Protection circuit for d.c. motors

Claim 1

A protective circuit for a d.c. motor driving a load that may experience excessive increases, such as paper jamming in a paper feeder driven by the motor, comprising: first circuit means connected to the motor for monitoring current flow therethrough and providing a signal representative thereof; transistor-switching means connected in series with the motor for controlling the current flow through the motor; a second circuit means including a bistable multivibrator and RC circuit means connected to inputs of the bistable multivibrator to render the multivibrator monostable and astable, depending upon a signal level applied to the inputs, the multivibrator connected to the transistor-switching means for operating the same; and the first circuit means connected to inputs providing thereto said first signal operating said multivibrator as a monostable multivibrator in response to said first signal in a first range for causing the transistor-switching means to turn the motor on intermittently whenever the multivibrator is in the astable state pursuent to its operation as an astable device and operating the multivibrator as a monostable multivibrator in response to said first signal in a second range.