H-bridge help

[Forgey]

I am trying to build a robot and i have been having trouble getting a working h-bridge for my motors and i was wondering if anyone could help me work this out.

i have 2 motors to drive with either a pic or a c-stamp pwm. the motors are HG16-120-AA Operating Voltage 5.4v-6.6v Rated Current 350ma Stall Current 1600ma.

i have some irf530 and irf9630 power mosfets that i think will work for those motors but i am not sure as i have yet to have any luck getting it to work right.

i also have some irl510 mostfets if they would help?

i plan on driving the motors off 4 AA battery's

any help would be greatly appreciated

 

[birdman0_o]

Those mosfets all need excess of 10V to be "turned on fully"

Look into logic level mosfets.

 

[birdman0_o]

I think they begin with "IRL___"

 

[Forgey]

i have irl 510 mosfets

 

[arhi]

you can use mosfet driver if you want to use those mosfets .. for e.g. TC4428A

 

[birdman0_o]

Did you try your H bridge with the IRL ones. Remember it is important to have the protection diodes. Is it a bidirectional H-bridge?

 

[Forgey]

arhi, will that work with the mosfets i have at 6v

birdman, last time i played with this was last winter so i am not sure but i think i did, it is bi directional and i did have diodes on it, i know one time i built it i fried one of them but i am not sure why just that i let out the magic blue smoke out of one of the mosfets. but dont i need the opposite channel mosfet to go with the irl510?

 

[arhi]

the motor operating voltage is 6V .. you can safely run it on 12V if you do not exceed 50% pwm. Also, if you limit the current, you can run it on 12V without any problem.

With regards to mosfets, irf530 is not 6V .. IIRC those are 100V mosfets and need 10-20V to open fully, irf9630 is 200V mosfet that need -10V to open ... so your major problem is that you are opening them with 6V so you do not get them open, and the Rds is too high. Using the driver like TC4428A or similar you can take digital input (0/5V) to open the mosfets. If your input is 6V, put a resistor and a zener and clamp it to 5V or check the datasheet for the driver, many of them are up to 10V tolerant

 

[Mr RB]

Why not just buy a motor driver hbridge for TWO motors, 1A per motor (3A peak) fully assembled, and only $10...
**broken link removed**
Pololu - TB6612FNG Dual Motor Driver Carrier

 

[Forgey]

what is the 15v input at C2, C5 and the diodes for? also what is J1 for?

 

[arhi]

diodes are for back EMF that motor will produce and that would otherwise burn the fet's. Some motor drivers have them embedded in chip, some do not, if you are not sure - add them

C2-C7 are there to handle motor peak draw's and to reduce sound motor is making during PWM so all in all, they smooth motor movement and reduce the "dirt" motor is putting back in to the circuit.

 

[Forgey]

i have some 4448 and bat54s on the way so i can try building this, just a few more questions i have. is the J1 the connection to the motor? also can i just trigger the mosfets with 12v and then power the motor with 6v?

 

[arhi]

yes J1 is the connector to the motor
yes I think you can open mosfet with higher voltage then the passing one but why would you do that, if that motor is 6V, if you are using 12V and 50% PWM that is effectively 6V. If you power it using 6V only on 25% PWM you will have 1.5V effective and the motor will run without any torque if it even had any strength to turn at all... When using PWM you have to increase the voltage in order to get any torque from the motor.

 

[Forgey]

thanks for all the help arhi. I built the h-bridge and its working good with my pwm but i have one strange issue after the motor has been running for about 20 seconds it just slows right down to nearly nothing. letting it sit it "recharges" and runs fine for another 20 seconds or so

 

[Forgey]

i figured it out, but thanks anyway for all your help