JP2000004583A - Switching power supply device and electronic apparatus equipped with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stable and high efficiency switching power supply device, which has no loss of input power at no-loading and whose operation state is switched between an on-load operation and a no-load operation, and an electronic apparatus equipped with the switching power supply device. SOLUTION: A load state is detected and decided by a mode-switching means 17. At the no-loading, a 2nd switch 25, a 4th switch 27 and a 3rd switch 26 are opened by the mode switching means 17, a power flow from a rectifying means 1 is made to be zero and the mode switching means 17, a VFO(variable frequency pulse oscillation means) 23, a PWM(pulsewidth modulation means) 9 and a drive means 19 are operated by a power stored in capacitors 31 and 22 for monitoring the load state. At on-loading, all the switches are closed, a feedback control loop is formed by a comparison detecting means 4, and the voltage of an output terminal 12 is controlled so as to be a predetermined constant DC voltage and is supplied to a load 11.

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 high-efficiency switching power supply with zero input power loss under no load and an electronic apparatus including the same.

[0002]

2. Description of the Related Art FIG.
9 is a schematic block diagram showing an example of Ninth Embodiment 9. FIG. The AC voltage input from the AC input terminal 13 is rectified by the rectifier 1 and periodically opens and closes the first switch 16 via the primary winding 14 of the mutual induction device. As a result, a sawtooth voltage is obtained in the secondary winding 15 of the mutual induction device by mutual induction. This voltage is rectified by the rectifying element 2 and the capacitor 3 and appears at the output terminal 12 as a predetermined DC constant voltage, and supplies DC power to the load 11.

On the other hand, in the comparison detecting means 4, the voltage of the output terminal 12 is divided by the voltage dividing means 6 and compared with the voltage of the constant voltage element 5 by the comparing means 7. It is supplied to variable means 9 (hereinafter referred to as PWM 9).

The PWM 9 is provided with a pulse oscillating means 10 (hereinafter referred to as O
The first switch 16 is opened and closed by controlling the pulse width of a pulse having a predetermined period generated in SC10) by the voltage of the comparison detection means 4.

[0005] When the power consumption of the load 11 increases, the voltage of the voltage dividing means 6 becomes lower than the terminal voltage of the constant voltage element 5. As a result, the pulse width for closing the first switch 16 becomes wide, The supplied power is large. Conversely, when the power consumption of the load 11 decreases, the voltage of the voltage dividing means 6 becomes higher than the terminal voltage of the constant voltage element 5, and as a result, the pulse width for closing the first switch 16 becomes narrow. Accordingly, control is performed so that the power supplied to the capacitor 3 is reduced, and a DC constant voltage is generated at the output terminal 12 by dividing the terminal voltage of the constant voltage element 5 by the voltage dividing ratio of the voltage dividing means 6. The switching power supply 29 as described above,
For example, they are used in notebook PCs and mobile phone AC adapters. In recent years, in particular, while energy saving is required, a high-efficiency switching power supply device that makes power loss at no load almost zero is required. ing.

[0006]

The conventional switching power supply has the following problems. That is, even when the switching power supply device has no load,
There is always power loss. Since the efficiency of the switching power supply is expressed by (power consumption of load / power input to the switching power supply), if there is a power loss inside the switching power supply even when there is no load, the efficiency is deteriorated.

[0007] The first reason for the power loss when there is no load is as follows.
When the switch that generates the induction power in the primary winding of the mutual induction device is not loaded, although the pulse width is narrowed, it is still opened and closed with a pulse of a constant cycle, so that a part of the input power is reduced. This is because power is supplied to the secondary winding of the mutual guiding device by the mutual induction, and power is supplied to the above-described comparison detection means connected to the secondary winding.

The second reason is that there is a limit in controlling the width of a pulse for closing a switch for generating electric power by mutual induction, which is limited by the response speed of the mutual induction device and the switch, and is somewhat narrow. If so, the control becomes unstable. For this reason, the switch is opened and closed with a certain minimum width pulse and a fixed cycle, and extra power loss occurs in the switch.

For the reasons 1 and 2 described above, in the conventional switching power supply, there is a power loss even when there is no load, and this is regarded as a basic power loss, so that the efficiency of the switching power supply is extremely deteriorated. there were.

[0010] The present invention has been made in view of the above points, and makes the above-described basic power loss zero, thereby increasing the efficiency of the switching power supply device and also increasing the power use efficiency of electronic equipment having the same. That is the task.

[0011]

In order to solve the above-mentioned problems, a switching power supply of the present invention and an electronic apparatus having the same comprise an input terminal for inputting an input voltage and a mutual induction connected to the input terminal. A device, a first switch connected to the primary winding of the mutual induction device, a pulse width variable means for controlling opening and closing of the first switch, and a first switch which is opened and closed, via the mutual induction device. A first rectifier for rectifying a voltage generated by mutual induction in a secondary winding of the mutual induction device, an output terminal for connecting an output of the first rectifier to a load, and detecting a voltage of the output terminal. And a comparison detection means for controlling the opening and closing of the first switch by comparing the output comparison voltage with the pulse width variable means and comparing the output comparison voltage with the reference voltage, wherein the primary winding of the mutual induction device is provided. When Second provided between the entry force terminal
, A third switch provided between the first rectifier and the output terminal, and a power supply terminal of the comparison detector and the first switch.
A fourth switch provided between the rectifying means, a second rectifying means for rectifying a voltage generated in the secondary winding of the mutual induction device and supplying power to the pulse width varying means, and a fourth switch provided for the first switch. Variable-cycle pulse oscillating means supplied from the second rectifying means capable of changing the opening / closing cycle, mode switching means supplied from the second rectifying means capable of switching the operation state of the switching power supply, and mode switching means And a drive means provided between the control terminal of the second switch and the control terminal of the second switch. The mode switching means detects the presence or absence of a load, and opens and closes the second, third, and fourth switches. And disconnect and connect the input voltage and the comparison detection means from the entire system of the switching power supply, respectively.
The operation state of the switching power supply device can be switched by controlling the variable period pulse oscillating means and the pulse width varying means.

Further, the switching power supply according to the present invention and the electronic apparatus including the switching power supply preferably have the following features (1) to (7).

(1) A drive means is provided between the control terminal of the second switch and the mode switching means, and can electrically insulate the second switch from the mode switching means.

(2) The second rectifying means comprises a rectifying element and a capacitor, and has a secondary battery as the capacitor.

(3) Power is supplied from the second rectifier and the CM
The semiconductor device includes a mode switching unit, a variable period pulse oscillating unit, a pulse width varying unit, and a driving unit, which are constituted by an OS semiconductor and can operate at a voltage higher than the threshold voltage of the CMOS semiconductor.

(4) When the voltage for controlling the pulse width varying means becomes equal to or less than a predetermined voltage, the apparatus has a mode switching means capable of determining that there is no load.

(5) A mode switching means is provided for allowing a current to flow to the load and determining that the load is applied when the current flows and that the load is not applied when the current is not applied.

(6) A rectifying element is provided between the load and the mode switching means, and is capable of preventing a reverse flow of current between the mode switching means and the third switch.

(7) The second switch is closed and the second switch is closed.
And a starting means for supplying power for starting to the rectifying means.

The functions of the above-described means are as follows (1) and (2). (1) When there is no load, the mode switching means detects that there is no load, and the second switch is opened via the driving means. Therefore, the input power is not supplied to the second and subsequent switches. That is, all the means after the second switch operate with the stored power remaining in the capacitor in the system of the switching power supply device, and the loss from the input power is eliminated. That is, the aforementioned basic loss is zero.

(2) As described above, when there is no load, all means following the second switch operate with the stored power remaining in the capacitor in the system of the switching power supply, and consume the stored power. Specific power consumption targets are categorized into the first rectifier, the first switch, and the second rectifier. Each of these is described below.

First, as for the first rectifying means, the power supply from the first rectifying means is cut off when the comparison detecting means opens the third switch and the fourth switch when there is no load. In addition, the power loss of the first rectifier by the comparison detector is eliminated.

Next, as for the second rectifying means, the mode switching means, the variable period pulse oscillating means, the pulse width varying means, and the driving means are composed of CMOS semiconductors.
Since each of the means operates at a voltage equal to or higher than the threshold value of the CMOS semiconductor, for example, a voltage of 1 V and consumes little power, the power loss of the second rectifying means for feeding each means is small.

Further, the power loss of the first switch is small for the following reasons. That is, when there is no load, the mode switching means, the variable period pulse oscillating means, the pulse width varying means, and the driving means receive power supply from the second rectifying means and operate even after the input power is cut off by the second switch. are doing. The power corresponding to the power loss of the second rectifier is supplemented by the opening / closing of the first switch and the mutual induction by the accumulated power remaining in the capacitor connected to the primary winding of the mutual induction device. On the other hand, when there is no load, the mode switching means lengthens the pulse cycle for opening and closing the first switch and narrows the pulse width, that is, shortens the time during which the first switch is closed and increases the cycle during which the first switch is closed. To reduce power loss due to the first switch.

As described above, the mode switching means, the variable period pulse oscillating means, the pulse width varying means,
The operation of the driving means can be continued for a long time, and the load state can be continuously observed for a long time. Therefore, when a load is applied, the operation state can be immediately switched to the load mode by the mode switching means.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a switching power supply 30 according to the present invention will be described with reference to FIGS. First, the operation of the switching device 30 will be described step by step with reference to FIG. 1 which is a schematic configuration diagram of the switching power supply device 30 and FIG. 2 which is a flowchart diagram.

"S0"<The second switch 25 is closed by the starting means 24> AC input is input to the AC input terminal 13, and a voltage rectified by the rectifying means 1 is generated at the terminal of the second switch 25. Then, the second switch 25 is closed by the activation means 24 instantaneously.

The activating means 24 is, for example, a differentiating circuit composed of a capacitor C and a resistor R as shown in FIG. 6, and controls the second switch 25, that is, for example, the gate of a thyristor or the like, to establish a conductive state. I do.

"S1"<The width and period of the pulse for driving the first switch 16 are set> The capacitor 22 is charged for a moment by the starting means 24, and the charged power makes the variable period pulse oscillating means 23 (hereinafter referred to as VFO23) and pulse width varying means 9
When (hereinafter PWM9 hereinafter) is activated, VFO 23 for the period T ₀ in the no-load described below, also, PWM9
Is set to a pulse width B ₀ at the time of no load described later, and a period T ₀
Thus, a pulse having a pulse width B ₀ is supplied to the first switch 16. Such a starting means 24 is one of the desirable modes of the switching power supply of the present invention and the electronic equipment provided with the same.

As shown in FIGS. 8A and 8B, the PWM
9 changes the pulse width by the control voltage from the mode switching means 17. When the control voltage from the mode switching means 17 is higher than the predetermined voltage E _0, the pulse width is increased substantially in proportion to the voltage, such as B _V. When the control voltage is the predetermined voltage E ₀
When the voltage becomes lower, the mode switching means 17 sets the pulse width to the set value B ₀ at the time of starting by changing the voltage discontinuously. As for the VFO 23, but in the control voltage of the mode switching means 17 is the pulse period is set, this setting during a load-to T _L, the no-load and the varying binary to T _0.

VFO2 supplied from the capacitor 22
3. The PWM 9, the mode switching means 17 and the driving means 19 are composed of low power consumption elements such as the above-mentioned CMOS semiconductor elements. Therefore, the VFO 23, the PWM 9, the mode switching means 17, and the driving means 19 can be easily activated by the activation means 24 at the time of activation.

In a preferred embodiment of the switching power supply of the present invention and an electronic apparatus having the same, the capacitor 22 may be formed of a secondary battery. In this case, power can be supplied for a long time, so that the chance of charging the capacitor 22 at startup is reduced.

Further, desirable modes of the switching power supply of the present invention and electronic equipment having the same are as follows.
As shown in FIG. 7, the output is taken out from the middle of the secondary winding 15 of the mutual induction device, rectified, and
A voltage equal to or higher than the threshold value of the MOS semiconductor is generated.
9, the mode switching means 17 and the driving means 19 may be supplied with power. With such a configuration, an appropriate voltage for power matching, for example, a low voltage such as 1 V can be selected. Power loss can be reduced.

"S2"<After power supply, the second switch 2
5 is open. > When the VFO 23 and the PWM 9 are activated, the first switch 1
6 open and close and switch the voltage from the rectifying means 1 through the primary winding 14 of the mutual induction device, through the second switch 25 which is closed, so that the secondary winding of the mutual induction device by mutual induction. A sawtooth voltage is generated from line 15. When this is rectified by the second rectifier comprising the rectifier 21 and the capacitor 22, a rectified voltage is obtained at the non-ground side terminal of the capacitor 22. That is, power is transferred from the rectifier 1 to the capacitor 22. PWM
9, the VFO 23, the mode switching means 17, and the driving means 19 can be stably supplied with power by the capacitor 22 and can operate stably. At this time, the mode switching means 17 opens the second switch 25. Therefore, thereafter, the power stored in the capacitor 31 is transported, and the power loss of the capacitor 22 is supplemented while the PWM is added.
9, the VFO 23, the mode switching means 17, and the driving means 19 operate. This state is equivalent to a no-load control state S11 described later.

"S3"<determines whether or not the load 11 is connected to the output terminal. As shown in FIG. 4, the mode switching means 17 is configured such that the built-in current source 35 is connected to the output terminal 12 of FIG.
If the load 11 is connected to the output terminal, it is determined that the load 11 is connected because the current flows, and if the current does not flow, it is determined that the load 11 is not connected. I do. This is one of the desirable modes of the switching power supply of the present invention and the electronic equipment provided with the same. Further, as described later, in the state of S3, the third
Since the switch 26 is open, all the current flows into the load 11.

When the load 11 is not connected to the output terminal 12, the state of S3 is maintained. That is, load 1
Until the terminal 1 is connected to the output terminal 12, the device stands by in the state S3. At this time, as described above, VFO 23 for the period T ₀ in the no-load, also, PWM9 is set to the pulse width B ₀ in the no-load, with a period T _0, the pulse width B
A pulse of ₀ is supplied to the first switch 16. Period T
Value of ₀ and the pulse width B ₀ is, VFO 23, PWM9, by opening and closing of the power lost from the capacitor 22 the first switch 16 by the mode switching means 17, and drive means 19, in the power delivered from the capacitor 31 to the capacitor 22 The value is chosen to be sufficient to compensate.

That is, when no load is applied, the minimum power is transmitted, and an increase in the power loss of the first switch 16 caused by driving the first switch 16 with a cycle and a pulse width longer than necessary is prevented. I have. In addition, when no load is applied, the fourth switch 27 is open, so that no power is consumed by the comparison detection means 4 described later.

[S4] <When the load 11 is connected to the output terminal 12, the second switch 25, the third switch 26, and the fourth switch 27 are closed. When the load 11 is connected to the output terminal 12, the mode switching unit 17 detects and determines this, closes the second switch 25 through the driving unit 19, and power is input from the rectification unit 1 to the first switch 16. Is done. Here, as a desirable mode of the switching power supply device of the present invention and an electronic apparatus including the same, the driving means 19 can electrically insulate the mode switching means 17 from the second switch 25. This is because the second switch 25 operates at a high voltage and the mode switching means 17 operates at a low voltage. Therefore, unless both are electrically insulated, the operation becomes unstable and a failure easily occurs. For example, a photocoupler as shown in FIG.

Further, when the load 11 is connected to the output terminal 12, the mode switching means 17 detects and determines this,
The third switch 26 and the fourth switch 27 are closed.
Therefore, the comparison detection means 4 is activated. Third switch 2
6. After the fourth switch 27 is closed, the mode switching means 17 does not detect the load 11. The mode switching means 17 determines that the load 11 has been detected,
Thereafter, this determination result is stored. The third switch 2
6 is closed, the mode switching means 17 is provided with the rectifying means 1.
, The reverse current flows. To prevent this, a rectifying element 33 is provided. This is one of the desirable modes of the switching power supply of the present invention and the electronic equipment including the same.

"S5"<Cycle of VFO 23 is set to T _L. > The mode switching means 17 sets the cycle of the pulse generated by the VFO 23 to the predetermined cycle _TL during the loaded operation of the switching power supply device 30. T _L is a predetermined cycle set according to the magnitude of the maximum load, and is selected as T _L <T ₀ .

"S6"<the output of the comparing means 7 is input to the PWM 9. > The mode switching means 17 outputs the PWM
Send to 9. As a result, the PWM 9 → the first switch 16 →
The mutual induction between the primary winding 14 and the secondary winding 15 of the mutual induction device → the rectifying element 2 → the comparison detecting means 4 → the mode switching means 17 → the closed loop of the PWM 9 is formed and the output terminal 1 is formed.
The operation state shifts to the control of the voltage 2.

"S7"<Control state at the time of load> The switching power supply 30
A predetermined voltage is generated at the output terminal 12. That is, the voltage dividing means 6 divides the voltage of the output terminal 12, compares the divided voltage with the terminal voltage of the constant voltage element 5 by the comparing means 7, and sends the output of the comparing means 7 to the mode switching means 17. . Here, the voltage dividing means 6 is a circuit having a high impedance input and a low impedance output. For example, a voltage follower made of a CMOS semiconductor as shown in FIG. 3 may be used. The constant voltage element 5 may use, for example, a Zener diode.

Since the mode switching means 17 sends the output of the comparison means 7 to the PWM 9 as it is, the PWM 9 controls the pulse width in proportion to the magnitude of the comparison output. As a result, the first switch 16 is switched and driven with the period T _L and the controlled pulse width, and an output that compensates for the power consumed by the load 11 is output to the secondary winding 15 of the mutual induction device by mutual induction. The DC voltage at the output terminal 12 is controlled to a predetermined value obtained by dividing the terminal voltage of the constant voltage element 5 by the voltage dividing ratio of the voltage dividing means 6.

That is, when the voltage at the output terminal 12 drops, the output of the comparing means 7 rises, the pulse width of the PWM 9 widens, and the closed period of the first switch 16 becomes long. More power is sent to the side winding 15, and as a result, the voltage at the output terminal 12 returns to the original value.

Conversely, when the voltage at the output terminal 12 rises, the output of the comparison means 7 falls, the pulse width of the PWM 9 becomes narrower, and the closed period of the first switch 16 becomes shorter, and therefore, the mutual induction device Less power is sent to the secondary winding 15, and as a result, the voltage at the output terminal 12 returns to the original value.

"S8"<P from the mode switching means 17
For voltage to WM9 is the pulse width of a predetermined potential E ₀ less than or equal to a determined unloaded> PWM9 which increases in proportion to the magnitude of the load, as described above, narrowest at no load. As a result, the voltage for controlling the PWM 9 by the mode switching means 17 also reaches the minimum predetermined potential E ₀ , and when it becomes equal to or less than E ₀ ,
The mode switching means 17 determines that the load 11 is disconnected from the output terminal 12, that is, determines that there is no load, and stores the result. The operation of the mode switching means 17 is also one of the desirable modes of the switching power supply of the present invention and the electronic equipment having the same.

"S9"<VFO23 → T ₀ , PWM9 →
Set to B ₀ > When the voltage from the mode switching means 17 to the PWM 9 reaches E ₀ , the mode switching means 17 sets the cycle of the VFO 23 to T ₀ and the pulse width of the PWM 9 to B ₀ . That is, as described above, this pulse causes the first switch 16
When the power is transmitted to the capacitor 22 by driving the power supply, the power supplied from the capacitor 22 is set to a value sufficient to compensate for the power consumed by the VFO 23, the PWM 9, the mode switching means 17, and the driving means 19.

"S10"<The second switch 25, the third switch 26, and the fourth switch 27 are opened> The mode switching means 17 opens the second switch 25 through the driving means 19, and , The third switch 2
6. Open the fourth switch 27. That is, the switching power supply 30 is disconnected from the load 11 and the output of the rectifier 1.

[S11] <No-load control state> Operating in this state is the VFO 23, the PWM 9,
A mode switching unit 17 and a driving unit 19;
As a result, the first switch 16 is driven by a pulse having a period T ₀ and a pulse width B ₀ , and power is supplied from the capacitor 31 to the capacitor 22.

As described above, since T _L <T ₀ , the state S
In 11, loss due to opening and closing of the first switch 16 is small, and only necessary power is sent from the capacitor 31 to the capacitor 22 in order to keep the VFO 23, the PWM 9, the mode switching means 17, and the driving means 19 operating. Therefore, as described above, at the time of no load, input power does not flow in, and operation can be performed with power due to residual charge of the capacitor, so that the basic loss can be reduced to zero.

Next, in the state of S11, it waits for a change in load at the output terminal. That is, this is equivalent to the state of S3 described above. In this manner, the operation of the switching power supply of the present invention makes one cycle.

[S12] <Stopped state> Next, after the switching power supply 30 is started, it is in either the loaded state in S7 or the no-load state in S11. Therefore, when the operation of the switching power supply device 30 of the present invention is stopped, that is, when the AC power supply is disconnected from the AC input terminal 13, the operation is stopped from the state of S7 or S11.

In the case of the stop from S7, the state of S7 is maintained by the electric power accumulated in the capacitor 22, but since the residual charge of the capacitor 31 is limited, the load 11 is connected to the output terminal 12 and the second When the switch 25, the third switch 26, and the fourth switch 27 are closed, the charge of the capacitor 31 is supplied to the load 11 in a short time, and the switching power supply 30 completely stops operating.

In the case of stopping from the state S11, S
The state of 11 is mainly held by the power from the rectifying means 1,
Since the second switch 25, the third switch 26, and the fourth switch 27 are closed, the rectifier 1
Are all supplied. Thereafter, the mode switching means 17 and the driving means 1 which are supplied with power by the capacitor 22 are used.
9, only the PWM 9 and the VFO 23 are in operation, but when the charge from the capacitor 31 runs out, the switching power supply 30 completely stops operating.

The states of S7 and S11 are determined by applying an AC input to the AC input terminal 13 to obtain the state of S0, ie,
It returns to the starting state again.

The configuration and operation of the switching power supply 30 have been described above.
In recent years, with the demand for energy saving, a wide range of applications to electronic devices are possible, from portable devices such as notebook personal computers and mobile phones to stationary devices such as televisions, video recorders and stereos.

[0057]

According to the present invention, there is provided a second switch for cutting off and connecting the input voltage from the first switch. When no load is applied, the input voltage is cut off from the first switch, and the input power is reduced to zero. The third and fourth switches are opened at the same time, and the unnecessary comparison detection means is cut off from the system when there is no load, the mode switching means, the variable period pulse oscillation means, the pulse width The variable means and the driving means are operated for a long time by the electric power of the residual charge, and when a load is present, the load state is detected and determined by the mode switching means, the second switch is immediately closed, and the power is supplied to the load. And the third and fourth switches are closed, and the output terminal voltage is feedback-controlled by the comparison detection means so that the output terminal voltage becomes a predetermined DC constant voltage. Providing an electronic device including a switching power supply device and which can be switched stably to the operating state when the load becomes possible.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a switching power supply of the present invention.

FIG. 2 is a flowchart showing the operation of the switching power supply of the present invention shown in FIG. 1;

FIG. 3 is a schematic diagram illustrating details of a pressure dividing unit in FIG. 1;

FIG. 4 is a schematic diagram illustrating details of a mode switching unit in FIG. 1;

FIG. 5 is a schematic diagram showing details of a driving unit of FIG. 1;

FIG. 6 is a schematic diagram illustrating details of a starting unit in FIG. 1;

FIG. 7 is a schematic diagram showing another method of outputting from the secondary winding of the mutual guidance device of FIG. 1;

FIG. 8 is a schematic diagram for supplementarily explaining the operation of the variable period pulse oscillating means and the pulse width varying means of FIG. 1;

FIG. 9 is a block diagram illustrating a schematic configuration of a conventional switching power supply device.

[Explanation of symbols]

1 rectifying means, 2, 21, 33 ... rectifying element, 3, 22,
DESCRIPTION OF SYMBOLS 31 ... capacitor, 4 ... comparison detection means, 5 ... constant voltage element, 6 ... voltage dividing means, 7 ... comparison means, 9 ... pulse width variable means, 10 ... pulse oscillation means, 11 ... load, 12 ... output terminal, 13 ... AC input terminal, 14 ... Primary winding of mutual induction device, 15 ... Secondary winding of mutual induction device, 16 ... First switch, 17 ... Mode switching means, 19 ... Drive means, 23 ... Variable Periodic pulse oscillating means, 24 starting means, 25 second switch, 26 third switch, 2
7: fourth switch, 29: switching power supply device, 3
0: switching power supply unit, 35: current source

Claims (9)

[Claims] An input terminal for inputting an input voltage; a mutual induction device connected to the input terminal; a first switch connected to a primary winding of the mutual induction device; Pulse width varying means for controlling opening and closing of a switch; first rectifying means for rectifying a voltage generated by mutual induction in a secondary winding of the mutual induction device; and an output of the first rectifying means connected to a load. An output terminal for performing the operation, a comparison detection unit that obtains an output comparison voltage that is a difference between the voltage of the output terminal and a reference voltage, and feeds it back to the pulse width variable unit; a primary winding of the mutual induction device; A second switch provided between the input terminal, a third switch provided between the first rectifier and the output terminal, a power supply terminal of the comparison detector and the first rectifier. Fourth switch provided between the means A second rectifier for rectifying a voltage generated in a secondary winding of the mutual induction device and supplying power to the pulse width variable unit, and a variable opening / closing cycle of the first switch;
A variable period pulse oscillating unit fed from the second rectifying unit, a mode switching unit supplied with power from the second rectifying unit, which can switch an operation state of a switching power supply device; And a driving means provided between the control terminal of the second switch and the control terminal of the second switch, wherein the mode switching means detects the presence / absence of the load and the second, third, and fourth modes. A switch is set to either open or closed, and the input voltage and the comparison and detection means are respectively cut off and connected from the entire system of the switching power supply device, and the variable period pulse oscillation means and the pulse width variable A switching power supply device for controlling the operation state of the switching power supply device. 2. The switching power supply device according to claim 1, wherein said driving means can electrically insulate a control terminal of said second switch from said mode switching means. 3. The switching power supply device according to claim 1, wherein the second rectifying unit includes a rectifying element and a capacitor, and uses a secondary battery as the capacitor. 4. The mode switching means, the variable cycle pulse oscillating means, the pulse width varying means, and the driving means are composed of CMOS semiconductors, and the mode switching means and the variable cycle pulse oscillating means are provided. 2. The pulse width varying means and the driving means are operable by being supplied with a voltage equal to or higher than a threshold value of the CMOS semiconductor from the second rectifying means. A switching power supply device according to claim 1. 5. The switching power supply device according to claim 1, wherein said mode switching means determines that there is no load when a voltage controlling said pulse width varying means becomes equal to or lower than a predetermined voltage. 6. The apparatus according to claim 1, wherein the mode switching means supplies a current to the load, and determines that the load is applied when the current flows and that the load is not applied when the current does not flow. Switching power supply. 7. A rectifying element is provided between the load and the mode switching means, and the rectifying element prevents a backflow of a current between the mode switching means and the third switch. The switching power supply device according to claim 1. 8. The switching power supply device according to claim 1, further comprising a starting unit that starts the second switch and supplies initial power to the second rectifying unit. 9. An electronic apparatus comprising the switching power supply device according to claim 1.