BETAProvide startup headroom
An 18 V supply exceeds the specified maximum start threshold. A 12 V supply is not sufficient for guaranteed cold startup.
Current-mode PWM controller
UC3842A Basic Circuit
Build a basic UC3842A circuit with labeled pins, component values and connection guidance.
Package view
UC3842A in a circuit
An RC oscillator, a low-voltage control and a scope.
Connect it, step by step
Follow the component values and pin connections
Connect the oscillator
RT connects to VREF and CT connects to ground, meeting at pin 4.
Raise the sense input
Increase the pot wiper from zero toward 1.25 V and observe shorter pulses. Very narrow pulses may remain above the threshold.