JP2013099006A - Semiconductor integrated circuit device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance power supply conversion efficiency under light-load by easily changing the light-load detection level, or the switching stop period in a switching element.SOLUTION: When the voltage level VFB of a feedback terminal FB becomes light-load level, a light-load detection comparator OP2 turns a transistor Q5 off, and a current I1 is compensated from a resistor R1. Voltage drop of the resistor R1 increases by "current I1×resistor R1", and the voltage level VFB becomes "resistor R2×current I2-resistor R2×current I1". The voltage drop "resistor R1×current I1" increased by the resistor R1 becomes the hysteresis voltage for adjusting the switching off period of a switching transistor. When the resistance of a resistor R5 connected with the adjustment signal terminal adj of a drive signal controller 10 is decreased, the current I1 flowing through a transistor Q3 increases. Since the hysteresis voltage increases, the switching off period of a transistor can be prolonged.

Description

  The present invention relates to a technique for improving conversion efficiency in a power supply device, and more particularly to a technique effective for reducing switching loss at light load in an AC / DC converter.

  In power supply apparatuses used for electronic devices such as computers and servers, energy saving has become an important issue in recent years. For example, power supply manufacturers spend a lot of ingenuity and cost to achieve the efficiency specified by light loads (for example, 20% of the maximum load) according to power saving standards such as ENERGY STAR4.0 and 80plus. Yes.

  As this type of power supply device, for example, a flyback AC / DC converter is widely known. The flyback AC / DC converter is provided with a drive signal controller. This drive signal controller comprises, for example, a single semiconductor integrated circuit device, and controls the on duty of a switching element (MOSFET: Metal Oxide Semiconductor Field Effect Transistor) that drives the transformer.

  Based on the output signal from the error amplifier that monitors the voltage level of the secondary output voltage, the drive signal controller receives a feedback signal output from a photocoupler that transmits secondary side output voltage change information to the primary side. The

  The drive signal controller controls the on-duty of the switch element so that the secondary output voltage becomes constant based on the feedback signal output from the photocoupler. When the load power on the secondary side increases and the voltage level of the secondary output decreases, a feedback signal indicating that the voltage level of the secondary output has decreased is input via the error amplifier and the photocoupler.

  Accordingly, the drive signal controller outputs a PWM (Pulse Width Modulation) signal in which the on-duty is controlled so that the drive (on) period of the switching element becomes longer. As a result, the energy stored in the transformer increases and the voltage level of the secondary output increases.

  Conversely, when the load power decreases, the voltage level of the secondary output increases. In this case, a feedback signal indicating that the voltage level of the secondary output has risen is input via the error amplifier and the photocoupler.

  Thus, the drive signal controller outputs a PWM (Pulse Width Modulation) signal in which the on-duty is controlled so that the drive (on) period of the switching element is shortened. As a result, the energy stored in the transformer is reduced, and the voltage level of the secondary output decreases.

  It should be noted that the power efficiency technology in this type of switching power supply is controlled so that the off period of the switching element that intermittently supplies a DC voltage to the primary winding becomes longer as the load becomes lighter. Therefore, the difference between the output of the detector and a predetermined voltage is added to the output of the detector that improves the power efficiency of the switching element at a light load (see, for example, Patent Document 1) There is known an offset circuit that applies a voltage lower than the lower limit of the current command value, and that has a low loss at light load and no load (see Patent Document 2).

JP 2003-219639 A JP 2004-357417 A

  However, the present inventors have found that the secondary side output voltage control technology in the AC / DC converter as described above has the following problems.

  There are two main types of power loss. One is a so-called conduction loss, which is a loss that occurs when a current flows through an impedance or other location of the switching element (MOSFET).

  The other is so-called switching loss, which is loss associated with changes in gate drive current and drain voltage and drain current when the switching element (MOSFET) is turned on / off.

  Since the conduction loss depends on the impedance of each component, there is no choice but to select a component with a performance commensurate with the allowable loss. On the other hand, the switching loss becomes lower as the period for stopping the switching is longer, that is, the smaller the number of times of switching per unit time is.

  Since the conduction loss depends on the impedance of the component, the loss increases with a heavy load in which a large amount of current flows in each component. On the other hand, since the switching loss depends on the number of switchings per unit time, it becomes a constant loss without depending on the load condition.

  For this reason, it is generally known that the switching loss ratio in the total loss increases at light loads, and the conduction loss ratio increases at heavy loads. Therefore, in order to realize high efficiency in the AC / DC converter, it is necessary to reduce the switching loss.

  In order to reduce switching loss, the drive signal controller detects a light load, and when a light load is detected, does not output a pulse signal for driving the switching element, and performs control to stop switching of the switching element. ing.

  However, since the detection level of the light load is preset in the drive signal controller, there is a problem that the detection level of the light load cannot be easily changed. In addition, when a light load is detected, the period during which the driving of the switching element is stopped also depends on the drive signal controller. In this case as well, there is a problem that the switching stop period of the switching element cannot be easily changed.

  This makes it difficult to set the optimal light load detection level and switching element drive stop period according to specifications such as the size of the load connected to the power supply, reducing power conversion efficiency. I will let you.

  Also, when changing the light load detection level or switching element drive stop period setting according to the size of the load, various power supplies such as adjusting the transformer inductor value for each power supply with different specifications The design of the apparatus needs to be changed, which requires a great amount of man-hours, cost, and design period.

  An object of the present invention is to provide a technique capable of easily changing the detection level of a light load or the switching stop period in a switching element and improving the power conversion efficiency at the time of light load.

  The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

  Of the inventions disclosed in the present application, the outline of typical ones will be briefly described as follows.

  That is, in order to achieve the above-described object, an output terminal is provided in a semiconductor integrated circuit device provided in a power supply device that generates a DC output power supply from an AC input power supply, and a current flowing through the output terminal is controlled. This realizes a mechanism capable of easily changing the light load detection level for detecting the light load or the switching stop period of the switching element at the time of the light load.

  According to one embodiment, the semiconductor integrated circuit device is provided in a power supply device that generates a DC output power supply from an AC input power supply, and the semiconductor integrated circuit device is connected to the DC output power supply from the AC input power supply. A switching control circuit that performs drive control of a switching element that switches a transformer provided in the power supply device that generates the power supply, and detects that the load connected to the power supply device has become a light load, and stops switching of the switching element A switching stop control circuit.

  Further, the switching stop control circuit determines whether or not the power supply device has become a light load based on the first reference voltage that is varied according to the current level of the adjustment signal.

  Furthermore, the outline | summary of the other invention of this application is shown briefly.

  According to another embodiment, the switching stop control circuit switches the switching element based on the second reference voltage that is varied according to the current level of the adjustment signal when the power supply device is lightly loaded. Change the duration of the outage.

  Among the inventions disclosed in the present application, effects obtained by typical ones will be briefly described as follows.

  (1) The design of the power supply device can be facilitated.

  (2) Moreover, the power conversion efficiency at the time of light load can be improved.

  (3) The switching loss at the time of light load can be reduced and the power consumption can be reduced.

It is explanatory drawing which shows an example of the power supply device by Embodiment 1 of this invention. FIG. 2 is an explanatory diagram illustrating an example of a drive signal controller provided in the power supply device of FIG. 1. 3 is a timing chart showing signal timings of respective units in the drive signal controller of FIG. 2. FIG. 3 is an explanatory diagram illustrating a setting example of a threshold voltage in a light load detection comparator provided in the drive signal controller of FIG. 2. It is explanatory drawing which shows an example of the drive signal controller provided in the power converter device by Embodiment 2 of this invention. It is explanatory drawing which shows an example of the power supply device by Embodiment 3 of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiment, and the repetitive description thereof will be omitted.

(Embodiment 1)
FIG. 1 is an explanatory diagram showing an example of a power supply device according to Embodiment 1 of the present invention, FIG. 2 is an explanatory diagram showing an example of a drive signal controller provided in the power supply device of FIG. 1, and FIG. FIG. 4 is an explanatory diagram showing an example of setting a threshold voltage in a light load detection comparator provided in the drive signal controller of FIG. 2.

<Outline of the embodiment>
The first outline of the present embodiment includes a semiconductor integrated circuit device (drive signal controller 10) provided in a power supply device (power supply device 1) that generates a DC output power supply from an AC input power supply.

  The semiconductor integrated circuit device detects a switching control circuit (PWM control circuit 10a) that controls driving of a switching element (transistor 11) that switches a transformer, and that a load connected to the power supply device is a light load, A switching stop control circuit (switching stop control circuit 10b) for stopping switching of the switching element.

  In addition, the switching stop control circuit determines whether or not the power supply device has become lightly loaded based on a first reference voltage (light load detection level) that is varied according to the current level of the adjustment signal.

  Further, the first outline of the present embodiment is composed of a semiconductor integrated circuit device (drive signal controller 10) provided in a power supply device (power supply device 1) that generates a DC output power supply from an AC input power supply. A switching control circuit (PWM control circuit 10a) for controlling driving of a switching element (transistor 11) for switching a transformer provided in a power supply device (power supply device 1) that generates a DC output power supply from the input power supply of the power supply, and a power supply device And a switching stop control circuit (switching stop control circuit 10b) for detecting that the load connected to is a light load and stopping switching of the switching element.

  The switching stop control circuit changes the switching stop period of the switching element based on the second reference voltage that is changed according to the current level of the adjustment signal when the power supply device is lightly loaded.

  Hereinafter, the embodiment will be described in detail based on the above-described outline.

<Configuration of power supply>
In the first embodiment, the power supply device 1 is a power supply device that supplies a power supply voltage to, for example, a personal computer, and includes a flyback AC / DC converter. As shown in FIG. 1, the power supply device 1 includes a full-wave rectifier circuit 2, capacitors 3 and 4, resistors 5 to 9, a drive signal controller 10, a transistor 11, a diode 12, an error amplifier 13, a photocoupler 14, and a transformer 15. It is composed of

  The full-wave rectifier circuit 2 is configured by, for example, a bridge circuit using four diodes, and is connected so that an AC power source AC such as a commercial power source is input to two input units. The input AC power supply AC is full-wave rectified by the full-wave rectifier circuit 2.

  One terminal on the output side of the full-wave rectifier circuit 2 is connected to one connection portion of the capacitor 3 and one end portion of the primary winding of the transformer 15. The other connection portion (reference potential VSS) of the full-wave rectifier circuit 2 is connected to the other connection portion of the capacitor 3.

  The other connection portion of the capacitor 3 is connected to one connection portion of a resistor 5 for setting a reference voltage, which will be described later. The adjustment signal of the drive signal controller 10 is connected to the other connection portion of the resistor 5. Terminal adj is connected. The capacitor 3 is composed of, for example, an electrolytic capacitor, and smoothes the voltage signal that has been full-wave rectified by the full-wave rectifier circuit 2.

  One end of the transistor 11 is connected to the other end of the primary winding of the transformer 15, and the other end of the transistor 11 is connected to the monitor voltage terminal CS of the drive signal controller 10, and One connection portion of the resistor 6 is connected to each other. A reference potential VSS is connected to the other connection portion of the resistor 6.

  The transistor 11 is composed of, for example, an N channel MOS-FET (Field Effect Transistor). The transistor 11 performs switching based on the drive signal output from the signal terminal GD of the drive signal controller 10 to drive the primary winding of the transformer 15.

  The feedback terminal FB of the drive signal controller 10 is connected to one connection part of the phototransistor constituting the photocoupler 14, and the reference potential VSS is connected to the other connection part of the phototransistor. .

  The anode of the diode 12 is connected to one end of the secondary winding of the transformer 15, and one connection of the capacitor 4, one connection of the resistor 7, and the resistance are connected to the cathode of the diode 12. 8 and a cathode of a photodiode constituting the photocoupler 14 are connected to each other.

  The diode 12 rectifies the energy transmitted to the secondary side of the transformer 15. The capacitor 4 is made of, for example, an electrolytic capacitor, and smoothes the power supply voltage rectified by the diode 12. The smoothed power supply is output as the output voltage Vout of the power supply device 1.

  The output part of the error amplifier 13 is connected to the anode of the phototransistor constituting the photocoupler 14 and the other connection part of the resistor 7. The other connection portion of the resistor 8 is connected to the negative (−) side input terminal of the error amplifier 13, and the reference voltage Vref is input to the positive (+) side input terminal of the error amplifier 13. Yes.

  One connection portion of the resistor 9 is connected to a connection portion between the negative (−) side input terminal of the error amplifier 13 and the resistor 8. The other end (reference potential GND) of the secondary winding of the transformer 15 is connected to one connection portion of the capacitor 4 and the other connection portion of the resistor 9.

  The drive signal controller 10 includes, for example, one semiconductor integrated circuit device, generates a drive signal for driving the transistor 11, and outputs the drive signal from the signal terminal GD. The drive signal output from the signal terminal GD is a PWM signal, and the ON time of the transistor 11 is controlled by increasing or decreasing the ON duty based on the feedback signal input to the feedback terminal FB. .

<Configuration of drive signal controller>
As shown in FIG. 2, the drive signal controller 10 includes a PWM control circuit 10a and a switching stop period control circuit 10b. The PWM control circuit 10a generates a drive signal (PWM signal) for driving the transistor 11 and outputs it from the signal terminal GD.

  The PWM control circuit 10a controls the on time of the transistor 11 based on a feedback signal input via the feedback terminal FB. The switching stop period control circuit 10b detects that the load of the power supply device 1 is light, and sets the switching stop period of the transistor 11.

  The light load of the power supply device is, for example, a state where the load power is about 25% or less with respect to the maximum load power (current) of the power supply device 1. However, the light load state varies depending on the specifications of the power supply device and the connected load.

  The light load detection level and the switching stop period of the transistor 11 are arbitrarily set by the resistor 5 externally connected to the drive signal controller 10.

  The PWM control circuit 10a includes a flip-flop FF1, an OR circuit OR1, and an inverter Iv1. The switching stop period control circuit 10b includes a buffer B1, transistors Q1 to Q5, a comparator OP1, a light load detection comparator OP2, and resistors R1 and R2. Transistors Q1-Q5 are made of, for example, a P-channel MOS.

  The set terminal S of the flip-flop FF1 is connected so as to receive the internal clock signal CLK, and the output terminal of the OR circuit OR1 is connected to the reset terminal R of the flip-flop FF1.

  The signal terminal GD is connected to the output terminal Q of the flip-flop FF1, and a drive signal is output from the signal terminal GD. The output part of the inverter Iv1 is connected to one input part of the OR circuit OR1, and the output part of the comparator OP1 is connected to the other input part of the OR circuit OR1.

  The monitor voltage terminal CS is connected to the positive (+) side input terminal of the comparator OP1 via the level shift power supply Vls1. A signal obtained by converting the source current that flows when the transistor 11 is turned into a voltage by the resistor 6 is input to the monitor voltage terminal CS.

  In the switching stop period control circuit 10b, the positive (+) input terminal of the buffer B1 is connected so that the reference voltage Vref1 is input. The internal power supply voltage VDD is supplied to one connection portion of the transistors Q2 to Q4 and one connection portion of the resistor R1, and a current mirror circuit is configured by the transistors Q2 to Q4.

  The other connection portion of the transistor Q2 is connected to the gates of the transistors Q2 to Q4 and one connection portion of the transistor Q1. The other connection portion of the transistor Q1 is connected to the negative (−) side input terminal of the buffer B1 and the adjustment signal terminal adj.

  One connection portion of the transistor Q5 is connected to the other connection portion of the transistor Q3, and the output portion of the light load detection comparator OP2 and the input portion of the inverter Iv1 are connected to the gate of the transistor Q5, respectively. ing.

  The negative (−) side input terminal of the light load detection comparator OP2 is connected to the negative (−) side input terminal of the comparator OP1, the other connection portion of the resistor R1, and the feedback terminal FB.

  The light load detection comparator OP2 compares the reference voltage input to the positive (+) side input terminal with the voltage level VFB applied to the feedback terminal FB input to the negative (−) side input terminal, and based on the reference voltage. If the voltage level VFB is low, it is determined that the load is light, and a light load detection signal is output.

  The other connection portion of the transistor Q4 is connected to the positive (+) side input terminal of the light load detection comparator OP2 and one connection portion of the resistor R2. A reference potential VSS is connected to the other connection portion of the resistor R2.

<Operation of drive signal controller>
Next, an example of the operation of the drive signal controller 10 at a light load will be described.

  FIG. 3 is a timing chart showing signal timing of each part of the drive signal controller 10 at light load. In FIG. 3, from the top to the bottom, the internal operation clock signal CLK, the drive signal output from the signal terminal GD, the voltage level VFB input to the comparator OP1, and the voltage input to the monitor voltage terminal CS are level-shifted power supply Vls1. , The voltage VCS input to the monitor voltage terminal CS, the gate voltage of the transistor Q5, and the signal timing of the secondary output voltage Vout of the transformer 15 are shown.

  As described above, the drive signal controller 10 is provided with the adjustment signal terminal adj for setting the light load detection level. The adjustment signal terminal adj is a constant voltage output terminal, and a constant current is generated inside the drive signal controller 10 by connecting the resistor 5 to the reference potential VSS. This constant current is I2 (FIG. 2, current flowing through the transistor Q4) that determines the light load detection level and hysteresis current I1 (current flowing through the transistor Q3) that turns off switching when a light load is detected.

  By providing the adjustment signal terminal adj, it is possible to easily change the setting of the reference voltage of the light load detection comparator OP2 that detects the light load.

  The current I2 is determined by the resistor 5 connected to the adjustment signal terminal adj, and “I2 × R2” that is a reference voltage of the light load detection comparator OP2 that detects a light load by changing the resistance value of the resistor 5. Can be easily changed.

  The error amplifier 13 operates so that the positive (+) side input terminal and the negative (−) side input terminal have the same potential. For example, the potential of the negative (−) side input terminal is the positive (+) side input terminal. If the potential of the negative (−) side input terminal is lower than the potential of the positive (+) side input terminal, the output of the error amplifier 13 performs an operation of drawing a large amount of current. The output of the error amplifier 13 does not draw current.

  As the load power decreases, the secondary output voltage level increases. As a result, the voltage level of the negative (−) side input terminal of the error amplifier 13 rises, and the photodiode of the photocoupler 14 is turned on. Then, when the phototransistor of the photocoupler 14 operates, the voltage level VFB applied to the feedback terminal FB decreases.

  When the voltage level VFB of the feedback terminal FB becomes equal to or less than “resistance value of the resistor R2 × current I2”, the light load detection comparator OP2 turns off the transistor Q5 to lower the voltage level VFB of the feedback terminal FB, and the voltage again. The drive signal output from the signal terminal GD is stopped for a period until the level VFB becomes higher than “resistance value of the resistor R2 × current I2”.

  Thereby, the transistor 11 is stopped, energy stored in the transformer 15 is reduced, and the output voltage Vout on the secondary side decreases.

  The current flowing through the phototransistor of the photocoupler 14 becomes a current flowing through the transistor Q5 (current flowing through the current I1 and the resistor R1) until just before the transistor Q5 is turned off.

  When the transistor Q5 is turned off, the current I1 is supplied by the resistor R1, and the voltage level VFB of the feedback terminal FB is “the resistance of the resistor R1 relative to the voltage value when the transistor Q5 is turned on. Value × current I1 ”.

  The voltage of “resistance value of resistor R1 × current I1” becomes a hysteresis voltage, and can be arbitrarily set according to the resistance value of resistor 5. By increasing the current I1, the hysteresis voltage can be increased, and the period during which the drive signal output from the signal terminal GD is stopped, that is, the period of the voltage level VFB of the feedback terminal FB <the level shift voltage Vls1 is increased. Thus, the efficiency of the power supply device 1 at the time of light load can be improved.

<Operation of Switching Stop Period Control Circuit 10b>
Next, the operation of the switching stop period control circuit 10b provided in the drive signal controller 10 will be described in detail.

  The reference voltage Vref1 is output from the buffer B1 to the adjustment signal terminal adj of the drive signal controller 10. A resistor 5 is connected to the adjustment signal terminal adj, and the drain current of the transistor Q1 becomes a substantially constant current.

  As this current, a mirror current is generated by a current mirror circuit constituted by the transistors Q2, Q3, and Q4. Therefore, the current flowing through the transistor Q2, the current I1 flowing through the transistor Q3, and the current I2 flowing through the transistor Q4 are in a proportional relationship.

  As described above, the power supply device 1 detects the error voltage of the output voltage Vout by the error amplifier 13 so that the output voltage Vout on the secondary side becomes substantially constant, and the photocoupler 14 is based on the detection result. Is turned on, the proportional current controls the voltage level VFB applied to the feedback terminal FB, the pulse width of the drive signal output from the signal terminal GD is adjusted, and the output voltage Vout becomes substantially constant. It is controlled to become.

  Even if the load changes, the current flowing through the photocoupler 14 is adjusted and controlled so that the output voltage Vout is substantially constant. If the load is constant, the current flowing through the photocoupler 14 is substantially constant. .

  Therefore, when the voltage level VFB of the feedback terminal FB becomes a light load level, that is, when the voltage level VFB becomes equal to or lower than the voltage generated by the current I2 flowing through the transistor Q4 flowing through the resistor R2, the light load detection comparator OP2 Turns off transistor Q5.

  When the transistor Q5 is turned off, the current I1 flowing through the transistor Q3 is not supplied to the feedback terminal FB. On the other hand, even when the transistor Q5 is turned off, the photocoupler 14 passes a current necessary for the output voltage Vout to be substantially constant. Therefore, the current I1 that has stopped flowing when the transistor Q5 is turned off is compensated by the resistor R1. .

  Therefore, the voltage drop in the resistor R1 increases by “current I1 × resistance value of the resistor R1”, and the voltage level VFB of the feedback terminal FB is substantially constant because the power supply voltage to which the resistor R1 is connected is substantially constant. R2 resistance value × current I2−resistance R2 resistance value × current I1 ”.

  The voltage drop amount “resistance value of resistor R1 × current I1” increased by the resistor R1 becomes a hysteresis voltage for adjusting the switching-off period of the transistor 11. For example, when the resistance value of the resistor 5 connected to the adjustment signal terminal adj of the drive signal controller 10 is decreased, the current I1 flowing through the transistor Q3 increases, and the voltage drop at the resistor R1 increases.

  That is, since the hysteresis voltage is increased, the switching off period of the transistor 11 can be extended. Thereby, switching loss can be improved.

  However, the ripple of the output voltage Vout on the secondary side increases by increasing the switching off period of the transistor 11. When it is desired to suppress the ripple voltage of the secondary output voltage Vout at a light load, the light load detection function of the light load detection comparator OP2 can be stopped by removing the resistor 5. As a result, the ripple voltage can be improved to the same level as in the state without the light load function.

  Conversely, when the resistance value of the resistor 5 connected to the adjustment signal terminal adj is increased, the current I1 flowing through the transistor Q3 is decreased, and the voltage drop in the resistor R1 is decreased. Therefore, since the hysteresis voltage is reduced, the switching off period of the transistor 11 is shortened. By shortening the switching-off period of the transistor 11, the ripple voltage of the output voltage Vout on the secondary side can be improved.

  Therefore, in the power supply device 1, when it is desired to reduce the switching loss and prioritize higher efficiency, it can be realized by setting the resistance value of the resistor 5 small. This is because, as described above, by reducing the resistance value of the resistor 5, the hysteresis voltage increases and the switching off period of the transistor 11 increases.

  On the other hand, when it is desired to change the light load detection level in the power supply device 1, the resistor 5 is set to a desired resistance value. By changing the resistance value of the resistor 5, the current I2, which is a mirror current generated by the transistor Q4, is adjusted, and the reference voltage of the light load detection comparator OP2 can be changed.

  The reference voltage of the light load detection comparator OP2 is a voltage drop generated when the current I2 flows through the resistor R2, that is, “resistance value of the resistor R2 × current I1”. Decreasing the resistance value of the resistor 5 increases the current I2 and increases the light load detection level. Conversely, if the resistance value of the resistor 5 is increased, the current I2 decreases and the light load detection level decreases. Become.

  Thereby, even if it is a power supply device from which a specification differs, a light load level can be determined easily only by changing the resistance value of the resistor 5, and the setting of the power supply device 1 can be facilitated.

<Example of threshold setting for setting the light load detection level>
FIG. 4 is an explanatory diagram showing a setting example of the threshold voltage in the light load detection comparator OP2.

  When importance is attached to the high efficiency of the power supply device 1, the light load detection level is increased by making the reference voltage of the light load detection comparator OP2 sufficiently higher than the level shift power supply Vls1 (the resistance value of the resistor 5 is reduced) ( For example, the switching load of the transistor 11 is reduced by reducing the maximum load power (current) of the power supply device 1 to about 25% or less.

  When the ripple voltage of the power supply device 1 is to be suppressed, the light load detection level is lowered by making the reference voltage of the light load detection comparator OP2 sufficiently lower than the level shift power supply Vls1 (increasing the resistance value of the resistor 5). (For example, about 20% or less with respect to the maximum load power (current) of the power supply device 1), the switching stop of the transistor 11 is delayed.

  Furthermore, in order to achieve both high efficiency of the power supply device 1 and suppression of the ripple voltage, the reference voltage of the light load detection comparator OP2 is set slightly higher than the level shift power supply Vls1 (the resistance value of the resistor 5 is reduced). .

  As a result, the light load detection level is set to an intermediate level between high-efficiency importance and ripple voltage suppression (for example, about 20% or less with respect to the maximum load power (current) of the power supply device 1).

  Thereby, according to the first embodiment, the light load detection level can be easily changed in a short time simply by changing the resistance value of the resistor 5 externally attached to the drive signal controller 10.

  In addition, the switching stop period of the transistor 11 at light load can be easily changed in a short time simply by changing the resistance value of the resistor 5.

  By the above, the setting of the power supply device 1 can be facilitated, the switching loss can be reduced, and the power conversion efficiency can be improved.

(Embodiment 2)
FIG. 5 is an explanatory diagram showing an example of a drive signal controller provided in the power conversion apparatus according to Embodiment 2 of the present invention.

<Outline of the embodiment>
The outline of the present embodiment is that a switching control circuit (transistor 11) that controls the driving of a switching element (transistor 11) that switches a transformer provided in a power supply device (power supply device 1) that generates a DC output power supply from an AC input power supply ( Semiconductor integrated circuit device having PWM control circuit 10a) and a switching stop control circuit (switching stop control circuit 10b) for detecting that the load connected to the power supply device is light and stopping switching of the switching element Consists of.

  The switching stop control circuit sets the power supply device to a light load based on a first reference voltage (light load detection level) that is variable according to the current level of the first adjustment signal (current flowing through the adjustment signal terminal adj). Based on the second reference voltage that is varied according to the current level of the second adjustment signal (current flowing through the power supply terminal VREG) when the power supply device is lightly loaded. The switching stop period of the switching element is varied.

  Hereinafter, the embodiment will be described in detail based on the above-described outline.

<Configuration example of drive signal controller>
In the configuration of the drive signal controller 10 (FIG. 2) in the first embodiment, as described above, the current I1 and the current I2 are in a proportional relationship, so the threshold voltage and the hysteresis voltage of the light load detection comparator OP2 are You can only set the proportional relationship.

  In the second embodiment, a drive signal controller 10 that can easily set the light load detection level and set the hysteresis voltage will be described.

  In this case, as shown in FIG. 5, the drive signal controller 10 includes a PWM control circuit 10a and a switching stop period control circuit 10b.

  The PWM control circuit 10a includes a flip-flop FF1, an OR circuit OR1, and an inverter Iv1. These connection configurations are the same as those of the PWM control circuit 10a shown in FIG.

  The switching stop period control circuit 10b has a configuration in which the resistor R1 is removed from the PWM control circuit 10a shown in FIG. 2, and a power supply terminal VREG that is an external terminal is newly provided. The power supply terminal VREG is supplied with a power supply voltage VDD that is an operating voltage of the drive signal controller 10. The other connection configuration excluding the resistor R1 is the same as that of the PWM control circuit 10a shown in FIG.

  Further, a newly provided resistor 5a is externally connected between the newly provided power supply terminal VREG and the feedback terminal FB. Thereby, the reference voltage and hysteresis voltage of the light load detection comparator OP2 can be set independently and independently.

  When setting the light load detection level (threshold voltage of the light load detection comparator OP2), the current value flowing through the feedback terminal FB is set by changing the resistance value of the resistor 5.

<Setting example of switching stop period>
Further, the switching stop period of the transistor 11 can be arbitrarily set by changing the resistance value of the resistor 5a. When a light load is detected and the transistor Q5 is turned off, the current I1 flowing through the transistor Q3 becomes a voltage drop generated by flowing through the resistor 5a. Therefore, by adjusting the resistance value of the resistor 5a as described above, the hysteresis voltage, That is, the switching stop period of the transistor 11 can be determined.

  Thereby, in the second embodiment, the setting of the light load detection level and the setting of the hysteresis voltage (switching stop period of the transistor 11) in the power supply device 1 can be easily performed only by changing the resistance values of the resistors 5 and 5a. It becomes possible to change. Therefore, the specification change of the power supply device 1 can be easily performed in a short time.

(Embodiment 3)
FIG. 6 is an explanatory diagram showing an example of a power supply device according to Embodiment 3 of the present invention.

  In the first embodiment, an example in which the power supply device 1 is formed of a flyback AC / DC converter has been described. However, in the third embodiment, the power supply device 1 is formed of a quasi-resonant AC / DC converter. Will be described.

<Other configuration examples of the power supply device>
As shown in FIG. 6, the power supply device 1 includes a full-wave rectifier circuit 2, capacitors 3, 4 and 17, resistors 5 to 9 and 16, a drive signal controller 10, a transistor 11, a diode 12, an error amplifier 13, and a photocoupler 14. And a transformer 15a.

  The transformer 15a has a configuration having a first primary winding that is a main winding and a second primary winding that is an auxiliary winding on the primary side. The output of the full-wave rectifier circuit 2 is connected to the end of the first primary winding, and one connection of the transistor 11 is connected to the end of the other primary winding. Yes.

  One end of the second primary winding is connected to one connecting portion of the resistor 16, and the other connecting portion of the resistor 16 is connected to a terminal provided in the drive signal controller 10. ZCD is connected.

  This terminal ZDC is provided in the drive signal controller 10 and connected to the set terminal S of the flip-flop FF1 (FIG. 1) via an inverter (not shown). In addition, the reference potential VSS is connected to the other end of the second primary winding.

  Further, a capacitor 17 is connected to both connection portions (source-drain) of the transistor 11. Other connection configurations are the same as those of the power supply device 1 of FIG.

  In the drive signal controller 10 as well, the connection configuration other than that in which the inverter connected to the set terminal S of the flip-flop FF1 is newly provided is the same as that in FIG. To do.

<Operation of power supply>
Next, the operation of the power supply device 1 composed of a quasi-resonant AC / DC converter will be described.

  The quasi-resonant power supply device 1 performs switching using self-excited oscillation, not switching operation with a fixed frequency using the operation clock signal CLK. This self-excited oscillation generates a start timing.

  First, when the transistor 11 is turned on, the drain current Id of the transistor 11 rises from substantially zero V. The value of the current flowing through the transistor 11 is converted into a voltage by the resistor 6 and input to the monitor voltage terminal CS.

  When the current of the transistor 11 reaches the voltage FB1 determined by the voltage level VFB of the feedback terminal FB, a Hi level signal is input to the reset terminal R of the flip-flop FF1, and the transistor 11 is turned off.

  When the transistor 11 is turned off, the winding voltage of the transformer 15a is inverted, and the current IF is supplied from the transformer 15a to the secondary side via the diode 12. At this time, the voltage Vsub in the second primary winding is also inverted. A positive voltage is applied.

  When the current supply from the transformer 15a to the secondary side is completed and the current of the OD-12 becomes substantially zero, the voltage of the transistor 11 rapidly decreases due to the resonance of the inductance of the transformer 15a and the capacitor 4.

  At this time, the voltage Vsub generated in the second primary winding that is the auxiliary winding of the transformer 15a also decreases. When the voltage (voltage Vsub) input to the terminal ZDC of the drive signal controller 10 becomes lower than the threshold voltage of the inverter connected to the terminal ZDC, a Hi level signal is input to the set terminal S of the flip-flop FF1. The transistor 11 is turned on again.

  Thereby, also in the third embodiment, the drive signal controller 10 having the switching stop period control circuit 10b (FIG. 2) can be applied even to the power supply device 1 including a quasi-resonant AC / DC converter. The setting of the light load detection level or the setting of the hysteresis voltage (switching stop period of the transistor 11) can be easily changed.

  In the third embodiment, the drive signal controller 10 is provided in the quasi-resonant AC / DC converter. However, the AC / DC converter may have other configurations, such as a forward type. The AC / DC converter may be used.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment. However, the present invention is not limited to the embodiment, and various modifications can be made without departing from the scope of the invention. Needless to say.

  The present invention is suitable for a technique for improving the conversion efficiency when the power supply device is lightly loaded.

DESCRIPTION OF SYMBOLS 1 Power supply device 2 Full wave rectifier circuit 3 Capacitor 4 Capacitor 5 Resistor 5a Resistor 6 Resistor 7 Resistor 8 Resistor 9 Resistor 10 Drive signal controller 10a PWM control circuit 10b Switching stop period control circuit 11 Transistor 12 Diode 13 Error amplifier 14 Photocoupler 15 Transformer 15a transformer 16 resistor 17 capacitor FF1 flip-flop OR1 OR circuit Iv1 inverter OP1 comparator OP2 light load detection comparator B1 buffer Q1 transistor Q2 transistor Q3 transistor Q4 transistor Q5 transistor R1 resistor R2 resistor

Claims (9)

A switching control circuit that performs drive control of a switching element that switches a transformer provided in a power supply device that generates a DC output power supply from an AC input power supply;
A switching stop control circuit that detects that the load connected to the power supply device has become a light load, and stops switching of the switching element;
The switching stop control circuit is
A semiconductor integrated circuit device comprising: determining whether or not the power supply device is lightly loaded based on a first reference voltage that is varied according to a current level of an adjustment signal. The semiconductor integrated circuit device according to claim 1.
An adjustment signal terminal through which the current of the adjustment signal flows;
The amount of current of the adjustment signal is
The semiconductor integrated circuit device is variable according to a resistance value of a resistor externally connected to the adjustment signal terminal. The semiconductor integrated circuit device according to claim 1 or 2,
The switching stop control circuit is
A current generation circuit for generating a first current proportional to the current level of the adjustment signal;
A voltage generator that generates the first reference voltage from the first current;
The first reference voltage generated by the voltage generator is compared with the feedback signal indicating the output voltage information on the secondary side of the transformer. When the voltage level of the feedback signal becomes lower than the first reference voltage, the light level is reduced. A semiconductor integrated circuit device comprising: a light load detection unit that determines a load, outputs a light load detection signal, and stops switching of the switching element by the switching control circuit. A switching control circuit that performs drive control of a switching element that switches a transformer provided in a power supply device that generates a DC output power supply from an AC input power supply;
A switching stop control circuit that detects that the load connected to the power supply device has become a light load, and stops switching of the switching element;
The switching stop control circuit is
A semiconductor integrated circuit characterized in that, when the power supply device is lightly loaded, the switching stop period of the switching element is varied based on a second reference voltage that is varied according to the current level of the adjustment signal. Circuit device. The semiconductor integrated circuit device according to claim 4.
An adjustment signal terminal through which the current of the adjustment signal flows;
The amount of current of the adjustment signal is
The semiconductor integrated circuit device is variable according to a resistance value of a resistor externally connected to the adjustment signal terminal. The semiconductor integrated circuit device according to claim 4 or 5,
The switching stop control circuit is
A current generation circuit for generating a second current proportional to the current level of the adjustment signal;
A voltage variable control unit that varies the voltage level of the feedback signal indicating the output voltage information on the secondary side according to the second current generated by the current generation circuit;
The monitor voltage indicating the amount of current flowing through the primary winding of the transformer is compared with the voltage level of the feedback signal whose voltage level is varied by the voltage variable control unit, and the voltage level of the feedback signal is higher than the monitor voltage. A semiconductor integrated circuit device comprising: a switching stop period detection unit that outputs a switching stop signal for a low period and stops switching of the switching element by the switching control circuit. A switching control circuit that performs drive control of a switching element that switches a transformer provided in a power supply device that generates a DC output power supply from an AC input power supply;
A switching stop control circuit that detects that the load connected to the power supply device has become a light load, and stops switching of the switching element;
The switching stop control circuit is
Based on a first reference voltage that is varied according to the current level of the first adjustment signal, it is determined whether or not the power supply device has become a light load, and when the power supply device has become a light load, A semiconductor integrated circuit device, wherein a switching stop period of the switching element is varied based on a second reference voltage that is varied according to a current level of the second adjustment signal. The semiconductor integrated circuit device according to claim 7,
A first adjustment signal terminal through which a current of the first adjustment signal flows;
A second adjustment signal terminal through which the current of the second adjustment signal flows;
The amount of current of the first and second adjustment signals is:
A semiconductor integrated circuit device, wherein the semiconductor integrated circuit device is variable depending on a resistance value of a resistor externally connected to the adjustment signal terminal. The semiconductor integrated circuit device according to claim 7 or 8,
The switching stop control circuit is
A first current generation circuit that generates a first current that is proportional to the current level of the first adjustment signal;
A voltage generator that generates the first reference voltage from the first current;
The first reference voltage generated by the voltage generator is compared with the feedback signal indicating the output voltage information on the secondary side of the transformer. When the voltage level of the feedback signal becomes lower than the first reference voltage, the light level is reduced. A light load detection unit that determines a load and outputs a light load detection signal, and stops switching of the switching element by the switching control circuit;
A second current generation circuit for generating a second current proportional to the current level of the second adjustment signal;
A voltage variable control unit that varies the voltage level of the feedback signal indicating the output voltage information on the secondary side according to the second current generated by the second current generation circuit;
The monitor voltage indicating the amount of current flowing through the primary winding of the transformer is compared with the voltage level of the feedback signal whose voltage level is varied by the voltage variable control unit, and the voltage level of the feedback signal is higher than the monitor voltage. A semiconductor integrated circuit device comprising: a switching stop period detection unit that outputs a switching stop signal for a low period and stops switching of the switching element by the switching control circuit.

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