Voltage regulation

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Voltage regulation

Postby t » Wed Apr 11, 2007 5:22 am

I am using a Adapt9S12C32 MCU Module and I am using Port
A to drive a 16 x 2 LCD character display. The module is being
powered by a 9V battery.

When I originally connect the 9V battery to the MCU Module, the
output on the LCD is correct. The output pin on the MCU Module
that supplies 5V is used to power the LCD. Using a multimeter
if I continually check the output pin, every couple of seconds it
reduces by 0.01V. Eventually the supply voltage gets below
the minimum level required and the display disappears.

Now if I disconnect the battery and wait a small period of time. I can
reconnect the battery and the above process repeats all over again. How can I make the supply from the MCU Module maintain a steady 5V?
t
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Postby Jazake » Wed Apr 18, 2007 2:09 pm

I am working with a 16 X 4 display, powering my microcontroller with a 5 v regulator also. I am just having trouble with my SCI. Do you have any capacitors discharging somewhere on your circuit. Also what you might need is some bypass capacitors at the input and output of the voltage regulator. Usually you need them for AC power but I would suggest them to you if you continue to have an unstable output of 5v. I also had a similar problem where the output of the regulator increased or decreased linearly based on the input voltage. In that instance, I just replaced the regulator with a new one and it worked perfectly. I must have overloaded it somewhere and blew it. I suggest the bypass capacitors and a new regulator, get a 7805. Hope all goes well.
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Postby t » Fri Apr 20, 2007 8:41 pm

The voltage regulator is part of the Adapt9S12C32 MCU Module I bought from Technological Arts. It looks like they have a capacitor on the output line and an optional capacitor on the input line. You may be right about the voltage regulator being faulty but how can I check to be sure?
t
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Postby ed taylor » Mon Apr 23, 2007 4:43 pm

hi:

the regulator may be going into thermal shutdown. try and see if it is hot. **** caution *** it may be very hot be careful not to burn your fingers.

you may also be reverse powering the regulator from your lcd supply. ansure that only the ground is common between the two devices, not the 5v supply.


regards,

ed
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Postby t » Wed Apr 25, 2007 8:14 pm

The regulator does not feel hot so I don't think it's going into thermal shutdown.

Both devices share a common ground so your right about that. I'm not sure about the reverse powering. I am powering the MCU with a 9V supply. The board supplies VCC (5V) to pin 47 and I use this to run the display. Is this a potential problem?
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Postby cbarnes » Mon Apr 30, 2007 10:29 am

This does not sound like a regulator or board problem. I suspect if you try it with a power supply instead of a battery, you'll find it works. Don't forget, a 9V battery has about 90mAh of energy capacity, so if you are drawing 30 mA of current from it, it would last a maximum of 3 hours, under ideal conditions.
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