UC2845ADTR Integrated Circuits (ICs)

Frequency - Switching:	500kHz
Base Part Number:	UC2845A
Supplier Device Package:	14-SOIC
Package / Case:	14-SOIC (0.154", 3.90mm Width)
Operating Temperature:	-40°C ~ 85°C (TA)
Control Features:	Frequency Control
Serial Interfaces:	--
Clock Sync:	No
Synchronous Rectifier:	No
Duty Cycle (Max):	48%
Series:	--
Voltage - Supply (Vcc/Vdd):	7.6 V ~ 30 V
Output Phases:	1
Number of Outputs:	1
Topology:	Boost, Flyback, Forward Converter
Output Configuration:	Positive, Isolation Capable
Function:	Step-Up, Step-Up/Step-Down
Output Type:	Transistor Driver
Part Status:	Active
Packaging:	Tape & Reel (TR)

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UC2845ADTR Application Field and Working Principle

UC2845ADTR is an integrated pulse-width modulation switching current mode controller designed for off-line and dc-to-dc converter applications. It is part of a broad range of integrated single-chip regulators and driver switches which Texas Instruments (TI) offers for a wide variety of power supply control applications.UC2845ADTR belongs to the family of onboard DC-DC switching controllers from TI and is at the core of several AC/DC and DC-to-DC power conversion systems. The device is suitable for off-line, as well as DC-to-DC applications including battery chargers, switch mode power supplies (SMPSs), and DC-to-DC converters for a variety of consumer and industrial applications.

Features

The UC2845ADTR controller IC enables the design engineer to create some of the most reliable power supplies and converters in the market. It is designed to perform the following functions in the power supply designs:

• Pre-regulator/PFC stage regulation
• Two-transistor forward/flyback converter feedback regulation
• Fixed frequency resonance/slope compensation
• Master–slave synchronization
• Current limiting
• Transformer reset

The features of UC2845ADTR depend upon its configuration and operating conditions. Its features include:

• Wide input voltage range from 9V to 75V
• Current mode operation
• Soft-start for soft-limiting output current
• Low minimum on-time
• 2mA minimum current limit
• Circuit temperature protections
• Thermal protection
• Output over-voltage protection
• Output short-circuit protection

Architectural Block Diagram

The architectural block diagram of the UC2845ADTR is presented below. The various blocks indicate the individual functions of the device which can be executed one at a time or in combination.

Working Principle

The controller is based on a DVM (Digital Voltage Monitor) architecture that provides wide line and fast line response for continuous SMPS (switched-mode power supplies) operation even at low voltage levels. In the UC2845ADTR, the switching current is sensed by an opto-coupler and is compared with an external reference. The error signal produced is used to control the switching pulse width. The primary drive voltage is compared with an internal reference voltage to produce a linear modulation signal. The output of the opto-isolation circuit forms the primary current limit loop.The output of the opto is compared with a voltage derived from the external reference. The resulting error then connected to the error amplifier at the opto-coupler output.The DVM circuit provides a means for the termination of the output current in the switch-mode regulator. A voltage sense input can be used to compare a sensed voltage at the output to the zener reference voltage. The output of the opto-coupled switch is a current controlled on/off switch and the output is PWM controlled by the current error.The UC2845ADTR can be employed in a variety of power regulation applications that require wide input range, programmable/cyclic on-times, overvoltage protection, short-circuit protection, brownout/dummy-load protection, and soft-start.

Conclusion

The UC2845ADTR is an integrated, pulse-width modulation switching current mode controller designed for off-line and dc-to-dc converter applications. It is designed to perform several functions in the power supply designs including pre-regulator/PFC stage regulation, two-transistor forward/flyback converter feedback regulation, fixed frequency resonance/slope compensation, master–slave synchronization, current limiting, and transformer reset. The device features wide input voltage range from 9V to 75V, current mode operation, soft-start for soft-limiting output current, low minimum on-time, 2mA minimum current limit, circuit temperature protections, thermal protection, output over-voltage protection, and output short-circuit protection. It is based on a DVM (Digital Voltage Monitor) architecture that provides wide line and fast line response for continuous SMPS (switched-mode power supplies) operation even at low voltage levels. The controller is suitable for various power regulation applications that require wide input range, programmable/cyclic on-times, overvoltage protection, short-circuit protection, brownout/dummy-load protection, and soft-start.

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