Abstract: When in control circuit for varying the current through an inductive load the current is sent as pulses of variable width and each time that occurs is cut off by the electronic switch in series with the load across the power line a high inductive voltage is generated. When the electronic switch control terminal is disabled, the electronic switch will turn off and no current can flow through the switch. Thus, the inductive energy in the load, since it cannot continue to flow, generates a very high inductive voltage which can do damage to equipment and personnel. A clamping circuit is provided by means of two series diodes. One diode is a Zener diode with known breakdown potential. The other is a simple diode. The Zener diode has its cathode tied to the junction between the switch and the load and the simple diode has its cathode attached to the control electrode of the electronic switch.

Abstract: An apparatus for controlling the inductive currents and voltages of a load when the current through the load is suddenly switched off. It comprises primarily a series connection of a diode with its cathode connected to the high voltage of the power supply, connected through a NPN transistor which is connected to the junction between the load and the electronic switch. The control electrode of the NPN is operated by a PNP transistor whose control comes from the voltage at the junction between the load and the electronic switch with respect to ground potential. Normally, the NPN transistor is cut off and blocks the flow of inductive current from the load from passing through the NPN transistor and the diode to the high voltage lead to the motor. However, when the current through the motor or other inductive load is cut off, an inductive voltage appears at the junction between the load and the switch.

Abstract: This invention forms a basic circuit for the input to a voltage control device for an inductive load. It consists of a basic constant frequency oscillator comprising a Schmitt trigger and inverter having an input with a capacitor to ground and an output which feeds back to the input to one end of a potentiometer or feeds forward from the other end of that potentiometer to the output. A point in between the ends of the potentiometer is connected to the input to the Schmitt trigger. If the input potential of the Schmitt trigger is low its output will be high and vice versa. If its input is low, current flows from the output through a diode to the potentiometer and to the capacitor to ground and if it is high, current flows from the capacitor through the potentiometer and a diode to the output of the Schmitt trigger. Thus, a clean square wave pulse current is provided of variable width pulse ratio dependent upon the setting of the contact between the input to the Schmitt trigger and a point on the potentiometer.