In many cases can be very handy to be able to convert 1.5V to 5V. Then you can power a microcontroller or an LED from a single AA or AAA battery. It is simple to do this as there are special IC’s as MAXIM MAX1674 or MAX7176. This is a step-up DC-DC converter that can convert voltages from 0.7V to any in the range from 2V to 5.5V. MAX1676 already has preset pins for 3.3V and 5V, making easier integration in 3.3 and 5V circuits. IC can dissipate up to 444mW.
Bellow is a circuit that converts 1.5V to 5V.
We need to get the maximum output of the current 300mA; then, we need to put some effort. Because output power is 5V·0.3A=1.5W, let’s say efficiency is 100%, then the power drawn from the battery will be 1.5W too. At 1.5V voltage, this will be 1A current. Not all batteries can drive such currents. Another important part is an inductor. For this wee need inductor with high current saturation, which usually leads to an increase in size.
- If the current is over 300mA, then inductor inductance 47uH;
- If the current is over 120mA, then inductor inductance 22uH;
- If the current is over 70mA, then inductor inductance 10uH;
You will find recommended inductors in datasheet.
In this case, if the FB pin of MAX1614 is connected to the ground, then the output voltage is equal to 5V. If FB would be connected to the OUT pin, then the output voltage would be 3.3V. If we put voltage between OUT and ground, we can control output voltage from 3.3V to 5V.
Biggest real efficiency of IC is at 120mA – 94%.
The manufacturer recommends designing PCB with sort and thick traces. The inductor should have minimal resistance.
The real device shows considerable efficiency at high loads. Circuit and PCB are really compact, allowing to make small designs.
You can see how the circuit works with LED Luxeon without a current limiting resistor in the picture. A 1.5V alcaline battery powers the circuit. This circuit can be used to power LED flashlights, emergency cell phone charging, compact embedded designs with microcontrollers, and bugs.