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UC2717 数据表(PDF) 7 Page - Texas Instruments |
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UC2717 数据表(HTML) 7 Page - Texas Instruments |
7 / 9 page UC1717 UC2717 UC3717 Figure 14: Half-Step, Bidirectional Drive Logic Half-Stepping: In the half step sequence the power in- put to the motor alternates between one or two phases being energized. In a two phase motor the electrical phase shift between the windings is 90 degrees. The torque developed is the vector sum of the two windings energized. Therefore when only one winding is energized the torque of the motor is reduced by approximately 30%. This causes a torque ripple and if it is necessary to compensate for this, the VR input can be used to boost the current of the single energized winding. Ramping: Every drive system has inertia and must be considered in the drive scheme. The rotor and load iner- tia plays a big role at higher speeds. Unlike the DC motor the stepping motor is a synchronous motor and does not change its speed due to load variations. Examining typi- cal stepping motors, torque vs. speed curves indicates a sharp torque drop off for the start-stop without error curve, even with a constant current drive. The reason for this is that the torque requirements increase by the square of the speed change, and the power need in- creases by the cube of the speed change. As it can be seen, for good motor performance controlled accelera- tion and deceleration should be considered. Iron Core Losses: Some motors, especially the Tin-Can type, exhibit high iron losses mostly due to eddy currents which rise in an exponential manner as the frequency or step rate is increased. The power losses can not be cal- culated by I 2R where I is the chopping current level and R the DC resistance of the coil. Actual measurements in- dicate the effective resistance may be many times larger. Therefore, for 100% duty cycle the current must be lim- ited to a value which will not overheat the motor. This may not be necessary for lower duty cycle operation. Interference: Electrical noise generated by the chopping action can cause interference problems, particularly in the vicinity of magnetic storage media. With this in mind, printed circuit layouts, wire runs and decoupling must be considered. 0.01 to 0.1 µF ceramic capacitors for high fre- quency bypass located near the drive package across V+ and ground might be very helpful. The connection and ground leads of the current sensing components should be kept as short as possible. Ordering Information UNITRODE TYPE NUMBER UC3717N - 16 Pin Dual-in-line (DIL) "Bat Wing" Package UC1717J - 16 Pin Dual-in-line Ceramic Package UC1717SP - 16 Pin Dual-in-line Hermetic Power Package CONSIDERATION 7 |
类似零件编号 - UC2717 |
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类似说明 - UC2717 |
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