intend to use npf 7.4V batteries on a project that needs two voltage levels:
6V for an audio device
5V for an ATtiny85 controller
How should I reach these two different levels?
Should I use two LDO regulators in seriesr? or should I use an LDO parallel to a regular regulator?
ps. I left out buck converters because of the coil and the noisy output that can be picked up by the audio signal.
What's a "regular regulator"?
If currents are low, use 1 LDO for 7.4V -> 6V and another LDO for 7.4V -> 5V
Be aware of the end-of-discharge voltage of your battery, which probably is well below 7.4V.
You might have to step-up the voltage beforehand.
regular regulator, meaning a linear voltage regulator instead of an LDO
I understand that, as long as the dropout voltage exceeds 1,5 V, the LDO can be replaced with a more stable NPN Darlington linear regulator
A regular regulator is a linear voltage regulator that's not LDO, ie 78xx series.
Use two regulators in parallel - you don't want the ground currents in the digital part injecting noise into the
audio part. Use star-grounding of course.
Simplest to use two identical LDO regulators, make them both LDO, then you only have one datasheet
to check for decoupling capacitor requirements and can step/repeat the circuit design.
An LDO is a linear regulator, it's just optimized to work at low voltage differences (0.2V and less are possible)
got it!
so they are both linear but they are not both regular.
one is more of a particular regulator.
Low dropout regulators are usually much more fussy about decoupling capacitors and their ESR, as the stability
criterion is much more constrained for the output stage of an LDO, so check the datasheet about this.
MarkT. I don't understand how I could use two identical LDOs. I thought that LDOs have an absolute output, not a relative one.
Do you mean identical in terms of datasheet capacitor values needed for noise suppression?
orinocopaul:
I thought that LDOs have an absolute output, not a relative one.
Both exist.
For example, the LM2931 is an adjustable regulator
following forum advice, I measured the 7,4 V Li-ion battery and it turns out at end-of-discharge voltage goes as low as 6 or even 5 volt. moreover, when fully charged it puts out 8,3 V.
should these large voltage range influence the choice of LDO regulator?
Does the audio device need 6v because it has a regulator built in???
Good question wolframore.
orinocopaul:
should these large voltage range influence the choice of LDO regulator?
No linear regulator is able to deliver a voltage higher than its input.
If you really need 6V from 5-8.4V, there's no way around a switching solution like a boost converter or charge pump.
the audio device has a few voltage regulators.
(schematic attached)
but officially it takes either
9V AC
or
6 V DC (four type C batteries)
do you think I could plug in my 7,4 V battery instead of the four type C batteries and rely solely on the already built in voltage regulator? (it is already suppose to take 9V AC anyway, isn't it?)
The MAX887 tolerates up to 11V on its inputs.
great!
could I also tap in for 5V?
(for the ATtiny controller)
Why don't you just use the onboard-regulator of the arduino as it is intended?
I intend to use an ATtiny85. A whole arduino is a bit overkill for what I want to do.
Ah sorry, confused this thread with another one
The Attiny85 operates at 2.7-5.5V, so the 3.3V from the MAX887 should be usable.
