Motor Current Limiting Circuit
Original Publication Date: 1981-Oct-01
Included in the Prior Art Database: 2005-Feb-12
Upon receiving a start command from the digital to analog converter (DAC) the base voltage on line 3 increases, turning the motor driver transistor T1 on. As motor current Im increases, the voltage Vo at node 4 increases. The voltage at node 4 is the product of current Im and the value of resistance Rs. Resistance Rs should be small compared to the resistance of the motor 7 to minimize effects on speed variations. Amplifier A1 is a non-inverting amplifier with its output voltage Eo equal to Vo + VoRF over Ri . The gain resistors are chosen such that Eo is equal to 0.7 volt at the time current limiting is to occur. When Eo reaches 0.7 volt, T2 turns on, thereby shorting line 3 to ground. This action turns T1 off, and current Im decreases until it drops below the predetermined level.