UC3843 PWM Controller: Pinout, Datasheet and Uses

UC3843 is basically a current mode Pulse Width Modulation (PWM) controller having fixed frequency. It is basically designed for DC to DC converter purposes as well as off line applications with minimum external components. UC3843 has three different packages.

UC3843 has several different features which make it ideal and useful for a lot of real life applications. These features may include trimmed oscillator for the control of accurate duty cycle, high gain amplifier, a temperature compensated reference, current sensing comparator and to control power MOSFET, there is a high current totem-pole output. 

Moreover, some other features include temperature compensated reference and current sensing. UC 3843 can be used at several different places e.g.in switching regulators having any of the polarities as well as in transformer coupled DC to DC converters. The UC3843 have UVLO thresholds of 8.5V(on) The  UC3843 can operate within 100% duty cycle. 

Symbol

Footprint

3D Model

● Current-Mode PWM controller

● Operating Voltage: 7.0V to 8.2V

● Output pin current: 1A

● Analog input range: -0.3 to 6.3V

● Oscillation Frequency: 52 Typically Gain: 3V

● Maximum source current: 22mA

● Low Output Voltage: 0.08V

● High Output Voltage: 13.5V

● Low startup current(<1 mA)

● Pulse by pulse current limiting

● Low output resistance

● Double pulse surpression

● High current totem pole outputs

● Maximum Duty Clamp

● UVLO With Hysteresis

● Operating Frequency up to 500KHz

● Optimized For Off-line and DC-to-DC Converters

● Automatic Feed Forward Compensation Internally implemented circuits include under-voltage

● Internally Trimmed Bandgap Reference

● Low RO Error Amp

ON Semiconductor UC3843D technical specifications, attributes, parameters and parts with similar specifications to ON Semiconductor UC3843D.

The UC3843 IC is a current Mode PWM Controller, meaning it can be used to provide a constant current by varying the output voltage to the load. While building Switch mode supplies with feedback there are two modes of control that is commonly used, one is voltage mode control where the output voltage will kept constant irrespective of the current (CV mode) and the other is current mode control where the output current will be constant (C mode) irrespective of the voltage.

The UC3843 can be used to regulate or limit current in application like SMPS, RPS, DC-DC Converters, Line voltage regulators etc.. So if you are looking for an IC to  produce PWM signals for controlling a power switch based on the current flowing through the circuit then this IC might be the right choice for you.

Although the IC performs a sophisticated job, using it in a circuit is fairly simple and can be done with minimum number if external components which make this IC to be a preferable choice among designers. A sample application circuit of this IC is shown below.

The IC has an under voltage protection, so care should be taken to make sure that it has an operating voltage between 7V to 8.2V. The output pin of the IC is connected to the gate driver circuit of the Power switch which is to be switched. The output pin can source upto 1A ad hence a current limiting resistor will be required. The VFB (Voltage feedback) pin acts as a feedback based on which the PWM signal is controlled. A shunt resistor is used to monitor the change in current in the circuit and then this difference voltage across the shunt is provided to the feedback pin.

The IC also has an internal oscillator which can be configured using by connecting the right value of capacitor and resistor to the pin Rt/Ct. The Datasheet recommends a value of between 470pf to 4.7nf and for the resistor a value between 5k to 100k. Refer the datasheet at the end of the page to know more about this IC. Also check out the Layout diagram at the bottom of the datasheet for a quick start. A more detailed application circuit is shown below.

■ SMPS (Switch mode Power Supplies) circuits

■ Transformers coupled DC-DC converter circuits

■ Electronics power supply

■ Battery drain circuit

■ Load machines

■ Switching regulators having any polarity

ON Semiconductor is a semiconductor supplier company, Products include power and signal management, logic, discrete, and custom devices for automotive, communications, computing, consumer, industrial, LED lighting, medical, military/aerospace and power applications. ON Semiconductor runs a network of manufacturing facilities, sales offices and design centers in North America, Europe, and the Asia Pacific regions. Its Headquarter is in Phoenix, Arizona.

Download datasheets and manufacturer documentation for ON Semiconductor UC3843D.