Different Voltage Supply

Hi, I'm designing a breathalyzer using MQ303A sensor.

Accourding to the datasheet the sensor needs a warm up time of several minuties when supplied with 0.9V, however when designing a breathalyzer that's not a great idea.

So in the datasheet it is mentioned that i can supply the sensor with 2.2±0.2V high voltage for 5-10secs which would make it stable, i'm assuming then i can bring it down to the normal value of 0.9V

So does anyone know how to do that? To feed the sensor with 2.2±0.2V for a certain time and then reduce it back to 0.9 V ?
here is the datasheet of the sensor

How do you consider not following the manufacturer's own data and recommendations "not a great idea"?

The commercial breathalyzers use these sensors and you don't see them asking to wait for several minutes but only few seconds, also the manufacturer's own data states that it is possible to finish the warm up within seconds.
"Not a great idea" as in implementing it into a breathalyzer

“ or you could give 2.2±0.2V high voltage for 5-10secs before test, which make sensor easily stable.”

Why do you think this is Alternating Voltage.

I'm not sure what's the correct term, my issue here is how to do this

2.2±0.2V is in the range of 2.0v to 2.4v

I know this, The thing is i want to supply with this range for 5-10 sec ONLY and then bring it back to 0.9 to avoid damaging the sensor

If you have just the device, you need to add a 0.9v power supply to it.

Suggest you get a complete unit that has all the necessary components to get the project to work.

It looks like it's not an easy task. Look for a regulator such as TLV758P or other adjustable low voltage regulator.
You can choose here what you need Linear regulators (LDO).

I don't get it...
At first i want to feed the sensor with 2.2v for 8sec and then cut that voltage and let it run on 0.9v
How can i add the 0.9v and stop the 2.2v at the same time ?

You need two voltage regulators for 0.9V ± 0.1V and 2.2±0.2V or one adjustable (switchable) regulator. There are few such regulators. These are specialized regulators with low output voltage.
You cannot take a cheap regulator like the LM317 because it has a minimum output voltage of 1.25V.
Or you have to build such a regulator yourself. Then take a good book and read how voltage regulators are built.

It depends on the regulator. You should either change the value of the feedback resistor (for example, using the MOSFET or relay) or apply a digital signal to another input of the regulator (as with programmable regulators).

Let’s say you have the two power supplies.

You can use a relay form C contact arrangement to switch between the two.

It's just a heater. Current control could be easier.
Drop to the required 0.9volt with two resistors in series (from a 3.3volt supply), and bridge one of the resistors with a mosfet to the required ~2volt. Something similar has been done here.

1 Like