3V to 5V Converter Step-up Circuit

There are several ways to convert an AC voltage at a wall receptacle into the DC voltage required by a microcontroller. Traditionally, this has been done with a transformer and rectifier. However, in applications that involve providing a DC voltage to only the microcontroller and a few other low-current devices, transformer-based power supplies may not be cost effective.

Presented here is the simple circuit of one boost (step-up) converter, which can output steady 5VDC supply from a 3VDC input. This circuit can be used to power your 5V microcontroller/similar circuits from two standard AA cells (1.5V x2).

Schematic of 3V to 5V Booster Circuit

At the heart of the circuit is one tiny chip HT7750A, which is a “pulse frequency modulation” (PFM) step-up DC/DC converter with high efficiency and low ripple. The chip features extremely low start-up voltage and high output voltage accuracy.
They require only three external components to provide a fixed output voltage of 5.0V. CMOS technology ensures ultra low supply current and makes them ideal for battery-operated applications powered from one or more cells. HT7750A consists of an oscillator, a PFM control circuit, a driver transistor, a reference voltage unit, and a high speed comparator.

If you do not have a LCR meter the inductive part (L1) of the circuit is a bit more complicated to make! Capacitors (C1 & C2) also recommended by the manufacturer for this circuit is a bit hard to get, I have used tantalum types recovered from a discarded smps circuit board. Last but not least, say that the diode (D1) has to be a fast, not worth as the 1N400X rectifiers, the 1N5817 is recommended schottky type, characterized by high response time and low internal resistance, which is what ideal for this type of boost-converter circuits.

In my prototype, I have used a “home-made” 100uH inductor as L1. I wound near 8 turns of 0. 3 mm enamelled copper wire on a small toroidal core, lifted from an old CFL circuit board.

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