AN993 datasheet(25/27 Pages) STMICROELECTRONICS

Part #	AN993

Description	Electronic ballast with PFC using L6574 and L6561

PDF	27 Pages

Scroll/Zoom	100%

Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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25 / 27 page

AN993

Dimming the lamp

Doc ID 5656 Rev 10

25/27

6.1

Dimming level and lamp turn-on

During the start-up sequence the frequency always goes from fmax to fmin, regardless of the

dimming level, and it is only after this that the lamp’s turn-on frequency moves towards

higher frequencies. The delay during which f = fmin allows the lamp to turn on, but has the

drawback of causing a "flash" that can be unpleasant. As the minimum length of this delay

depends on the type of lamp, it is better to set it as low as possible, finding the best

compromise.

The easiest way to set this delay is to act on the amplifier’s compensation, that is, on C9: the

higher C9, the longer the delay and the easier the lamp turn-on. Values up to 200 nF and

more are commonly used.

AN993 Datasheet(PDF) 25 Page - STMicroelectronics