The NCP1239 is a fixed-frequency current-mode controller featuring the Dynamic Self-Supply. This function greatly simplifies the design of the auxiliary supply and the Vcc capacitor by activating the internal startup current source to supply the controller during start-up, transients, latch, stand-by etc. With a supply range up to 35 V, the controller hosts a jittered 65 or 100-kHz switching circuitry operated in peak current mode control. When the power on the secondary side starts to decrease, the controller automatically folds back its switching frequency down to minimum level of 26 kHz. As the power further goes down, the part enters skip cycle while limiting the peak current that insures excellent efficiency in light load condition. It features a timer-based fault detection that ensures the detection of overload and an adjustable compensation to help keep the maximum power independent of the input voltage.

• Fixed-frequency 65-kHz or 100-kHz current-mode control operation
• Frequency foldback down to 26 kHz and skip mode
• Adjustable Over Power Protection (OPP) circuit
• High-voltage Current Source with Brown-out (BO) detection
• High-voltage Current Source with Brown-out (BO) detection
• Internal fixed 8-ms soft-start
• Frequency jittering in normal and frequency foldback modes
• 64-ms timer-based short-circuit protection with auto-recovery or latched operation
• Pre-short ready
• Latched OVP on Vcc (NCP1239 A & B versions)
• Latched OVP/OTP input for improved robustness
• +500 mA/ -500 mA peak source/sink drive capability
• Internal thermal shutdown
• Pin-to-pin compatible with the existing NCP1236/1247 series
• Internal ramp compensation
• 35-V Vcc operation