C1888CT

Manufacturer Part NumberC1888CT
DescriptionC1888CT_Texas Instruments.pdf C1888CTOff-line Power Supply Controller
ManufacturerTexas Instruments, Inc.
C1888CT datasheet
 


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Off-line Power Supply Controller
FEATURES
Transformerless Off-line
Power Supply
Wide 100VDC to 400VDC
Allowable Input Range
Fixed 5VDC or Adjustable
Low Voltage Output
Output Sinks 200mA, Sources
150mA Into a MOSFET Gate
Uses Low Cost SMD Inductors
Short Circuit Protected
Optional Isolation Capability
TYPICAL APPLICATION
Note: This device incorporates patented technology used under license from Lambda Electronics, Inc.
3/97
DESCRIPTION
The UCC3888 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, both driven from a single external power switch. The significant benefit
of this approach is the ability to achieve voltage conversion ratios as high as 400V
to 2.7V with no transformer and low internal losses.
The control algorithm utilized by the UCC3888 sets the switch on time inversely
proportional to the input line voltage and sets the switch off time inversely propor-
tional to the output voltage. This action is automatically controlled by an internal
feedback loop and reference. The cascaded configuration allows a voltage conver-
sion from 400V to 2.7V to be achieved with a switch duty cycle of 7.6%. This topol-
ogy also offers inherent short circuit protection since as the output voltage falls to
zero, the switch off time approaches infinity.
The output voltage is set internally to 5V. It can be programmed for other output
voltages with two external resistors. An isolated version can be achieved with this
topology as described further in Unitrode Application Note U-149.
OPERATION
With reference to the application diagram below, when input voltage is first applied,
the current through R
into T
is directed to V
ON
ON
capacitor, C3, connected to V
. As voltage builds on V
CC
tage lockout holds the circuit off and the output at DRIVE low until V
8.4V. At this time, DRIVE goes high turning on the power switch, Q1, and redirect-
ing the current into T
to the timing capacitor, C
ON
with a current I
=0.8
(V
- 4.5V)/R
CHG
IN
long as C
charges, the power switch on time will be inversely proportional to line
T
voltage. This provides a constant (line voltage) (switch on time) product.
UCC1888
UCC2888
UCC3888
where it charges the external
CC
, an internal undervol-
CC
reaches
CC
. C
charges to a fixed threshold
T
T
. Since DRIVE will only be high for as
ON
UDG-96013

C1888CT Summary of contents