Hi All,

This may be a stupid question to most, but I got tired of searching the net so i thought i'd just ask.

Do i have to have a voltage regulator for an electronics project if my supply is a set of batteries whose output matches my required voltage? I'm using a pic16 micro controller and I want to power it with two AAA batteries in series which would give out over 3volts that the pic can use. I guess i'll need to put in some diodes and capacitors to make sure there's no overvoltage spikes or reverse current when i flip on a switch or something, but other than that is there a real reason for me to use one? the pic can operate between 1.8 - 3.6 volts. for the batteries to reach 1.8 volts that would mean that they'd be completely dead anyways before the pic stops working, correct?

also, to get maximum battery life i was thinking of going with a switching regulator instead of linear. is there going to be a huge difference in batt life between the two?

i'm just making things up as i go along with no one here to tell me otherwise . any input/suggestion is appreciated.

thanks

 

No, you do not need a regulator.

A switching regulator is never 100% efficient. You will get maximum battery life by connecting directly to the two AAA batteries and using all the tips for low power operation:

• disable all subsystems not needed or when not in use
• reduce all loads, pullup and pulldown currents
• use the lowest operating frequency
• go into SLEEP mode as often as possible

 

Whether or not you "have to have a voltage regulator for an electronics project" depends on how the circuit supplied the power acts under varying DC voltage input. Battery voltage varies with load and with length of operation and with battery charge. How does your controller act with low voltage? How critical is reliable operation of your controller? What is the ramification of your controller supplying bad output data or control?

Mr Chips provided tips for low power operation but lots of questions need to be answered to fully answer "do I have to have a voltage regulator?"

 

oh i see, i haven't gone through the data sheet extensively to see what effect a slightly varrying power supply would have on it's operation. but i assume it shouldn't cause too much problems. I know it has a low power mode at 1.8V, although i dont think i'd be able to use that feature if i were to connect the batteries straight to the pic. and i guess it's not critical the reliability of the pic's operation, it's driving a display and sends some data to another chip on power up but other than that it should sit idle for the rest of the time.

but thank you wmodavis and Mr Chips for your tips and advice.

 

The PIC LF (low voltage) parts will generally work fine from 3.3v down to 1.8v.

I think what Wmodavis is saying is that it depends a lot on what the PIC is interfacing with, and if it can interface ok with only 1.8v Vdd. It can still light a LED at 1.8v but it will be many times dimmer than at 3.3v.

Of if the PIC needs to connect to serial or a LCD or a memory chip, something like that, the interface to the other device might fail.

If you post more details of what your project actually does we can offer better advice!

 

Of course, as other said, you can run without a regulator. But you have to understand the issues.

Some microcontrollers (not sure abou PICs), need certain voltages to run at certain clock speeds. For example, some MSP430's have an internal oscillator that can run at 25MHz, but ONLY if the voltage is above 3V. So if you have configured the oscillator to run at 25MHz, once your voltage dips below 3V the system may hang up.

This highlights the main issue with running without a regulator. Your system will likely have unstable or unpredictable behavior at low voltages. As the battery voltage decreases, some parts may stop working before others and the system behavior may get wierd, or just lock up. If you use a regulator, you are guaranteed a fixed voltage to your system until the battery gets to a certain point. This make sit easier to design a predictable and stable system.


It just all depends on the specifics of your system.