JPH1127936A - Switching power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow a load to operate with a high efficiency, regardless of its variation and prevent the waste of power. SOLUTION: In switching circuit sections 21, 22 for stabilizing the output voltage to be applied to a load, a plurality of systems having different efficiency for various currents are installed. A current value detecting section 23 is also installed for detecting the value of a current to be supplied to the load. According to the value of the current detected by the current value detecting section 23, either one of the switching circuit section 21, 22 that has the more efficient switch-on time is selected and operated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a switching power supply, and more particularly to a switching power supply for supplying power to a device that causes a load change.

[0002]

2. Description of the Related Art FIG. 4 schematically shows a circuit configuration of a conventional switching power supply. This switching power supply is an AC power supply 1
From the power supply voltage of +24 volts and the output power supply b of, for example, +5 volts, to the loads R1 and R2, respectively. As shown
A primary electrolytic capacitor 3 is connected between both output terminals of a rectifier diode bridge circuit 2 for inputting an AC power supply 1 and performing full-wave rectification, and a primary element composed of a field effect transistor is connected between both terminals of the primary electrolytic capacitor 3. The primary winding 5a of the transformer 5 is connected via the side switching element 4.

[0003] A first secondary-side electrolytic capacitor 7 is connected to a secondary winding 5b of the transformer 5 via a rectifier circuit 6 composed of a diode.
Between the two terminals is the output power source a. Further, a PN is connected to a secondary winding 5b of the transformer 5 through the rectifier circuit 6.
A series circuit of a secondary switching element 8 composed of a P-type transistor, a choke coil 9 and a second secondary electrolytic capacitor 10 is connected, and the output between the two terminals of the second secondary electrolytic capacitor 10 is output. Power supply b.

The primary side switching element 4 is controlled by a primary side pulse width modulation (PWM) control circuit 11 to switch on and off times. The primary side pulse width modulation control circuit 11 uses the output voltage of the output power source a via a feedback circuit (not shown) to output the primary side switching element 4.
Is modulated to stabilize the output voltage of the output power supply a.
The secondary-side switching element 8 is controlled by a secondary-side pulse width modulation control circuit 12 to switch on and off times. The secondary-side pulse width modulation control circuit 12 outputs an output power source b fed back via a feedback circuit (not shown).
Modulates the pulse width of a signal for switching the secondary switching element 8 on and off with the output voltage of
The output voltage of the output power supply b is stabilized.

As described above, in this type of conventional switching power supply, an output power supply a is obtained by the switching element 4 whose switch-on / off time is controlled by the primary-side pulse width modulation control circuit 11, and the secondary-side switching power supply is obtained. An output power source b is obtained by the switching element 8 whose switch on / off time is controlled by the pulse width modulation control circuit 12,
One switching element is operated for one output power supply to obtain an output power supply of a required voltage. For this reason, a transistor for a large current has been used as a switching element so that it can cope with an increase in current flowing into the loads R1 and R2 due to an increase in the loads R1 and R2.

[0006]

As described above, in this type of conventional switching power supply, a transistor for a large current is used as a switching element, so that the load is small and the current flowing into the load is small. There is a problem in that the loss consumed by the transistor is increased, the power is wasted, and the efficiency is low. Therefore, an object of the present invention is to provide a switching power supply that can always operate with high efficiency irrespective of load fluctuation and can prevent waste of power.

[0007]

According to the present invention, a plurality of systems having different current efficiencies are provided as switching circuit units for stabilizing an output voltage applied to a load. Further, a current value detection unit for detecting a current value supplied to the load is provided. Then, according to the current value detected by the current value detection section, one of the plurality of switching circuit sections having the most efficient switch-on time is selected and operated.

[0008] Specifically, a first switching circuit section that performs a switching operation during a first switch-on time to stabilize an output voltage applied to a load, and a second switching circuit section that is shorter than the first switch-on time. A second switching circuit that operates during the switch-on time to stabilize the output voltage applied to the load, a current value detector that detects a current value supplied to the load, and a current value detected by the current value detector. A comparing unit for comparing whether the current value is larger than a preset reference value, and operating the first switching circuit unit when the current value is larger than the reference value by the comparing unit; And a switching circuit selecting unit for operating. In this device, the current value detecting section is a resistor for converting the current supplied to the load into a voltage, and the comparing section takes in the potential difference between both ends of the resistor and switches the output signal to the switching circuit selecting section depending on the magnitude of the potential difference. It is a comparator.

[0009]

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

In this embodiment, the present invention is described with reference to FIG.
In the switching power supply shown in FIG. 5, the load R1 to which the output power a is supplied is constant but the load R2 to which the output power b is supplied is variable, and the same parts as those in FIG. The detailed description is omitted.

FIG. 1 is a schematic diagram showing a circuit configuration of a switching power supply according to this embodiment. One of the differences from the switching power supply shown in FIG.
As a switching circuit section for stabilizing the output voltage of the output power supply b supplied to the power supply, a secondary-side switching element 8, a choke coil 9, an electrolytic capacitor 10, and a switch of the above-mentioned switching element 8, which are conventional PNP transistors. A first switching circuit section 21 constituted by a secondary-side pulse width modulation control circuit 12 for controlling ON / OFF
Separately, a second-side switching element 13, which is also a PNP transistor, a choke coil 14, an electrolytic capacitor 15, and a second-side pulse width modulation control circuit 16 for controlling the switching on and off of the switching element 13 The second switching circuit unit 22 is provided in parallel with the first switching circuit unit 21. Another difference is that a difference between a resistor 23 connected to the output terminals of the first switching circuit section 21 and the second switching circuit section 22 and a voltage generated at both ends of the resistor 23 is detected, and A comparator 24 that changes an output signal according to the difference, and a secondary-side pulse width modulation control circuit 12 and a secondary-side switching element 8 in a first switching circuit unit 21 are connected according to an output signal from the comparator 24. And the second switching circuit section 2
2 is provided with a selection circuit 25 for selecting whether the secondary side pulse width modulation control circuit 16 and the secondary side switching element 13 are separated or vice versa.

The first switching circuit section 21 is designed so that the efficiency is improved when the variable load R2 is large and the current flowing into the load R2 is large. On the other hand, the second switching circuit section 22 is designed to improve the efficiency when the variable load R2 is small and the current flowing into the load R2 is small. That is, as shown in FIG. 2A, the secondary side pulse width modulation control circuit 12 of the first switching circuit section 21 is configured to output a signal having a long switch-on time T1, and A transistor corresponding to a large current is used as the switching element 8. On the other hand, as shown in FIG. 2B, the secondary-side pulse width modulation control circuit 16 of the second switching circuit unit 22 is configured to output a signal with a short switch-on time T2, and As the switching element 13, a transistor corresponding to a small current is used. The output signal from the secondary pulse width modulation control circuit 12 and the secondary pulse width modulation control circuit 16 are controlled so that the oscillation frequency of the secondary switching element 8 and the oscillation frequency of the secondary switching element 13 match. Has the same period as that of the output signal from.

The resistor 23 is connected to the first switching circuit 2
It detects a current value output from the first and second switching circuit units 22 and supplied to the variable load R2, and functions as a current value detection unit. As shown in FIG. 3, the comparator 24 determines whether the potential difference Δ between the voltages input to the positive terminal (+) and the negative terminal (−) is a predetermined threshold value S,
When it is smaller than HL, a low level “L” signal is output,
When the potential difference Δ exceeds the threshold value SHL, a high level “H” is set.
And functions as a comparison unit. The selection circuit 25 connects the secondary side pulse width modulation control circuit 16 and the secondary side switching element 13 of the second switching circuit section 22 when the output signal from the comparator 24 is a low level “L” signal. When the output signal from the comparator 24 is a high level “H” signal, the secondary side pulse width modulation control circuit 12 of the first switching circuit unit 21
And the secondary-side switching element 8 and functions as a switching circuit selection unit.

In the present embodiment configured as described above, when the variable load R2 is large and the current flowing into the load R2 is large, the value of the current flowing through the resistor 23 is also large. As a result, the voltage difference generated between both ends of the resistor 23 also increases, and the potential difference Δ exceeds the threshold value SHL preset in the comparator 24.
4 is at a high level "H". As a result, the selection circuit 25 connects the secondary-side pulse width modulation control circuit 12 of the first switching circuit unit 21 to the secondary-side switching element 8, and the secondary-side switching element 8 oscillates,
The output power b is supplied to the variable load R2. This output power b
Is fed back to the secondary side pulse width modulation control circuit 12 by a feedback circuit (not shown), and the output voltage of the output power supply b is stabilized.

Thereafter, when the variable load R2 decreases and the current flowing into the load R2 decreases, the value of the current flowing through the resistor 23 also decreases. As a result, the difference between the voltages generated at both ends of the resistor 23 also becomes small, and when the potential difference Δ becomes equal to or less than the threshold value SHL preset in the comparator 24,
The output signal of the comparator 24 switches to low level “L”. As a result, the selection circuit 25 disconnects the secondary-side pulse width modulation control circuit 12 of the first switching circuit unit 21 from the secondary-side switching element 8, and controls the secondary-side pulse width modulation control of the second switching circuit unit 22. The circuit 16 and the secondary-side switching element 13 are connected. As a result, the secondary switching element 13 oscillates and supplies the output power b to the variable load R2. This output power supply b is fed back to the secondary side pulse width modulation control circuit 16 by a feedback circuit (not shown), and the output voltage of the output power supply b is stabilized.

As described above, according to the present embodiment, the first switching circuit unit 21 which is efficient with respect to a large current is provided as a switching circuit unit for stabilizing the output voltage applied to the load R2. And two systems of the second switching circuit section 22 which are efficient with respect to a small current. Also, a resistor 23 is provided as a current value detecting unit for detecting a current value supplied to the load R2, and a comparator 24 is provided as a comparing unit for comparing whether the current value detected by the resistor 23 is larger than a preset reference value. ,further,
A selection circuit 25 is provided as a switching circuit selection unit. The selection circuit 25 allows the comparator 2
In 4, when the current value is determined to be larger than the reference value, the first switching circuit section 21 is operated, and when it is determined to be smaller, the second switching circuit section 22 is operated.

Therefore, the variable load R2 is large and the load R
When the current flowing into the load 2 is large, the output voltage of the output power source b can be stabilized by operating the first switching circuit unit 21 which is efficient with respect to the large current, and the variable load R2 is small and the current flowing into the load R2. Is small, the output voltage of the output power source b can be stabilized by operating the second switching circuit section 22 which is efficient with respect to a small current, so that it can always operate with high efficiency regardless of the fluctuation of the load R2. . As a result, it is possible to prevent waste of power and contribute to energy saving.

In the above-described embodiment, the switching circuit units 21 and 22 are described as having two systems. However, by setting the threshold value in the comparison unit in multiple stages, three or more switching circuit units are provided so that more efficiency can be obtained. Switching power supply may be configured. In the embodiment, the pulse width modulation control circuit 1 is provided for each of the switching circuit units 21 and 22.
2, 16 are provided, but a common pulse width modulation circuit is used for each switching circuit unit, and the switching circuit selection unit connects the shared pulse width modulation control circuit to the most efficient switching circuit unit. Thus, the output voltage may be stabilized.

[0019]

As described in detail above, according to the present invention,
It is possible to provide a switching power supply that can always operate with high efficiency irrespective of load fluctuations and can prevent waste of power.

[Brief description of the drawings]

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

FIG. 2 is an explanatory diagram of a pulse width modulation control circuit in the embodiment.

FIG. 3 is an explanatory diagram of a comparator according to the embodiment;

FIG. 4 is a circuit diagram schematically showing a configuration of a conventional switching power supply.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... AC power supply 2 ... Rectifier diode bridge circuit 3 ... Primary side electrolytic capacitor 4 ... Primary side switching element 5 ... Transformer 6 ... Rectifier circuit 7, 10, 15 ... Secondary side electrolytic capacitor 8, 13 ... Secondary side switching Elements 9, 14 Choke coil 11 Primary pulse width modulation control circuit 12, 16 Secondary pulse width modulation control circuit 21 First switching circuit section 22 Second switching circuit section 23 Resistance (current Detection unit) 24 comparator (comparison unit) 25 selection circuit (switching circuit selection unit)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI H02M 3/28 H02M 3/28 F

Claims (3)

[Claims] 1. A switching circuit for stabilizing an output voltage applied to a load, a plurality of systems having different current efficiencies are provided, and a current value detecting unit for detecting a current value supplied to the load is provided. One of the plurality of switching circuit sections having the most efficient switch-on time is selected and operated according to the current value detected by the current value detection section. Switching power supply. 2. A first switching circuit for performing a switching operation in a first switch-on time to stabilize an output voltage applied to a load, and a second switch-on shorter than the first switch-on time. A second switching circuit that operates over time to stabilize the output voltage applied to the load, a current value detector that detects a current value supplied to the load, and a current value detected by the current value detector. A comparing unit for comparing whether the current value is larger than a preset reference value, and operating the first switching circuit unit when the current value is larger than the reference value by the comparing unit; And a switching circuit selecting section for operating the switching circuit section. 3. A current value detecting section is a resistor for converting a current supplied to a load into a voltage, and a comparing section takes in a potential difference between both ends of the resistor and outputs an output signal to a switching circuit selecting section based on the magnitude of the potential difference. 3. The switching power supply according to claim 2, wherein the switching power supply is a comparator for switching.