Application Note Closed-Loop Motor Control

Transcription

1 Application Note ClosedLoop Motor Control Contact: Brazen Tek, Inc. 011 Ventura Blvd. Suite 10 Woodland Hills, CA 916 Tel/Fax: (818) January 009

2 Introduction Based on the review in the Application Note Closed Loop Control System, the latter paper is the reference to this application. System Overview The following diagram provides a scheme for the closedloop motor control application: Voltage IR Diode to frequency Feedback Speed Converter Motor Figure 1 ClosedLoop Motor Control Diagram One important feature of the design is revolved around the circuit being stable. This is achieved by having the closedloop circuit operate at its best in an electrically noisy environment. The use of IR diode as a detector in the circuit at its input is by implementing a phototransistor that generates radiation. This radiation is splitted into pulses by the motor fan blades. The quantity of pulses from the phototransistor is supplied to VFC (Voltagetofrequency converter) that has a voltage proportional to the speed of the motor. VFC0 from Texas Instruments is a good option for motor speed and control applications. It can take either positive or negative voltages as input. The output of the converter is a voltage with following conditions: amplified, lowpass filtered and comparable with a manually adjustable control voltage that represents the commanded speed. Manually adjustable is mainly driven from the monitoring circuit or in simpler way, a microcontroller that is performing the operations based on user inputs. The difference between the speedmeasurement and speed command signals is a control voltage that is amplified and supplied to an external power amplifier that drives the motor. A selector switch at the output of the final amplifier of such a

3 circuit also enables the operator to bypass the circuit manually set the control voltage for the external amplifier. The chosen operational amplifiers are mainly due to their voltage supply constraints. The circuit can be controlled via a PC graphical user interface (GUI), the communication between hardware and software can be between any of USB, RS, etc. depending on the enduser s needs. Figure described such a configuration: PC Interface Motor Control GUI Circuit Figure User s control over the circuit Power supply for this circuit should be dual output with ac coupled capacitors, these should be comprised of small and large capacitors. In this application note, 1V and 1V are the supply voltages. The schematic of the closedloop motor control is displayed in figure. Resistors in the circuit are 0.W with % tolerance. The unused pins of LM900 should be tied to ground.

4 1V MCU I/O R R18 68k UB LM V R6 1.k R1 R1 0 R k C 100uF R1 R16 k R1 680 D1 Q1 R 1k C1 0.01uF R 1k C 0.1uF R 68k U1 IN FOUT IN VOUT 1SC CPI COM VCC VCC VFC0 1 R8 R9 1.k 10.8k U R1 1 C 0.1uF 6 6 UA LF6 LM900 C uf R10 1k 1 R11 R1 1M 1 R19 10k 1V 1V 1V MCU I/O Title ClosedLoop Motor Control Size Document Number Rev A A Date: Thursday, January 9, 009 Sheet 1 of 1

5 Important Notes 1. This document is provided for reference purposes only. Brazen Tek neither makes warranties or representations with respect to the accuracy or completeness of the information contained in this document nor grants any license to any intellectual property rights.. Brazen Tek shall have no liability for damages or infringement of any intellectual property or other rights arising out of the use of any information in this document, including, but not limited to, product data, diagrams, charts, programs, algorithms, and application circuit examples.. This application note or the technology described in this document is not for the purpose of military applications such as the development of weapons of mass destruction or for the purpose of any other military use.. Brazen Tek assumes no liability whatsoever for any damages incurred as a result of errors or omissions in the information included in this document.. When using or otherwise relying on the information in this document, you should evaluate the information in light of the total system before deciding about the applicability of such information to the intended application. Brazen Tek makes no representations, warranties or guaranties regarding the suitability of its products for any particular application and specifically disclaims any liability arising out of the application and use of the information in this document. 1. This document may not be reproduced or duplicated, in any form, in whole or in part, without prior written approval from Brazen Tek.