Driving LEDs With a SEPIC Regulator

Unlike inductor-less converters (such as charge pump DC-to-DC converters), the Single-Ended Primary Inductance Converter (SEPIC) regulator topology uses an additional inductor but provides the following advantages for battery-powered applications:

  • The converter can buck or boost as the input voltage changes.
  • The circuit topology provides inherent short-circuit protection due to the use of a coupling capacitor.

MCP1651 750 kHz Gated Oscillator Boost Controller

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MCP1651 Features

  • 560/440 Output Current (mA)
  • Output Power Capability Over 5 W
  • Output Voltage Capability From 3.3 V to Over 100 V
  • 750 kHz Gated Oscillator Switching Frequency
  • Adaptable Duty Cycle for Battery or Wide-Input, Voltage-Range Applications
  • Input Voltage Range: 2.0 V to 5.5 V
  • Capable of SEPIC and Flyback Topologies
  • Shutdown Control with IQ < 0.1 µA (Typical)
  • Low Operating Quiescent Current: IQ = 120 µA
  • Voltage Feedback Tolerance (0.6%, Typical)
  • Popular MSOP-8 Package
  • Peak Current Limit Feature
  • Two Undervoltage Lockout (UVLO) Options: 2.0 V or 2.55 V
  • Operating Temperature Range: -40°C to +125°C

MCP1651 SEPIC Converter LED Driver Application

In many applications, the input voltage can vary above and below the regulated output voltage. A standard boost converter cannot be used when the output voltage is below the input voltage. In this case, the MCP1650/51/52/53 can be used as a SEPIC controller. A SEPIC requires two inductors or a single coupled inductor, in addition to an AC coupling capacitor. As with the previous boost-converter applications, the SEPIC converter can be used in either bootstrap or non-bootstrap configuration. The SEPIC converter can be a very popular topology for driving high-power LEDs. For many LEDs, the forward voltage drop is approximately 3.6 V which is between the maximum and minimum voltage range of a single-cell Li-Ion battery as well as three alkaline or nickel-metal hydride batteries. The figure below shows an example of a battery operated LED driver using MCP1650 SEPIC Converter topology.


MCP1650 SEPIC Power Supply Demo Board (Part Number: MCP1650DM-DDSC1 )

This board demonstrates MCP1650 boost controller in a low power application that requires a regulated output voltage from an input source that can be greater than, less than, or equal to the output voltage. The demo board generates a 5.0 V output from a 3.0 V to 7.0 V source.

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