Originally by Anisimov Ivan

In many cases can be very handy to be able to convert 1.5V to 5V. Then you can power microcontroller or 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 step-up DC-DC converter that can convert voltages from 0.7V to any in range from 2V to 5.5V. MAX1676 have already preset pins for 3.3V and 5V, that makes easer integration in 3.3 and 5V circuits. IC can dissipate up to 444mW.

Bellow is a circuit that converts 1.5V to 5V.

Lets say wee need to get maximum output current 300mA, then wee need to put some efforts. Because output power is 5V·0.3A=1.5W. Lets say efficiency is 100% then the power drawn from battery will be 1.5W too. At 1.5V voltage this will be 1A current. Not all batteries can drive such currents. Other important part is inductor. For this wee need inductor with high current saturation which usually leads to increase of size.

• If current is over 300mA, then inductor inductance 47uH;

• If current is over 120mA, then inductor inductance 22uH;

• If current is over 70mA, then inductor inductance 10uH;

You will find recommended inductors in datasheet.

In this case if FB pin of MAX1614 is connected to ground, then output voltage is equal to 5V. If FB would be connected to OUT pin then output voltage would be 3.3V. If put voltage between OUT and ground, then we can control output voltage in range from 3.3V to 5V.

Biggest real efficiency of IC is at 120mA – 94%.

Manufacturer recommends to design PCB with sort and thick traces. Inductor should have minimal resistance.

Real device shows really big efficiency at high loads. Circuit and PCB is really compact allowing to make small designs.

In picture bellow you can see how circuit works with LED Luxeon without current limiting resistor. Circuit is powered with 1.5V Kodak battery. This circuit can be used for powering LED flashlights, emergency cell phone charging, making compact embedded designs with microcontrollers, bugs.

Original source: www.radiokot.ru

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This entry was posted on Thursday, February 22nd, 2007 at 10:49 am and is filed under Electronics. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.