JPH10323027A - Power supply circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power supply circuit by which a battery can be efficiently utilized in an electronic apparatus having a DC-DC converter as a power supply circuit, by a method wherein an optimum frequency is set in accordance with the change of the consumed current value of a load. SOLUTION: A CPU 7 judges an optimum oscillation frequency successively in accordance with the change of the consumed current value of a load, and turns on one transistor included in a group of oscillation frequency changing transistors. By turning on the one transistor, one RC circuit 5 connected to its emitter is selected, and an oscillation frequency with which a high conversion efficiency can be obtained is set.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a power supply circuit,
In particular, the present invention relates to a power supply circuit for an electronic device including a DC-DC converter.

[0002]

2. Description of the Related Art Conventionally, a portable electronic device powered by a battery such as a digital camera or a PHS usually includes a DC-DC converter as a power supply circuit for supplying power to a load. The DC-DC converter is a circuit for keeping the output voltage constant even when the battery voltage fluctuates.
The principle block diagram is shown in FIG.

In FIG. 3, a battery voltage is applied to Vin, and power is supplied from Vout to a load as an output voltage. The oscillation circuit 3 performs switching of the transistor 2, and the oscillation frequency at that time is determined by the RC circuit 5 having one time constant. During the ON period of the transistor 2, energy flows through the coil 1 due to a current flowing from Vin. Transistor 2 OFF
During the period, the energy stored in the coil 1 is supplied to the Vout side. At that time, it is rectified by the diode 4,
It becomes a constant voltage.

The oscillation circuit 3 monitors Vout. V
The output voltage is maintained at a constant value by changing the duty ratio of the switching waveform of the transistor 2 according to the fluctuation of out. The above is the operation principle of the DC-DC converter.

[0005]

However, in the conventional DC-DC converter, the oscillation frequency greatly affects the energy conversion efficiency. The optimum value of the oscillation frequency for increasing the conversion efficiency changes depending on conditions such as the input voltage and the current consumption on the output side. Here, even with the same electronic device, the current consumption value changes depending on the type of operation and the like.

The oscillation frequency of a DC-DC converter in one electronic device is fixed. In this case, a situation occurs in which the optimum oscillation frequency in one operation is not optimum in another operation, and this is an inefficient use of the battery.

An object of the present invention is to provide a DC-D power supply circuit.
It is an object of the present invention to provide a power supply circuit that can effectively use a battery by setting an optimum oscillation frequency in accordance with a change in a current consumption value of a load in an electronic device including a C converter.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a DC-DC converter capable of converting the battery output into a constant voltage DC power and varying the oscillation frequency for supplying power to a load. And a variable control means for varying the oscillation frequency according to the output current of the DC converter.

According to the above configuration, in an electronic device or the like,
A power supply circuit with high energy conversion efficiency is realized by changing the oscillation frequency of the DC-DC converter according to the change in the current consumption value of the load.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit block diagram of an embodiment of a power supply circuit according to the present invention. In the figure, 1 is a coil, 2 is a switching transistor, 3
Is an oscillation circuit, 4 is a diode, 5 is an RC circuit group each having one time constant, 6 is an oscillation frequency switching transistor group, and 7 is a CPU.

FIG. 2 is a diagram for explaining the operation principle of the present invention. The horizontal axis represents the output current of the DC-DC converter, and the vertical axis represents the energy conversion efficiency for each oscillation frequency. The specific operation of the power supply circuit configured as described above will be described below with reference to FIGS.

In FIG. 1, it is assumed that a battery voltage is applied to Vin and a constant voltage is output from Vout. The oscillation circuit 3 performs switching of the transistor 2. The oscillation frequency at that time is determined by one RC circuit included in the RC circuit group 5.

During the ON period of the transistor 2, energy flows through the coil 1 due to a current flowing from Vin. During the OFF period of the transistor 2, the energy stored in the coil 1 is supplied to the Vout side. that time,
It is rectified by the diode 4 and becomes a constant voltage.

The oscillation circuit 3 monitors Vout. V
The output voltage is maintained at a constant value by changing the duty ratio of the switching waveform of the transistor 2 according to the fluctuation of out.

Here, the CPU 7 performs the following operation. In FIG. 2, the relationship between the output current of the DC-DC converter and the optimum oscillation frequency is obtained in advance from Experiment 2 and stored as data in a memory unit in the CPU 7. For example, when the output current of the DC-DC converter is ia or a value near ia, the oscillation frequency is f
It is assumed that the energy conversion efficiency is highest when a. Similarly, in the case of ib, fb, in the case of ic, fc
Is the optimum oscillation frequency.

The CPU 7 sequentially determines an optimum oscillation frequency in accordance with a change in a current consumption value of a load of the electronic device. Then, based on the determination, one transistor included in the oscillation frequency switching transistor group 6 is turned on. When one transistor is turned on, one RC circuit connected to its emitter is selected,
The oscillation frequency is determined. The power supply circuit operates as described above.

[0017]

As described above, according to the present invention, in an electronic device having a DC-DC converter as a power supply circuit, an optimum oscillation frequency is sequentially determined according to a change in a current consumption value of a load, and the oscillation is determined. By selecting the RC circuit corresponding to the frequency, the energy conversion efficiency of the DC-DC converter can be increased, and an efficient use of the battery can be realized.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram of an embodiment of a power supply circuit according to the present invention.

FIG. 2 is a diagram illustrating the operation principle of the embodiment of the power supply circuit according to the present invention.

FIG. 3 is a circuit block diagram of a conventional power supply circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Coil 2 Switching transistor 3 Oscillation circuit 4 Diode 5 RC circuit (group) 6 Oscillation frequency switching transistor group 7 CPU

Claims (1)

[Claims] 1. A DC-DC converter that converts a battery output into DC power of a constant voltage and supplies an electric power to a load, and a variable DC-DC converter that changes the oscillation frequency according to an output current of the DC-DC converter. A power supply circuit having control means.