$14.5 All-Purpose Switched-Mode Power Supply

Switching technology devices and integrated circuits are growing fast providing solutions that obtain power for different kind of circuits and devices, and they are proposed in different variations. A useful little known kind which is suitable for mixed supply systems is called SEPIC,single-ended primary-inductor converter.

Torpedo is a switched-mode power supply with a SEPIC configuration which is produced by Open Electronics, an open source solutions producer and the brainchild of Futura Group Srl. It supports three different wide-range voltage sources, battery, USB, and external source from 3 to 20 volts with up to 1 A output current and integrated LiPo battery cell charger.

Torpedo comes with these features:

• Triple power source, that is to say: the USB, the battery and an external one
• Wide range of values as for the input voltage: from 3 to 20 volts
• Minimum output current of 500mA, with the possibility to reach 1A and more, via an external source
• High efficiency, above 70% and possibly above 80-90%
• Single-cell LiPo battery charger incorporated
• A transition from battery power to another source that is without interruptions
• 5 V output with high stability, having a low ripple and when varying the load.

Torpedo’s circuit structure can be functionally divided into three different parts; Input Stage, Battery Charger, and SEPIC Converter.

At first, the Input Stage is composed of two diodes and a MOSFET transistor. This set forms a power source selector by allowing the highest voltage power source to pass through Vin pin and prevent it from going to another input having a lower voltage.

The Battery Charger is based on the MCP73831-2 integrated circuit, that is envisaged for charging single-cell LiPo batteries having a voltage of 4.2 volts. It comes with a red LED indicating the statues of charging, and a two-resistor bridge giving two different output current, 100mA and 500mA.

The SEPIC Converter in general is a DC/DC converter which control its output to be greater than, less than, or equal to that at its input. In Torpedo circuit, the SEPIC integrated circuit contains 1.2Mhz oscillator with variable duty cycle, a low-RDSON MOSFET, and a feedback circuit. This combination provides constant 5V output voltage from variant input voltage between 2.5V to 20V.

Torpedo is available for $14.5 from Open Electronics store, and its technical details are reachable here.

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