Mosfet recommendations

Hi everyone,

I’m currently develping a tracker for my personal usage.

Using arduino pro mini 3.3v without regulator consuming 0.0045 mAh in sleep mode.

I’m still using breakout boards for GPS (UBLOX NEO 6M), GSM (SIM800L, still working in Brazil) and SW-420 vibration module.

Now looking for mosfets to switch power for my GPS and GSM modules.

Do you think FQP30N06L is a good option (at least based on the datasheet)?

Also, I’m not sure where and which resistors I should use. I saw so many different approaches so far.

Any help would be appreciated.

You need a high side mosfet. Check mic94060.

What do you need the resistors for? Is it for a logic level converter, a voltage reference, or a pull-up maybe?

@viedana I was talking about resistors connected to the mosfet, like a pull down resistor on mosfet gate.

@RaviPujar thank you for the recommendation.

The N-mosfet FQP30N06L initially worked well, but as the battery voltage dropped bellow 50%, SIM800L started to reset on current peak.

I’m now trying to find a good place to import this mosfet, is alliexpress (can’t post link :frowning:) a good option?

Aliexpress is fine if you buy from reputed sellers. For prototype i suggest to buy from standard sites like Mouser or digikey or element14

Be careful with the battery voltage! The SIM800l needs at least 3.7v and 2a for the peaks during comms. If you are using a Lithium battery which could not provide this energy, you should recharge it instead of forcing it to work. 3.7v is the minimum recommended voltage for lithium batteries.

@viedana Yes, I’m using a Lithium battery for this project.

With the N-Mosfet acting as a low side switch, the SIM800l started to reset when battery dropped bellow 50%.

When I connected the SIM800l directly to the ground (bypassing the mosfet) it worked again, even with the battery bellow 50%.

I’m not sure why, looking at the FQP30N06L datasheet it was supposed to allow 2A current between drain to source with a Vgs @ 3.7V.

@RaviPujar the mic94060 is a SMD component. I believe it’s time for me to stop using THT components and breakout boards.

Sorry to bother you again, but what software do you recomment for a beginner to design PCBs?

As an intermediate point, you can try soldering your THT components into a prototyping board. This will give you a lower resistance on the connections compared to the protoboard and jumper wires and would save you from the hassle of PCBs and SMD components for the time being.

If I’m reading the datasheet correctly, the 2a @ 3.7v seems almost like an edge case, or out-of-specification, for the FQP30N06L; I wouldn’t be surprise to have stability issues but I’m not sure. Most values in the datasheet go only as low as 5v, so that might be a hint for its intended minimum Vgs.

Also, when you say that the battery drops “bellow 50%”, how are you measuring that value?

@viedana Thank you for the help. That’s true, the datasheet isn’t very clear on lower voltages.

All my components are currently soldered to a prototyping board like the image bellow

I’m using AT+CBC and internal arduino 1.1V to measure battery voltage, not sure if it is the best option .

Ok, that seems like a very good setup! Maybe you can try controlling your power mosfet using another smaller “signal” mosfet, just to check if the problem is related with your 3.7v on the gate. Something like the 2n7000, which although it doesn’t specificly say to support 3.7v logic, it seems to have a lower threshold and the range of 3v-4v seems to be in its “sweetspot” of operation.

Of course, you’ll have to find a way to drive the power mosfet with, ideally, 5v or more.