IBM Technical Disclosure Bulletin (TDB 04-83 p5809-5810)
Schroeder, EN - Author
English (United States)
2 pages / 44.7 KB
Polarity Reversing Circuit for DC Motors
A reversing circuit (commonly referred to as an "H" drive) for a DC motor serves the function of a double-pole double-throw switch with the motor connected to the common terminals, and power connected to the normally open and normally closed contacts in a cross-connected manner. Disclosed is an electronic means for reversing the direction of a DC motor wherein, as with the switch configuration, it is required that: 1) the action be break-before-make (so the power supply will not be shorted); (2) the "switch blades" are interconnected such that the action is synchronized; and (3) over-current protection is provided to protect the circuit from fault conditions effecting excessive current.
Referring now to the drawing, the break-before-make requirement is implemented by way of capacitors C1 and C2, and integrated circuits IC1-1 and 3 and IC2-5 and 6. With the motor driven in the reverse direction, integrated circuit ICl-1 is at a down level, maintaining capacitor C1 in a discharged state. When the "switch" opens, capacitor C1 charges through the Schmidt trigger input of integrated circuit IC2-5 and must reach the switching threshold before the output IC2-5 goes low, allowing the forward "switch" contacts to close. If both the forward and reverse input signals are identical, the "switch" will be inhibited (i.e., in the open position).
The electrical equivalent of mechanically connected switch blades is implemented by way of transistors T1 and T2. With integrated circuit IC1-2 at a down level, transistor T1 is turned off and no collector current flows. The Darlington transistors T3 and T4 are therefore non-conducting by virtue of the respective base-to-emitter resistors R1, R2. With the output of integrated circuit IC1-2 at...