JPH06205582A - Switching power supply - Google Patents

Abstract

PURPOSE:To improve the power factor of a device by controlling a high frequency current. CONSTITUTION:In a rectifying circuit 3, output current from an AC power source 1 flows through a primary coil L1, being full-wave-rectified and switched with a transistor Q1. And, from the tertiary coil L3 connected in series to the primary coil L1, the voltage corresponding to the flyback voltage V2 generated in the secondary coil L2 of a transformer 4 is detected, and in a PWM control circuit 7, the ON/OFF of the transistor Q1 are controlled so that the voltage V3 may be a specified value.

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 suitable for use in a flyback type switching power supply.

[0002]

2. Description of the Related Art FIG. 6 is a block diagram showing the configuration of an example of a conventional separately excited flyback type switching power supply.
The AC power supply 1 supplies a voltage (current) having a commercial frequency such as 50 Hz or 60 Hz to the AC line filter 2
Supply to. The AC line filter 2 removes noise on the voltage (current) supplied from the AC power supply 1,
Output to the rectifier circuit 3. The rectifier circuit 3 is composed of, for example, a diode bridge circuit (not shown), and includes an AC power supply 1
Full-wave rectify the voltage (current) supplied via the AC line filter 2.

The capacitor C ₁₁ is a capacitor for smoothing the full-wave rectified output from the rectifier circuit 3, one end of which is directly connected to one end of the rectifier circuit 3, and the other end of which is a resistor R for limiting current (rush current). It is connected to the other end of the rectifier circuit 3 via ₁₁ .

The snubber circuit 12 is connected in parallel with the primary coil L ₁₁ of the transformer 11 and prevents an overcurrent from flowing into the primary coil L ₁₁ of the transformer 11 when the apparatus is started. Primary coil L of snubber circuit 12 and transformer 11
Connection point _11, at both ends of the capacitor C ₁₁ through the switching circuit 13 are connected.

The switching circuit 13 is a photocoupler 1.
A current rectified and smoothed by the rectifier circuit 3 and the capacitor C ₁₁ corresponding to the output voltage from the transformer 6, that is, the transformer 11
Of the current flowing in the primary coil L ₁₁ of the
OFF).

The secondary coil L ₁₂ of the transformer 11 is connected to the smoothing circuit 14 via a diode D ₃ . The diode D ₃ is a diode for rectifying the current flowing in the secondary coil L ₁₂ of the transformer 11, its anode is connected to one end of the secondary coil L ₁₂ of the transformer 11, and its cathode is connected to one end of the smoothing circuit 14. It is connected. The smoothing circuit 14 smoothes the current output via the diode D ₂ and supplies it to the load 5.

The voltage detection circuit 15 detects the voltage applied to the load 5 and supplies it to the photocoupler 16. The photocoupler 16 is composed of a light emitting element 16a and a light receiving element 16b. The light emitting element 16a emits light corresponding to the voltage applied to the load 5 supplied from the voltage detection circuit 15, and the light receiving element 16b is , Receives light from the light emitting element 16a and outputs a voltage corresponding to the amount of light. Therefore, the photocoupler 16 is the primary coil L of the transformer 11.
_{The 11} side and the secondary coil L ₁₂ side are electrically insulated,
The voltage applied from the voltage detection circuit 15 to the load 5 is output to the switching circuit 13.

The switching circuit 13 includes a photo coupler 1
The current flowing through the primary coil L ₁₁ of the transformer 11 is switched according to the voltage applied to the load 5 supplied from the voltage detection circuit 15 via 6. That is, when the voltage applied to the load 5 is lower than the predetermined voltage, the switching circuit 13 performs switching so that more current flows through the primary coil L ₁₁ in order to increase the voltage applied to the load 5. When the voltage applied to the load 5 is higher than the predetermined voltage, the switching operation is performed so that a smaller current flows through the primary coil L ₁₁ in order to lower the voltage applied to the load 5.

In the separately-excited flyback type switching power supply configured as described above, when the device is started, the output of the AC power supply 1 is supplied to the rectification circuit 3 via the AC line filter 2 and the rectification circuit 3 and Rectification and smoothing are performed in the capacitor C ₁₁ .

In the switching circuit 13, the current rectified and smoothed by the rectifier circuit 3 and the capacitor C ₁₁ is switched, and this switching current flows through the primary coil L ₁₁ of the transformer 11.

[0011] When the switching circuit 13 is in the short-circuit state, current rectified smoothed by the rectifier circuit 3 and the capacitor C ₁₁ flows through the primary coil L _11, a magnetic flux is generated in the transformer 11. Then, when the switching circuit 13 is opened, no current flows in the primary coil L ₁₁ , and the magnetic flux generated in the transformer 11 starts to decrease.
To counter this change (decrease) in the magnetic flux, the secondary coil L
_A voltage (flyback voltage) is generated at 12.

A current corresponding to the voltage (flyback voltage) generated in the secondary coil L ₁₂ is supplied to the smoothing circuit 14 via the diode D ₃ , and the smoothing circuit 14 smoothes the current to load 5 Is supplied to.

At this time, the voltage applied to the load 5 is detected by the voltage detection circuit 15 and supplied to the switching circuit 13 via the photocoupler 16. In the switching circuit 13, the current flowing in the primary coil L ₁₁ of the transformer 11 is switched according to the voltage applied to the load 5 supplied from the voltage detection circuit 15 via the photocoupler 16. That is, in the switching circuit 13, when the voltage applied to the load 5 is lower than the predetermined voltage, switching is performed so that more current flows through the primary coil L ₁₁ in order to increase the voltage applied to the load 5. When the operation is performed and the voltage applied to the load 5 is higher than the predetermined voltage, the switching operation is performed so that a smaller current flows through the primary coil L ₁₁ in order to decrease the voltage applied to the load 5. Be seen.

In the conventional device, the voltage applied to the load 5 is controlled to a predetermined voltage as described above.

[0015]

By the way, in such a device, when the full-wave rectified output from the rectifying circuit 3 in the capacitor C ₁₁ is smoothed, a current suddenly flows into the capacitor C ₁₁ , so that the AC power supply 1 The current waveform input from AC to AC line filter 2 is 50Hz or 60H
Instead of a sine wave having a commercial frequency of z, a current (high frequency current) waveform including a high frequency as shown in FIG. 7 is obtained.
For this reason, the power factor of the device deteriorates, and further, the load 5 connected to the secondary coil L ₁₂ side, such as a television receiver, malfunctions and is destroyed in the worst case. .

Therefore, there is a method of inserting an inductance (coil) in front of the smoothing capacitor C ₁₁ to suppress high frequency current, but this method not only increases the size of the apparatus but also increases its manufacturing cost. There was a problem that became.

Further, although the high frequency current can be suppressed by using the active filter having the step-up converter structure, there is a problem that the device also becomes large and the power consumption of the entire device increases.

The present invention has been made in view of such circumstances, and suppresses high frequency current without increasing the size and cost of the device or increasing the power consumption, and the power factor of the device. Is to be able to improve.

[0019]

A switching power supply of the present invention is a rectifying circuit 3 as a rectifying means for rectifying an output of an AC power supply 1, and a transistor Q as a switching means for switching a current rectified by the rectifying circuit 3. ₁
And the current switched by the transistor Q ₁ flows in the primary coil L ₁ , so that the secondary coils L ₂ and 3
Transformer 4 as a coupling means for supplying a current to the next coil L _3.
If, from the tertiary coil L ₃ provided in the transformer 4, the voltage V ₃ corresponding to the voltage V ₂ at the secondary coil L ₂ of the transformer 4
A diode D ₁ and capacitor C ₁ as a voltage detection means for detecting, diode D ₁ and capacitor C ₁
Corresponding to the voltage V ₃ detected by the transistor Q ₁
And a PWM control circuit 7 as a control means for controlling the third coil L ₃ and the third coil L ₃ are connected in series with the primary coil L ₁ .

[0020]

[Action] In the switching power supply of the above configuration, the output of the AC power supply 1 is rectified, flow is switched by the transistor Q ₁ to the primary coil L _1. Then, from the primary coil L ₁ and the tertiary coil L _3, which are connected in series, the voltage V ₃ is detected corresponding to the voltage V ₂ at the secondary coil L ₂ of the transformer 4, in response to the detection result , The transistor Q ₁ is controlled. Therefore, the voltage V ₂ in the secondary coil L ₂ of the transformer 4 can be controlled without smoothing the rectified output of the AC power supply 1, so that the high frequency current can be suppressed and the power factor of the device can be improved. it can.

[0021]

1 is a block diagram showing the configuration of an embodiment of a separately excited flyback type switching power supply to which the switching power supply of the present invention is applied. In the figure, parts corresponding to those in FIG. 6 are designated by the same reference numerals.
The rectifier circuit 3 is directly connected to one end of the primary coil L ₁ of the transformer 4 without the smoothing capacitor C ₁₁ shown in FIG. One end of the primary coil L ₁ that is not connected to the rectifier circuit 3 is connected to the ground via the collector and emitter of the transistor Q ₁ .

One end of the tertiary coil L ₃ has a rectifying circuit 3
And the primary coil L ₁ are connected, and the other end is connected to the anode of the diode D ₁ . Resistors R ₂ and R
₃ is connected in series, one end of the resistor R ₂ that is not connected to the resistor R ₃ is connected to the cathode of the diode D ₁ , and is connected to the resistor R ₃ and the resistor R _2. The other end is connected to ground. Resistors R ₂ and R ₃
The connection point with and is connected to the inverting input terminal of the differential amplifier 6. Therefore, the series circuit composed of the resistors R ₂ and R ₃ includes the diode D ₁ and the capacitor C ₁ (or the resistor R ₁ ) as seen from the ground. The voltage at the connection point (point A) is divided and supplied to the differential amplifier 6.

At the connection point between the diode D ₁ and the resistor R ₂ ,
One end of the capacitor C ₁ and one end of the resistor R ₁ are connected, and the other end of the capacitor C _{1 and} the other end of the resistor R ₁ are connected to the connection point between the primary coil L ₁ and the tertiary coil L _3. It is connected.

The resistors R ₄ and R ₅ are connected in series, and one end of the resistor R ₄ which is not connected to the resistor R ₅ is a connection point between the primary coil L ₁ and the tertiary coil L _3. Connected to
One end of the resistor R ₅ which is not connected to the resistor R ₄ is connected to the ground. The connection point between the resistors R ₄ and R ₅ is
The series circuit, which is connected to the non-inverting input terminal of the differential amplifier 6 and thus includes the resistors R ₄ and R ₅ , has a connection point between the tertiary coil L ₃ and the capacitor C ₁ (or the resistor R ₁ ) as seen from the ground. The voltage at (point B) is divided and supplied to the differential amplifier 6.

The differential amplifier 6 has a resistor R_FourAnd R_FiveIs divided by
Also, the tertiary coil L seen from the ground₃And capacitor C
₁(Or resistance R₁) Voltage at the connection point (point B) with
R₂And R ₃Diode D seen from ground divided by
₁And capacitor C₁(Or resistance R₁) Connection point (point
Amplify the difference from the voltage in A) and supply to the PWM control circuit 7.
To do. That is, the differential amplifier 6 includes the capacitor C₁To char
Voltage corresponding to the generated charge, that is, the tertiary coil L₃To
The generated voltage is the diode D₁And capacitor C₁so
Peak-rectified (rectified and smoothed) voltage V₃Amplifies
It is supplied to the PWM control circuit 7.

The PWM control circuit 7 turns on / off the transistor Q ₁ in response to the voltage V ₃ amplified by the differential amplifier 6.
A drive pulse for FF is supplied to the base. That is, the PWM control circuit 7 supplies to the base of the transistor Q ₁ a drive pulse in which the ratio of the pulse width to the cycle is changed according to the voltage V ₃ amplified by the differential amplifier 6.

The secondary coil L ₂ of the transformer 4 is connected to the capacitor C ₃ through the diode D _3, the cathode of the diode D ₃ is connected to one end of the secondary coil L _2,
Its anode is connected to one end of the capacitor C ₃ . Further, both ends of the capacitor C ₃ are respectively connected to a load 5 such as a television receiver.

Next, the operation will be described. When the device is started up, a drive pulse for starting up is applied from the PWM control circuit 7 to the base of the transistor Q ₁ , and the output of the AC power supply 1 having a commercial frequency such as 50 Hz or 60 Hz becomes an AC line filter. Two
Is supplied to the rectifier circuit 3 through the rectifier circuit 3 and full-wave rectified in the rectifier circuit 3.

In the transistor Q ₁ , the PWM control circuit 7 turns ON / OFF the collector and the emitter between the collector and the emitter according to the cycle and the pulse width of the drive pulse for activation applied to the base of the transistor Q ₁ . ), the series circuit composed of the primary coil L ₁ and the transistor Q _1, the output voltages V ₁ from the rectifier circuit 3 (FIG. 2) is applied, the primary coil L _1, as shown in FIG. 3 It should be noted that a so-called sawtooth waveform current having an envelope of the waveform of the output voltage V ₁ of the rectifier circuit 3 (shown by a dotted line in the figure) flows.

When the transistor Q ₁ is in the ON state, the full-wave rectified current in the rectifier circuit 3 flows through the primary coil L ₁ .
Magnetic flux is generated in the transformer 4. Then, when the transistor Q ₁ is turned off, no current flows in the primary coil L ₁ and the magnetic flux generated in the transformer 4 starts to decrease. However, in order to counter this change (reduction) of the magnetic flux, the primary A voltage (flyback voltage) is generated in the coil L ₁ , the secondary coil L _2, and the tertiary coil L ₃ .

The secondary coil L ₂ in generated voltage current corresponding to the (flyback voltage) flows into the capacitor C ₃ through the diode D _3, the charge in the capacitor C ₃ is charged, charged in the capacitor C ₃ A voltage V ₂ corresponding to the electric charge is applied to the load 5.

On the other hand, a current corresponding to the voltage (flyback voltage) generated in the tertiary coil L ₃ flows into the capacitor C ₁ via the diode D ₁ and the capacitor C ₂ is charged. That is, in the diode D ₁ and the capacitor C ₁ , the voltage generated in the tertiary coil L ₃ is peak rectified. Capacitor C with voltage V ₃ across capacitor C ₁
The voltage at the connection point between ₁ and the diode D ₁ (potential at the point A) is applied to one end of the resistor R ₂ that is not connected to the resistor R _3, and the capacitor C ₁ and the tertiary coil L ₃ are connected. The voltage at the connection point (potential at point B) is the resistance R ₄
Is applied to one end which is not connected to the resistor R ₅ .

The resistor R _2, one end of the applied voltage of a direction which is not connected to the resistor R ₃ is divided by a series circuit including a resistor R ₂ and R ₃ min, to the inverting input terminal of the differential amplifier 6 is input, the resistor R _4, one end of the applied voltage of a direction which is not connected to the resistor R ₅ is divided by a series circuit composed of the resistor R ₄ and R ₅ min, the non-inverting differential amplifier 6 It is input to the input terminal. In the differential amplifier 6, the difference between the voltage applied to its non-inverting input terminal and the voltage applied to its inverting input terminal is amplified and output to the PWM control circuit 7.

Here, the number of turns of the primary coil L ₁ or the tertiary coil L ₃ is T ₁ or T ₃ , respectively, and when the transistor Q ₁ is in the OFF state, the primary coil L ₁ When the voltage (flyback voltage) generated in the coil is V, the flyback voltage generated per turn of the winding of the primary coil L ₁ is V / T ₁ , and therefore the tertiary coil L ₃
The flyback voltage generated at (T ₃ / T ₁ ) V becomes. Further, since the point B side of the capacitor C ₁ is connected to the connection point of the primary coil L ₁ and the tertiary coil L ₃ , the voltage (potential) on the point A side of the capacitor C ₁ is the dotted line in FIG. As shown by, the output voltage V ₁ of the rectifier circuit 3 is superimposed. Therefore, a flyback voltage generated in the tertiary coil L ₃ and peak rectifier, (both ends of the potential difference of the capacitor C ₁₎ V ₃ the voltage at the capacitor C ₁ is corresponding to the flyback voltage V generated in the primary coil L ₁ (Similar)
It will be what you did.

Therefore, in the differential amplifier 6, the voltage V ₃ corresponding to the flyback voltage V generated in the primary coil L ₁ is amplified and output to the PWM control circuit 7.

In the PWM control circuit 7, the differential amplifier 6
In amplified, corresponding to the flyback voltage V generated in the primary coil L _1, so that the voltage V ₃ becomes a predetermined value, the drive pulse of changing the ratio of pulse width to period, the transistor Q ₁ Supplied to the base. In the transistor Q ₁ , the collector and emitter of the transistor Q ₁ are turned on / off in response to the drive pulse supplied to the base from the PWM control circuit 7, and the flyback voltage V generated in the primary coil L ₁ is responded to. , A current flows through the primary coil L ₁ so that the voltage V ₃ becomes a predetermined value.

When the voltage V ₃ becomes a predetermined value, the voltage V ₂ applied to the load 5 is constant, for example, the rated voltage of the load 5, corresponding to the flyback voltage generated in the secondary coil L _2. Become a voltage.

[0038] Thus, from the primary coil L ₁ and are connected in series tertiary coil L _3, the voltage V ₃ corresponding to the voltage V ₂ at the secondary coil L ₂ of the transformer 4 is detected,
The transistor Q ₁ is controlled so that the voltage V ₃ has a predetermined value. Therefore, the voltage V ₂ in the secondary coil L ₂ of the transformer 4 can be controlled without providing a capacitor for smoothing the rectified output of the AC power supply 1, and thus the AC power supply 1 via the AC line filter 2 can be controlled. Rectifier circuit 3
As shown by the dotted line in FIG. 5, the current input to is not in high frequency and has the same phase as the voltage (shown by the solid line in the figure).

[0039]

As described above, according to the switching power supply of the present invention, the output of the AC power supply is rectified, switched by the switching means, and flows into the primary coil. Then, a voltage corresponding to the voltage in the secondary coil of the coupling means is detected from the tertiary coil connected in series with the primary coil, and the switching means is controlled according to the detection result. Therefore, the voltage in the secondary coil of the coupling means can be controlled without smoothing the rectified output of the AC power supply, so that the high frequency current can be suppressed and the power factor of the device can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of a separately excited flyback type switching power supply to which the switching power supply of the present invention is applied.

FIG. 2 is a waveform diagram showing the output voltage of the rectifier circuit 3 of the embodiment of FIG.

FIG. 3 is a waveform diagram showing a current flowing through the primary coil L ₁ of the embodiment of FIG.

4 is a potential (voltage) at points A and B in the embodiment of FIG.
It is a waveform diagram showing.

5 is a waveform diagram showing an output voltage and an output current in the AC power supply 1 of the embodiment of FIG.

FIG. 6 is a block diagram showing a configuration of an example of a conventional separately excited flyback type switching power supply.

FIG. 7 is a waveform diagram showing an output voltage and an output current in the AC power supply 1 of the separately excited flyback type switching power supply shown in FIG.

[Explanation of symbols]

 1 AC power supply 2 AC line filter 3 Rectifier circuit 4 Transformer 5 Load 6 Differential amplifier 7 PWM control circuit

Claims (1)

[Claims] 1. A rectifying means for rectifying an output of an AC power source, a switching means for switching a current rectified by the rectifying means, and a current switched by the switching means flowing through a primary coil, so that a secondary coil is formed. A coupling means for supplying a current to the coil and the tertiary coil; a voltage detection means for detecting a voltage corresponding to a voltage in the secondary coil of the coupling means from the tertiary coil provided in the coupling means; and the voltage detection means. A switching means for controlling the switching means in accordance with the detected voltage, wherein the tertiary coil is connected in series with the primary coil.