Using MT3608 Voltage Regulator with STM32 Blue Pill

How much current can you really draw?

The 2 A on the label does not mean 2 A at the output. It is a rating of the chip's internal switch, and the input has to carry more current than the output. The input current is roughly:

Iin = (Vout × Iout) ÷ (Vin × efficiency)

The table below assumes 85 % efficiency, which is realistic for a small module:

Input	Output	Load	Input current needed
3.7 V	5 V	0.5 A	about 0.8 A
3.7 V	5 V	1 A	about 1.6 A
3.0 V (cell nearly empty)	5 V	1 A	about 2.0 A
3.7 V	9 V	0.5 A	about 1.4 A
3.7 V	12 V	0.3 A	about 1.1 A

See the third row. As a battery drains, the voltage falls and the current it must supply for the same load rises. A cell with a weak protection board can cut out right when the demand is highest. For a 5 V board that draws 1 A, size the battery and wiring for 2 A or more of input current.

The idle drain

The MT3608 uses about 100 to 200 µA on its own even when nothing is connected (datasheet figure for the chip, and the trimmer network adds a little more). That is small for a project that is always awake, but large for one that sleeps. An ESP32 chip in deep sleep draws about 10 µA, so a boost converter feeding it can use ten times more than the sleeping board.

The module has no way to switch off: the converter stays connected to the battery, and the boost path would still pass the battery voltage through to the output even if it were disabled. For a node that sleeps most of the time, either power it through a low-quiescent regulator, or add a switch in front of the converter.

Troubleshooting

Symptom	Likely cause	Fix
Output roughly equals the input	Trimmer is set below the input voltage	Turn the trimmer to raise the output, watching the meter
Output sags or the board resets under load	The source cannot supply the higher input current, or the wires are thin	Use a stronger source, shorter and thicker wires, and a larger capacitor on the input
Module gets hot	High current at a large step-up ratio	Reduce the load or the ratio
Noisy sensor or ADC readings	Switching ripple at 1.2 MHz	Add 100 µF and 100 nF across the load, and keep analog sensors on a filtered supply
No output at all	Reversed polarity damage, or the input is below about 2 V	Check the polarity and measure the input

Frequently asked questions

Can I power an ESP32 from a single Li-ion cell with it? Yes. Set the output to about 5.1 V and feed the 5V or VIN pin. See the wiring section for your board.

Can it charge a battery? No. It only boosts. Use a charger such as the CN3065 or TP4056 for charging.

Can it step the voltage down? No. Use a buck converter such as the LM2596.

What is the lowest input it works from? The chip is specified from 2 V. For a reliable startup with a load, keep the input a little higher, and remember that the input current rises as the voltage falls.