Enoki has planned programming Arduino Pro Mini (3.3V 8MHz) on a bread board. But Enoki has no 3.3V regulator. sells 3.3V step-down DC-DC converter by HiLetgo. So Enoki has tried it to supply power for 2 pieces of Arduino Pro Mini and a wireless module.


However it was not DC-DC converter but linear dropper by AMS1117 simply. And the dropout voltage was 1.3V. it needs 4.65 V to run Arduino Pro mini at least.

背景 が出力 3.3V の LDO ステップダウン DC-DC を取り扱っている。


AMS1117 とは,実際にはリニアドロッパであり,ドロップアウト電圧は 1.3V であった。

3.3V regulator (AMS1117) trial for Arduino Pro Mini (8MHz) 2021-06-06

Dropout voltage threshold measurement

Enoki's self made tiny variable voltage regulator (250mA) supplied power.

The regulator on breadboard

DMM PC510 monitored current to flow in the regulator. DSO SDS1102 measured the input CH1 and output voltage CH2 at 2V/div 20ms/div.

The measurement result

The 2 Arduino Pro mini and a wireless module consumed 35 mA total.

The consumption decreased to 31 and 30 mA at 4.03 V and 3.87V each.

At 3.83 V input (2.70V output), 2 Arduino run wrong. The both LEDs began to blink which are connected to DIO. And the consumption current varied about 10 mA at 3.83 V.


The HiLetgo 3.3V regulator is able to insert on a bread board easily. It is unnecessary for a few capacitors. It has a power-on LED.

Although HiLetgo describes that it is step-down DC-DC converter at But its dropout voltage measurement was bigger 1.3 V. Usual LDO regulator dropout voltage is less than 1V.

HiLetgo refers to AMS1117. Enoki should check the data sheet before clicking BUY.

Arduino Pro Mini includes Atmel ATmega328P MPU.

Although it operates safe more than 2.7 V at 8MHz (p260 ATmega328P data sheet), The test worked wrong at 2.8V.

3.3V regulator characteristics

© Enoki 2021 June 6