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A Low Cost Boost Converter Current Supply

IP.com Disclosure Number: IPCOM000004711D
Publication Date: 2001-Apr-16
Document File: 4 page(s) / 24K

Publishing Venue

The IP.com Prior Art Database

Abstract

For applications that require a back-light for their displays or keyboards (such as those using an LED), a simple low cost constant current source is provided to supply a current load. Furthermore, when the power source for the system is a battery, the system provides a boosted voltage to operate these constant current loads.

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A Low Cost Boost Converter Current Supply

For applications that require a back-light for their displays or keyboards (such as those using an LED), a simple low cost constant current source is provided to supply a current load. Furthermore, when the power source for the system is a battery, the system provides a boosted voltage to operate these constant current loads.

Theory of operation

The brightness of an LED is typically proportional to its current. Since LEDs clamp voltage, the output voltage is fixed dependant upon its current level. With the output power level determined, the remaining system variables are the input voltage and current. The average input current is proportional to the peak current in the switching device. Ratioing the peak current and the input voltage will result in a fixed output power. Several different pin out configurations using this basic concept are disclosed.

Key features

boost converter solution providing a constant current to a load that has a fixed or clamped voltage.

uses ratioing of the input voltage of the system to the average current or peak current of a boost converter to provide a constant current to a load that has a fixed or clamped voltage.

uses ratioing of the input voltage of the system to the average current or peak current of a boost converter to provide a fixed voltage or current output.

Eliminates the diode and capacitor of a typical boost converter to provide a pulsed constant current to a load that has a fixed or clamped voltage.

A three pin solution to provide a constant current output to a voltage clamped load. D2 and Cout can be removed for a pulsed current output.

Three pin solution with optional 3 additional features: Shutdown pin, Current adjust for variable brightness control, Over Voltage Protection to guard against loss of a voltage clamped load.

Two pin constant output current boost converter.

Pinout Description

Name

Number

Description

VCC

VCC supplies Blizzard with internal bias to operate the part. It also is divided down and inputted to the Reset comparator.

LX

Drain of the power switch.

GND

Ground.

Iadj (optional)

Adjusts the peak current level. Connects directly to non-inverting input to the comparator.

Vout (optional)

Provides output over-voltage protection to the system. Alternate method of over-voltage protection is to monitor the LX Pin (shut switching down for X cycles).

Enable (optional)

On Off control for the converter.

Using the LX Pin for Over-Voltage Protection.