UC3843 – PWM Controller IC

COMP (Comparator) It is an output pin which outputs low impedance 1MHz single based in the difference between he set and current voltage. It is normally connected to the voltage feedback pin of the IC through resistor and capacitor.
2 VFB (Voltage Feedback) It is an input to the error amplifier that inside the IC. The difference in voltage level is supplied to this pin
3 Current Sense A shunt resistor is used to monitor the current through the circuit and the voltage across it is provided as a feedback to the current sense pin
4 RT/CT (Timing Resistor/ Timing Capacitor) The IC has an internal oscillator which can be set using an external Resistor and capacitor connected to this pin.
5 Ground Connected to the ground of the circuit
6 Output This pin outputs the PWM signal based on the feedback provided and we can use this to switch the power electronic device.
7 Vcc Supply voltage for the IC (Nominal 11V)
8 VREF Reference voltage based on which the PWM signal is produced.
Note: This IC also comes in 14-Pin, 16-Pin and 20-Pin packages. This article covers only on the 8-Pin version of the IC.

UC3843 Specifications
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

UC3843 Equivalent/Substitute
UC3842

Alternatives PWM controller ICs
UC2842, UC3844, SG2524

Where to use the UC3843 PWM Controller IC
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.

How o use UC3843 IC
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.