tailieunhanh - Crc Press Mechatronics Handbook 2002 By Laxxuss Episode 2 Part 9

Tham khảo tài liệu 'crc press mechatronics handbook 2002 by laxxuss episode 2 part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | FIGURE Using diodes to reduce swithcing voltage when driving inductive loads. FIGURE Open-collector output. storage elements where the energy is stored in the induced magnetic field. The voltage across an ideal inductor VI t is Vi t L ịiflt dt where iI t is the current going through the inductor and L is the inductance. When the current to the inductor is suddenly switched off . by switching off a driving transistor Equation indicates that there will be a large transient voltage build-up across the inductor. If not properly suppressed this transient voltage can shorten or even damage the driving transistor. This is sometimes called inductor kickback. A simple method of reducing the instantaneous switching voltage surge is to create a loop for the excess energy to flow. This can be done by placing diodes in parallel with the load see Fig. . Figure illustrates two methods of using flyback or free-wheeling diodes to suppress switching voltage surge when driving inductive loads. Open-Collector Output For some digital devices the output stage pin is simply the collector of a transistor. This is called an open-collector output see Fig. . Since the output of the device is only the collector of a transistor it has no output drive capacity. The output value can be measured through a pull-up resistor see Fig. . Open-collector output is convenient for driving electromechanical devices if the output transistor can sink adequate current see Fig. . Isolation Recall that the power amplification modulation part of an electromechanical actuator contains both low-and high-energy signals see Fig. . For safety and reliability reasons it is desired to prevent transients or noise spikes in the high power side of the system from the signal processing low power side of the circuit. Mechanical relay is one option. Optoisolators or optocouplers use light to couple the high and low 2002 CRC Press LLC FIGURE Using diodes to reduce