Black Decker Inc.

Frank Faez Athari

Tomy Sebastian

Larry T Albert

A self-oscillating buck mode battery charger apparatus 10. The apparatus 10 includes a main switching transistor 22, a first control transistor 34 and a second control transistor 36. The control transistors 34 and 36 are arranged such that neither control transistor sees the full input mains voltage across input terminals 12 of the apparatus 10 when the switching transistor 22 is turned off. An alternative embodiment of the invention includes a high and low main sensing circuit 102 in which a controller 120 is used to detect an excessively high mains voltage condition as well as an undesirably low mains voltage condition. The controller 120 turns off a PWM control circuit 104 when either condition is present for a predetermined length of time. Turning off the PWM control circuit 104 causes the main switching transistor 106 to be turned off, thereby preventing damage to the components of the charger apparatus 100. The charger apparatus is especially well-suited for applications where a rectified DC mains voltage is used to provide a charging current to a rechargeable battery.

Self-oscillating buck mode battery charger

The pulse width modulated DC motor speed control circuit indirectly senses motor current using sense MOSFETs and a peak detector circuit with storage capacitor for deriving an average motor current signal. The average motor current signal is used both in the feedback loop of the pulse width modulated speed control circuit and also in the motor shutoff or clutch circuit. The clutch circuit shuts off power to the motor when a user-settable torque is reached. The motor speed control circuit is therefore adapted for use in hand-held DC power tools such as screwdrivers and nutdrivers which stop rotation at a predefined torque.

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Baltimore, MD, United States of America

Frank Faez Athari