Supplying voltage to two circuits from the same source

[kjiwa]

Hi, I have two circuits that I would like to power from a single power source (e.g. a battery). The first circuit requires a supply voltage of 1.8V and the second circuit requires 1.9V. I'm having trouble understanding how I can use a single power source to provide an accurate and consistent voltage to each circuit. Should they be connected in series? In parallel? What if I use a 9V battery -- how can I go from 9V to 1.8V and 1.9V? Thanks!

[tron9000]

Hi


For those 2 voltages you require I would connect them in parallel or in other words: connect the input to both from the power source.

Have you come across voltage regulators? If not look into them, there's loads.

Careful of the pitfalls of using a battery source and linear voltage regulators, especially using a 9V battery, it'll be flat before you know it!

[homebrew]

Hi, I have two circuits that I would like to power from a single power source (e.g. a battery). The first circuit requires a supply voltage of 1.8V and the second circuit requires 1.9V. I'm having trouble understanding how I can use a single power source to provide an accurate and consistent voltage to each circuit. Should they be connected in series? In parallel? What if I use a 9V battery -- how can I go from 9V to 1.8V and 1.9V? Thanks!

Please give us some more info on the types of loads. What exactly are you powering?

[kjiwa]

Thanks for your replies. I'm trying to power an ATTiny45 and an nRF24L01+. I'd like to take advantage of each of their low power modes, so using a voltage regulator concerns me.

As for voltage regulators, I have some 5V ones, but I'm not clear about how I can use those to supply 1.8V and 1.9V.

Thanks!

[Zero999]

If you're bothered about efficiency, you need to use a switching regulator.

Using a linear regulator to get 1.8V from 9V will give a crappy efficiency of just 20%.

Another option is to use a 1.5V battery and a boost converter.

[alexanderbrevig]

I would use a buck converter and they can be bought as a module if you don't want to build one.

Don't bother thinking in terms of 1.8 and 1.9 volts, they will both run fine off of 2 volts.

Attached is the buck.xls buck converter calculator from Texas Instruments

[homebrew]

Thanks for your replies. I'm trying to power an ATTiny45 and an nRF24L01+. I'd like to take advantage of each of their low power modes, so using a voltage regulator concerns me.

As for voltage regulators, I have some 5V ones, but I'm not clear about how I can use those to supply 1.8V and 1.9V.

Thanks!

That's perfect... because we are apparently designing quite similar same things :-) I work on a wireless sensor node, too and I have to make the same decisions right now. At the moment I'm thinking about using an LDO regulator as well as a switch mode one. In standby the system would be powered by the LDO one, in operational mode the SM regulator would kick in. With these LDOs you get an incredibly low quiescent down to 500nA. Hence the system would draw something around 2.5uA when in power down mode. I would call that acceptable. However, I do need the full 3.3V for all the sensors I have on my board. So when the node wakes up every couple of minutes or so I would enable the switch mode Boost-Regulator to drive the 3.3V rail. I'll use Schotky Diodes (i.e. STPS1L30) to OR the supplies together.

The whole device will be powered from two AAA Batteries (or NiMH cells) and hence provide a voltage of max. 3V input voltage. Given the 0.3V Schottky forward voltage drop and the 0.1V LDO drop, the assembly should work down to approx. 0.92V per cell which is perfectly fine for me.

I'll post the schematic once I'm done with that. Probably this evening (CET timezone).

Pete

[homebrew]

As promised, here is the design.
As said, absolutely untested! Maybe it contains severe errors.

Would be happy to hear some feedback ...

[lgbeno]

You do know that both of these devices can be run direct from the two AAA cells.  If you save power with this circuit, great but I would think that simply putting then in deep sleep modes at battery voltage would be lower power.


Sent from my iPhone using Tapatalk

[homebrew]

You do know that both of these devices can be run direct from the two AAA cells.  If you save power with this circuit, great but I would think that simply putting then in deep sleep modes at battery voltage would be lower power.


Sent from my iPhone using Tapatalk

Yes of course! No regulator is saving even more power in this case ...
However, other components on MY board (i.e. attached sensors) require 3.3V. Hence I cannot skip the boost regulator. I assumed the same for the TO's project ...

Nevermind, if it happily runs without the regulators, go for it!
 

[alexanderbrevig]

What's great about running it off of batteries is that someone can make another Batterizer joke soon