KA3843B

Frequency - Switching:	Up to 500kHz
Base Part Number:	KA3843
Supplier Device Package:	8-DIP
Package / Case:	8-DIP (0.300", 7.62mm)
Operating Temperature:	0°C ~ 70°C (TA)
Control Features:	--
Serial Interfaces:	--
Clock Sync:	No
Synchronous Rectifier:	Yes
Duty Cycle (Max):	97%
Series:	--
Voltage - Supply (Vcc/Vdd):	7.6 V ~ 30 V
Output Phases:	1
Number of Outputs:	1
Topology:	--
Output Configuration:	Positive
Function:	--
Output Type:	Transistor Driver
Part Status:	Active
Packaging:	Tube

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KA3843B Application Field and Working Principle
The KA3843B is a general-purpose, fixed frequency PWM voltage regulator designed in SGS-Thomson\'s advanced BiCMOS process. It is primarily intended for use in off-line switch mode power supplies (SMPS). This device offers low standby power losses, improved line and load regulation and improved start-up time. It includes a reference voltage source, differential input stages, a precision woofer amplifier, a current-sense comparator and an error amplifier. The KA3843B is a versatile device, it can be used as a low power regulator (2A) or a high power regulator (up to 8A) and is also capable of operating as a step-up or step-down converter. As it has a minimum of external components, it is easily integrated into a variety of power supplies or voltage regulator systems.
Features
The KA3843B is a very versatile device and its features make it well suited for a wide variety of applications. Some of the key features and benefits of KA3843B are highlighted below.

• Wide range of input voltage: As the input voltage range of KA3843B is huge, it can be used in many applications whether operating on AC/DC or DC/DC networks.
• Low power loss: The KA3843B is designed with low power losses which help make the SMPS more efficient and reduces heat generated, thus prolonging the life of the device.
• Improved line and load regulation: KA3843B features improved line and load regulation, greatly improving the accuracy of the output voltage.
• Improved start-up time: KA3843B is designed to start quickly, enabling the SMPS to be turned on much quicker than conventional devices.
• Versatile use: The KA3843B can used as a low power regulator (2A) or a high power regulator (up to 8A). It can also be used as a step-up or a step-down converter.

Working Principle
The KA3843B follows a fixed frequency PWM (Pulse Width Modulation) voltage regulator topology. The device comprises of a reference voltage source, differential input stages, a precision woofer amplifier, an error amplifier, a current-sense comparator and a flip-flop. The device consists of a two-stage regulator circuit, the first stage consists of the error amplifier and the second consisting of an internal power switch.The differential input stages allow the error amplifier to accept either a high or a low input voltage and amplify this until it is similar to the reference voltage. The output from the error amplifier acts as the input to the current-sense comparator, which in turn monitors the current drawn by the power switch. If the current drawn by the switch exceeds the preset threshold value, then the comparator output goes high and the power switch turns off. The reference voltage source provides a constant, stable voltage for the error amplifier to monitor. The woofer amplifier is used as a buffer between the error amplifier and the comparator. The flip-flop acts as a gating device, controlling ON and OFF timings of the internal power switch thus regulating the output voltage. The output voltage is regulated by setting the ON and OFF times of the power switch, the ON time is determined by the error amplifier and the OFF time is determined by the threshold value set by the current-sense comparator.Conclusion
The KA3843B is a versatile, fixed frequency PWM voltage regulator that is suitable for many applications, from low power regulators to high power regulators. It offers low standby power losses, improved line and load regulation and improved start-up time. The device comprises of numerous functional components, such as a reference voltage source, a precision woofer amplifier, an error amplifier, a current-sense comparator and a flip-flop, which enable the KA3843B to operate as a low power regulator (2A) or a high power regulator (up to 8A) in either step-up or step-down converter topologies.

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