6V DC motor control with transistors

[case-sensitive]

Yes, looks like the TC4424 could do the trick, 3A peak current...

 

[haytham]

thank u for this information

 

[case-sensitive]

only thing, it has .25 V voltage drop and has seemingly 0.25V at the outputs when the inputs are 0.

Case.

 

[blueroomelectronics]

Then pull the inputs to one. As long as both outputs are identical the voltage across the motor is zero.

 

[case-sensitive]

Yes, should be no problem. Just the imagination, that at logic 0 input its not 0V output. 0.25 V voltage drop at logic 1 resp 0.25V output at logic 0 Input are just max levels, means from 6V input I will get 5.5V worst case. Its actually 4 Accus, so we are looking at 4.8 less .5 V. More than enough for the motors anyway, just don't want to waste energy for heating the chips.

And yes, stops anyway, if both outputs are about similar voltage, inertia does the rest (if there was 0.25V between them say)

Case

EDIT: PS: its driven by 4 AA accus, tho voltage will be 4.8 V or less, the 4424 needs more than 4.5 V. MOSFETS then.

 

[case-sensitive]

created the TIPs using a SPICE model. Am not impressed (see picture). What to do now? Unfortunately I bought them already.

Case

 

[ericgibbs]

created the TIPs using a SPICE model. Am not impressed (see picture). What to do now? Unfortunately I bought them already.

Case

Measure the current thru R7 and R8 [91R], post what you find.

 

[case-sensitive]

Updated the software, now it comes with TIP31/32 models, used the TIP31C/TIP32C, thats what I have got at Jaycar today. Strangely enough, the SPICE data supplied with the software is different to what I have found in the **broken link removed** now it looks better. Should set R7/8 to around 50 ohm?

Case.

 

[audioguru]

Should set R7/8 to around 50 ohm?

You reduced the supply voltage but did not reduce the value of the base resistors.

The collector current in the TIP transistors is almost 1.5A. The datasheet for the TIP transistors shows a typical saturation voltage loss of 0.25V when the collector current is 1.5A and the base current is 150mA. Your circuit has a base current of only 34mA.
The BC338 transistors saturate well when their collector current is 150mA when their base current is 15mA but their base current in your circuit is only 4.1mA.

Reduce the value of the 91 ohm resistors R7 and R8 to 18 ohms/1W and reduce the value of the 1k resistors R5 and R6 to 270 ohms.

 

[case-sensitive]

ok, there we go.

Thanks!

Case

 

[ericgibbs]

ok, there we go.

Thanks!

Case

hi,
That looks better.
Remember the important point when driving motors is to ensure there is enough base current to drive the transistors hard into saturation.

The hFE [high collector current] of the transistor is lower than the hfe [low collector current].

Look at the graphs on the TIP datasheet.

BTW: dont forget the back emf protection diodes across the motor.

 

[case-sensitive]

this should be it...

Schwere Geburt (heavy birth ,-) )

Case.

@audioguru: could not find the diagram with the saturation voltages/currents...

 

[ericgibbs]

this should be it...

Schwere Geburt (heavy birth ,-) )

Case.

@audioguru: could not find the diagram with the saturation voltages/currents...

hi,

TIP32 graph attached.

 

[case-sensitive]

looks like it won't go below 0.3 V at all?

 

[ericgibbs]

looks like it won't go below 0.3 V at all?

Thats a limitation of transistors.
Its not a serious problem if the motor supply is a highish voltage say 12V or 24V, but at 5V its in the order 10% considering two series transistor.

You can get power FET's with a very low ON resistance, milliohms, if the Vsat is causing you a problem.

Whats the end project going to be.?

 

[audioguru]

looks like it won't go below 0.3 V at all?

The graph shows a typical transistor. Some are better and some are worse. You don't know if your transistors are good or not so good.

The max saturation voltage loss is 1.2V when the collector current is 3A and the base current is a whopping 375mA.

 

[case-sensitive]

@audioguru: just don't know, how to read these values from that graph, but that is another story.

@eric: its for a robotic project, one of these cars driving on 4 AA cells. 4.2 V is more than enough for the motors anyway, starting current will be quite high, but then it goes down to 100-200mA

so the transistor story is just an extra, not meant to do it, its more about the programming

 

[audioguru]

It is easy to read the graph. How much collector to emitter voltage loss there will be is on the left side. A line is for the amount of collector current and the amount of base current you provide is at the bottom.

If the transistors are not turned on enough then the motor might not start. It is good to have them turned on hard so the motor gets almost full power to start.

 

[case-sensitive]

yes, but you have to make up anything else then 03, 1 and 3 A in this case.
60mA at the base gets you 0,3V voltage drop at 1A, ok thats easy to see... Anyway, getting the idea.

 

[case-sensitive]

routed it with Eagle, soldered it on strip/vero board, works, voltage drops from 5.1 V no load to 4,05 V across the motors, when running, good enough.

Thanks again,

Case.