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[Ideas For Design]
Bidirectional H-Bridge DC-Motor Motion Controller

John Peterson, W. Stephen Woodward  |   ED Online ID #6199  |   July 26, 1999


In applications requiring absolute accuracy in the speed control of dc servo motors, there’s no substitute for the traditional tachometer-based feedback loop. But for somewhat less demanding situations, adequate accuracy often can be achieved without the complication and expense of a tach. This can be done by taking advantage of the built-in electromechanical constants of the motor itself.

For example, the fact that every permanent-magnet dc motor exhibits a stable relationship between rpm and armature back-EMF implies that a reasonable job of constant-speed operation can be accomplished merely by driving the motor from a well-regulated voltage supply.

Even better speed regulation, sometimes rivaling tachometer feedback, can be achieved by adding a armature current, to the motor drive voltage. If this term is trimmed to accurately cancel armature resistance equal to motor-rated-voltage/lockedrotor-stall-current, the motor rpm will remain nearly constant over a wide range of loads. Although armature resistance cancellation via positive current feedback is hardly a new idea, the circuit described here gives it a novel twist by combining this trick with a motion-reversing H-bridge circuit topology (see the figure).

The circuit works as follows: A speed-setpoint control voltage is produced by multi-turn precision potentiometer R3, acting in concert with VR1’s 1.25-V reference voltage. The resulting 0-0.75 V is scaled by a factor of 16 by op-amp A1 to produce a 0-12 V no-load M1 target armature voltage.

Speed-stabilizing, current-proportional positive feedback comes from current-sensing R1, is attenuated by R2, and summed by A1 with the speed-setpoint voltage. Optimum adjustment of R2 can produce almost perfect cancellation of M1’s parasitic resistance, resulting in a very “stiff” torque-versus-rpm characteristic. Motor speed-control performance will therefore be nearly independent of mechanical loading up to the voltage limit of the drive circuit.

The regulation of the motor drive in response to the composite control signal output by A1 (speed-setpoint plus current-feedback) is the job of either differential amplifier A3 or A4. It depends on the desired motordrive polarity and consequent direction of rotation as indicated by the state of direction-control flip-flop A2. For positive (clockwise) rotation, A2’s output is low and A4 is in control. This occurs because A3’s low output turns on Q3, which pulls Q5’s gate high, grounding the negative M1 connection via R1. Meanwhile, the same Q3 voltage applied to A3’s positive input causes A3 to rail Q6’s gate positive, holding the p-channel FET off. This prevents the possibility of “shoot-through” conduction between Q5 and Q6. A4 then can accurately sense, via the R5-R6-R7-R8-R9 differential network, the voltage applied to M1 and regulate it via power MOSFET Q4.

Thus, M1 is forced to run at the speed set by R2 until optical retrosensor E2/Q2 senses the arrival of the mechanical load at its clockwise limit. Light reflected into Q2 results in conduction, which overcomes the detection threshold set by feedback pot R4.This pulls A2’s positive input high and toggles the state of the directioncontrol flip-flop. The resulting positive excursion of A2’s output turns on Q7 and forward-biases D1, disabling the A4/Q4 control loop.

Meanwhile, Q3 turns off, releasing Q5 and A3. This results in reversal the motor drive polarity and the initiation of speed-regulated counterclockwise motion. The motor will now continue to run counterclockwise until retro-sensor E1/Q1 senses the arrival of the mechanical load at the counterclockwise limit. Bridge polarity will consequently toggle again, causing the motor to reverse again and so forth ad infinitum (or at least until power is removed!).


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    Reader Comments

    Can't you posters read a datasheet or perform some experiments? Or better yet search the internet? Do you think the author has time to do your design work for you?

    Anonymous -September 30, 2008

    I would like to control to DC motor with accurate position in bidirection.How to design and program for this circuit with PIC16F84A and mosfects(or)relay.Please answer for me.

    ak47mtu -August 18, 2008

    Dear sir i want to design an circuit to control a 60v bipolar 3-10A servo motor and i would like a typical current sensing circuit for an h-bridge with a lm111 and lm358.....could you please help me out

    Anonymous -August 05, 2008

    can we achiecve speed and position control for permanent magnet brushed DC motor with PWM o/p and encoder feedback with minimum or no analog devices.Kindly suggest.

    chet -July 19, 2008

    Dear Sir I am using L 293 H Bridge Ic to impliment dc motor system with bi directional speed control. In this regard pwm signal is required as one of the input to dc motor inorder to control the speed. Will be looking forward for simple ckt to get pwm signal.

    Anonymous -May 02, 2008

    Dear Sir, Im making control system for a DC motor selectable between speed and position.I'm using 8051 microcontroller to feed the motor driving H bridge circuit IC MC33887 with PWM input which then feeds the motor.For position control im using an optical encoder which is connected to the shaft of the dc motor chossing which im confused.Do you think , this logic will work?? my questions are : 1) can MC33887 replace an H bridge circuit , or something else needs to be added in the circuitry. 2) which Optical or Shaft encoder would you recommend and explain how does it work ? All i know is this encoder gives a PWM feedback to the microcontroller but still the picture is not clear in ma mind as to how it works ? you earliest and detailed reply will be highly appreciated as im short on time line too. thanks

    Haris -April 14, 2008

    i am trying to make a line following robot. the sensors are working well but i cant control speed of the wheels . i m using ATmega8515 microcontroller. how can i use this "PWM" thing . could u reply on my address . thanks

    Sohail Khan -April 12, 2008

    i am doing mini project on speed control of dc motor using H bridge circuit. could u please hepl me for circuit of H bridge and how to connect that circuit thank u sir

    Anonymous -March 16, 2008

    I am trying to design a motor speed control ckt for a dc motor. I am having doubts on how to isolate my atmega16 microprocessor and the motor ckt because the motor ckt is a high rating ckt.could you please help me on how to design. thank you beakal

    beakal Teshome -June 24, 2007   (Article Rating: )

    Rating Only

    Rating Only -June 24, 2007   (Article Rating: )

    Dear Sir, I'm trying to control two DC motors based on four sensor readings from a microcontroller.One motor moves an RC car forward/reverse and the other motor moves the car left/right.I'm using two pwm signals that are fed into an H-bridge driver (L298) which in turn controls each motor.How can I control the control the motors and the sense of rotation using the two pmw signals? I'd greatly appreciate any feedback.Thanks in advance!

    anika -June 03, 2007

    Dear sir, Iwant know about DC moter which is know using in e-bike that iget surprise when u brake your bike it would not burn what type of tecnology which they are using pl let me know detail about it I will be very thankfull if it is send me as soon as possible on my mail thanking u

    Anil burade -May 19, 2007

    Dear sir, Iwant know about Hub type DC moter which is know using in e-bike that iget surprise when u brake your bike it would not burn what type of tecnology which they are using pl let me know detail about it I will be very thankfull if it is send me as soon as possible on my mail thanking u

    Anil burade -May 19, 2007

    Dear sir, Iwant know about Hub type DC moter which is know using in e-bike that iget surprise when u brake your bike it would not burn what type of tecnology which they are using pl let me know detail about it I will be very thankfull if it is send me as soon as possible on my mail thanking u

    Anil burade -May 19, 2007

    Dear sir, Iwant know about Hub type DC moter which is know using in e-bike that iget surprise when u brake your bike it would not burn what type of tecnology which they are using pl let me know detail about it I will be very thankfull if it is send me as soon as possible on my mail thanking u

    Anil burade -May 19, 2007

    please send to an article about dc motors using PID feed back

    Anonymous -March 16, 2007

    pic16F84A to control dc motors, how?

    yasser -March 09, 2007

    hello sir im a new user to this site and i want how to control dc motor using pwm teqn. and rf remot control cicuite my project is robot and i use AT89c52 micro controller

    ahmed gad -March 01, 2007

    Please send me in details that how control of DCgeared motor is obtained with H bridge driver L293... thank you

    priyanka -January 21, 2007

    VERRY WELL

    PHUOC -January 03, 2007   (Article Rating: )

    very nice

    Anonymous -September 03, 2006   (Article Rating: )

    i want to use bidirectional h bridge with PIC16F84/PIC16F84A that can be controlled by the internal timer of the PIC. im wondering how can i do it..any ideas?

    kaydee -September 02, 2006

    Santa Claus,

    Can I have a Ferrari with a trunk full of gold bars?

    Some of your questions are ridiculous.

    GetReal -July 10, 2006

    Hello sir, i need to design a h bridge which runs of 6V and supplies a current of 1A. This is going to be run of an ATMEGA16L microcontroller. please can you help me with the design. im from india so im quite poor in english so please explain it in simple words!!!!

    indian -May 04, 2006   (Article Rating: )

    Hello sir, i need to design a h bridge which runs of 6V and supplies a current of 1A. This is going to be run of an ATMEGA16L microcontroller. please can you help me with the design. im from india so im quite poor in english so please explain it in simple words!!!!

    indian -May 04, 2006

    Hello sir, i need to design a h briged which runs of 6V and supplies a current of 1A. This is going to be run of an ATMEGA 32L microcontroller. please can you help me with the design.

    Thank you

    Tejal Dowlath -May 04, 2006   (Article Rating: )

    good

    gajendra -April 15, 2006   (Article Rating: )

    hello sir, Article was very usefull. Student of melbourne university ,i have to design ""motor speed controller"" for a dc motor, the speed of the motor should be directly propotional to the voltage supplied to it , and if positive voltage is supplied it sholud rotate clockwise and if negative voltage supplied it should rotate counter clockwise,i am using PWM and H-bridge,please asist me with a circuit. Thank you yours faithfully.

    sunny Mohan -March 31, 2006   (Article Rating: )

    I want drive a high voltage dc motor for position and speed control(v=250v dc naminal 1A) please help me for descrete circuit driver Thanks morteza jadidi

    Anonymous -March 18, 2006

    I want drive a high voltage dc motor for position and speed control(v=250v dc naminal 1A) please help me for descrete circuit driver Thanks morteza jadidi

    Anonymous -March 18, 2006

    Hi sir,

    I want to make a high school level projects on bidirectional control of dc motor that may take 45 days for its completion.Plz send me the circuits and its workings.

    Hope favourably

    rajaram -March 12, 2006   (Article Rating: )

    Morning Sir

    Im designing a remote control toy car that can roll a cricket ball at a distance of 1.5 m and in my design im doing the elctrical part and ive been given two DC motors.Can you please assist me with the circuit that can control the wheels of this car and what type of gear must i use to control the wheels of this car.

    Zimbini -February 24, 2006

    please give me an article about dc motors

    sayyed ali -February 18, 2006

    Hello sir, i am doing a line following robot in that i need the circuit for control the dc geared motor with PWM ckt. if it is possible plz give the schematic ckt for that.i am using At89C52 microcontroller and a H-bridge[l293].plz send the schematic thanking u sir

    K.Anil Kumar

    Anil Kumar -February 15, 2006   (Article Rating: )

    Dear Sir/Madam,

    I am currently to design a rversible dc motor drive using a mosfet transisitor. I need to iclude a feedback to assist in turning the motor in the oposite direction when it is needed. I have just finished design a circuit that runs the motor in one direction and what is left is to progress to a circuit that runs that motor in both direction. Is there anything you can do to help me achieve this objective?

    Thank you.

    Nickson.

    Anonymous -February 01, 2006

    can u send me the article of DC motor controller that combine with PID controller??

    soelistiyo -January 26, 2006

    Dear sir/Madam,

    This artical is very useful. but the fig is not visible properly. if it is in PDF format would be more useful.

    Thank you

    Bhagyashree -November 17, 2005   (Article Rating: )

    please send to an article about dc motors

    ali -November 07, 2005   (Article Rating: )

    The circuit is very interesting. I would like to know if you could help me with an electronic circuit I have to design for University. It has to do with Bidirectional DC-DC Converters with dual half bridges placed on each side of an isolation transformer.

    Casanova -September 13, 2005

    .The circuit is excellent. Could you please show me how I can connect a digital display to indicate the speed of motor?

    Anonymous -August 23, 2005   (Article Rating: )

    Hi, we are manufacturer and offer Electric motors, Diesel Generators, alternators, Pumps and the Accessories concerned. Anyone in this line pls feel free to contact me by Email yangb2b@163.com or yangb2b@hotmail.com

    regards

    yang shine

    Yang shine -July 30, 2005   (Article Rating: )

    i want the schematics of an h-bridge which can allow me locking that is the combination of 1-1 on both the mosftes doesnt cause a shoot through please contact asap

    Anonymous -July 27, 2005

    Dear Sir/Madam

    I please would like to know how to control the motion of the DC motor to lift the load with a speed of 5r/s to certain height, and to have a frictional brake before bringing the load down. To control the direction of the DC motor I used the L293 driver. (the weight of the load is 2Kg)

    I am looking forward for a help from you

    Yours sincerely Phillip

    Phillip -July 13, 2005   (Article Rating: )

    well, i am danish from pakistan and i am agent here i deal in electronic emergency eqiupment like ambulance siren and big light bar and small please contact me i have special item for you don,t west the time start near future business with me bye contact me at this phone no.0300-2388414 mobilinkgsm. danish741@yahoo.com

    mirza danish baig -June 13, 2005

    Good, usefull article for practicing engineers like me.

    I have been working on another way of doing away with tacho. It involves measuring the voltage across the motor armature, when the H bridge is switched off completelyfor a short duration. The idea needs to be tested for correct and reasonable operation with the actual hardware.

    Any one thinking on these lines?

    Vinod Tatti -April 28, 2005   (Article Rating: )

    Good circuit for me as I will be breadboarding motion control in the near future. However, as others suggest, PDF would be useful because the image given is just too low resolution, The part numbers are not always readable for example. Excellent feature, keep the schematics coming!

    Glen Birbeck -April 18, 2005   (Article Rating: )

    thankyou

    nguyenhaquang -April 10, 2005

    pls need help on h-bridge

    bisi -April 02, 2005

    Thanks.

    Vikram -March 14, 2005   (Article Rating: )

    nice

    Anonymous -February 27, 2005

    Good

    Anonymous -February 22, 2005   (Article Rating: )

    I have read through it and find it quite useful but too difficult to understand, especially the circuit. Can I use a L293D chip instead? I have a link to the chip information: http://www.alltronics.com/download/1330.pdf. Does anyone know?

    Ah Sim -February 01, 2005   (Article Rating: )

    Sure wish this was in PDF format!

    BOBJ -January 31, 2005   (Article Rating: )

    I want to know something practical about regenerative braking.

    Balaji -January 15, 2005   (Article Rating: )

    Are the articles in your ideas for design section available in PDF format?

    Thanks,

    Barry Smith

    Barry Smith -January 04, 2005

    The online articles are great, but they would be far more useful in .pdf format... (we are always wanting more)

    Jonny Doin -December 13, 2004

    It's an approach to a known application.

    E. Pietrobon -October 21, 2004

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