching element 5 to a certain specified value, and the noise level emitted from the input / output terminals to a certain specified value, the capacitance value of the capacitor 6 is set. Field-effect transistor 8 with appropriate reverse recovery time characteristics
Alternatively, if a PN junction diode is used, the switching element 5
It is clear that zero-cross switching of is possible.

Further, in order to reduce loss and switching noise as a switching power supply device, a field effect transistor 8 or a rectifying element having a sufficient reverse recovery time is connected in parallel to both ends of the capacitor by connecting a capacitor in parallel, and after the reverse current period, The secondary current in the reverse direction rapidly decreases, the polarity of the induced voltage generated in each winding of the transformer 4 is reversed, and the induced voltage generated in the secondary winding 4c of the transformer 4 is the parasitic diode 8a of the field effect transistor 8 or , When reverse biasing a rectifying element having a sufficient reverse recovery time, absorbs a spike voltage generated by the leakage inductance of the secondary winding 4c of the transformer 4 and the first primary winding 4a to prevent a sudden voltage change. Therefore, switching noise can be reduced, and further, the parasitic diode 8a of the field effect transistor 8 or sufficient reverse recovery can be achieved. It is also possible to reduce the reverse recovery loss of the rectifying element having between.

The secondary winding 4 of the transformer 4 in FIG.
Even if the configuration is such that one end of c is connected to the output terminal 12, the other end is connected to the drain of the field effect transistor 8, and the gate and source of the field effect transistor 8 are connected to the output terminal 13, the same operation as described above is performed. Will be the same. Also in this configuration, the field effect transistor 8 may be a rectifying element having a sufficient reverse recovery time.

[0040]

As described above, according to the present invention, the same control range as the conventional one can be maintained, the turn-on and turn-off losses of the switching element can be greatly reduced with a simple structure, and the spike applied to the switching element at the same time. The voltage and spike current are greatly reduced, and switching noise is also reduced. For example, high efficiency and low noise of the switching power supply device can be achieved, and further high frequency can be achieved.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing a switching power supply device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing operation waveforms of the circuit configuration diagram of FIG.

FIG. 3 is a characteristic diagram showing characteristics of a field effect transistor.

FIG. 4 is a circuit configuration diagram showing a conventional switching power supply device.

5 is an explanatory diagram showing operation waveforms of the circuit configuration diagram of FIG. 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DC power supply 2-3 Input terminal 4 Transformer 5 Switching element 5a Diode 6 Capacitor 7 Synchronous oscillation control circuit 8 Field effect transistor 9 Smoothing capacitor 10 Error amplifier 11 Reference voltage 12-13 Output terminal 14 Load 15 Insulation signal transmission means

Claims (6)

[Claims] 1. An input voltage is applied to a primary winding of a transformer through a switching element that repeatedly turns on and off, and the energy stored in the transformer is formed from a secondary winding of the transformer by a field effect transistor and a capacitor. It is stored as an output voltage through the rectifying and smoothing means, and the output voltage obtained through the rectifying and smoothing means is applied to the secondary winding of the transformer through the field effect transistor and stored in the transformer. A switching power supply device configured to regenerate energy to the input voltage via the primary winding of the transformer. 2. An input voltage is applied to a primary winding of a transformer through a switching element that repeatedly turns on and off, and energy stored in the transformer has a sufficient reverse recovery time from a secondary winding of the transformer. It is supplied as an output voltage via a rectifying and smoothing means consisting of a rectifying element and a capacitor,
By applying the output voltage obtained through the rectifying / smoothing means to the secondary winding of the transformer through the rectifying element having the sufficient reverse recovery time, the energy stored in the transformer is transferred to the primary winding of the transformer. A switching power supply device configured to regenerate the input voltage via a winding. 3. The rectifying device having a sufficient reverse recovery time is a PN junction diode having a sufficient reverse recovery time.
A switching power supply as described. 4. The switching power supply device according to claim 1, wherein a capacitor is connected in parallel to both ends of the switching element. 5. The switching power supply device according to claim 1, wherein a capacitor is connected in parallel to both ends of the field effect transistor. 6. The switching power supply device according to claim 2, wherein a capacitor is connected in parallel to both ends of a rectifying element having a sufficient reverse recovery time.