JP3518386B2 - Switching power supply - Google Patents

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, and more particularly to a technique for reducing power consumption and improving power conversion efficiency.

[0002]

2. Description of the Related Art Conventionally, switching power supply devices having various circuit configurations have been developed and widely put into practical use.

Among them, PWM (Pulse Width Modulation) control, that is, pulse width modulation control is adopted as the control method for stabilizing the output voltage, and the circuit element is housed in a hybrid type IC package. It is widely used because of its ease of mounting and mounting.

[0004]

As described above, in the switching power supply device that has been widely used in the past, its circuit elements are housed in a hybrid type IC package, and P
The output voltage was stabilized by the WM control.

In such a switching power supply device, high power conversion efficiency is desired from the viewpoint of energy saving. Further, since there is a great demand for miniaturization of the switching power supply device, it is usually desirable that the circuit accommodated in this package has a high degree of integration.

However, in the conventional switching power supply, the power consumption of the circuit elements in the package is large, so that good power conversion efficiency cannot be obtained. Further, it is difficult to increase the degree of integration and reduce the size of the package due to heat generated from the circuit element.

Therefore, the present invention has been made in view of the above conventional problems, and an object thereof is to provide a switching power supply device which consumes less power and has high power conversion efficiency.

[0008]

A switching power supply device according to the present invention comprises a switching element for generating pulse power from a DC power supply by an on / off operation, and a smoothing means for smoothing the generated pulse power and outputting a voltage. The detection means for detecting the output voltage and the detection signal from the detection means are input to the comparison circuit 10 via the comparison circuit 9.
And a pulse train generating means for generating a pulse train for stabilizing the output voltage, a driving means for turning on and off the switching element in synchronization with the generated pulse train , and a pulse train generating means. Comparison times
Power is constantly supplied to the path 10, while the switching element is used.
When the pulse train is turned off,
The power supply stopping means for stopping the power supply to circuits other than the comparison circuit 10 is provided.

With the above structure, the switching element generates pulse power from the DC power supply by the on / off operation, and the smoothing means outputs the smoothed voltage to the load.
The detection means detects the output voltage and outputs a detection signal, and the pulse train generation means generates a trigger signal,
Generate a pulse train to stabilize the output voltage,
The driving means turns the switching element on and off in synchronization with the generated pulse train.

In the switching power supply device of the present invention, attention is paid to the fact that once the trigger signal is generated by the pulse train generating means and the switching element is turned off, the trigger operation is not necessary during the period when the switching element is off. The power supply stopping means is provided so that the pulse train generating means operates during the period when the switching element is off.
By stopping the power supply to the circuit that does not need to operate during the OFF period, the power consumption in the pulse train generating means during the OFF period is reduced.

[0011] The switching power supply apparatus according to the present invention, the pulse train generating means includes an oscillation circuit, the power supply stop means includes a feature that stops the power supply to the pre-Symbol oscillator circuit period of the off To do.

According to this structure, the power supply stopping means stops the power supply to the oscillation circuit during the off period, thereby reducing the power consumption in the oscillation circuit.

Further , the switching power supply device of the present invention
Generates pulsed power from DC power supply by on / off operation
Switching element and the generated pulse power
Smoothing means for smoothing and outputting a voltage, and the output voltage
Stabilizes the output voltage with detection means for detecting pressure
And a comparator for outputting a pulse train for
Ratio including a transistor that changes the potential of one input terminal
Comparator circuit, oscillation connected to the other input terminal of the comparator
Based on the detection signal from the circuit and the detection means
Equipped with a circuit that triggers a potential change in the transistor
Pulse train generation means for synchronizing with the generated pulse train
To drive the switching element on and off
And the switching element is off during the pulse period.
Applying the oscillation circuit and the trigger of the sequence generator
Power supply stopping means for stopping power supply to the circuit
It may be configured to.

Further, in the switching power supply device of the present invention, the power supply stopping means is composed of an opening / closing element which cuts off a power supply path in response to a signal given during the off period. . According to this configuration, the switching element surely stops power supply, which is preferable.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a switching power supply device according to the present invention will be described below with reference to FIGS.

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

In the main circuit 100, the power supply 1 is a DC power supply and the transformer 2 is for transmitting pulsed power to the secondary side. One end of the primary winding of the transformer 2 has a power source 1
Of the NPN MOSFET 3 that is turned on and off as a switching element. The source terminal of the MOSFET 3 is connected to the negative pole of the power source 1 via the current detection resistor R7.
Hereinafter, the terms "on period" and "off period" are referred to as a conduction period and a non-conduction period of MOSFET 3, respectively.

The rectifying / smoothing circuit 4 is for rectifying and smoothing the pulse current transmitted through the transformer 2 after being generated by the main circuit 100, and is composed of a rectifying diode, a smoothing capacitor and the like (not shown). It Then, the load 5 is connected to the subsequent stage. Hereinafter, the positive voltage of the load 5 will be referred to as the output voltage Vo. The rectifying / smoothing circuit 4, the load 5, and the detection circuit 8 described later constitute a secondary side circuit insulated from the main circuit 100, and the secondary side ground is shown as GND2.

The drive circuit 6 is a circuit for driving the MOSFET 3 and has a comparator CMP1 input to the IN terminal.
The output signal OUT from the push-pull emitter follower type outputs a high (HI) level / low (LOW) level signal in synchronism with the output signal from the MOSFET 3 to turn the MOSFET 3 on and off, and the main circuit 100 receives a pulse current. Is generated. Further, it is provided with open collector outputs OUT2 and OUT3 which change states in synchronization with the on / off operation.

The drive circuit 6 sets the OUT1 and OUT3 terminals to the low (LO) level when the IN terminal is at the high (HI) level.
When the output terminal W2 is set to the W level and OUT2 is set to the high (HI) level, while the IN terminal is set to the low (LOW) level, the opposite state is set. Further, the drive circuit 6 is supplied with the power REG1 generated from the power supply 1. Although not shown, a mirror circuit or the like as a current source is included inside the drive circuit 6.

The oscillating circuit 7 is an oscillating circuit utilizing the charging / discharging operation of a capacitor. The transistor Q1 is for charging the capacitor C1 from the power supply REG1 when it is conductive, and the resistor R1 connected in parallel is a resistor for discharging the charge charged in the capacitor C1. The Zener diode ZD1 connected to the base of the transistor Q1 fixes the terminal voltage when the capacitor C1 is fully charged. A resistor R9 connected between the base of the transistor Q1 and the output terminal OUT3 of the drive circuit 6.
Are provided to cut off the Zener diode ZD1 during the off period.

The detection circuit 8 is for feeding back a signal obtained by detecting the deviation between the target voltage of the output voltage Vo and the actual voltage and the drain current of the MOSFET 3 to the comparison circuit 9 described later.

The anode of the light emitting diode on the input side of the photocoupler PC1 is connected to the positive side of the load 5, while the cathode is connected to the positive electrode of the reference power source Eref. The collector of the phototransistor on the output side of the photocoupler PC1 is the power source R
It is connected to EG1, while the emitter is connected to one end of resistor R8. The other end of the resistor R8 is connected to the connection point between the MOSFET 3 and the current detection resistor R7.

The comparison circuit 9 is a circuit for generating a trigger signal for turning off the MOSFET 3 from the detection signal of the detection circuit 8.

The emitter of the phototransistor of the photocoupler PC1 is connected to the non-inverting input terminal of the comparator CMP2 (hereinafter, the voltage of this terminal is referred to as V2), while the inverting input terminal receives the voltage of the power supply REG1 to be described later. The voltage divided by the resistors R5 and R6 is input (hereinafter, this voltage is referred to as V1). This comparator CMP2 has a power supply REG.
2 is supplied.

The comparison circuit 10 is a circuit that determines the on / off state of the drive circuit 6 and the main circuit 100 from the output signal of the comparator CMP2 and the output signal of the oscillation circuit 7.

The output terminal of the comparator CMP2 is connected to the base of the transistor Q2 whose emitter is grounded. The collector of the transistor Q2 has resistors R2 and R3.
Connected to the power supply REG1 via the series circuit of the resistor R2
The connection point between R3 and R3 is connected to the inverting input terminal of the comparator CMP1 (hereinafter, the voltage at this terminal is referred to as V3). The collector of the transistor Q2 is also connected to the output terminal OUT3 of the drive circuit 6.

On the other hand, the positive voltage of the capacitor C1 is input to the non-inverting input terminal of the comparator CMP1 (hereinafter,
The voltage of this terminal is called V4). And the comparator CMP1
Is connected to the input terminal IN of the drive circuit 6.

The transistor Q3 is a PN for generating a power supply REG2 which is turned on / off according to the operation of the drive circuit 6.
It is a P-type transistor. The transistor Q3 is provided to open and close the power supply path from the power supply REG1 depending on the state of the output terminal OUT2 of the drive circuit 6. That is, in this embodiment, the power source REG2 is used as the emitter of the transistor Q3. The power supply REG2 is supplied to the resistor R4, the comparator CMP2 and the resistor R5.

Next, the circuit operation in the first embodiment having the above configuration will be described.

FIG. 2 is a timing chart showing the operation of each part in this embodiment.

FIGS. 2A and 2B show MOSFs, respectively.
It is the waveform of the drain-source voltage and drain current of ET3. The same figures (c) and (d) show resistors R7 and R8, respectively.
It is a voltage waveform that occurs at. FIG. 7E shows the voltages V1 and V2. FIG. 6F shows the waveform of the base-emitter voltage of the transistor Q2. The figure (g) is
The voltages V3 and V4 are shown. Figure (h) shows
It shows the voltage of the power supplies REG1 and REG2.

In this embodiment, since the MOSFET 3 is turned on / off by the output from the drive circuit 6, its drain-source voltage changes as shown in (a).

During the ON period, the drain current is (b)
As shown in, the inductance of the primary winding of the transformer 2 linearly increases with time. By detecting this drain current, so-called current mode switching is performed.

Since a voltage proportional to the drain current (b) is generated across the current detection resistor R7, its waveform is (c).
As shown in, it is similar to (b). On the other hand, when the output voltage Vo exceeds the voltage of the reference power supply Eref, the phototransistor of the photocoupler PC1 becomes conductive and a current flows through the resistor R8. Therefore, the voltage across the phototransistor PC1 becomes as shown in (d).
It changes regardless of the on / off operation of the main circuit 100. For example, immediately after the switching power supply device is started (at time t1 in the figure).
(Before), since the output voltage Vo has not risen, no voltage is generated in the resistor R8, and the voltage is generated in the output voltage V
After o rises (after time t1).

Non-inverting input terminal voltage V2 of the comparator CMP2
Since the waveform of is the sum of the waveforms shown in (c) and (d), it becomes like V2 of (e). On the other hand, the comparator CMP2
The inverting input terminal voltage V1 of the
It becomes a value obtained by dividing the voltage of 2 by the resistors R5 and R6. During the off period, the power supply REG2 is cut off as will be described later, so that the potential becomes zero.

When the voltage V2 exceeds the voltage V1, the output of the comparator CMP2 is inverted and becomes the high (HI) level, and the base current is supplied to the transistor Q2. By this operation, as shown in (f), the base-emitter voltage of the transistor Q2 instantaneously rises. As a result, as shown in (g), the voltage V3 at the inverting input terminal of the comparator CMP1 drops and becomes lower than the voltage V4, so that the output of the comparator CMP1 becomes a high (HI) level.

The drive circuit 6 to which this signal is input is
Turn off SFET3. That is, as shown in FIG. 2A, the period thereafter is the off period (Toff).

Although not shown, the energy stored in the transformer 2 during the ON period is supplied to the load 5 through the rectifying / smoothing circuit 4 during the OFF period.

Once the main circuit 100 is turned off, the MOS
Since the FET3 is turned off, no voltage is generated in the current detection resistor R7, and therefore the transistor Q2 cannot be maintained in the ON state depending on the signal for detecting the drain current.
Since the output terminal OUT3 of the drive circuit 6 maintains the low (LOW) level in the off period, the output state of the comparator CMP1 is maintained.

In the off period, the output terminal OU of the drive circuit 6
Since T3 becomes low level, the base of the transistor Q1 connected via the resistor R9 becomes almost zero potential, and the Zener diode ZD1 and the transistor Q1 are connected.
1 cuts off. As a result, the electric charge charged in the capacitor C1 is discharged through the resistor R1. Therefore, as shown in (g), the voltage V4 gradually decreases in the off period. Then, when the voltage becomes equal to or lower than the voltage V3, the output of the comparator CMP1 becomes a low (LOW) level, and the drive circuit 2 turns on the MOSFET 3. That is, at this time, the main circuit 100 turns on.

The length of the off period is constant due to the time constant determined by the capacitor C1 and the resistor R1.

In the off period, the output terminal OU
T2 becomes a high (HI) level (high impedance), the transistor Q3 is turned off, and the power supply to the power supply REG2 is cut off as shown in (h). Therefore, the power supply to the comparator CMP2 is stopped during the off period.

In this embodiment in which the output voltage Vo is stabilized by the above-mentioned operation, the comparator CMP2 is required to operate at high speed, so that it is necessary to use a high speed one because it consumes a lot of power. However, since this comparator only triggers the transistor Q2 to end the ON period, once the main circuit 100 is turned OFF, the operation is unnecessary in the OFF period thereafter. With this in mind, the transistor Q3 is turned off by the signal from the output terminal OUT2 of the drive circuit 6 only in the off period, and the power supply path from the power supply REG1 to the power supply REG2 is cut off. In the form, the power consumption in the comparator CMP2 was reduced, and the power conversion efficiency could be improved.

Regarding the charging / discharging operation in the oscillation circuit 7, the bias of the resistor R4 required only in the ON period for turning on the transistor Q1 and charging the capacitor C1 is released by the power supply REG2 being cut off. Therefore, the power consumption of the resistor R4 is reduced.

Further, heat generation is reduced due to the reduction of power consumption, and it becomes possible to house the circuit element in a smaller hybrid package.

In the first embodiment of the switching power supply device of the present invention described above, the feedback signal for stabilizing the output voltage Vo is input to the comparison circuit 9. In addition, the ON time may be controlled by inputting a signal that detects an overvoltage of the output voltage Vo or a signal that detects a temperature rise of the circuit element to the comparison circuit 9. Also,
Instead of varying the on-time, the switching operation may be stopped.

The circuit for which the power supply is stopped is not limited to the above-mentioned comparison circuit 9 and the like, and may be any circuit that does not need to operate during the off period.

As for the switching element, the MOSFE
In addition to T, other switching elements such as a bipolar type and a junction type can be used, and the number of switching elements is not limited to one, and a plurality of switching elements may be connected in series with a primary winding interposed therebetween. The same effect can be obtained not only in the flyback type switching power supply device but also in the forward type power supply device. In addition to the isolated power source, the non-insulated D
The C / DC converter also has the same configuration, and the power conversion efficiency can be improved.

[0050]

As described above, according to the switching power supply device of the present invention, since the trigger signal generating operation of the pulse train generating means is unnecessary during the period when the switching element is off, the power supply stopping means is provided to provide the pulse train. As a means of generation
The comparator circuit 10 provided is always supplied with power, while
Provided in the pulse train generation means while the switching element is off.
By stopping the power supply to the comparator circuit 9 and / or the oscillating circuit , the power consumption in the pulse train generation means can be reduced and the power conversion efficiency of the device can be improved.

Further, by stopping the power supply to the oscillation circuit by the power supply stopping means during the off period, the power consumption in the oscillation circuit can be reduced.

Moreover, since the heat generated from the circuit elements is reduced with the power consumption, it is possible to reduce the size of the IC package that houses these elements.

[Brief description of drawings]

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

2 is a timing chart of the operation of each part in the device shown in FIG. 1, FIG. 2 (a) is a drain-source voltage of the MOSFET 3, FIG. 2 (b) is a drain current of the MOSFET 3, and FIG. , (D) is a voltage generated in the resistor R8, (e) is voltages V1 and V2, (f) is a base-emitter voltage of the transistor Q2, g) shows voltages V3 and V4, and FIG. 7 (h) shows voltage waveforms of the power supplies REG1 and REG2, respectively.

[Explanation of symbols]

1 power supply 2 transformer 3 MOSFET 4 Rectification smoothing circuit 5 load 6 drive circuit 7 Oscillation circuit 8 Detection circuit 9, 10 Comparison circuit 100 main circuit

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H02M 3/00-3/44

Claims (4)

(57) [Claims] 1. A switching element that generates pulse power from a DC power supply by an on / off operation, a smoothing unit that smoothes the generated pulse power and outputs a voltage, and a detection unit that detects the output voltage. The detection signal from this detection means is compared via the comparison circuit 9.
Pulse train generation means for generating a pulse train for inputting to the circuit 10 and stabilizing the output voltage, driving means for turning on and off the switching element in synchronization with the generated pulse train , and the pulse train generation means. The comparison circuit 10 provided in
Power is supplied to the switching element while the switching element is off.
And the comparison circuit 1 provided in the pulse train generation means.
A switching power supply device comprising: a power supply stopping unit that stops power supply to a circuit other than 0 . 2. The pulse train generating means has an oscillating circuit, and the power supply stopping means stops power supply to the oscillating circuit during the off period.
The switching power supply described. 3. A switching element that generates pulse power from a DC power supply by an on / off operation, a smoothing unit that smoothes the generated pulse power and outputs a voltage, and a detection unit that detects the output voltage. A comparator that outputs a pulse train for stabilizing the output voltage, a comparator circuit that includes a transistor that changes the potential of one input terminal of the comparator, and an oscillation connected to the other input terminal of the comparator. A circuit, and a pulse train generating means that includes a circuit that triggers a potential change in the transistor based on a detection signal from the detecting means, and a driving means that turns on and off the switching element in synchronization with the generated pulse train, A circuit for applying the oscillation circuit and the trigger of the pulse train generation means while the switching element is off. Switching power supply device, wherein the power supply stop means for stopping the power supply, in that it comprises a. 4. The power supply stopping means is composed of an opening / closing element that cuts off a power supply path in response to a signal applied during the off period. The switching power supply device according to any one of claims.