Seed Grove Gas Sensor(MQ2) module. What does the chip do?

[741]

I have one of these modules, and I am interested to know the function of the 6-pin i.c, whick looks like SC-70/SOT-323, (marking "19AHK"), located on the back of the PCB.

The sensor heater needs 5V +/-0.2.

The supply to the PCB is listed as 5V. This surprises me because the chip "looks like" a switch-mode regulator. Maybe it is a SEPIC type, and I can feed in VDD under or over 5V? I found a circuit diagram (http://www.highcube.org/files/Gas_Sensor_Schematic.pdf) but not a chip part number.

[SiliconWizard]

I don't see any IC on the pictures though: https://www.seeedstudio.com/Grove-Gas-Sensor-MQ2.html
* perplexed *

[NiHaoMike]

Could that be a boost converter for a 3.3V version?

[SiliconWizard]

Maybe a version that's not sold anymore, or something.

Anyway: judging by the schematic you provided, the capacitor between the SW and OUT pins would IMO suggest a SEPIC indeed. I couldn't find this IC based on the SMD marking you gave though.

[741]

I see the back of the PCB is just tracks on the image. The one I have has the same "SKU" 101020055 but has PCB v1.5.

[SiliconWizard]

I see. Looks like Seed's web site is not up to date as they are only showing v.1.3b!
No documentation talks about it either. Seed sells undocumented stuff? 

I actually only found the schematic you posted for the MQ5 version. We can assume the power supply section would be the same. There are Eagle files too, I opened them, and this is the same as on the PDF: absolutely no reference for the regulator IC. Both the symbol and PCB layout show a SOT23-5 package though, and not a SOT23-6. What a mess.

Seeing your picture though, I think the marking may be 9AHK instead of 19AHK (the 'I' being a bar that shows pin 1's side IMO). I didn't have more luck finding the reference from this marking though... it would probably be best to directly ask Seed's support? (Unless they have as poor a support as their documentation? )

[NiHaoMike]

That does appear to be a boost converter for the 3.3V version.

[floobydust]

Winsen gas sensors the majority use a heater resistor. It's a high power load, 170-200mA at 5V.
MQ-2 flammable gas sensor uses 172mA at 5V for its heater.
MQ-7B CO sensor needs a high/low heater where high heat (5V 172mA) burns off impurities and low heat (1.5V 52mA) to take a reading.

The problem is the Seeed Studio "Grove Connector" shield fits on an Arduino Uno and has a 3.3V or 5V switch for VCC to who knows.
So using 3.3V power, the gas sensor and heater need 5V so there is a need for a boost-converter. The IC smt marking code I9AHK is SOT23-6, Foster Semiconductor but no datasheet on it.

Either way I would expect the main board voltage reg to get overloaded from the high drain, up to ~325mA with a 3.3V feed.
The module it's not a good design, it should take raw 9V or something in on another connector. No schematic for the shield either.