Electrical Apparatus Connected With A Battery Charger System

What is this patent about?

'656 is related to the field of battery charger systems, specifically those used in small, cordless electrical devices like electric shavers and toothbrushes. These devices require fast charging capabilities to provide sufficient power for a single use, but overcharging can damage the battery. The prior art includes timer-based systems to control charging current, but these are often too large or expensive for small devices, or they have limitations in repeated fast-charging cycles.

The underlying idea behind '656 is to use a capacitor-based timer to control the fast-charging period, but with a circuit that allows for repeated fast charges without overcharging the battery. The capacitor charges during battery charging and discharges during battery usage. The key is to use the capacitor's voltage to control a switch that regulates the charging current, allowing a large current for fast charging initially, then switching to a smaller current for normal charging once the capacitor reaches a certain voltage.

The claims of '656 focus on an electrical apparatus with a battery charger system, comprising a rechargeable battery, a charge current source, a charge current controller, an electrical load, a switch, a switch operator, and a fast-charging-period controller. The fast-charging-period controller includes a capacitor that charges proportionally to the battery's charge and discharges proportionally to the battery's discharge, and controls the charge current based on the capacitor's voltage.

In practice, the capacitor's charging and discharging characteristics determine the fast-charging period. When the battery is low, the capacitor is discharged, allowing a large charging current to flow. As the capacitor charges, its voltage rises, eventually triggering a switch to reduce the charging current to a trickle charge. When the device is used, the capacitor discharges, resetting the timer for the next fast-charge cycle. This allows for repeated fast charges without relying on a fixed timer duration.

The invention differentiates itself from prior approaches by incorporating a thermosensitive resistor thermally coupled to a transistor in the switching circuit. This resistor influences the capacitor's discharge rate based on the transistor's temperature, which is related to the load current and usage time. This dynamic adjustment of the discharge rate prevents overcharging by shortening the fast-charging period if the battery was not fully discharged during the previous use, ensuring that only the necessary amount of charge is delivered.