JP4272870B2 - Switching regulator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a switching regulator, and more particularly to improving its efficiency.
[0002]
[Prior art]
The switching regulator is designed so that the maximum efficiency can be exhibited in the maximum load condition required for the apparatus. This is natural from the thermal design.
[0003]
However, many switching regulators have lower efficiency as the load becomes lighter. This is more noticeable as the load becomes lighter.
[0004]
Therefore, when a device equipped with a switching regulator has two states of operation and rest and there is a significant difference in current consumption between the two states (generally, it is considered that the current consumption is lower in the rest state). The efficiency of the switching regulator is reduced in the rest state.
[0005]
In order to solve this problem, the reference voltage of the error detection circuit of the switching power supply is intermittently changed to the GND level when the device is inactive, or the detection voltage is intermittently applied with a voltage higher than the target voltage. A method has been proposed in which the excitation-type switching power supply is operated intermittently (hereinafter referred to as intermittent operation) to increase the efficiency when the apparatus is stopped (see Patent Document 1). In addition, proposals have been made to increase the efficiency by providing means for transmitting an oscillation stop signal from the secondary side to the primary side of the switching power source at light loads, or by intermittently operating the switching power source by switching two detection voltages. (See Patent Document 2).
[0006]
[Patent Document 1]
Japanese Patent No. 3219145 [Patent Document 2]
JP 2000-156977 A [0007]
[Problems to be solved by the invention]
The present invention has been made under the circumstances as described above, and an object thereof is to provide a switching regulator capable of further improving the efficiency as compared with the case where the switching regulator is simply intermittently operated as described above. Is.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, in the present invention, the switching regulator is configured as follows (1 ) .
(1) A transformer having a primary winding and a secondary winding that are insulated from each other, a switching element that performs a switching operation in order to cause a current to flow intermittently through the primary winding, and rectifying and outputting an output of the secondary winding An error detection circuit for detecting a difference between a DC voltage obtained by smoothing and a reference voltage, and a transmission means for transmitting an output corresponding to the detection result of the error detection circuit to the primary side of the transformer via an insulating element. A switching regulator for controlling the switching operation of the switching element based on the output of the transmission means,
It said error detection circuit includes two switching elements for switching a target voltage of the DC voltage,
When the device that is the load of the switching regulator is operating, one of the two switching elements is turned on, the other is turned off, and the target voltage is switched to the first voltage. When the device that is the load of the switching regulator is idle, the switching element that was in the on state during the operation state is turned off and the other switching element is turned on and off. switching regulator the second voltage and the GND level lower than the first voltage target voltage to chromatic and hibernation which operates periodically switched.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to examples of switching regulators.
[0014]
【Example】
(Example 1)
FIG. 1 is a circuit diagram of a “switching regulator” according to the first embodiment.
[0015]
In FIG. 1, D11, D12, D13, and D14 are rectifying elements, and full-wave rectifies AC power supplied from a commercial power source.
[0016]
C11 is a smoothing capacitor, which smoothes the full-wave rectified waveform rectified by the rectifying element to obtain a DC voltage.
[0017]
T21 is an insulating transformer, and includes a primary winding, a secondary winding, and a feedback winding.
[0018]
Q21 is a MOSFET which is a main switching element, and causes current to flow intermittently through the primary winding by oscillating on / off.
[0019]
Reference numeral 101 denotes a rectifying / smoothing circuit including a rectifying element D21 and a capacitor C23. The rectifying / smoothing circuit smoothes and rectifies the secondary winding voltage generated while the main switching element Q21 is off, and outputs a DC voltage.
[0020]
An error detection circuit 102 uses the Zener voltage of the Zener diode ZD21 as a reference voltage and inputs it to the plus input terminal of the operational amplifier IC22. Information on the secondary output voltage is input to the negative terminal of the operational amplifier IC22. A voltage corresponding to the difference between the two potentials appears as an output voltage of the operational amplifier. The capacitor C24 and the resistor R26 are phase compensation circuits.
[0021]
In the optocoupler PC21, a current corresponding to the output voltage of the operational amplifier IC22 flows through the light emitting diode, and the information is transmitted as a current of a phototransistor arranged on the primary side.
[0022]
When the power is turned on, the main switching element Q21 is turned on because the current from the starting resistor R21 is charged in the capacitor C21 and the voltage at the control terminal rises. Further, during continuous oscillation, it is turned on by ringing generated in the feedback winding of the transformer T21. This ringing occurs when the energy stored in the transformer T21 is completely discharged to the secondary side through the secondary winding. The turning-off is performed when the voltage of the control terminal of the main switching element Q21 is lowered by turning on the switching element Q22. A capacitor C22 is attached to the control terminal of the switching element Q22, and when the main switching element Q21 is turned on, the voltage of the feedback winding of the transformer T21 rises to charge through the resistor R24. The current flowing through the phototransistor of the optocoupler PC21 is also charged from the control terminal of the main switching element Q21.
[0023]
The on-time of the main switching element Q21 is determined by the charging speed of the capacitor C22. This is because when the voltage of the capacitor C22 exceeds the threshold voltage at the control end of the switching element Q22, the switching element Q22 is turned on and the main switching element Q21 is turned off. The charging current to the capacitor 22 is the sum of the current of the resistor R24 and the phototransistor of the optocoupler PC21. The current of the phototransistor of the optocoupler PC21 depends on the output voltage of the error detection circuit 102 on the secondary side. Since the output of the error detection circuit 102 is low when the voltage at the negative input terminal of the operational amplifier IC22 is high and high when it is low, the current of the phototransistor of the optocoupler PC21 is large when the voltage at the negative input terminal is high and small when the voltage is low. Therefore, the on-time of the main switching element Q21 is short when the voltage at the negative input terminal is high, and is long when the voltage is low.
[0024]
Here, the operation when the apparatus provided with the present switching regulator is operating, that is, when the load is large, and when it is idle, that is, when the load is small, will be described.
[0025]
While the device is operating, the control terminal of the switching element Q24 is HI, the control terminal of the switching element Q23 is LOW, Q24 is on, and Q23 is off. Therefore, a voltage obtained by dividing the secondary output voltage by R31 and R32 is input to the negative terminal of the operational amplifier IC22. Accordingly, when the Zener voltage of the Zener diode ZD21 is Vzd, the secondary output voltage V1 is controlled to be V1 = Vzd / R32 * (R31 + R32).
[0026]
On the other hand, the control terminal of the switching element Q24 has a pulse waveform in which the control terminal of the switching element Q24 is LOW and the control terminal of the switching element Q23 repeats HI / LOW while the apparatus is at rest. This pulse is usually set to several hundred Hz to several kHz.
[0027]
Since the terminal of the switching element Q24 becomes LOW, Q24 is turned off, and the target voltage V2 when the switching element Q23 is off is V2 = Vzd / (R32 + R33) * (R31 + R32 + R33). Further, when the switching element Q23 is on, GND is the target voltage.
[0028]
Therefore, when the device shifts from the operating state to the resting state, the target voltage is changed from V1 to V2 or GND, and the oscillation of the switching regulator is stopped. Thereafter, the secondary output voltage gradually decreases due to the load of the device. When the secondary output voltage reaches V2, the switching regulator operates intermittently around V2.
[0029]
Further, when shifting from the sleep state to the operation state, the control terminal of the switching element Q24 is HI, the control terminal of the switching element Q23 is LOW, Q24 is on, and Q23 is off. Therefore, the present switching regulator rapidly increases the output voltage, and obtains a stable voltage when V1 is reached.
[0030]
This operation shifts as shown in FIG. The operation of switching the control terminal of the switching element Q23 in the resting state is as follows.
[0031]
While the control terminal of the switching element Q23 is HI, the output of the error detection circuit 102 is instantaneously LOW. Therefore, a current limited by the resistor R27 flows through the light emitting diode of the optocoupler PC21. This current is sufficiently larger than that during normal control. When the current is transmitted to the phototransistor of the optocoupler PC21 on the primary side, the voltage of the capacitor C22 is instantaneously increased to turn on the switching element Q22 and turn off the main switching element Q21. If this state continues for about 2 to 20 times the oscillation frequency of the self-excited switching power supply, the energy of the transformer T21 is completely discharged, and the primary side of the self-excited switching power supply becomes the same as before the start-up.
[0032]
On the other hand, since the secondary output has a small load and a short time, the output voltage can be maintained almost as it is. When the control terminal of the switching element Q23 returns from HI to LOW, the output of the error detection circuit 102 returns to the original state, and the light-emitting diode current of the optocoupler PC21 also returns to the original state. For this reason, the current of the phototransistor on the primary side of the optocoupler PC21 is also almost restored to the previous state. When the voltage drop of this current due to the resistor R24 is set larger than the threshold voltage of the switching element Q22, the switching element Q22 continues to be in the ON state, and all the current of the starting resistor R21 flows into the switching element Q22. Therefore, the main switching element Q21 cannot be turned on, and the present switching regulator (self-excited switching power supply) continues to be stopped.
[0033]
Thereafter, as time elapses, the load consumes the electric charge stored in the capacitor C23, and the voltage of the secondary output gradually decreases. Along with this, the output voltage of the error detection circuit 102 also rises, the current of the phototransistor of the primary optocoupler PC21 also decreases, and when the voltage drop of the resistor R24 due to this current becomes lower than the threshold value of the switching element Q22, the starting resistor R21 The capacitor C21 is charged to turn on the main switching element Q21, and then the switching regulator starts to oscillate.
[0034]
The circuit configuration of the error detection circuit 102 in this embodiment shown in FIG. 1 can be variously modified. A representative one is shown in FIGS.
[0035]
As described above, according to this embodiment, two target output voltages are provided in the switching regulator, and the higher target output voltage is continuously used during the operation of the apparatus, and the lower target output is provided during the apparatus suspension. By periodically switching between the voltage and GND, the switching regulator can be operated intermittently to reduce power consumption when the apparatus is inactive and to increase efficiency.
[0036]
The pulse applied to the switching element Q23 may use an oscillator. However, when there is a microcomputer controlling the apparatus, it is easier to directly apply the pulse to the microcomputer. In addition, it is better to output a signal to be supplied to the switching element Q24 by this microcomputer. In this case, it is desirable that a step-down converter or a linear regulator is provided at the output of the switching regulator. The output voltage of the step-down converter or the linear regulator is set to a voltage lower than the voltage V2. The microcomputer is driven by the output of this step-down converter or linear regulator.
[0037]
(Example 2)
In the first embodiment, the GND level is provided as one of the target voltages at the time of rest. However, in the “switching regulator” according to the second embodiment, another operation that can maintain the operation at the rest is performed instead of the GND level. Set the target voltage.
[0038]
In the circuit, only the error detection circuit 102 is changed from the first embodiment.
[0039]
Some examples are shown in FIGS. 6 (a) to (i).
[0040]
In the case where there is a load fluctuation at the time of rest, in the first embodiment, an abnormal decrease in the output voltage may occur when the load increases rapidly.
[0041]
If another target voltage capable of maintaining the operation at the time of rest is set as in the present embodiment, there is no fear that the output voltage will drop below the set minimum voltage.
[0042]
For example, in a device in which 3.3V is generated from the output 24V of this switching regulator by a DC-DC converter, the output of the DC-DC converter cannot be maintained when the 24V output drops below 4V. There is a possibility. Therefore, by setting the target voltages at rest, for example, to 7V and 5V, the input voltage of the DC-DC converter does not become 4V or less. It is safer to use this method when load fluctuations at rest are expected.
[0043]
For example, when the error detection circuit of FIG. 6A is used and the device as a load is operating, the switching element Q24 is turned on and the voltage dividing ratio of the resistance voltage divider for output detection is set to R32 / (R31 + R32). When the device as a load is inactive, the switching element Q24 is turned off, the switching element Q23 is turned on and off, and the voltage dividing ratio of the resistance voltage divider is set to (R32 + R33) / (R31 + R32 + R33), (R32 + R33 + R34) / ( R31 + R32 + R33 + R34) can provide an output of 7V to 5V.
[0044]
As described above, according to the present embodiment, when a load change is expected at the time of the apparatus stop, three target output voltages are provided in the switching regulator, and the target output voltage of a higher voltage is continuously applied during the operation of the apparatus. The power consumption when the device is inactive is made by intermittently switching the switching regulator without undesirably reducing the output voltage by periodically switching the other two low target output voltages when the device is inactive. Can be reduced and efficiency can be further increased.
[0045]
【The invention's effect】
As described above, according to the present invention, it is possible to further reduce the power consumption when the apparatus as a load is stopped and to improve the efficiency, compared with the case where the switching regulator is simply operated intermittently.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a first embodiment. FIG. 2 is a diagram showing a change in output voltage in the first embodiment. FIG. 3 is a diagram showing a modification of an error detection circuit. FIG. 5 is a diagram showing a modification of the error detection circuit. FIG. 6 is a diagram showing an example of the error detection circuit used in the second embodiment.
Q21 Switching element T21 with control terminal Transformer IC22 Operational amplifier ZD21 Zener diode PC21 Optocoupler 101 Rectifier smoothing circuit 102 Error detection circuit

Claims (1)

A transformer having a primary winding and a secondary winding that are insulated from each other; a switching element that performs a switching operation in order to cause current to flow intermittently through the primary winding; and rectifying and smoothing the output of the secondary winding. An error detection circuit for detecting a difference between the obtained DC voltage and a reference voltage, and a transmission means for transmitting an output corresponding to the detection result of the error detection circuit to the primary side of the transformer via an insulating element, In a switching regulator for controlling the switching operation of the switching element based on the output of the transmission means,
It said error detection circuit includes two switching elements for switching a target voltage of the DC voltage,
When the device that is the load of the switching regulator is operating, one of the two switching elements is turned on, the other is turned off, and the target voltage is switched to the first voltage. When the device that is the load of the switching regulator is idle, the switching element that was in the on state during the operation state is turned off and the other switching element is turned on and off. switching regulator, characterized in that the second voltage and the GND level lower than the first voltage target voltage to chromatic and hibernation which operates periodically switched.

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