PWM controller integrates programmable volt-second clamp
Linear Technology Corporation has launched a current-mode PWM controller for use in a synchronous forward converter with active clamp reset, allowing up to 100V input operation for power levels up to 400W.
The LT3753 has a programmable volt-second clamp, which enables primary switch duty cycles above 50 per cent for high switch, transformer, and rectifier utilisation. When the volt-second clamp is set above the natural duty cycle of the converter, it provides a duty cycle guardrail to limit primary switch reset voltage and prevent transformer saturation during load transients.
The LT3753 is an active clamp synchronous forward controller with a volt-second clamp and input voltage range of 8.5V to 100V.
The volt-second clamp also limits maximum VOUT if the opto path breaks open or, alternatively, defines VOUT in no-opto applications. For non-isolated high step-down ratio applications, the cevice contains a voltage error amplifier, allowing a very simple non-isolated fully regulated synchronous forward converter.
Additional features include programmable over-current protection, adjustable input under-voltage, and over-voltage lockout along with built-in thermal shutdown. The device has a programmable 100kHz to 500kHz operating switching frequency and can be synchronised to an external clock, allowing the use of a wide range of output inductor values and transformer sizes.
The controller is available in a TSSOP-38 package with several pins removed for high voltage spacing.
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