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UCC1889

Unitrode
Part Number UCC1889
Manufacturer Unitrode
Description Off-line Power Supply Controller
Published Sep 18, 2019
Detailed Description Off-line Power Supply Controller UCC1889 UCC2889 UCC3889 FEATURES DESCRIPTION • Transformerless Off-line The UCC188...
Datasheet PDF File UCC1889 PDF File

UCC1889
UCC1889

Overview
Off-line Power Supply Controller UCC1889 UCC2889 UCC3889 FEATURES DESCRIPTION • Transformerless Off-line The UCC1889 controller is optimized for use as an off-line, low power, low voltage, Applications regulated bias supply.
The unique circuit topology utilized in this device can be • Ideal Primary-side Bias Supply visualized as two cascaded flyback converters, each operating in the discontinuous mode, and both driven from a single external power switch.
The significant • Efficient BiCMOS Design benefit of this approach is the ability to achieve voltage conversion ratios of 400V • Wide Input Range to 12V with no transformer and low internal losses.
• Fixed or Adjustable Low Voltage Output 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 inversely proportional to the output voltage.
This action is automatically controlled by • Uses Low Cost SMD Inductors an internal feedback loop and reference.
The cascaded configuration allows a volt- • Short Circuit Protected 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 • Optional Isolation Capability 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 programmed for other output voltages less than 18V with a few additional components.
An isolated version can be achieved with this topology as described further in Unitrode Application Note U-149.
TYPICAL APPLICATION OPERATION With reference to the application diagram below, when input voltage is first applied, the RON current into TON is directed to VCC where it charges the external capacitor, C3, connected to VCC.
As voltage builds on VCC, an internal undervoltage lockout holds the circuit off and the output at DRIVE low until VCC reaches 8.
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