I'm using a TA7267 (H-Bridge) to drive a small Mabuchi DC motor. I'm suplying the IC with a reference voltage of 3V, and the operational voltage is 5V. The terminals of the DC motor are connected directly to the OUT1 and OUT2 pins. However, the motors are working pretty slow.
I've been checking the datasheet and they suggest you can add a resistance in parallel to the motor, but I don't know what value it should be, and if it would make a difference. Any idea why this would happen?
UPDATE I've verified without connection the DC motor, and the IC is giving the correct voltages in its outputs. So why isn't the motor drawing enough current?
UPDATE I've tried adding some resistances in parallel but nothing good happened :(
**Hi tatofoo,Its possible the**<br><p>Hi tatofoo,</p><p>Its possible the voltage is too low. The datasheet says it needs a minimum 6v on pin 7 to operate properly. Try adding another battery or 2 temporarily to see if that helps.
Since I had a 9V around, I’ve tried putting 9V directly to pin 7, but still the same problem. The voltage for the motors come from 2 AAA batteries, which works fine when I have my motors going in one direction. I have a snubber diode for each robot.
At first I though the H-Bridges could be broken or something, but I bought two, and the two of them give me the same problem. I guess that I’ll just stick with unidirectional by now, and hope that the turns in the line follower competition aren’t that harsh
According to the datasheet, pin 7 is Vcc, the logic supply voltage pin. Vs on pin 6 is the motor supply voltage pin.
The transistors inside the h-bridge are BJTs which will use a portion of the voltage themselves when fully on in saturation. It lists 1.2 and 1.05 volts for upper and lower transistor loses, leaving about 0.75 volts to drive the motor from a 3 volt supply.
A 9 volt battery is somewhat less than capable of delivering larger amounts of current typcially required by small motors. It might work as a supply battery, but probably not for long, or very powerfully, unless the motors are somewhat efficient. AA batteries are probably about the smallest that should be used in small hobby robots.
Now I have a pretty basic question about circuits.
I’m using two mabuchi motors that works with 3V and a current of 1A+ or so. Currently, I’m using just a transistor connected to a 3V power source to drive them. When they are spinning, if I measure its voltage with the tester it says 1.10V.
The same thing happens with the h-bridge. When the motors are not spinning, if I measure the voltage on the outputs, they give 3V, but if the motors are spinning, they give like 0.75V.
I’m afraid of using a higher voltage power source for the motors, because I could break them and they are not mine ;P. So, what I want to know is which voltage should not be higher than 3V? the voltage measured when the motors are not spinning, or when they are? I ask this because I don’t know if the spinning motor can alter the voltage in some way.
And then, could I use 3xAA batteries to power them with the h-bridge, confident that the transistors will eat approximately 2V+ and let me my motors get the rest without exceeding its nominal voltage?
I really appreciate all the help you have given me so far.
You say you measure the voltage on the outputs while the motors are spinning, but it’s not clear what outputs you are measuring from. Is this pin 3 and pin 5 of the TA7267 which are also connected to the motor wires? If so, and you are using a 3 volt supply, 2 AA batteries, you should not see a 3 volt reading, as the transistors will always lose about 2 volts from the supply, when fully turned on.
Vs (pin 6) of the TA7267 should be possible to safely connect to 3 AA primary cells, or 4 AA rechargables, as the 4.5 to 4.8 volts should be safely limited down to the 3 volts or less required for the motors, when delivered through the transistors of the h-bridge. Bipolar transistors usually always loose a diode drop (or more) of voltage across their collector emitter circuit path.
Now I have a pretty basic