ALTAIR04-900TR Просмотр технического описания (PDF) - STMicroelectronics

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ALTAIR04-900TR

Off-line all-primary-sensing switching regulator

STMicroelectronics 

ALTAIR04-900

1

Description

Description

This device combines two silicons in the same package: a low voltage PWM controller and a

900 V avalanche-rugged power section.

The controller is in current-mode specifically designed for off-line quasi-resonant flyback

converters.

The device provides a constant output voltage using the primary-sensing feedback. This

eliminates the need for the optocoupler, the secondary voltage reference, as well as the

current sensor, still maintaining an accurate regulation. Besides, the maximum deliverable

output current can be set so to increase the end-product safety and reliability during fault

events.

Quasi-resonant operation is guaranteed by a transformer demagnetization sensing input

which turns on the power section. The same input also serves the output voltage monitoring,

to perform CV regulation, and to achieve mains-independent maximum deliverable output

current (line voltage feed-forward).

The maximum switching frequency is top-limited 166 kHz, so that at light-to-medium load a

special function automatically lowers the operating frequency still maintaining the valley

switching operation. When the load is very light, the device enters a controlled burst-mode

operation that, along with the built-in high voltage start-up circuit and the low operating

current, minimizes the standby power.

Although an auxiliary winding is required in the transformer to correctly perform CV/CC

regulation, the chip powers itself directly from the rectified mains. This is important 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 strict

energy-saving recommendations, then the device needs to be powered by the auxiliary

winding.

These functions optimize power handling under different operating conditions. The device

offers protection features that, in auto restart-mode, increase end-product safety and

reliability:

• Auxiliary winding disconnection, or brownout

• Detection

• Shorted secondary rectifier, or transformer saturation

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