Hi,

I am driving a motor (12v 2A) using an H-bridge. The supply use is from a bench power supply which with the same supply, the PIC, LCD and other ICs are connected using the 5v.

Now the problem is when the motor starts, the 5v supply rail (which is supplying the PIC, LCD etc.) is increasing to approx 5.25V.

Is this normal? and how can i eliminate the 0.25v increase in the 5v supply?

Any help is appreciated.

Thanks in advance.

 

Hello,

Do you have the complete schematic of the H-bridge with the driver?
(including all caps for decoupling and diodes to prevent back EMF troubles).
It can happen that the motor is giving pulses on the powersupply lines, that are giving trouble in the powersupply itself.

Bertus

 

Hi, thanks for the reply. Attached is a diagram of the H-bridge used. The only cap which i am not using is the .1uF which is connected in parallel with the motor.

 

Is this normal? and how can i eliminate the 0.25v increase in the 5v supply?

No it's not normal. What instrument did you use to measure the 5V? Scope or Meter? Are you sure the increase is real?

I've also seen bench top supplies doing or displaying strange things when drawing a non-DC current.

 

What instrument did you use to measure the 5V? Scope or Meter?

I used both the scope and meter to measure the output voltage

 

Another question; i am using a single schmitt trigger from the 40106 IC. The remaining five schmitt triggers are not being used. Is there another IC with a single or dual schmitt (which is not SMT) ??

 

Ok finally i found out what was causing the problem. When the motor is active, the h-bridge is draining approx 0.2V to ground. This slight increase in ground is causing the 7805 to increase the output voltage.

Is it normal that when an h-bridge drives a 12v 2A motor, slight voltage drops to ground ?? if yes, how can i provent the 0.2V from going to the 7805 ground pin ??

 

any suggestions please?

 

Hello,

What kind of wires are you using to connect the H-bridge to the powersupply?
Can you try to use thicker wires?

Bertus

 

Hi, i think the wires used are not thick enough. The reason for using tin wires is since the circuit is on a breadboard and thick wires won't clip. Can this be the reason for the 0.2V leakage to ground? if so, why?

Thanks.

 

Hello,

The thin wrires have a higher resistance as the thicker wires.
Ohms law is applying here V=IxR.
You can use thick wires with a very short piece of thin wire soldrered at the end to adapt it to the breadboard.

Bertus

 

Bertus, If i make the wires thicker, will the circuit work?

 

Hello,

The voltage drop over the wires will be less if you use thicker wires.

Bertus

 

Sorry, i didn't see post 11. Can i use 2 thin wires in parallel instead?

 

Hello,

If you run two thin wires parallel, the voltage drop with be half.
If you run 4 thin wires parellel, the voltage drop will be 1/4.

Bertus

 

Thanks a lot Bertus for your help as you said, the thin wire was causing the problem