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DESCRIPTION

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Transformerless Off-Line

Operation

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Low Voltage Operation to 0.8V

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Ideal for Battery Trickle Charger

Applications

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Current Mode Operation With

100mV Shunt

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Voltage Mode Operation With

Fixed 1.25V Output or Resistor

Adjustable Output

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Efficient BiCMOS Design

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Inherent Short Circuit Protection

The UCC3890 controller is optimized for use as an off-line, low power, low

voltage, regulated current supply, ideally suited for battery trickle charger

applications. The unique circuit topology used in this device can be visual-

ized as two cascaded flyback converters; each operating in the discon-

tinuous mode, and both driven from a single external power switch. The

significant benefit of this approach is the ability to charge low voltage bat-

teries in off-line applications with no transformer, and low internal losses.

The control algorithm used by the UCC3890 forces a switch on time in-

versely proportional to the input line voltage, while the switch off time is

inversely proportional to the output voltage. This action is automatically

controlled by an internal feedback loop and reference. The cascaded con-

figuration allows a large voltage conversion ratio with reasonable switch

duty cycle.

While the UCC3890 is ideally suited for control of constant current battery

chargers, provision is also made to operate as a fixed 1.25V regulated

supply, or to use a resistor voltage divider to obtain output voltages higher

than 1.25V.

UCC1890

UCC2890

UCC3890

Off-Line Battery Charger Circuit

FEATURES

BLOCK DIAGRAM

UDG-96052

Note:

This device incorporates patented technology used under license from

Lambda Electronics, Inc.