JP2002058238A - Switching power supply - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To reduce power consumption by reducing switching loss at light load and improve power supply efficiency at light load. A control circuit includes an output voltage detection circuit.
A feedback voltage conversion circuit 22 which receives a feedback signal Icc from the input and converts it into a feedback voltage signal VCO which changes in a direction opposite to the increase and decrease, and an element which detects a drain current Id and outputs it as an element current detection signal VCL Current detection circuit 23
And an element current detection comparator 24 for comparing the feedback voltage signal VCO with the element current detection signal VCL. Further, when the feedback voltage signal VCO is smaller than the lower limit value, the output of the switching signal to the switching element 12 to the switching signal control circuit 25 is stopped, and when the feedback voltage signal VCO is larger than the upper limit value, the switching is stopped. A light load detection circuit 40 that starts outputting a switching signal to the signal control circuit 25 is provided.

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, and more particularly, to a step-down chopper type switching power supply capable of reducing power consumption at a light load.

[0002]

2. Description of the Related Art FIG. 6 shows a circuit configuration of a conventional switching power supply device disclosed in Japanese Patent Application Laid-Open No. 10-191625. In the conventional switching power supply device shown in FIG. 6, a positive DC voltage applied to a main input terminal 101 is reduced to a predetermined voltage value by a switching element 102 composed of an N-type MOSFET and a voltage conversion circuit 103 to reduce a main output voltage. This is a step-down chopper type switching power supply that outputs to the terminal 104.

A switching power supply device includes a control circuit power supply capacitor 10 connected in parallel between a source of a switching element 102 and an output side of an output voltage detection circuit 105.
6 has a control circuit 107 driven by the power supply voltage Vc generated by the control circuit 6. The switching element 102 is controlled by a control signal Vg output from the control circuit 107. The power supply voltage Vc is output from the output voltage detection circuit 105.
Varies with the control current Ic output from the controller.

Hereinafter, an outline of the operation of the switching power supply device configured as described above will be described. FIG. 7 shows a current-voltage waveform in each part of the switching power supply device shown in FIG.

First, until the control circuit 107 is activated, the power supply switching block 108 is operated by the power supply block 10 for activation.
9 and the control circuit power supply capacitor 106 are closed.

Next, when an input voltage Vin is applied to the main input terminal 101, the control circuit power supply capacitor 10 is switched from the starting power supply block 109 via the power supply switching block 108.
6, the power supply voltage Vc of the control circuit 107 increases. When the value of the power supply voltage Vc reaches the starting voltage value of the control circuit 107, the control circuit 107 operates. At this time, the output voltage Vo applied to the main output terminal 104 is 0 V
It is.

When the control circuit 107 starts operating, the comparator 111 compares the triangular wave carrier signal voltage generated by the triangular wave generation circuit 110 constituting the control circuit 107 with the voltage obtained by dividing the power supply voltage Vc of the control circuit 107 by resistance. Be compared.

The comparison signal output from the comparator 111 is P
The signal is input to the WM (pulse width modulation) pulse generation circuit 112, and as a result, the control signal Vg shown in FIG. 7 is applied to the control terminal of the switching element 102. This control signal Vg
Is turned on for a predetermined time width, and this time width is equal to the power supply voltage V
It becomes variable by c. The switching element 102 is turned on while the control signal Vg is on, and the drain current Ip flowing through the switching element 102 is
3 flows into the coil.

Next, when the switching element 102 is turned off by the control signal Vg of the control circuit 107, the electric energy stored in the coil is supplied to the main output terminal 104 through the diode of the voltage conversion circuit 103. You. Here, the output voltage of the main output terminal 104 increases,
The power supply voltage Vc of the control circuit 107, the forward voltage Vf of the diode of the voltage conversion circuit 103, the output voltage detection circuit 105
Forward voltage Vf of diode and output voltage detection circuit 1
When the voltage becomes larger than the sum of the respective voltage values (Vc + Vf−Vf + Vz = Vc + Vz) of the breakdown voltage Vz of the Zener diode 05 in FIG. The control current I flows to the control circuit power supply capacitor 106 through the diode and the Zener diode of the circuit 105.
c flows in, and the value of the output voltage Vo is fed back to the control circuit 107. Here, when the power supply voltage Vc of the control circuit 107 becomes sufficiently high, the power supply switching block 108 switches so that the power supply voltage Vc is supplied from the main output terminal 104 to the control circuit 107.

Next, the comparator 111 compares the triangular wave carrier signal voltage generated by the triangular wave generation circuit 110 with a voltage obtained by dividing the power supply voltage Vc by resistance, and the switching element for one triangular wave, ie, one carrier. The on-duty of the PWM pulse generation circuit 11
2 so that the switching element 10
2 is determined.

As described above, the conventional switching power supply device variably controls the duty ratio of the switching element 102 by feeding back the output voltage Vo, and
The output voltage Vo of the main output terminal 104 is adjusted to a predetermined value by improving the accuracy of the voltage of the voltage 04.

[0012]

However, in the conventional switching power supply, the drain current Ip flowing through the switching element 102 is small at the time of light load or no load at the time of standby or the like.
Therefore, a certain amount of current flows even at a light load. Therefore, even when the load is light, a loss due to switching occurs in the switching element 102, and the lighter the load, the greater the proportion of the loss in the switching element 102. As a result, power supply efficiency is reduced, so that there is a problem that power saving during standby of the power supply cannot be achieved.

The present invention solves the above-mentioned conventional problems, reduces switching loss at light load, and reduces power consumption.
It is an object of the present invention to improve the power efficiency of a chopper type switching power supply at a light load.

[0014]

In order to achieve the above-mentioned object, the present invention provides a switching power supply device in which a switching power supply is detected by an output voltage detecting circuit for detecting an output voltage and is fed back to a control circuit for controlling a switching element. The output of the switching signal to the switching element is stopped based on the generated power supply voltage of the control circuit.

More specifically, a switching power supply device according to the present invention includes a switching element for receiving a first DC voltage at an input terminal, receiving an output signal from the switching element, and converting the first DC voltage to the first DC voltage. A voltage conversion circuit that converts and outputs a second DC voltage smaller than the absolute value of the voltage, a control circuit that controls the operation of the switching element, and a detection signal that detects the voltage value of the second DC voltage and detects the second DC voltage And an output voltage detection circuit for outputting a feedback signal to the control circuit, an anode connected to the output side of the output voltage detection circuit, and a cathode connected to the output side of the switching element to generate a power supply voltage for the control circuit. A control circuit for generating a switching signal to be applied to the switching element and outputting the generated signal, and detecting a current flowing through the switching element, A current detection circuit that outputs a current detection signal, a feedback voltage conversion circuit that detects a feedback signal included in the power supply voltage, converts the detected feedback signal into a feedback voltage signal that changes in a direction opposite to the increase or decrease, and outputs the feedback signal. A comparator that compares the element current detection signal with the feedback voltage signal and outputs the compared signal; a switching signal control circuit that controls the output of the switching signal based on the comparison signal; If the feedback voltage signal is larger than the upper limit voltage value, the output of the switching signal to the switching element is stopped for the switching signal control circuit. And a light load detection circuit for starting the operation.

According to the switching power supply of the present invention,
When the current consumed at the time of light load decreases and the second DC voltage, which is the output voltage of the device, increases, the current fed back to the control circuit from the output voltage detection circuit that detects the voltage value of the second DC voltage As the amount increases, the power supply voltage of the control circuit increases. At this time, the feedback voltage transformer detects the feedback signal included in the power supply voltage, converts the detected feedback signal into a feedback voltage signal that changes in the direction opposite to the increase or decrease, and outputs the feedback signal. The value drops. On the other hand, the light load detection circuit receiving the feedback voltage signal stops outputting the switching signal to the switching element to the switching signal control circuit when the feedback voltage signal is smaller than the lower limit voltage value. Since the loss is reduced and the power consumption at the time of light load can be reduced, the power efficiency of the chopper type switching power supply device can be improved.

In the switching power supply of the present invention,
Preferably, the value of the upper limit voltage is about 20% of the maximum value of the amplitude in the element current detection signal, and the value of the lower limit voltage is about 15% of the maximum value of the amplitude in the element current detection signal.
Here, when the feedback voltage signal becomes larger than the lower limit voltage value, the light load detection circuit immediately starts outputting the switching signal to the switching signal control circuit, so that the output suspension period of the switching signal can be almost set. Disappears. However, if the above-mentioned difference of about 5% is provided between the upper limit voltage value and the lower limit voltage value, a time margin (hysteresis characteristic) occurs until the feedback voltage signal exceeds the upper limit voltage value. Can be set reliably. In addition, the lower limit voltage value is set to 15% of the maximum value of the amplitude in the element current detection signal.
By setting the degree of the switching operation, a period during which the switching operation is stopped can be secured.

In the switching power supply of the present invention,
It is preferable that the light load detection circuit has a detection voltage varying means for variably setting the value of the lower limit voltage or the upper limit voltage.
By doing so, the load current value during standby can be optimized, so that the number of options for a system incorporating the power supply device can be increased.

In the switching power supply of the present invention,
Preferably, the reference potential of the control circuit is the same as the output terminal of the switching element, and the control circuit detects the second DC voltage when the switching signal is off.
With this configuration, control using the high-speed switching frequency becomes easy, and the second DC voltage that is the output voltage can be controlled with high accuracy. Further, since the reference potential of the control circuit is the same as the output terminal of the switching element, the control circuit and the switching element can be easily integrated into one chip.

In the switching power supply of the present invention,
It is preferable that the output voltage detection circuit includes a series connection circuit of an output voltage setting element and a diode. With this configuration, the second DC voltage value can be easily set or changed only by replacing the output voltage setting element such as a Zener diode or the like. Power supply device can be realized.

In the switching power supply of the present invention,
It is preferable that the polarity of the second DC voltage is negative.
This makes it possible to cope with a system requiring a negative control voltage source.

In the switching power supply of the present invention,
It is preferable that the value of the first DC voltage is approximately 100 V or more and the value of the second DC voltage is approximately 25 V or less.
In this case, when the first DC voltage which is the input voltage is converted from the commercial AC power and input, the cost, size, and performance are more remarkably improved.

In the switching power supply of the present invention,
The switching element and the control circuit are preferably housed in one package such that the input terminal and the output terminal of the switching element, and the input terminal on the anode side of the power supply capacitor for the control circuit in the control circuit are external connection terminals. . With this configuration, the number of components of the power supply device can be reduced, and the size of the switching power supply device can be reduced.

In the switching power supply of the present invention,
A switching element and a control circuit are integrated and formed on one semiconductor substrate such that an input terminal and an output terminal of the switching element, and an input terminal on the anode side of a power supply capacitor for the control circuit in the control circuit are external connection terminals. It is preferred that With this configuration, since the switching element and the control circuit can be integrated into one chip, the number of components of the power supply device can be significantly reduced, and the size can be further reduced.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a schematic circuit configuration of a switching power supply according to an embodiment of the present invention. As shown in FIG. 1, the switching power supply according to the present embodiment converts an input voltage Vin, which is a first DC voltage having a positive polarity, applied to a main input terminal 11 to a switching element 12 composed of an N-type power MOSFET and This is a step-down chopper type switching power supply device which drops to an output voltage Vo which is a second DC voltage of a predetermined voltage value by a voltage conversion circuit 13 and outputs the output voltage to a main output terminal 14.

A smoothing capacitor 10 for smoothing the input voltage Vin is connected between the high level side and the low level side of the main input terminal 11. A predetermined load 15 is connected between the high level side and the low level side of the main output terminal 14, and a load current Io flows through the load 15.

The present switching power supply device has a power supply voltage Vc generated by a control circuit power supply capacitor 17 connected in parallel between a source as an output terminal of the switching element 12 and an output side of an output voltage detection circuit 16. The switching element 12 is controlled by a control signal Vg output from the control circuit 18. That is, since the reference potential of the source of the switching element 12 and the reference potential of the control circuit 18 are the same, the switching element 12 is substantially controlled by the power supply voltage Vc. The power supply voltage Vc varies according to a feedback signal Icc which is a control current output from the output voltage detection circuit 16.

The voltage conversion circuit 13 has an anode connected to the main output terminal 1.
A first diode 131 connected to the low-level side of the main output terminal 14 and a cathode connected to the high-level side of the main output terminal 14;
A coil 132 connected in series between the cathode of the first diode 131 and the high level side of the main output terminal 14,
A capacitor 133 whose cathode is connected to the low level side of the main output terminal 14 and whose anode is connected to the output side of the coil 132
It is composed of

The output voltage detecting circuit 16 comprises a second diode 161 having anodes connected in series and a zener diode 162 as an output voltage setting element.
The cathode of the second diode 161 is connected to the anode of the power supply capacitor 17 for the control circuit, and the Zener diode 162
Is connected to the high level side of the main output terminal 14.

Further, the present switching power supply device has a configuration in which the switching element 12 and the control circuit 18 can be integrated,
For example, the configuration is such that it can be housed in one package or formed monolithically on a semiconductor substrate. A region surrounded by a broken line as a reference numeral 19 in FIG. 1 is an integrated formation region that can be integrally formed, and an end of the integrated formation region 19 is connected to a drain of the switching element 12. There are provided at least three input / output terminals serving as external connection terminals: a drain terminal TD, a source terminal Ts connected to the source of the switching element 12, and a control terminal Tc connected to the anode of the control circuit power supply capacitor 17. ing.

When housed in one package, the switching element 12 and the control circuit 18 need not necessarily be formed on one semiconductor substrate, but may be formed on separate substrates. Is also good.

The control circuit 18 includes an oscillator 21 for generating and outputting a switching signal having an oscillation signal frequency of about 100 kHz applied to the switching element 12 and a feedback signal Icc fed back from the output voltage detection circuit 32 to a resistor. A feedback voltage conversion circuit 22 which is input via a shunt regulator 34 and converts it into a feedback voltage signal VCO which changes in the direction opposite to the increase / decrease, and outputs the feedback voltage signal VCO;
2, an element current detection circuit 23 that converts the detected drain current Id into a voltage and outputs it as an element current detection signal VCL, and a feedback voltage signal V
An element current detection comparator 24 that compares CO with the element current detection signal VCL and outputs the compared signal; a switching signal control circuit 25 that controls the current amount and output of the switching signal based on the comparison signal; Feedback voltage signal V
When CO is smaller than the lower limit voltage value, the output of the switching signal to the switching element 12 is stopped for the switching signal control circuit 25, and when the feedback voltage signal VCO is larger than the upper limit voltage value, the switching signal control circuit 25 and a light load detection circuit 40 for starting output of a switching signal.

Further, the control circuit 18 includes a drain terminal TD of the switching element 12 and a control terminal T
c and an internal circuit current supply circuit 29 for supplying a start-up current to the control circuit 18, and an output side of the internal circuit current supply circuit 29 connected via a switch to the control circuit 18. And a start / stop circuit 30 for controlling the operation of the switching signal control circuit 25 at the time of starting or stopping.

The feedback voltage conversion circuit 22 receives a gain adjustment resistance generation voltage V35 generated in the gain adjustment resistor 35 by the feedback signal Icc at the opposite phase terminal, a comparator 221 receiving the reference voltage at the positive phase terminal, and a gate. , A P-type MOSFET 222 receiving the output signal of the comparator 221, a first N-type MOSFET 223 having a gate and a drain receiving the output voltage of the P-type MOSFET 222, and a first N-type MOSFET 223.
Second N-type MOSFET sharing gate with ET223
224. The drain of the second N-type MOSFET 224 that receives the power supply voltage via the resistor 225
An output terminal of the feedback voltage signal VCO, and a first N-type MO
The sources of the SFET 223 and the second N-type MOSFET 224 are connected to the source terminal Ts, respectively.

The switching signal control circuit 25 receives an output signal of the light load detection circuit 40 at a set terminal S and an output signal of an element current detection comparator 24 at a reset terminal R; Receives an output signal of the start / stop circuit 30 at a second input terminal, and receives a maximum duty cycle signal MDC from the oscillator 21 at a second input terminal.
And the third input terminal receives the RS flip-flop circuit 2
6, a NAND circuit 27 receiving an output signal from NAN6,
And a gate driver 28 formed of an inverter which receives an output signal of the D circuit 27 and outputs a control signal Vg obtained by inverting and amplifying the received output signal.

A gain adjusting resistor 35 for the feedback voltage conversion circuit 22 is connected between the input terminal of the feedback voltage conversion circuit 22 and the source terminal Ts of the switching element 12.

The shunt regulator 34 receives a voltage obtained by stepping down the feedback signal Icc at its source, and has a drain connected to a gain adjusting resistor 35.
Receiving the source potential of the P-type MOSFET at the opposite phase terminal,
The reference voltage is received at the positive phase terminal, and the comparison result is P-type MOSFET.
And a comparator for outputting to the gate of T. Thereby, until the power supply voltage Vc reaches a predetermined voltage,
The feedback voltage conversion circuit 22 does not start.

The light load detection circuit 4 which is a feature of this embodiment
0 is a light load detection comparator that receives the reference voltage source 41 and the feedback voltage signal VCO from the feedback voltage conversion circuit 22 at the positive-phase input terminal and receives the reference voltage VR from the reference voltage source 41 at the negative-phase input terminal. 42, and one input terminal receives the output signal VO1 of the load detection comparator 42, and the other input terminal
And an AND circuit 43 for receiving the clock signal CLK from the C.I. The reference voltage source 41 is configured to be able to change the value of the reference voltage VR in response to the output signal of the light load detection comparator 42.

The light load detection comparator 42 compares the input feedback voltage signal VCO with the reference voltage VR, and when the feedback voltage signal VCO is higher than the reference voltage VR,
A high level signal is output to the D circuit 43. Conversely, when the feedback voltage signal VCO is lower than the reference voltage VR, a low-level signal is output to the AND circuit 43, so that the output signal of the RS flip-flop circuit 26 becomes low level. The output of the control signal Vg from the controller 28 can be stopped.

On the output side of the feedback voltage conversion circuit 22, a PNP for clamping the maximum value of the feedback voltage signal VCO is provided.
Overcurrent protection circuit 31 composed of a bipolar transistor
Is provided, and when the feedback voltage signal VCO exceeds the clamp value, the source terminal T
By short-circuiting the overcurrent to s, the switching element 12 can be protected.

In the switching power supply according to the present embodiment, the voltage values of the input voltage Vin and the output voltage Vo are not limited, but as an example, the value of the input voltage Vin is 100 V to 20 V.
If the output voltage Vo is 0 V and the value of the output voltage Vo is 25 V, the number of parts of the switching power supply can be greatly reduced by forming the integrated formation region 19 into one package or one chip. Can be reduced, and further reduction in size and cost can be realized.

Note that the switching element 12 is an N-type MOS
Although an FET is used, an NPN-type bipolar transistor may be used instead.

Hereinafter, the operation of the switching power supply device configured as described above under a light load will be described with reference to the drawings.

FIG. 2 shows the operation timing of the switching power supply according to this embodiment. First, in FIG. 1, until the control circuit 18 is started, the start / stop circuit 30 is closed so as to connect the internal circuit current supply circuit 29 and the anode of the control circuit power supply capacitor 17.

Next, when the present power supply device is activated and an input voltage Vin is applied to the main input terminal 11, a current is supplied from the internal circuit current supply circuit 29 to the anode of the control circuit power supply capacitor 17, and The power supply voltage Vc of the control circuit 18 increases. When the power supply voltage Vc reaches the activation voltage of the control circuit 15, the operation of the control circuit 18 becomes possible.
The stop circuit 30 disconnects the connection between the internal circuit current supply circuit 29 and the power supply capacitor 19. As described above, since the internal circuit current supply circuit 29 operates only at the time of startup, power consumption of the control circuit 18 during normal operation can be suppressed.

Next, as shown in FIG.
In 1, the value of the reference voltage VR of the reference voltage source 41 is set to the lower limit voltage value VR1.

Thereafter, a transition period t2 to the standby state in which a load change to a light load occurs and the load current Io decreases.
In, the power supply to the load 15 becomes excessive, and the voltage value of the output voltage Vo slightly increases. As the value of the output voltage Vo increases, the power supply voltage Vc of the control circuit 18 increases, and the current amount of the feedback signal Icc increases. When the amount of current of the feedback signal Icc injected into the control terminal Tc increases, the voltage of the control terminal Tc becomes higher than the reference potential of the shunt regulator 34, and when the shunt regulator 34 operates, the gain adjusting resistance generation voltage V3
The value of 5 gradually increases. In the feedback voltage conversion circuit 22 receiving the gain adjustment resistance generation voltage V35, the output value from the comparator 221 to the gate of the P-type MOSFET 222 decreases, so that the P-type MOSFET 222 has low impedance and the drain potential of the P-type MOSFET 222 Rises, the second N-type MOSFET 224 receiving the drain potential at its gate also has low impedance, and the voltage value of the feedback voltage signal VCO output from the drain of the second N-type MOSFET 224 decreases. At this time, the voltage value of the element current detection signal VCL output from the drain current detection circuit 23 also decreases. in this way,
The switching power supply according to the present embodiment employs a so-called current mode PWM control method in which the pulse width of the switching signal is controlled by the load current Io.

The light load detection comparator 42 receiving the feedback voltage signal VCO at the positive phase terminal receives the feedback voltage signal VC
When the value of O becomes smaller than the lower limit voltage value VR1, AND
Since a low-level signal is output to the circuit 43, the gate driver 28 of the switching signal control circuit 25 outputs only the low-level control signal Vg, and the switching operation of the switching element 12 stops. At about the same time, the output voltage VR of the reference voltage source 41 is changed from the lower limit voltage value VR1 to the upper limit voltage value VR2 in response to the low level output signal of the light load detection comparator 42, and the switching operation stop period t3 Becomes

In the switching operation stop period t3, power is not supplied to the output voltage generation circuit 16, so that power is supplied only to the load 15 from the output capacitor 133. Therefore, the output voltage Vo is output. Gradually decreases. As a result, the amount of current of the feedback signal Icc injected into the control terminal Tc via the output voltage detection circuit 16 decreases, and the output value of the shunt regulator 34 also decreases, so that the value of the gain adjustment resistor generation voltage V35 also decreases. Become. This causes the feedback voltage signal VCO from the feedback voltage conversion circuit 22 to gradually increase, but the output voltage VR of the reference voltage source 41 is set to the upper limit voltage VR2 higher than the lower limit voltage VR1. Therefore, as shown in FIG. 3, the switching operation by the switching element 12 is not immediately restarted.

Further, when the output voltage Vo decreases and the feedback voltage signal VCO exceeds the upper limit voltage value VR2, the output signal from the light load detection comparator 42 becomes high level again and receives this. Since the AND circuit 43 can output a high-level output signal, the switching operation of the switching element 12 is restarted, and the operation transits to the switching operation restart period t4. Immediately after this transition, the output voltage VR of the reference voltage source 41 is reset from the upper limit voltage value VR2 to the lower limit voltage value VR1 in response to the high level output signal of the light load detection comparator 42.

In the switching operation restart period t4,
When the switching operation by the switching element 12 is restarted, the drain current I
Since d is larger than the current value when the light load is detected, the power supply to the load 15 becomes excessive, the output voltage Vo rises again, and the feedback voltage signal VCO from the feedback voltage conversion circuit 22 becomes descend. Therefore, as described above, when the feedback voltage signal VCO becomes smaller than the lower limit voltage value VR1, the output of the switching signal to the switching element 12 is stopped again.

In the present embodiment, the switching operation is stopped by detecting the light load state of the reference voltage VR output from the reference voltage source 41, and the reference voltage V
By changing R from the lower limit voltage value VR1 to the upper limit voltage value VR2, a hysteresis characteristic is given to the reference voltage VR so that the switching operation is not immediately started even if the feedback voltage signal VCO rises. . As a result, while light load or no load is detected, the switching control of the switching element 12 is in an intermittent oscillation state in which the switching operation is repeatedly stopped and restarted.

The output voltage Vo drops during the switching operation stop period t3 in the intermittent oscillation state, but the degree of the drop depends on the load current Io. That is, as the load current Io decreases, the output voltage Vo decreases more gradually.

The switching operation stop period t3 in the intermittent oscillation state becomes longer as the load current Io becomes smaller. That is, as the load becomes lighter, the switching element 12
Will be reduced.

Here, a method of setting the light load detection voltage value for stopping or restarting the operation of the switching element 12 will be described. If the light load detection voltage value is set too high, coil 1
A noise occurs at 32. On the other hand, if the light load detection voltage value is set too low, the transition to the intermittent operation state (intermittent mode) becomes difficult. Therefore, the optimum light load detection voltage value is determined by these trade-offs. Therefore,
The lower limit voltage value VR1 that is one light load detection voltage is set to about 15% of the overcurrent protection voltage that regulates the drain current Id flowing through the switching element 12, and the upper limit voltage value VR2 that is another light load detection voltage value is exceeded. Preferably, it is about 20% of the current protection voltage.

In terms of power supply efficiency, for example, the output is 1
Taking a switching power supply of W as an example, the power consumption is 2.2 W and the power supply efficiency is about 45% in the conventional method, but the power supply according to the present embodiment consumes 1.2 W.
It is confirmed that the power supply efficiency is 83%, and that low power consumption and high efficiency are reliably achieved.

Further, the switching power supply device according to the present embodiment includes the control circuit 18 and the switching element 12 in the integrated formation region 19, so that it can be housed in one package or integrated into one chip as a semiconductor integrated circuit. Can be easily performed, and the number of parts can be greatly reduced.
The cost can be easily reduced.

The output voltage detection circuit 16 shown in FIG.
The circuit configuration of the feedback voltage conversion circuit 22 is not limited to these, and may be any circuit configuration having equivalent functions.

(First Modification) Hereinafter, a first modification of the embodiment of the present invention will be described with reference to the drawings.

FIG. 4 shows a schematic circuit configuration of a switching power supply according to a first modification of the embodiment of the present invention. In FIG. 4, the same components as those shown in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

As shown in FIG. 4, the switching power supply according to the first modification has a light load detection terminal TR provided at one end at the end of the integrated formation region 19. A light load detection voltage adjusting resistor 51 is connected to the negative-phase input terminal of the detection comparator 42 and has the other end connected to the source terminal Ts.

As described above, even when the switching element 12 and the control circuit 18 are integrated by the light load detection voltage adjusting resistor 51 provided outside the integrated formation region 19, the light load is reduced. Lower limit voltage value V of detection circuit 40
R1 or the upper limit voltage value VR2 can be changed according to the use of the power supply device.

In this modification, the light load detection voltage adjusting resistor 51 is provided outside the integrated formation region 19, but may be provided inside the integrated formation region 19. When the light load detection voltage adjusting resistor 51 is provided in the integrated formation region 19, the resistance value may be adjusted by a trimming technique such as a laser trimming method.

(Second Modification) Hereinafter, a second modification of the embodiment of the present invention will be described with reference to the drawings.

FIG. 5 shows a schematic circuit configuration of a switching power supply according to a second modification of the embodiment of the present invention. 5, the same components as those shown in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

As shown in FIG. 5, in the switching power supply according to the second modification, the configuration of the voltage conversion circuit 13A is the same as that of FIG.
4 is different from the configuration of the voltage conversion circuit 13 in the switching power supply device of FIG.

That is, the voltage conversion circuit 13A is connected in series so that the first diode 131 is connected between the source of the switching element 12 and the output terminal 14A and the cathode is connected to the source. And the first diode 13 in parallel with the first capacitor 133 and the source.
1 is connected to the cathode side.

By adopting such a configuration of the voltage conversion circuit 13A, the polarity of the main output terminal 14A can be made negative without changing the polarity of the main input terminal 11, so that the negative control voltage source , A negative voltage source can be realized without changing the configuration of each circuit on the integrated formation region 19 having the switching element 12 and the control circuit 18.

In the second modification, the light load detection voltage adjusting resistor 51 according to the first modification may be provided.

In the embodiments and the modifications of the present invention, the input voltage Vin is assumed to be a DC voltage. Therefore, for example, when inputting an AC voltage, the input AC voltage may be input after being rectified into a DC voltage.

[0072]

According to the switching power supply device of the present invention, when the value of the power supply voltage of the control circuit is larger than the upper limit value, the output of the switching signal to the switching signal control circuit is stopped, and the power supply of the control circuit is stopped. When the value of the voltage is smaller than the lower limit value, the light emitting device has a light load detection circuit that starts outputting a switching signal to the switching signal control circuit. Since the loss in the switching element is reduced, power consumption under light load can be reduced, and power efficiency can be improved.

[Brief description of the drawings]

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

FIG. 2 is a timing chart showing an operation of the switching power supply according to one embodiment of the present invention.

FIG. 3 is a timing chart showing a reference voltage used for a light load detection comparator in the switching power supply according to one embodiment of the present invention.

FIG. 4 is a schematic circuit diagram showing a switching power supply device according to a first modification of the embodiment of the present invention.

FIG. 5 is a schematic circuit diagram showing a switching power supply according to a second modification of the embodiment of the present invention.

FIG. 6 is a schematic circuit diagram showing a conventional switching power supply device.

FIG. 7 is a timing chart showing the operation of a conventional switching power supply device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Smoothing capacitor 11 Main input terminal 12 Switching element 13 Voltage conversion circuit 131 First diode 132 Coil 133 Capacitor 13A Voltage conversion circuit 14 Main output terminal 14A Main output terminal 15 Load 16 Output voltage detection circuit 161 Second diode 162 Zener diode Reference Signs List 17 power supply capacitor for control circuit 18 control circuit 19 integrated formation area 21 oscillator 22 feedback voltage conversion circuit 221 comparator 222 P-type MOSFET 223 first N-type MOSFET 224 second N-type MOSFET 225 resistor 23 element current detection circuit 24 Comparator for element current detection 25 Switching signal control circuit 26 RS flip-flop circuit 27 NAND circuit 28 Gate driver 29 Internal circuit current supply circuit 30 Start / stop circuit 31 Overcurrent protection circuit 34 Shunt regulator 35 Gain adjustment resistor 40 Light load detection circuit 41 Reference voltage source 42 Light load detection comparator 43 AND circuit 51 Light load detection voltage adjustment resistor (detection voltage variable means) Ts Source terminal TD Drain terminal Tc Control terminal TR Light load detection voltage adjustment terminal t1 Normal operation period t2 Transition period to standby time t3 Switching operation stop period t4 Switching operation restart period

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor ▲ Taka ▼ Koji 1-1, Sakaicho, Takatsuki-shi, Osaka Matsushita Electronics Industrial Co., Ltd. (72) Inventor: Yo Shiomi 1-1, Sayukicho, Takatsuki-shi, Osaka Matsushita Electronics Co., Ltd. (72) Inventor Osamu Takahashi 1-1, Sachimachi, Takatsuki-shi, Osaka Prefecture Matsushita Electronics Co., Ltd. (72) Inventor Yoshihiro Mori 1-1, Sachimachi, Takatsuki-shi, Osaka Matsushita Electronics Co., Ltd. In-company (72) Inventor Yuji Yamanishi 1-1 Sachicho, Takatsuki-shi, Osaka Matsushita Electronics Co., Ltd. F-term (reference) 5H730 AA14 AS05 BB13 DD04 DD21 FD01 FD41 FG01 XX03 XX23 XX44

Claims (9)

[Claims] A switching element for receiving a first direct-current voltage at an input terminal; receiving a signal output from the switching element;
A voltage conversion circuit that converts the DC voltage of the first DC voltage to a second DC voltage smaller than the absolute value of the first DC voltage and outputs the second DC voltage; a control circuit that controls the operation of the switching element; and the second DC voltage An output voltage detection circuit that detects the voltage value of the output voltage and outputs the detected detection signal as a feedback signal to the control circuit; an anode is connected to the output side of the output voltage detection circuit, and a cathode is connected to the output side of the switching element. A control circuit power supply capacitor for generating a power supply voltage for the control circuit, wherein the control circuit generates and outputs a switching signal to be applied to the switching element; and a current flowing through the switching element. A current detection circuit that detects the feedback signal contained in the power supply voltage, and increases or decreases the detected feedback signal. A feedback voltage conversion circuit that converts and outputs a feedback voltage signal that changes in the opposite direction, and compares the element current detection signal and the feedback voltage signal,
A comparator that outputs a compared comparison signal; a switching signal control circuit that controls the output of the switching signal based on the comparison signal; and a switching signal control circuit when the feedback voltage signal is smaller than a lower limit voltage value. Light load detection that stops outputting the switching signal to the switching element and starts outputting the switching signal to the switching signal control circuit when the feedback voltage signal is larger than the upper limit voltage value. And a switching power supply device. 2. The value of the upper limit voltage is about 20% of the maximum value of the amplitude in the element current detection signal, and the value of the lower limit voltage is about 15% of the maximum value of the amplitude in the element current detection signal. The switching power supply device according to claim 1, wherein 3. The switching power supply according to claim 1, wherein the light load detection circuit includes a detection voltage varying unit that variably sets a value of the lower limit voltage or the upper limit voltage. apparatus. 4. The reference potential of the control circuit is the same potential as the output terminal of a switching element, and the control circuit detects that the second DC voltage is detected when the switching signal is in an off state. The switching power supply device according to any one of claims 1 to 3, wherein 5. The switching power supply according to claim 1, wherein the output voltage detection circuit includes a series connection circuit of an output voltage setting element and a diode. 6. The switching power supply according to claim 1, wherein the polarity of the second DC voltage is negative. 7. The value of the first DC voltage is approximately 100 V
The switching power supply according to any one of claims 1 to 5, wherein the value of the second DC voltage is approximately 25 V or less. 8. The switching element and the control circuit, wherein an input terminal and an output terminal of the switching element, and an input terminal on the anode side of the power supply capacitor for the control circuit in the control circuit become an external connection terminal. 2. A package according to claim 1, wherein
8. The switching power supply device according to any one of 7. 9. The switching element and the control circuit, wherein an input terminal and an output terminal of the switching element, and an input terminal on the anode side of the control circuit power supply capacitor in the control circuit become an external connection terminal. The switching power supply device according to any one of claims 1 to 8, wherein the switching power supply device is formed integrally on one semiconductor substrate.