Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Controlling a DC Motor

Status
Not open for further replies.
Hello Everybody.

Finally I discard using brushless motors since I dont understand them. So I am going to use a DC Motor for my project.

**broken link removed** (sorry, in japanese)

to do this I have several questions.

1) First. I am thinking of using a chip with an h-bridge (Toshiba TA7257P)

TA7257P pdf, TA7257P description, TA7257P datasheets, TA7257P view ::: ALLDATASHEET :::

What are the advantages or disadvantages of using this as opposed to doing it myself with transistors and diodes??

2) talking about simple circuits (not h-bridge) take a look at the attached picture

2a) is R2 really necessary? i got some docs saying it is , other saying it isnt

2b) is D2 necessary?

2c) some book recommended putting a condenser in parallel to D1, but I wonder if that is a mistake of the book

3) Talking about the circuit in 2 and also about the H-bridge (either the chip or the one built with transistors) since this motor is 6~12V, should I use an opto-coupler to separate the chip from the motor as I did in my previous project?

btw, when the datasheet of the motor said 6~12V does that mean that I have to put 12V and only get the 6 V through PWM the signal from the microcontroller???

Thank you very much for your help

Kansai
 

Attachments

  • motorcircuit.JPG
    motorcircuit.JPG
    18.2 KB · Views: 208
1. someone has already done all the work for you.
2a It's required at powerup when the I/O pin is an input. However, not really needed with a transistor but is needed with a MOSFET.
2b not needed
2c probably helps if the diode isn't fast enough. Also helps reduce RF.
3 Keeping the motor supply and the logic supply separate would be a good thing. Most people just filter the logic supply.

Mike.
 
Yesterday I started trying circuits for the motor (in the figure). The motor can only work in the ranges of 6v to 12V. I am very confused so I would appreciate any help.

As transistor I used Fairchild 2N3904.
https://www.electro-tech-online.com/custompdfs/2010/06/2N3904.pdf

Diodes were 1N4004
https://www.electro-tech-online.com/custompdfs/2010/06/1N4001.pdf


I tried no R2. And for R1 I tried the following and I got the following voltage accross the motor whe applying 12V (not 5V) to the base

Code:
R1     Voltage across the motor   Current accross the motor   current in the base
82K     0.1 V                                  0.02A                               0.0524mA
27K     0.6V                                                                           0.16mA
4K       1.35V                               0.1A                                  1mA
1K       2.5V                                 0.18A                              7mA
520     3V                                   0.23A                                8mA
100      9.5V                              0.16A                                56mA

obviusly i could only move the robot with the 100 Ω resistor.

Now ok, I moved it but I am worried since I have to control the robot with all kinds of voltages from 6v to 12V. And also i have to control it with a microcontroller (providing only 5V)

my question is how can I increase the voltage passing through the motor? So far the only thing I have tried was changing the R1 resistor. Can someone enlighten me?

Kansai.



P.S. i can understand Ohms law for transistors. Somewhere I read that the voltage E-C is always 1.6V. but that is not the case of course. if this were true no matter what the current in the base the voltage in the collector would be the same and it is not like this. Can someone explain this to me???

Thanks a lot
 
The transistor has to be Darlington such as BD679.

Vcc can be 6v to 12v. R1 is 10k for BD679. The motor need a very heavy current to start-up. That's the problem - that's what no-one will tell you.
 
Last edited:
Is changing the resistor R1 the only way to augment the voltage and current in the motor???

R1 10K??? is this going to generate enough voltage? so far only 100 ohm has worked.
 
Gain

You have a couple of problems:
1- From your numbers it looks like your motor has a locked rotor current of nearly 1 amp. Your transistor is only good for .1 amp.
2- The Hfe of the transistor is 30 which means you can only get 30 time more collector current than you have base current before it comes out of saturation..

A better solution might be a logic level n Channel Mos Fet say maybe a IRLD024PBF. This would solve both problems.

You could then control it with a PWM from your micro- not an analog one but a digital one.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top