Hardware advice please. Switchable booster 3.7lipo to usb

[mdwelch]

Hi all.

I’m trying to power a 3g USB dongle from a simple booster powered by an 18650 lipo. I’m using a generic all in one converter board from my local hobby electronics store and it works fine.

The problem is I want to only power this circuit for short periods. When I try to control with a N-MOSFET switching ground via esp32, the dongle keeps resetting before it can establish a connection, presumably because of voltage drop?

I’m away from my workshop for a few days and can’t remember the specific MOSFET. I’m probably not using the best MOSFET for the job, but rather than asking another “which MOSFET should I use” thread, I thought I’d ask if anyone knows of a ready made 2-4v to usb booster which is controllable/switchable using 3v logic?

It would make life so much easier

Thanks👍

[lastchancename]

Your explanation is good, but it may help with a circuit diagram of how things fit together.
Modems can ask for a couple of amps max, so there may be better plans.

[mdwelch]

Fair call. I’ll update on a few days when I have computer access. Stuck on mobile for now.

[mdwelch]

So I finally have access to do some schematics.

As described, I can power the usb modem straight from a lipo battery putting out 3.7V by using a generic DC booster board I bought from jaycar.com.au, directly connected to the battery (A in pic) it works perfectly. Trying to control this circuit by switch GND using a 2N7000 MOSFET on a breadboard and opening gate by connecting to battery +ve (B in pic), results in power getting to the device but it keeps resetting before a connection can be established.

For fullness, I’ve documented via schematic the complete scenario I am trying to ultimately implement, where a solar powered esp32 periodically activates a solar powered usb modem to provide internet access once a day. For now, I’m just trying to get switching of the modem going on the breadboard.

As in the original question, if anyone knows of a DC booster that could run a modem from 3.7V input (lipo) that is switchable/controllable via 3.3V signal from an ESP32 or similar that would make life so easy.

Thanks and I hope that all made sense

EDIT: Updated schematic.

[gilshultz]

I think you need to consider the start up time of the converter, they take several milliseconds to come up to voltage, some even longer. I am not sure the 2N7000 can switch with that low of a VGS voltage. Try a different MOSFET with a lower VGS, you are in the sometimes maybe it might work area.

[mdwelch]

Thanks for your advice. I’ll see if I can find a better MOSFET for driving this.

As per the OP I was looking for a ready made switchable booster like these from seedstudio or adafruit, but I also need it to be able to trickle charge the lipo via solar which they can’t.

I’ll see what I can come up with on the MOSFET front.

Do you think a series of reasonably hefty capacitors might help to buffer out the large current draw upon switching the booster circuit?