I have a sensor that need a regulated 3.0 volts supply. The 3.3v output from the arduino uno pin is too high so I tried to place a diode in serie with the 3.3v pin to drop the voltage to 3.0v and supply my sensor.
The sensor do not need more than 100 mA (in fact closer to 50mA). The arduino 3.3v regulator can do it.
1- when I put a 0.3v diode in serie, I get a bigger drop than 0.3volts. I don't understand why? The diode read 0.314v on the diode tester on my DMM. It should drop 0.3volts.
2- I also tried a zener diode (1N5226 B - 500mW - 3.0 volts) + a resistor in a voltage divider configuration. This also don't really work. Depending on the resistor I use (from 15 ohm to 82 ohm), the voltage I get start from 3.3 and drop to 2.6 volts. With or without the sensor (load) connected.
I can and will provide schematic and other details to let you help me better (edit: now included in my next reply)! But before doing this, what is your tougth on this way of powering sensor? Maybe it is not a good idea in the first place and this is why I don't find much about this on the forum? Or it is very common and schematic are already available somewhere?
Could really do with knowing the spec of the sensor to see what supply it really needs
If it needs a regulated supply what you propose won’t work ( it doesn’t anyway ) .
Think you need to post some details
here is the schematic and some math for the Zener part. There is not much on the sensor data sheet but it say that Vin cannot exceed 3.1 volts. In reality, it can go higher but I fried 1 out of 2 sensors at 3.3v. It is best to aim 3.0v.
It also mention that the sensor current is between 30 and 50 mA (except a short (msec) period at power up) were it can reach not more than 96 mA.
if those option don't work, what is the most efficient method to have 3.0 volts for my device. Keep in mind that I want to power this device with batteries. The arduino regulators are already wasting much of it. In the end, I will use a 3.3volts arduino to save a bit more on that side.
I'd start from a higher voltage and use two mini buck converters of these makes: Mini buck converters
These modules have an extremely low quiescent current and are syncronously switching effeiciently for low voltages.
Use one for 3V and another one for 3,3V to power an Arduino Pro mini.
If you have an actual Ge diode, put it on Ebay. Guitar nerds value them for effects box re-creations. But sell it as-is because nobody makes them any more, and they have a problem with crystallization over time.
when I put a 0.3v diode in serie, I get a bigger drop than 0.3volts. I don't understand why? The diode read 0.314v on the diode tester on my DMM. It should drop 0.3volts.
The forward drop of any diode will vary as a function of the current.
Also if the current * voltage heats the diode the forward voltage will change as well.
If you really need 3.0 V I would recommend Linear Regulator or similar part.
My first inclination would be sure the sensor requires 3.0 volts and cannot run on 3.3V Requiring 3.0V is kind of an odd requirement worth checking and understanding the sensor's requirements.
aarg:
If you have an actual Ge diode, put it on Ebay. Guitar nerds value them for effects box re-creations.
ahah! been there done that! I learn so much with diystompbox. This is why I have germanium in my part bins.
RIN67630:
I'd start from a higher voltage and use two mini buck converters of these makes: Mini buck converters
I will go with one of these mini buck converters I think. How did you discrimate the good from the bad one?
to JohnRob: linear regulator are power hungry no? I am looking for high efficiency for battery powered device. The sensor really need 3 volt unfortunately.
RIN67630:
"The sensor do not need more than 100 mA (in fact closer to 50mA)"
50mA is far from being "minuscule" on battery power.
Yes, although what I did not mention is that I power the sensor only few minutes per day/cycle and I have a solar panel to help a bit.
Thank you for sharing the result of buck converter comparison.
The sensor is a methane pellistor (SGX) module. Model Mp7217-tc.
The D-SUN is ok for low power purpose as well, but the recommended HW813 staging a MP2315 synchronous chip is superior in every aspect, specially when you need low voltages.
Is it [this sensor](SGX (mp-7217-tc datasheet) v1.pdf)?
That would indeed call for a linear regulator (not a buck converter). There are LDO regulators out there that can produce a very stable 3.0V from a 3.3V input.
Why no buck converter? That's what you want for larger currents. They're bigger, costlier, and tend to produce far more ripple than a linear regulator (that's by nature). For a 3.3V to 3.0V drop they may even be more efficient than buck converters. Many linear regulators come with enable pin as well.
wvmarle:
They're bigger, costlier, and tend to produce far more ripple than a linear regulator (that's by nature). For a 3.3V to 3.0V drop they may even be more efficient than buck converters.
Quite a lot of false assumptions...
The buck converter is smaller than the last phalange of your little finger, and cost lees than one $.
A 3.3V to 3.0V drop is simply not doable with a buck converter, but you should start at the battery voltage not at 3.3V
And regarding the ripple at 700Khz... not a huge issue.
TomGeorge:
Hi,
Have you checked ALL the available documentation?
Look at this document and down in Application Window.
It shows the cycle times.
Tom...
PS, It would be good if you provided the links, so we can make sure we are looking at the same device.
Thank you for this document. Somehow I missed it and your rigth I should have post the link to the sensor data sheet in the first place. It is not exactly the same sensor since my version is mounted on a board and also output temperature data and have TC fonctionality (higher methane concentration capacity) but I am certain it work similarly with respect to cycle and energy efficiency. The problem, is that i only used PWM from the market to control motor and I have no clue of how to achieve this kind of duty cycle in this case. It need an oscilllator to trigger the enable pin of the sensor power supply ? (buck or linear) and this would also need to be sync with my already working ADC (ADS1118). I will go there only if I have no choice.
wvmarle:
Is it [this sensor](SGX (mp-7217-tc datasheet) v1.pdf)?
That would indeed call for a linear regulator (not a buck converter). There are LDO regulators out there that can produce a very stable 3.0V from a 3.3V input.
Why no buck converter? That's what you want for larger currents. They're bigger, costlier, and tend to produce far more ripple than a linear regulator (that's by nature). For a 3.3V to 3.0V drop they may even be more efficient than buck converters. Many linear regulators come with enable pin as well.
Yes this is the good sensor.
I tested L7805 / 7803 and similar and concluded that they were big energy waster. Most of you sent link to smaller version of linear regulator that I did not know about. I will have to dig into this a bit more. The enable pin is also a very interesting feature to have in such device. This is a keeper for sure.
The D-SUN is ok for low power purpose as well, but the recommended HW813 staging a MP2315 synchronous chip is superior in every aspect, specially when you need low voltages.
The regulator comparison is interesting but not only! This mppt solar charger + regulated output for microcontroller all in one small package is surely a handy device to have.
