1. Field of the Invention
The present invention relates to a battery remaining amount warning circuit applicable to an electrical product or electronic device using a battery.
2. Description of the Related Art
Today, many electrical products and electronic devices use batteries. As a conventional method for warning about a remaining amount of a battery, it is a general practice that a battery voltage is measured and a warning about the remaining amount is issued when the battery voltage falls below a specified value or DC resistance of the battery increases.
There are a variety of types of battery such as alkaline cell, nickel hydrogen cell, nickel cadmium cell, and there are also a variety of battery characteristics. However, with a monitoring of the battery voltage alone, depending on the type of the battery, the battery power may not be used to the full because a considerable amount of the battery can still be used after the warning is given about the insufficient remaining amount of the battery.
Furthermore, there is also a proposal of a method for constantly measuring a battery voltage by providing a dummy-load circuit (Japanese Patent Publication No. 63-3538). However, this method increases unnecessary power consumption.
There is also a proposal of a method for deciding whether a camera operates normally or not based on a boosting operation of a booster circuit when a flash capacitor is charged (Japanese Patent Application Publication No. 2000-56370), but when no flash is used or can be used, there is no way to decide it.
Furthermore, when the remaining amount of the battery is predicted from the battery voltage, the voltage varies depending on the type of the battery and when the battery voltage is low because of the nature of the type of the battery, a warning is issued earlier. For example, a warning is issued with an alkaline cell at 1.5 V/cell and with a NiCd cell at 1.2 V/cell.