Control circuit for controlling the driving of a dc motor

When a switch 12 is turned on, a relay coil 14b is excited by a current generated at the very moment when electric power of a dc power source 11 is supplied to a condenser 16 for actuation. Accordingly, a relay contact 14a is closed, and the power is given to a dc motor 15 via the switch 12 and the relay contact 14a. As a result, the dc motor 15 is actuated. At the same time, a part of a current running through the dc motor 15 is supplied to the relay coil 14b and brings about self-hold by which the dc motor 15 remains running. After that, when the driving of a device to be driven is forcibly regulated, an excess current passing through the dc motor 15 flows to a PTC thermistor (positive temperature coefficient thermistor) 13 which is connected in series to the dc motor 15. Owing to the excess current, the temperature of the PTC thermistor 13 is raised, and thereby the resistance of the PTC thermistor 13 is heightened. As a result, the relay contact 14a is opened to stop the dc motor 15. In a motor control circuit thus constructed, in order to prevent chattering which occurs when the dc motor 15 is operated to stop, and prevent the delay of the stop of the dc motor 15 and, additionally, lengthen the service life of the relay contact 14a, the PTC thermistor 13 is disposed to be in parallel with the condenser 16 with respect to the dc power source 11.