How to drop from 6V to 5V a "clean" way?

[BobP]

Hi,

As I am about to build a circuit powered from 4 x 1.5v cells I just looked at the maximum ratings for the 18F2525 and it says it can take a max of 7.5 volts! So running a 2525 from 4 x 1.5v cells should be ok. Check the datasheet for the PIC you are using.

But personally I would put a diode in series with the +ive supply. It’s surprising some of the kit I have seen where the user has 'overcome' the plastic mouldings preventing incorrect battery fitting!!!

Bob

[Luciano]

I just looked at the maximum ratings for the 18F2525 and it says it can take a max of 7.5 volts!
So running a 2525 from 4 x 1.5v cells should be ok. Check the datasheet for the PIC you are using.

Hi Bob,

The voltage 7.5V is not the maximum operating voltage of the chip.

The 7.5V visible in the "Absolute Maximum Ratings" page 323, is
the voltage where you can go without physical damage to the chip.
The PIC18F2525 will operate reliable only when the voltage is between
4.2V and 5.5V.

This note is visible on page 323:

NOTICE: Stresses above those listed under “Absolute Maximum Ratings” may cause permanent
damage to the device. This is a stress rating only and functional operation of the device
at those or any other conditions above those indicated in the operation listings of this
specification is not implied. Exposure to maximum rating conditions for extended periods
may affect device reliability.

See the datasheet page 326, parameter No. D001 for the operating voltage.

Datasheet:
http://ww1.microchip.com/downloads/e...Doc/39626b.pdf

Best regards,

Luciano

[BobP]

Many thanks Luciano, I thought it seemed a bit high but as usual I get interupted with phones etc. before reading it properly.

Thanks,
Bob

[mvs_sarma]

If possible, add another call and use 7805. but after an hour of use the voltahge will fall below the I/O differental of 2.5V.then the problem comes.

As many devices work upto 3.3V, why not consider using 3 cells at 4.5V?