JP2003052174A - Switching power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily and economically generate a timing signal for alternately repeating continuous switching operation and lasting off-state of a switching element 5, in order to reduce switching loss under a light load or no-load condition in the switching power supply for supplying to an external load 8, a stabilized DC power source generated by controlling the semiconductor switching element 5 connected via an inductive means, such as a transformer 4 or the like, to a DC power source obtained across a capacitor 3, by rectifying an AC power source 1 to continuously perform switching operation, for example, in a switching cycle of 100 kHz with the PWM-controlled drive pulse 14a from a switching power supply control circuit 14. SOLUTION: When a signal LLD, having detected a light-load condition is at 'H' (significant), a timing signal TM as the output of a comparator 10 goes to 'H' in a period in which a full-wave rectified output 9a of the AC power source 1 exceeds the reference DC voltage 11. Therefore, a switch 13 is turned off with 'H' output of an AND circuit 12, and thereby the switch element 5 goes to off-state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor switching element which is connected between DC power supplies obtained by rectifying an AC power supply through inductive means composed of transformers or reactors.
A switching power supply device as a power supply device which is repeatedly opened and closed by a WM-controlled drive pulse to generate a stabilized DC power supply and supplies it to an external load. The present invention relates to a switching power supply device that intermittently switches a continuous switching operation to perform an intermittent switching operation to reduce switching loss of a semiconductor switching element and improve the efficiency of the device.

In the following drawings, the same reference numerals indicate the same or corresponding parts.

[0003]

2. Description of the Related Art In a general switching power supply device, a semiconductor switching element (hereinafter simply referred to as a switching element) which is constantly and continuously used is one of the methods for reducing a loss generated at a light load or no load. A switching operation of (abbreviated) is performed intermittently (intermittently) in the case of a light load or no load.

FIG. 6 shows an example of the configuration of the main part of this type of switching power supply device, and this figure shows an example of a switching power supply device that receives an AC power supply such as a commercial power supply as an input. In the figure, 1 is an AC power supply, 2 is a diode bridge for full-wave rectifying the voltage of the AC power supply 1, 3 is a diode bridge 2
Capacitors 4 for smoothing the DC voltage that is full-wave rectified by 4 are flyback type transformers.

Reference numeral 5 repeatedly turns on / off the DC voltage generated across the capacitor 3 via the primary winding of the transformer 4.
A switch element that is turned off, in this example, is an N-channel MOSFET, 6 is a diode that rectifies the voltage generated in the secondary winding of the transformer 4 when the switch element is off, and 7 is a capacitor that smoothes the rectified output of the diode 6. Reference numeral 8 denotes an external load connected to this switching power supply device.

Reference numeral 14 detects the DC voltage supplied from the switching power supply device to the external load 8 through a means (not shown), and switches the switch element 5 to PWM (pulse width) so as to keep the supplied DC voltage constant. A switching power supply control circuit as a control circuit that performs on / off driving at a relatively high frequency (for example, 100 kHz) by a controlled (that is, the ratio of the ON period and the OFF period is variably adjusted by the control) driving pulse 14a. is there.

Next, 21 is an oscillator for intermittent operation for generating an oscillation pulse 21a having a frequency (eg, 1 kHz) sufficiently lower than the operating frequency of the switch element 5, and 15 is a light load detection for detecting a light load state of the load 8. Reference numeral 12 denotes an AND circuit for inputting the light load detection signal LLD as the detection output of the light load detection circuit 15 and the oscillation output pulse 21a of the oscillator 21 for intermittent operation to switch the switch 13 which is normally on to the off state. Is.

In the switching power supply device of FIG. 6, when the load 8 is sufficiently large as much as the rated capacity of the power supply device, the switch 13 is always turned on to operate. Then, the switch element 5 is, for example, 100 kHz by the drive pulse 14a output from the switching power supply control circuit 14.
The ON / OFF operation (switching operation) is repeated continuously with.

On the other hand, when the load 8 becomes lighter,
Since the light load detection circuit 15 outputs the light load detection signal LLD of "H" indicating that it is in the light load state, every time the oscillation output pulse 21a of the oscillator 21 for intermittent operation becomes "H", the AND circuit 12 outputs. When the output becomes "H", the switch 13 is turned off and the switch element 5 is turned off. Therefore, for example, if the oscillator for intermittent operation 21 oscillates at 1 kHz and the "H" period of the output pulse 21a is equal to the "L" period, both of the "H" and "L" periods are Since it takes 0.5 ms, the switching element 5 has 10
Every time the switching operation of 0 kHz continues for 0.5 ms, the operation of resting for 0.5 ms and remaining in the off state is repeated.

In this way, when the load is light or no, the switching element 5 intermittently performs the switching operation.
It becomes possible to reduce the switching loss.

[0011]

However, in the above-mentioned conventional switching power supply device, it is necessary to prepare a dedicated oscillator in order to intermittently perform the switching operation of the switch element under light load or no load. There was a problem that the circuit became complicated. It is an object of the present invention to solve this problem and provide a switching power supply device that uses the waveform of an AC power supply instead of the oscillator for intermittent operation.

[0012]

In order to solve the above-mentioned problems, a switching power supply device according to claim 1 is a DC power supply (via a diode bridge 2) generated from an AC power supply (1) (of a capacitor 3). A drive pulse (14a) PWM-controlled (output from the switching power supply control circuit 14) with a semiconductor switch element (5) connected via inductive means (transformer 4 etc.) consisting of a transformer or a reactor between both ends). To open and close continuously (hereinafter, this opening and closing operation is called switching operation,
A switching power supply device that generates a stabilized DC power supply and supplies it to an external load (8), wherein a cycle of switching operation that is continuously repeated (for example, at 100 kHz) is referred to as a switching cycle. Timing signal generation means for generating a periodic timing signal (TM) using a waveform, and a light load detection signal (LLD) (from the light load detection circuit 15 or the like) indicating that the load has fallen below a predetermined value. When present, a switching that causes the semiconductor switching device to alternately repeat the continuous switching operation for a period including at least one switching period and maintaining an open state for a period including at least a plurality of switching periods in accordance with the timing signal. A device provided with loss reduction means (AND circuit 12, switch 13, etc.) That.

A switching power supply device according to claim 2 is
2. The switching power supply device according to claim 1, wherein the timing signal generating means has an instantaneous value of an amplitude of a rectified waveform of the AC power supply and a predetermined reference voltage (DC voltage 11 or base-emitter voltage of the transistor 18). It is assumed to be provided with a means (comparator 10, transistor 18 or the like) for comparing with.

A switching power supply device according to claim 3 is
The switching power supply device according to claim 2, wherein the rectified waveform of the AC power supply is a full-wave rectified waveform (obtained from the AC power supply 1 through the diode bridge 9). The switching power supply device according to claim 4 is the same as that according to claim 2.
In the switching power supply device described in the paragraph 1, the rectified waveform of the AC power supply is a half-wave rectified waveform (appears between one end of the AC power supply 1 and the ground of the switching power supply).

That is, the function of the present invention is to eliminate the conventional intermittent operation oscillator and use the AC power supply voltage instead of the oscillation output.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1) FIG. 1 shows the first embodiment of the present invention.
FIG. 6 is a circuit diagram showing a configuration of a main part as an embodiment of FIG. The light load detection circuit 15 may directly detect the light load state from the external load 8 as shown in the figure, or the output section of the switching power supply device, the inside of the switching power supply control circuit 14, or the like. From the above, the light load state of the load 8 may be detected or any of them may be detected.

In FIG. 1 and FIGS. 2 to 4 described below, the portion surrounded by the broken line corresponds to the conventional oscillator for intermittent operation. In FIG. 1, the broken line includes a diode bridge 9, a comparator 10, and a reference DC power supply 11. Further, FIG. 5 is a waveform diagram for explaining the operation of the main part of FIG. Next, the operation of FIG. 1 will be described with reference to FIG.

By passing the AC power supply 1 through the diode bridge 9, a full-wave rectified output 9a having a sine wave waveform can be obtained at the DC output terminal of the diode bridge 9. This full-wave rectified output 9a is input to one of the input terminals (+ input terminal in this example) of the comparator 10. Further, the reference DC power supply 11 is input to the other input terminal (-input terminal in this example) of the comparator 10.

As a result, the timing signal TM as the output of the comparator 10 is "H" when the full-wave rectified output 9a exceeds the voltage of the DC power supply 11, and "L" when it is other than the AC. The signal becomes a rectangular wave having a frequency twice that of the power supply 1. Now, at time t1, the light load detection circuit 1
Suppose that 5 detects a light load or no load and outputs a light load detection signal LLD of "H", then, every time the timing signal TM as a comparator output becomes "H", A
The output of the ND circuit 12 becomes "H" and the switch 13 is turned off.

Thus, after the time t1, the switch element 5 is turned on / off (switching operation) at a relatively high frequency (100 kHz in this example) as in the example of FIG.
And the resting operation that remains in the off state are repeated. In other words, the switching operation is performed intermittently. In FIG. 5, Ts indicates a period of switching operation of the switch element 5, and Th indicates a rest period of the switch element 5.

In this case, the frequency at which the switching operation is repeated intermittently is determined by the frequency of the AC power supply 1.
Although it cannot be arbitrarily set, it is possible to achieve the purpose of intermittently switching the switch element 5 under a light load or no load to reduce loss. In this embodiment, the switch 13 is used for intermittently performing the switching operation of the switch element 5, but instead of this, for example, the output of the AND circuit 12 stops the switching power supply control circuit 14 itself. The switching element 5 may be intermittently switched by the above method.

(Embodiment 2) FIG. 2 is a circuit diagram showing a structure of a main portion as a second embodiment of the present invention. In FIG. 2, the full-wave rectified output 9a of the diode bridge 9 of FIG.
Is divided by resistors 16 and 17 and input to the + input terminal of the comparator 10. In this case, compared with the operation of FIG. 1, the amplitude of the full-wave rectified output 9a is compared with the voltage dividing resistors 16, 1.
Since it can be easily changed by selecting 7, DC voltage 11
And the voltage dividing resistors 16 and 17 are selected, the switch at light load or no load as a period in which the divided voltage of the full-wave rectified output 9a (voltage at the + input terminal of the comparator 10) exceeds the reference DC voltage 11. Rest period Th of element 5
Will be easier to adjust.

(Embodiment 3) FIG. 3 is a circuit diagram showing a structure of a main portion as a third embodiment of the present invention. In FIG. 3, the comparator 10, the reference DC power supply 11 of FIG. 2 are replaced with a transistor 18, a resistor 19, and a DC power supply 20. In the circuit shown in FIG. 3, the full-wave rectified output 9a from the diode bridge 9 is divided by the voltage dividing resistors 16 and 17 and the voltage appearing at the resistor 17 does not reach a voltage capable of conducting between the base and emitter of the transistor 18. In the period,
The transistor 18 is in the off state, and the timing signal TM given from the collector of the transistor 18 to the AND circuit 12 becomes "H".

On the other hand, during the period in which the voltage appearing at the resistor 17 reaches the voltage at which the base and the emitter of the transistor 18 are conducted, the timing signal TM becomes "L" because the transistor 18 is in the ON state. Therefore, when the light load detection signal LLD is "H", the transistor 18 is in the off state (that is, the voltage of the resistor 17 which is the divided voltage value of the full-wave rectified output 9a becomes the base-emitter conduction voltage of the transistor 18 as the reference voltage). (When it does not reach), the timing signal TM is "H", and therefore the output of the AND circuit 12 is "H".
Then, the switch 13 is turned off.

Here, replacing the full-wave rectified output 9a and the DC voltage 11 in FIG. 5 with the voltage of the voltage dividing resistor 17 and the base-emitter conduction voltage of the transistor 18, respectively,
In the case of the third embodiment, the "H" period and the "L" period of the timing signal TM for the AC power supply 1 are opposite to those in FIG. 5, and therefore the switch after the light load detection signal LLD becomes "H" The switching period Ts and the rest period Th of the element 5 have a relationship where FIG.

Thus, instead of the comparator 10,
Even if the cheaper transistor 18 is used, a rectangular-wave-shaped timing signal TM signal can be obtained, and the switch element 5 can be intermittently operated for switching under light load or no load. (Embodiment 4) FIG. 4 is a circuit diagram showing a structure of a main portion as a fourth embodiment of the present invention. In FIG. 4, the diode bridge 9 used in FIG. 1 is omitted.

In this case, the AC power supply 1 to the comparator 1
The voltage input to 0 has a substantially half-wave rectified waveform due to the diode bridge 2 on the switching power supply side. When this half-wave rectified waveform is used, the frequency of the intermittent operation when the switch element 5 is intermittently switched at the time of light load or no load becomes the same as the frequency of the AC power supply voltage, which is different from the case of FIG. However, there is no difference in that the effect of intermittently switching the switch element 5 can be obtained.

[0028]

According to the present invention, when the switching power supply device that obtains the stabilized DC power supply from the AC power supply is lightly loaded or unloaded, it is possible to match the periodic timing signal generated by using the waveform of the AC power supply. , The intermittent switching operation is performed by alternately repeating the continuous switching operation of the switching element and the maintenance of the OFF state of the switching element. Therefore, for the intermittent operation to obtain the periodic timing signal as in the past. It is possible to easily and inexpensively reduce the loss of the switching power supply device under a light load or no load without using an oscillator.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of a main part as a first embodiment of the present invention.

FIG. 2 is a circuit configuration diagram of a main part as a second embodiment of the present invention.

FIG. 3 is a circuit configuration diagram of a main part as a third embodiment of the present invention.

FIG. 4 is a circuit configuration diagram of a main part as a fourth embodiment of the present invention.

5 is a waveform diagram of each part for explaining the operation of FIG.

FIG. 6 is a circuit configuration diagram of a main part of a conventional switching power supply device.

[Explanation of symbols]

1 AC power supply 2 Diode bridge 3 Capacitor 4 Transformer 5 Switch element 6 Diode 7 Capacitor 8 Load 9 Diode bridge 10 Comparator 11 DC power supply 12 AND circuit 13 Switch 14 Switching power supply control circuit 14a Drive pulse 15 Light load detection circuit 16, 17 Resistor 18 Transistor 19 Resistor 20 DC power supply TM Timing signal LLD Light load detection signal

Claims (4)

[Claims] 1. A semiconductor switch element connected between a DC power supply generated from an AC power supply via an inductive means composed of a transformer or a reactor, is repeatedly opened and closed by a PWM-controlled drive pulse (hereinafter An operation of opening and closing is called a switching operation, and a cycle of continuously repeated switching operations is referred to as a switching cycle), which is a switching power supply device that generates a stabilized DC power supply and supplies it to an external load. Timing signal generating means for generating a periodic timing signal using the waveform of, in the presence of a light load detection signal indicating that the load is below a predetermined value, in accordance with the timing signal, the semiconductor switch element, At least the above-mentioned continuous switching operation over a period including at least one switching period; Switching power supply device is characterized in that a switching loss reduction means for alternately and maintenance of the open state over a period including a switching period of a few. 2. The switching power supply device according to claim 1, wherein the timing signal generating means includes means for comparing an instantaneous value of the amplitude of the rectified waveform of the AC power supply with a predetermined reference voltage. A characteristic switching power supply. 3. The switching power supply device according to claim 2, wherein the rectified waveform of the AC power supply is a full-wave rectified waveform. 4. The switching power supply device according to claim 2, wherein the rectified waveform of the AC power supply is a half-wave rectified waveform.