Can anyone explain the voltage drop?

Interfacing hardware, sensors, output drivers, chips.
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Can anyone explain the voltage drop?

Post by glata123 » Fri Jan 20, 2017 5:13 am

Hi guys

I'm using MSP430F2274 which needs a power supply of 1.8V - 3.6V.

I have a computer charger which gives 19V and maximum 1.5A. I regulate (correct word?) that with L7812CV down to 12V which I then use in a motor controller. I then regulate those 12V to 5V with L7805CV and use a voltage divider with 4.7kΩ and 9.4kΩ to get it down to 3.3V (I have some capacitors also connected just in case)

When measured without the MSP430 connected, it is just as predicted, 3.3V across. But when I connect the MSP430, it drops down to 1.04V which the MSP430 doesn't run on.

Someone suggest me to use LM317, and I have check it online and found some datails about it. From the details of LM317 ,do you think it is OK?

Any suggestions on what could be wrong? Thanks very much.

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Re: Can anyone explain the voltage drop?

Post by paul » Tue Jan 24, 2017 3:29 pm


the problem is your voltage divider, the high values you are using limit your current to about .3 mA not a useful amount of current. Your simplest solution is just to buy a 3,3V regulator.

If you want to know how the math works, read through voltage dividers in the Art of Electronics or find an online tutorials on voltage dividers.

We have some in the our shop or wherever you get your electronic supplies.


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