JP2555245Y2 - High efficiency power supply circuit - Google Patents

Description

[Detailed description of the invention]

[0001]

[Purpose of the invention]

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-efficiency power supply circuit such as a DC-DC converter particularly suitable for portable equipment such as personal computers.

[0003]

2. Description of the Related Art In portable equipment such as a personal computer, a DC-DC converter is used as a power supply. FIG. 2 shows a basic configuration of the DC-DC converter. D
C-DC converter is ON / OFF by external signal
, A switching element 21 composed of a bipolar or MOS transistor, an inductor element 22 such as a coil for storing energy or a choke for converting the magnitude of voltage, a smoothing capacitor 23 and a rectifying diode 24
It consists of.

The basic operation is as follows. First,
When the switching element 21 is turned on, a current I0n flows, and energy is supplied from the input side to the output side. Also,
When the switching element 21 is turned off, a current I0ff flows, and the energy stored in the inductor 22 is released. At this time, part of the energy stored in the inductor 22 is lost due to the forward voltage drop of the rectifier diode 24.

FIG. 3 shows a configuration of a DC-DC converter improved to reduce the loss due to the diode.
That is, a switching element 31 for performing bidirectional switching control in synchronization with the switching element 21 different from the switching element 21 is added to the configuration shown in FIG. The relationship between these timing operations is as follows.
When 1 is ON, the switching element 31 is OFF,
The switching element 31 is turned on when the switching element 21 is turned off. The fact that the voltage drop between the source and the drain of the bidirectional switching element 31 is much smaller than the forward voltage drop of the diode 24 is used.

[0006]

[Problem to be solved by the invention] In the configuration shown in FIG.
In the operation mode in which the switching element 21 is turned on after the energy stored in the inductor 22 is completely released, that is, when extra energy not consumed by the load returns to the power supply side, the extra energy not consumed by the load Is also temporarily stored as magnetic energy in the inductor 22,
This returns to the power supply in the form of electrical energy. As described above, since energy returns from the light load side to the power supply side, power loss sometimes occurs, and power supply efficiency is reduced.
Therefore, power cannot be supplied to a load having a large fluctuation under any load condition. In order to avoid this with the circuit configuration shown in FIG. 3, the capacity of the inductor 22 increases.

The present invention has been made in view of the above circumstances, and has as its object to provide a high-efficiency power supply circuit capable of efficiently supplying power even under a light load.

[0008]

[Structure of device]

[0009]

The present invention comprises a first switching element which is turned on / off by an external signal, an inductor for supplying energy to a load according to a state of the first switching element, a rectifying diode, and a smoothing capacitor. In the DC-DC converter configured, a second switching element connected in parallel with the rectifier diode and performing on / off control in both directions in synchronization with the first switching element, and the rectifier diode and the second switching element A comparator that detects a voltage drop, detects a direction of a current flowing through the inductor, and turns on and off the second switching element.

[0010]

In the configuration described above, the direction of the current flowing through the inductor is detected by the comparator, and the ON / OFF of the second switching element is controlled by the output of the comparator, thereby realizing a highly efficient power supply even at a light load. I do. As a result, the efficiency does not decrease even at a light load,
Further, it is not necessary to increase the inductor capacitance.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of the present invention.

In the figure, 11 is turned on by an external signal
A switching element composed of a bipolar or MOS transistor for turning on / off, 12 is a coil for storing energy or an inductor element such as a choke for converting the magnitude of voltage, and 13 is a smoothing capacitor. Reference numeral 14 denotes a switching element different from the switching element 11 for performing bidirectional switching control in synchronization with the switching element 11. A comparator 15 detects a voltage drop of the switching element 14, detects a direction of a current flowing through the inductor 12, and turns on / off the switching element 14 according to the direction. Here, 16 and 17 are parasitic diodes.

Hereinafter, the operation of the embodiment of the present invention will be described in detail. In the figure, first, the switching element 11
When the switching element 11 becomes N, if the switching element 14 is ON (in which operation mode the switching element is ON will be described later), the switching element 11 → the switching element 1
A current indicated by Ion1 flows through a path from 4 to GND. A signal (high-level signal) that is turned on by the output of the comparator 15 is given to the switching element 14.
When the current Ion flows, a slight voltage drop occurs at both ends of the switching element 14, and a point indicated by a in the figure has a polarity of (+) and a point b has a polarity of (-). Then, the output of the comparator 15 switches to low level, and the switching element 14 is turned off. Even when the current stops flowing through the switching element 14, the output of the comparator 15 is at the low level. When the switching element 14 is turned off, a current Ion2 starts flowing from the power supply side to the load side.

Next, when the switching element 11 is turned off, the energy stored in the inductor 12 is released and a current Ioff1 flows. At this time, the switching element 14 is OFF, but first flows through the parasitic diode 17 of the switching element 14. At this time, point a is (-), b
Since the point becomes (+), the output of the comparator 15 becomes high level, and the switching element 14 is turned on. The voltage drop at the switching element 14 at this time is considerably small, and compared with the conventional method using a diode,
Efficiency will be improved. If the switching element 11 is turned on before the energy stored in the inductor 12 is completely released, the same operation is repeated from the state described at the beginning of this operation description.

Next, even if the switching element 11 is turned off and the energy stored in the inductor 12 is completely discharged, if the switching element 11 is not turned on yet, that is, if the load is light, the energy stored in the capacitor 13 is stored. Energy flows through the inductor 12 to the GND side, and a current I0ff flows. At this time, point a is (+) and point b is (-).
Therefore, a low-level signal is supplied to the switching element 14, and the switching element 14 is immediately turned off. Therefore, since this current does not flow, there is no operation mode in which power returns from the load side to the power supply side. That is, the power supply efficiency does not decrease even when the load is light. Actually, since the comparator 15 turns off the switching element 14 only after the current Ioff2 flows, only a small amount of power is stored in the inductor 12 during this time.
Although the power returns to the power supply side through the current path Ioff3, the returned power is extremely small and the power lost in this mode is even smaller, so that there is no problem in practical use.

[0016]

As described above, according to the load of the present invention, the efficiency does not decrease even under a light load, and the inductor capacity does not need to be increased, which contributes to cost reduction.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention;

FIG. 2 is a circuit diagram showing a conventional example,

FIG. 3 is a circuit diagram showing a conventional example.

[Explanation of symbols]

 11, 14 ... Switching element 12 ... Inductor 13 ... Capacitor 15 ... Comparator 16, 17 ... Parasitic diode

Claims (1)

(57) [Scope of request for utility model registration] 1. A DC-DC converter comprising a first switching element that is turned on / off by an external signal, an inductor that supplies energy to a load according to a state of the first switching element, a rectifier diode, and a smoothing capacitor. A second switching element connected in parallel with the rectifier diode and performing on / off control in both directions in synchronization with the first switching element, and a voltage drop caused by the rectifier diode and the second switching element, and detected by the inductor. A high-efficiency power supply circuit comprising: a comparator that detects a direction of a flowing current and turns on and off a second switching element.