Speed control IC "brushed dc motors" I get confuse... - Page 1
Forum section: electronics / projects

author: nquantum
author_rank: Regular Contributor
timestamp: November 24, 2016, 05:03:01 pm
content: I'm plan to do project robot just for fun/hobby. In driver circuit small brushed dc motor 1-2A 12-25VDC. I plan for H bridge and PWM for speed control. I used to do that H bridge sometime ago but not that speed control just "stop,brake,clockwise,counter-clockwise".So I thinking of design in PWM for speed control into that so that I can even use PID. After I read some more series about H-bridge design and calculate: lock anti-phase drive, phase-magnitude drive, Sign-magnitude Drive , high-side transistor/fet drive...... etc. fromhttp://www.modularcircuits.com/blog/articles/h-bridge-secrets/h-bridges-the-basics/http://www.modularcircuits.com/blog/articles/h-bridge-secrets/sign-magnitude-drive/http://www.modularcircuits.com/blog/articles/h-bridge-secrets/lock-anti-phase-drive/http://www.modularcircuits.com/blog/articles/h-bridge-secrets/asynchronous-sign-magnitude-drive/(there are more in that web if you interest...)I feel headache too much. I plan for future reading and understanding more when I have more time. But to make my life easier. I look for IC driver. So I look at ST Brushed DC Motor Drivers: L6227 look okay. But point is after I read datasheet question is : How can I speed control? There is no for PWM input?All I can see is table logic: picture I have attached.Or do I put is PWM in IN1, LOW in IN2??? But it doesn't mean motor: BRAK,STOP,BREAK,STOP,BREAK,STOP.....?Or do I put PWM in EN then 1 in IN1, 0 in IN2??? So it mean FREE,RUN,FREE,RUN... then average current so that speed can adjusted??Or I choose the wrong IC?Or all is wrong? I miss any point? I just want to speed control the motor.I know some simple transistor circuit in around internet might work on this small projects. Maybe not well maybe need some more adjust some calculate when should do when PWM off time , that I read from article... So that the point I choose the IC so maybe it solve annoy problem then I can more time in coding.Please help/advice.Thank you so much.

author: nquantum
author_rank: Regular Contributor
timestamp: November 25, 2016, 01:05:23 pm
content: No one?

author: yngndrw
author_rank: Regular Contributor
timestamp: November 25, 2016, 01:34:09 pm
content: Looking at the block diagram that you posted and page 6 of the datasheet (http://www.st.com/content/ccc/resource/technical/document/datasheet/5d/da/89/c1/50/20/49/d4/CD00003312.pdf/files/CD00003312.pdf/jcr:content/translations/en.CD00003312.pdf), it looks like this IC does all of the PWM for you.You connect a current sense resistor from Sense A to ground and that is internally compared to the reference current voltage that you apply to VRefA - The PWM duty cycle is then internally generated from these. (And the same for channel B) You can either use an analogue voltage for VRefA or you can drive the pin using PWM and a low-pass filter. Please note that this controls the output current, not the voltage.Hope this helps.

author: nquantum
author_rank: Regular Contributor
timestamp: November 26, 2016, 02:54:13 pm
content: Oh I missed read that Vref pin. I have wonder why they provide PWM. Now I know.Thank you.Another question is once I want to reverse rotate motor , while the motor still rotate. What should do? Of course should stop then rotate. Is it will be problem or destroy component when I just signal to reverse it? Does current protection good for this?Another one what if someone rotate motor, let say electric car and someone push the car then motor rotate , will that fried the FET? Does diode protect this?

author: yngndrw
author_rank: Regular Contributor
timestamp: November 26, 2016, 03:15:57 pm
content: It's been a while since I've worked with brushed motors so don't take my word as a given, but Ibelievethat when you reverse the power on the motor it will essentially act as a generator which will push up the voltage on your supply. If the voltage gets too high, you will destroy the other components on the supply.Geckodrive published a circuit to prevent this issue on their larger drives (http://www.geckodrive.com/gecko/images/cms_files/Returned%20Energy%20Dump.pdf) but you might just be able to get away with a large capacitor on a smaller motor. Keep in mind that the load on the motor will affect it as a higher inertia will have more energy to be removed.Regarding the pushing question: If all of the FETs are off, nothing will happen as long as the motor terminal voltage doesn't rise too high. If the FETs are shorting the winding in order to act as a brake, well the circuit will have to dissipate any energy that's generated.