Low current PIC

[flatfootskier]

The last pic project I did (quite a while ago) I used a TDA3664 voltage regulator to get 5v. It had a quiescent current of less than 15uA & gave me great battery life with a low speed Xtal. IS this still the way to do it or is there some way a bit smarter.

 

[justDIY]

best way to do it is use a battery that is compatible with the pic's voltage range, needing no regulation

for example a 3.7v Lithium cell, 2-4 Nimh in series, or even a 3v lithium coin cell

 

[flatfootskier]

Sorry, I should have cleared that up - it has to come from a lead acid 12V cell - which drives a 100A motor occasionally for short periods. Suprisingly, the Wh load over a day from a dribbling 7805 is much greater than the short 100A bursts

 

[justDIY]

yea those old linear regulators are wasteful creatures.

how much current does your PIC circuit need when it's fully operating? you could use something like a shunt regulator to siphon off a 1mA (or less) of current from that 12v cell, and power the PIC from that. then use one of the pic's pins to enable a higher power regulator (look for LDO regulators with a shutdown pin) when you need to drive 'user interface components' like LEDs and other displays. this way the wasteful high-current linear regulator will only be in circuit when your pic needs to be fully operational. in standby, the shunt regulator will only siphon enough current to operate the pic in bare bones mode.

 

[Nigel Goodwin]

Sorry, I should have cleared that up - it has to come from a lead acid 12V cell - which drives a 100A motor occasionally for short periods. Suprisingly, the Wh load over a day from a dribbling 7805 is much greater than the short 100A bursts

As your previous regulator only used 15uA, that should be perfectly fine from a lead acid battery.

 

[picasm]

You could also save power by choosing a PIC18F series microcontroller, these have "nanoWatt Technology" - this provides more modes for power saving by turning-off some features etc.

 

[mramos1]

You could also save power by choosing a PIC18F series microcontroller, these have "nanoWatt Technology" - this provides more modes for power saving by turning-off some features etc.

The 12F and 16F chips have "nano watt" listed on their datasheets as well.

 

[picasm]

The 12F and 16F chips have "nano watt" listed on their datasheets as well.

Yes, you are right, but looking at some of the data sheets it appears that some don't have as many of the "nanowatt" features as others.
For example, in the 16F range, the two speed startup option is only available on a few devices such as the 16f87,88 whereas more of the 18F range have all of the features.

I think they just keep adding more power saving features to newer devices whilst still using the same "nanowatt technology" name.

 

[Nigel Goodwin]

It's still pretty pointless in this thread, as the power source is a lead acid battery - hardly need for 'nanowatt' technology?.

 

[justDIY]

sounded to me like the regulator was wasting the power, not the pic. (op mentioned 7805)

 

[picasm]

hardly need for 'nanowatt' technology?.

The original thread was "Low current PIC" and the op mentioned using a regulator with a quiescent current of less than 15uA.

 

[Nigel Goodwin]

The original thread was "Low current PIC" and the op mentioned using a regulator with a quiescent current of less than 15uA.

And then mentioned it's powered by a lead acid battery!.

 

[mramos1]

I have to agree. Lead acid is plenty of power if you run a pic at low speed, which he said he did as well. 15uA for the regulator, leave it in..