Battery Voltage for PIC micro

lm2965

I'm building a replacement remote control unit around a PIC16F88 chip.

The data sheet shows supply voltage must be between 4.5 and 5.5V.

The RC case I'm using holds 4xAAA batteries. If I use alkaline cells, my voltage will vary between 6.5V (briefly when new batteries are inserted), through 6V in normal operation and finally drop below 4.5 when the batteries are exhausted.

I thought of using a diode to prevent against incorrect polarity (dropping 600mV). Will this voltage drop will mean the 4.5V limit is reached earlier or are the batteries at the end of their life anyway ?

Should I use a 5v1 zener or a 7805 to limit the voltage to 5v ?

Look forward to hearing what others do !

fastbike said:

I'm building a replacement remote control unit around a PIC16F88 chip.

The data sheet shows supply voltage must be between 4.5 and 5.5V.

The RC case I'm using holds 4xAAA batteries. If I use alkaline cells, my voltage will vary between 6.5V (briefly when new batteries are inserted), through 6V in normal operation and finally drop below 4.5 when the batteries are exhausted.

I thought of using a diode to prevent against incorrect polarity (dropping 600mV). Will this voltage drop will mean the 4.5V limit is reached earlier or are the batteries at the end of their life anyway ?

Should I use a 5v1 zener or a 7805 to limit the voltage to 5v ?

Look forward to hearing what others do !

Click to expand...

Hi,

If you use a 5V1 zener or a 7805 regulator it will reduce the charge life of your battery a lot.

You can use a low drop-out regulator, or 1 AAA battery with a DC-DC convert to generate the 5V for the PIC.


Emanuel

emanuelcsm said:

If you use a 5V1 zener or a 7805 regulator it will reduce the charge life of your battery a lot.

You can use a low drop-out regulator, or 1 AAA battery with a DC-DC convert to generate the 5V for the PIC.
Emanuel

Click to expand...

I've taken a look at the Nat Semi web site and will use a LM2940/5 LDO regulator. As a bonus it also gives polarity protection.

Thanks for your help.

And you cannot use 7805, as you need at least 7V in order to have a regulated 5V output.

Use low drop out regulator as stated above.

Or you can use zener in case the LDO regulator not available.

Hi,

Use PIC16LF88 and connect only 2xAAA Batt.

Dont use regulators, they will drain the power for nothing. Also learn how to put the PIC in SLEEP mode, or how to reduce the clock to 32KHz.

Good luck.

gidimiz said:

Hi,

Use PIC16LF88 and connect only 2xAAA Batt.

Dont use regulators, they will drain the power for nothing. Also learn how to put the PIC in SLEEP mode, or how to reduce the clock to 32KHz.

Good luck.

Click to expand...

Hi,

Unfortunately I'm stuck with the 16F88 at this stage. For my next project I will ensure I use a 3volt version :wink:

I would just use some diodes to drop the voltage
and be done with it. If this is for a remote control,
the PIC will be powered up only on keypresses
anyway, right?

Nick

I think an LDO is the best choice. There are low quiescent current LDO's out there. The input to output differential is low, so you will not waste too much power. Yet you will get good regulation, unlike using diodes or Zeners.

Nick C. said:

I would just use some diodes to drop the voltage
and be done with it. If this is for a remote control,
the PIC will be powered up only on keypresses
anyway, right?

Nick

Click to expand...

PIC is powered up at all times so it can respond to key presses. It goes to sleep after each transmission of the IR remote control code and wakes up on a key press.

My final design uses the LM2965 - which has an extremely low drop out so will allow the PIC to operate even when the batteries are getting a bit flat.

Next time - I'll use the 3v version of the PIC !!


I looked at the diode suggestions and rejected them as the battery voltage can range from 6.5v (from really fresh batteries) down to about 4.8v from tired batteries. The voltage drop over the diode(s) would have needed to drop at least 1 volt, to protect from high voltage, which would have limited the usable lifetime of the batteries when the volatge dropped. Zener solutions would have wasted too much power.

Thanks for all your suggestions.