Browse Prior Art Database

Step Motor Drive Circuit

IP.com Disclosure Number: IPCOM000039894D
Original Publication Date: 1987-Aug-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 3 page(s) / 57K

Publishing Venue

IBM

Related People

Duncan, WS: AUTHOR [+3]

Abstract

A three-phase step motor uses only a lower switching transistor and one additional power transistor rather than both upper and lower transistors. This enables a high recovery voltage to be used when stepping to have faster stepping and a low recovery voltage to be used when needed such as during detent of a variable reluctance step motor, for example. A three-phase step motor has windings 1, 2 and 3 connected to a supply voltage, +V. The windings 1, 2 and 3 are connected through power transistors 4, 5 and 6, respectively, to a PWM control 7. A power transistor 8 has its emitter connected to +V, its base connected to a line 9 through a resistor R1, and its collector connected to the line 9.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 53% of the total text.

Page 1 of 3

Step Motor Drive Circuit

A three-phase step motor uses only a lower switching transistor and one additional power transistor rather than both upper and lower transistors. This enables a high recovery voltage to be used when stepping to have faster stepping and a low recovery voltage to be used when needed such as during detent of a variable reluctance step motor, for example. A three-phase step motor has windings 1, 2 and 3 connected to a supply voltage, +V. The windings 1, 2 and 3 are connected through power transistors 4, 5 and 6, respectively, to a PWM control 7. A power transistor 8 has its emitter connected to +V, its base connected to a line 9 through a resistor R1, and its collector connected to the line 9. The state of a transistor 10, which is connected to the base of the transistor 8 through a resistor R2, determines whether a recovery voltage, VR, on the line 9 is high or low.

(Image Omitted)

When VR is required to be high because of phase stepping from one of the windings 1, 2 and 3 to the next, the transistor 10 is turned on by a control signal, Vsw, going high. VR needs to be high when the decrease of current in the winding 1, 2 or 3 needs to be fast to have fast stepping of the motor. VR is approximately twice +V when the resistances of R1 and R2 are equal. The ratio of R1 and R2 can be changed to produce any desired high recovery voltage. When VR is required to be low because the rate of decrease in the current is to be low, the transistor 10 is turned off by Vsw going low. VR is approximately the base voltage of transistor 8 since the current through R1 is the base current of transistor 8, which is very small. The following equation describes the voltage VR: VR = (+V + Vbe) x (1 + R1/Rgnd) where: Vbe is the base-to-emitter voltage at transistor 8 and Rgnd is the resistance from the base of transistor 8 to ground. NOTE: Vbe is usually much less than +V so Vbe is zero in the following discussion. When Vsw is high, transistor 10 is turned on and the resistance Rgnd is R2. VR is two times +V and, therefore, high to allow a fast stepping rate. When Vsw is low, the resistance Rgnd is infinite, causing VR to be +V and, therefore, low for detent, etc. If VR is desired to be high continuously, transistor 8 can be replaced by a ground connection of R2. Thi...