TTL & TIP41 FOR DC MOTOR SPEED CONTROL

[labview1958]

I can contol my DC motor from my PC if the power supply is 12 Volts or less. If more than 12V, the DC motor RUNS on it's own!

[dyarker]

I only scanned previous posts to see what is going on here. If you had posted a schematic of what you've hooked up so far, it might have helped. I've a couple comments even though I haven't read all in detail. working backward:<p>"If more than 12V, the DC motor RUNS on it's own!" That sounds dangerous for the PC because we don't know where the leakage current is going.<p>"I am trying to connect a resistor from the base to the grounf. Hope it works!" What value resistor?<p>"A friend who says he knows these things says that the 5V TTL signal will only give an output from 0V to 5V." If the motor is connected between the transistor's emitter and ground, he is almost right; but that it wrong way to connect it.
--------------------<p>You still haven't said how much current your 40V motor uses (loaded). The TIP41 is 6A max, so I'll assume the motor as 4A max, with a 5A fuse or circuit breaker in case you stall the motor.<p>One motor terminal connected to 40V, other motor terminal connected to TIP41 collecter. TIP41 emitter connected to ground. The TIP41 base current is collector current divided by min hfe.
4A / 15 = 0.27A Too much for TTL! Too much for 2N3906 (though Stephen is correct for 1A max motor current).<p>(The motor "runs on it's own" with more than 12V MAYBE because of reverse leakage through the 2N3906.)<p>So connect collecter of a 2N2222 through a resistor to +5V. Emitter of 2N2222 to base of TIP41. Base current of 2N2222 is:
0.27A / 100 = 0.0027A (2.7mA)<p>Value of 2N2222 collecter resistor depends on voltage drops through the transistors; 2N2222 CEsat, 2N2222 BEsat, and TIP41 BEsat:
5V - 1V - 0.6V - 0.7V = 2.7V
Rc = 2.7V / .27A = 10 Ohms 1Watt (why FET is better)<p>2.7mA is more than LSTTL can source, though LSTTL can sink up to 16mA. So either we use a pullup resistor and TTL "1" for motor on, and TTL "0" for motor. Or, add a 2N3906 to reduce the "1" current load on the TTL. The first option is less parts and wastes less total current.<p>Base of 2N2222 connects to anode of small diode, cathode of diode to TTL output. ALSO from base of 2N2222 a resistor to +5V. Resistor value:
Rb = (5V - 1.3V) / 0.0027A = 1370 Ohms (1.2KOhm standard value).<p>Using open collecter TTL to drive the 2N2222 would eliminate the need for the diode and improve the "off is really off".

[labview1958]

Here is the link to the circuit. Somewhat simple may I add!<p>[img][img=http://img1.echo.cx/img1/9148/imagetest26fk.th.png][/img]

[sofaspud]

Looks like the filename was a little off, as if it was pointing to a (nonexistent?) thumbnail. This should be what you want:
<p>[ May 17, 2005: Message edited by: sofaspud ]</p>

[labview1958]

<p>I have pasted the circuit diagram. Can the 5V TTL signal control the 40V DC supply to the motor? Or should I change the 40V supply to a 5V supply?

[labview1958]

[img][img=http://img123.echo.cx/img123/820/ttl0tr.th.png][/img]<p>Trying to post the circuit. Hopes it suceed!

[labview1958]

I have manage to post the site! Why no image? Anyone?

[dyarker]

don't put the [img= before the http:// and don't put ] after .png<p>just the URL inside IMG tags.<p>------------------<p>You can control a 40V motor from TTL, but you need at least one more transistor between the TTL and TIP41. The base current needed by the TIP41 is probably more than TTL can provide.<p>You still haven't said how much current the motor needs. If it is much under an Amp, skip the TIP41 and use a transistor with more gain.

[labview1958]

[img]img123.echo.cx/img123/820/ttl0tr.th.png[/img]<p>Thanks. The current for the DC motor is about 1 Amp.
If I apply a TTL signal with a duty cycle of 50% would I get 50% of 40V = 20V for the DC motor? If I apply a duty cycle of 25% would I get 25% of 40V = 10V?

[labview1958]

Trying to post image!<p>

[rshayes]

A motor is an inductive load as well as a relay. When the transistor turns off you will probably get an inductive spike that is limited by the stray capacitance in the motor winding. This could easily reach 50 or 60 volts.<p>In some cases, this spike can be coupled back through the collector-base capacitance and disrupt the drive circuit.<p>This transient can be eliminated by using a backward connected diode across the motor. Connect the cathode to the positive supply and the anode to the transistor collector. A 1N4000 series diode should be adequate, since your motor only draws about an amp.<p>You also need more base drive for the transistor. Since the collector current is about an amp, the base current will need to be at least 50 to 100 milliamps. Your microcontroller probably cant supply this much current.<p>You also need some path to ground in the base circuit to insure that the transistor turns off.<p>Try adding an emitter follower to the drive circuit. Add an NPN transistor with its base connected to your microcontroller output and it collector connected to the 5 volt supply. The emitter will probably be around 4 volts when the controller output is high. If it isn't, a 1K pull up resistor from the TTL output to the 5 volt supply will probably help. The base-emitter voltage of the TIP41 could be as high as .8 volts when the transistor is conducting 1 amp. A 39 ohm resistor from the emitter of the added transistor to the base of the TIP41 will give you a drive current over 50 milliamps. Adding a 1K resistor from the base of the TIP41 to ground should guarentee that the transistor turns off with no signal.<p>The added transistor can be a small signal type such as the 2N3904 or 2N2222. Drive currents much over 50 milliamps would require a larger transistor.<p>[ May 23, 2005: Message edited by: stephen ]</p>

[labview1958]

Thanks.
If I apply a TTL signal with a duty cycle of 50% would I get 50% of 40V = 20V for the DC motor? If I apply a duty cycle of 25% would I get 25% of 40V = 10V?

[dyarker]

No, but that is the EFFECT you get. At low speeds PWM gives smoother changes in speed. Especially gradual increases from stopped.

[labview1958]

Trying to post image!http://img175.echo.cx/my.php?image=opto ... m.png<p>Is rise time or fall time important in a TTL signal. Is a square wave not sufficent?

[narender_aec_eee]

can any one provide me with the program for varying the duty cycle of the TTL output from a pc's printer port:<p>i need to control the speed of a small dc motor: