Datasheet > C1888CT

C1888CT

更新时间： 2022-11-24 21:40:24

品牌	Logo	应用领域
德州仪器 - TI		控制器
页数	文件大小	规格书
6页	301K
描述
Off-line Power Supply Controller

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C1888CT 数据手册

UCC1888

UCC2888

UCC3888

Off-line Power Supply Controller

DESCRIPTION

FEATURES

•

Transformerless Off-line

Power Supply

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.

Wide 100VDC to 400VDC

Allowable Input Range

Fixed 5VDC or Adjustable

Low Voltage Output

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.

Output Sinks 200mA, Sources

150mA Into a MOSFET Gate

•

Uses Low Cost SMD Inductors

Short Circuit Protected

Optional Isolation Capability

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 RON into TON is directed to VCC where it charges the external

capacitor, C3, connected to VCC. As voltage builds on VCC, an internal undervol-

tage lockout holds the circuit off and the output at DRIVE low until VCC reaches

8.4V. At this time, DRIVE goes high turning on the power switch, Q1, and redirect-

ing the current into TON to the timing capacitor, CT. CT charges to a fixed threshold

with a current ICHG=0.8 • (VIN - 4.5V)/RON. Since DRIVE will only be high for as

long as CT charges, the power switch on time will be inversely proportional to line

voltage. This provides a constant (line voltage) • (switch on time) product.

TYPICAL APPLICATION

UDG-96013

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

3/97

12 3 4 5 6

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