Simple Dc Motor Driver

Thread Starter

araba1980

Joined May 25, 2011
4
Hello

I have a project releated dc motor driver, In this project, I want to start Dc motor with parelel connection of alarm clock's speaker.

And I also made a proteus project, and image is:


I haven't enough knowledge of power electronic, so i cannot decide suitable thyristor, optocoupler, and resistors values.

Motor:
Rated voltage: 12V.
Voltage: DC6V-14V.
No-load rated current: 0.65A or less.
Rated load current: 0.8A ~ 1.2A.
Details: (http://www.aliexpress.com/snapshot/221945512.html)



Tyhristor:BD139 (http://www.datasheetcatalog.org/datasheet/fairchild/BD139.pdf)

Optocoupler: (http://pdf1.alldatasheet.com/datasheet-pdf/view/43371/SHARP/PC817.html)

Are this components suitable for this project? Or have you got any suggestion?

Thanks
 

crutschow

Joined Mar 14, 2008
23,798
An SCR will stay turned on until you cut off the power to it, and there is no way to do that on your schematic. Is that what you want?

If not, then you need to use a transistor such as an N-MOSFET. Any MOSFET with a current rating of 2A or more should work.
 

Thread Starter

araba1980

Joined May 25, 2011
4
An SCR will stay turned on until you cut off the power to it, and there is no way to do that on your schematic. Is that what you want?

If not, then you need to use a transistor such as an N-MOSFET. Any MOSFET with a current rating of 2A or more should work.
Yes i want to turned on, but I will add a basic switch for cut off the power.

I am not sure for BD139 thysistor, its Collector-Emitter Voltage about 40V, but my suply is only 9V.

And how can i calculate resistor values, I show R1=100 R2=220 with a different circuit, I only copy paste in this project, are these values correct?

And so, any advice for optocoupler?
 

#12

Joined Nov 30, 2010
18,167
That photo-coupler is a zero crossing type. It will not be happy with 9 volts waiting all the time. Use a MOC3011. 1.5V needed, 20 ma from the alarm clock needs a resistor of 75 ohms in series with the emitter diode.

There is no way a 9 volt, rectangular battery will throw an amp into that motor. They're just too small.

The collector-emitter voltage is SUPPOSED to be rated to survive more than the voltage you are supplying.

The BD139 is not a thyristor. It is a transistor. You want it saturated to give 1A to the motor so the base current is 1/10th of an amp. From 9 volts, make R2:
9/.1 = 90 ohms.
You can buy a 91 ohm resistor but you are going to change the power supply to get enough amps to drive the motor, so I gave you the math just now.

R1 can be 1000 ohms to 10,000 ohms when using a transistor for the current driver.
 

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Thread Starter

araba1980

Joined May 25, 2011
4
There is no way a 9 volt, rectangular battery will throw an amp into that motor. They're just too small.
It is sufficient for me,

The collector-emitter voltage is SUPPOSED to be rated to survive more than the voltage you are supplying.
Ok. I understand

The BD139 is not a thyristor. It is a transistor.
I am very sory, it has escaped my notice. I want to use a thyristor.


You want it saturated to give 1A to the motor so the base current is 1/10th of an amp. From 9 volts, make R2:
9/.1 = 90 ohms.
I think you decide current ratio from datasheet, Figure2. Collector-Emitter Saturation Voltage. Is it correct?

You can buy a 91 ohm resistor but you are going to change the power supply to get enough amps to drive the motor, so I gave you the math just now.

R1 can be 1000 ohms to 10,000 ohms when using a transistor for the current driver.
Is it an general knowledge or releated with datasheet? I can't found it in datasheet.


I want to use thyristor, so I search again and find a thyristor, BT151 (http://oldradio.tesla.hu/szetszedtem/385tapvedelem/BT151.pdf)

And I also think use mosfet, I has found irfz24n (http://www.irf.com/product-info/datasheets/data/irfz24n.pdf)

How can i calculate resistor values when i use thyristor or mosfet?

Thanks Very much
 

#12

Joined Nov 30, 2010
18,167
The 10 to 1 current ratio is "rule of thumb". It came from experience of many people over many years. It is not on the datasheet.

R1 keeps the transistor off when not in use by draining any leakage from the collector to the base. R1 takes that very small leakage current to ground.

A thyristor will stay on until you switch off the supply voltage. A transistor or mosfet will only work when voltage is applied from the opto-isolator. Pick one.

A mosfet will work just as I drew the circuit for a transistor or you can increase R2 to 1 tenth of R1.
Your thyristor needs .015A to fire its gate so R2 will be 390 ohms or a little bit less. You could use it with the circuit just as I drew it but the 91 ohm resistor will be wasteful.
 
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crutschow

Joined Mar 14, 2008
23,798
The 10 to 1 current ratio is "rule of thumb". It came from experience of many people over many years. It is not on the datasheet.

.....................
Some BJT data sheets do show the saturation voltage value and the measurement condition typically is with the base current being 1/10th of the collector current. :)
 

#12

Joined Nov 30, 2010
18,167
True. In this case, page 2, Fig. 2.

The problem is that it is not spelled out in English and it is not spelled out for various values of current in the charts of voltage and current values. Beginners might glance across the graph many times before realizing that it is telling them to use a gain of 10 to make a saturated switch.
 

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