Abstract: A frequency slider circuit for reducing power dissipation in the form of switching losses in a switching device when the switching device is near its desired maximum temperature limit is disclosed herein. The switching device controls an electric load, such as a motor. The frequency slider circuit samples a current of the switching device. The frequency slider circuit then uses a current transducer to convert the current to a signal level. The signal level is then processed by a model of the thermal response of the switching device. The output of the thermal model is compared to a reference signal, and if the output of the thermal model is greater than the reference signal, the switching frequency of the switching device will be lowered gradually to keep the power generated during the switching periods to be below a predetermined value. A minimum frequency clamping circuit is included to ensure that the switching frequency never drops below a minimum value, to ensure stable operation of the switching device.

Abstract: A dc motor drive includes a current limit circuit which produces a current limit signal that inhibits motor current to its commutation limit over a wide speed range. The current limit circuit includes an analog divider circuit which produces an output signal which decreases as an inversed function of motor speed.

Abstract: A pilot light as might be used for monitoring an industrial control circuit having a normal signal circuit connectable to a control circuit element for illuminating a lamp of the pilot light when such control circuit element is operated, and also having a test circuit connectable to a test switch for testing the integrity of the lamp when the test switch is operated. A circuit for supplying current to the lamp is light coupled to both the normal signal circuit and the test circuit.

Abstract: A switch circuit includes an input section which is connected to a detector section by a pair of leads. The input section draws a minimum current at all times through these leads and it draws more current when a shutter is operated to expose a photo sensor to a light source. The detector section senses the current level and thereby provides an indication of shutter operation. The detector section also indicates a fault condition when the minimum current is not drawn or excessive current is drawn.