ALTAIR04-900 Datasheet, PDF (3/29 Pages) STMicroelectronics – Off-line all-primary-sensing switching regulator

ALTAIR04-900
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Device description
Device description
The device combines two silicon in the same package: a low voltage PWM controller and a
900 V avalanche rugged power section.
The controller is a current-mode specifically designed for off-line quasi-resonant flyback
converters.
The device is capable of providing constant output voltage using all primary sensing
feedback. This eliminates the need for the optocoupler, the secondary voltage reference, as
well as the current sensor, still maintaining quite accurate regulation. Also, it is possible to
set the maximum deliverable output current, thus increasing the end-product's safety and
reliability during fault events.
Quasi-resonant operation is guaranteed by means of a transformer demagnetization
sensing input that turns on the power section. The same input serves also the output
voltage monitor, to perform CV regulation, and the input voltage monitor, to achieve mains-
independent maximum deliverable output current (line voltage feedforward).
The maximum switching frequency is top-limited below 166 kHz, so that at medium-light
load a special function automatically lowers the operating frequency still maintaining the
valley switching operation. At very light load, the device enters a controlled burst-mode
operation that, along with the built-in high-voltage start-up circuit and the low operating
current, helps minimize the standby power.
Although an auxiliary winding is required in the transformer to correctly perform CV/CC
regulation, the chip is able to power itself directly from the rectified mains. This is useful
especially during CC regulation, where the flyback voltage generated by the winding drops
below UVLO threshold.
However, if ultra-low no-load input consumption is required to comply with the most stringent
energy-saving recommendations, then the device needs to be powered via the auxiliary
winding.
In addition to these functions that optimize power handling under different operating
conditions, the device offers protection features that considerably increase end-product's
safety and reliability: auxiliary winding disconnection - or brownout - detection and shorted
secondary rectifier - or transformer's saturation - detection.
All of them are auto restart mode.
Doc ID 18211 Rev 2
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