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Motor--7805 Problem

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adrianvon

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Hi,

I am driving a 12VDC 2A motor with a MOSFET h-bridge, where with the same ground i have the 7805 voltage regulator connected. Now when the motor is active, the h-bridge is draining approx 0.2V to ground. This is causing the 7805 IC output to increase to approx 5.2V.

Is it normal that the h- bridge leak some voltage to ground ?? if yes, how can i prevent the 0.2V from going to the 7805 ground pin ??
 
Can you post a schematic? The 7805 should be referenced to ground. If the ground reference is elevated of the 7805 the output voltage will elevate. There is something to your circuit I am just not seeing.

Ron
 
It sounds like what you have is a voltage drop on your ground line - and a big one. Move the ground for the H bridge to the point where the main power supply comes in and make your measurements from that same point. Make sure your wires are big enough for 2 amps.
 
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Hi, thanks for the replies. Attached is the diagram of the H-bridge with the list of components used. The other diagram shows how the 7805 ground is connected to the h-bridge.

So it is not normal to have voltage leak to ground when the motor is on ??
 
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The 7805 is supplying the PIC, LCD and other ICs. The motor is being supplied from a bench top power supply. The only thing that the H-bridge and the 7805 are sharing is the ground.
 
.2 volts is a lot of drop across a ground wire. Place your probe ground directly on the 7805 ground and then measure the 5 volts.
 
Hi,

I am driving a 12VDC 2A motor with a MOSFET h-bridge, where with the same ground i have the 7805 voltage regulator connected. Now when the motor is active, the h-bridge is draining approx 0.2V to ground. This is causing the 7805 IC output to increase to approx 5.2V.

Is it normal that the h- bridge leak some voltage to ground ?? if yes, how can i prevent the 0.2V from going to the 7805 ground pin ??
Single point ground layout.
 
Single point ground layout

What is a single point ground layout please?

yep, check the peak current needed by the motor.

The 7805 is supplying the PIC, LCD and other ICs. The motor is being supplied from a bench top power supply. The only thing that the H-bridge and the 7805 are sharing is the ground.


Is there a kind of a filter which keeps the ground to 0V??
 
Glad it was figured out, :)

Ron
 
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