UCC1889 Unitrode Semiconductor, UCC1889 Datasheet

UCC1889

Manufacturer Part Number

UCC1889

Description

Off-line Power Supply Controller

Manufacturer

Unitrode Semiconductor

Datasheet

1.UCC1889.pdf (6 pages)

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Off-line Power Supply Controller

FEATURES

TYPICAL APPLICATION

2/95

Note: This device incorporates patented technology used under license from Lambda Electronics, Inc.

Applications

Low Voltage Output

Transformerless Off-line

Ideal Primary-side Bias Supply

Efficient BiCMOS Design

Wide Input Range

Fixed or Adjustable

Uses Low Cost SMD Inductors

Short Circuit Protected

Optional Isolation Capability

The UCC1889 controller is optimized for use as an off-line, low power, low voltage,

regulated bias supply. The unique circuit topology utilized in this device can be

visualized as two cascaded flyback converters, each operating in the discontinu-

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

benefit of this approach is the ability to achieve voltage conversion ratios of 400V

to 12V with no transformer and low internal losses.

The control algorithm utilized by the UCC1889 is to force the switch on time to be

inversely proportional to the input line voltage while the switch off time is made in-

versely proportional to the output voltage. This action is automatically controlled by

an internal feedback loop and reference. The cascaded configuration allows a volt-

age conversion from 400V to 12V to be achieved with a switch duty cycle greater

than 10%. This topology also offers inherent short circuit protection since as the

output voltage falls to zero, the switch off time approaches infinity.

The output voltage can be easily set to 12V or 18V. Moreover, it can be pro-

grammed for other output voltages less than 18V with a few additional compo-

nents. An isolated version can be achieved with this topology as described further

in Unitrode Application Note U-149.

DESCRIPTION

OPERATION

With reference to the application diagram below, when input voltage is first applied,

the R

C3, connected to V

holds the circuit off and the output at DRIVE low until V

time, DRIVE goes high turning on the power switch, Q1, and redirecting the current

into T

charges, the power switch on time will be inversely proportional to line voltage.

This provides a constant line voltage-switch on time product.

CHG

=0.8

current into T

to the timing capacitor, C

- 4.5V)/R

. As voltage builds on V

is directed to V

. Since DRIVE will only be high for as long as C

. C

charges to a fixed threshold with a current

where it charges the external capacitor,

, an internal undervoltage lockout

reaches 8.4V. At this

UCC1889

UCC2889

UCC3889

UDG-93060-1

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UCC1889 Summary of contents

Page 1

... The control algorithm utilized by the UCC1889 is to force the switch on time to be inversely proportional to the input line voltage while the switch off time is made in- versely proportional to the output voltage ...

Page 2

... R C OFF S T Regions 1 and 3.7V /(V - 0.7V) OFF OFF T OUT Region 2, excluding the effects of R which have a minimal impact on T equals 9V. The CC increases from approximately 2. charging. To take this into account UCC1889 UCC2889 UCC3889 DCHG S . OFF IN . The voltage UDG-93062-3 ...

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UCC1889 Unitrode Semiconductor, UCC1889 Datasheet

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