UC3843 ic series that provides the offline or DC to DC fixed frequency current mode control scheme. The properties of this type of circuit are designed with low-cost components and minimal components. The IC internally implemented circuits are Undervoltage lockout (UVLO), which features a startup current of fewer than 1 milliamps (mA). And a precision reference trimmed for its accuracy at the error amplifier input.
The other internal circuit consists of logic to ensure latched operation. A PWM modulation comparator is designed to provide current limit control. The totem pole output stage is designed to sink high peak current. The output stage of UC3843 is suitable for driving N channel Mosfet. The UC3843 is specified for the operating temperature of 0 degrees Celsius to 70 degrees Celsius.
Introduction to UC3843
UC3843 is a simple current mode pulse width modulation controller. So it is especially designed for the DC to DC voltage converters and also the offline applications. The IC performs its task with fewer external components to avoid its complexity. The IC is most common usage due to its features of Current sensing, High gain amplifier and high current totem pole output to control a powerful N channel Mosfet.
UC3843 IC Pinout
| PINOUT | DESCRIPTION |
| PIN 1 Comp | Comparator – Normally connected to the voltage feedback pin. |
| PIN 2 VFB | Voltage feedback – It is a input to the main error amplifier inside in the IC. |
| PIN 3 ISENSE | Monitoring the current using shunt resistor |
| PIN 4 RT/CT | Timing resistor and capacitor for setting oscillation. |
| PIN 5 Gnd | Ground connection |
| PIN 6 OUT | PWM signal output pin |
| PIN 7 VCC | Supply voltage to the IC (11V normal) |
| PIN 8 VREF | Reference voltage based on which PWM signal is generated |
UC3843 PWM controller IC functional block diagram
Sample working model
