I working on project that will connect two digital sensors to a 3.3V Sparkfun Pro Micro Arduino. One sensor requires 2.6V and the other requires 3.0V. Normally I would just use a regulator to convert the voltages, but I have been unable to find any regulators that takes in 3.3V and output 2.6V. The regulators I have seen require at least 4.75V VIN. Does anybody have suggestions on a regulator or other IC that step the voltage down? Would a voltage divider do the trick? If so would a divider impact the stability of the sensors? (I have decoupling caps between the VCC and GND pins on each sensor.)
I would try 2 "schottky" diodes in series, first one drops 3.3V to 3V, and 2nd drops
3V to 2.7V, or thereabouts.
You have a complex regulator requirement What you want to do could be done easily 2 ways one would be to get 2 switching regulators (buck mode) the other would be 2 LM317L regulators. Switchers are sometimes a little noisy and require simple LC filters for Clean DC But they are almost a drop in part the Linear regulators are a good choice also but they require a resistor and a Small value pot 50 - 100 ohms for each one for final Trim not adjust. The formula is simple and the output voltages are easily done... with either device.
Doc
LM317 would require a minimum of 5V or so in to produce 3V out.
Dan, there are LDO variables too... Diodes are a poor choice as they don't regulate very well the output voltage can swing as the load current does. This will show up as noise on the output... maybe ok for digital but Not for linear. The voltage drop across any diode is a function of the diode material and type as well as the current drain...
Doc
What are these sensors?
Voltin:
I working on project that will connect two digital sensors to a 3.3V Sparkfun Pro Micro Arduino. One sensor requires 2.6V and the other requires 3.0V. Normally I would just use a regulator to convert the voltages, but I have been unable to find any regulators that takes in 3.3V and output 2.6V. The regulators I have seen require at least 4.75V VIN. Does anybody have suggestions on a regulator or other IC that step the voltage down? Would a voltage divider do the trick? If so would a divider impact the stability of the sensors? (I have decoupling caps between the VCC and GND pins on each sensor.)
The 'best' solution is only apparent when one knows all the parameters required to make such a judgment. A couple of simple resistor/zener networks and a few bypass caps might be it.
So what information is missing?
What is the maximum current requirement for both the 2.6vdc and the 3.0vdc voltage sources you require?
What is the maximum excess current capacity of your existing 3.3vdc voltage source after you subtract whatever current it is presently providing to the Sparkfun Pro Micro Arduino and any other components you have wired to it?
Proper engineering solutions require as many of the parameters possible before selecting components and devices to accomplish the task.
Lefty
The 2.6V has a max current of 9mA and the 3V 6mA. I am not sure how much current the pro micro uses, but the processor is an ATMega 32U4 running at 3.3V/8MHz and these are the only two devices on the board. The power supply is not final yet, but I am thinking about a 1000mAh 3.7V LiPo battery that would run through the arduino's onboard regulator.
Thanks for the help.
Voltin:
The 2.6V has a max current of 9mA and the 3V 6mA. I am not sure how much current the pro micro uses, but the processor is an ATMega 32U4 running at 3.3V/8MHz and these are the only two devices on the board. The power supply is not final yet, but I am thinking about a 1000mAh 3.7V LiPo battery that would run through the arduino's onboard regulator.Thanks for the help.
Well for just 9ma and 6ma required I would think that two simple resistor/zener diode supply feed from the 3.3vdc bus would be the best solution. Be sure to check what the drop-out voltage is for the on-board 3.3v regulator on your Pro Micro is. Your LiPo battery will have a output terminal voltage of from 4.2vdc when fully charged to 3.0 or so when fully discharged. So using a single cell Lipo you won't be able to use all the charge that a cell can deliver without your 3.3vdc regulator dropping out of regulation.
Lefty
Thanks for the help. I will try that tomorrow. I am not too concerned about the drop out on the LiPo. I would rather it cut out before it fully discharged anyway.
Voltin:
Thanks for the help. I will try that tomorrow. I am not too concerned about the drop out on the LiPo. I would rather it cut out before it fully discharged anyway.
Well the LiPo battery will not 'cut out', it will continue to discharge through the 3.3vdc regulator, but the regulator's output voltage will not continue to be a steady 3.3vdc once it's input voltage drops below it's drop out voltage specification. Drop out does not mean turned off, just dropping out of regulation. You must have some other means to detect overdischarge of your LiPo cell unless you know for a fact (datasheet confirmed) that it has some form of built in protection, a few higher priced cells do, many don't.
I lost a few LiPo batteries from allowing discharge voltage on the cell to drop below it's allowable discharge voltage in my R/C airplane days, so the threat to cell damage is real. It's not as dramatic as the damage from overcharging a Lipo (think fire and flame), over-discharge just makes the cell unable to be recharged so useless.
Lefty