LD7833VGS datasheet(13/17 Pages) LEADTREND

13 / 17 page

LD7833V

01/20/2015

Leadtrend Technology Corporation

www.leadtrend.com.tw

LD7833V-DS-00 January 2015

TRIAC Dimming Mode

Phase angle detection by HV pin

The HV pin can detects TRIAC phase by main bulk

capacitor and get PD signal in compare with VDC2L

through phase detector as shown in Fig. 19. The PD

signal controls OUT status according to the TRIAC

phase condition and determines the internal reference

for current control.

Fig. 19

Programmable

Phase

Angle

Cut-off

Function

To prevent shimmering in small conduction angle of

TRIAC, the LD7833V provides the function of phase

angle cut-off to force the LED load shut off before the

shimmer appears.

Fig. 20 shows the operation of the phase angle cut-off

function. If HV peak voltage descends to BNO level with

TRIAC dimming down, LD7833V will shut the gate off

until TRIAC dimming resumes to BNI level.

Fig. 20

The phase angle cut-off setting is adjustable with the

ZCD resistance, see Fig. 21. The ZCD resistance can

be obtained from below equation.

ZCD







Fig. 21

The following table is a suggestion for phase angle

cut-off setting. The cut phase angle corresponds to the

threshold of BNO/ BNI.

RZCD

Input

Angle

BNO/BNI

Suggestion

VDC2L

55.1k<RZCD

220VAC

40/ 55

255V/293V

58k



20V

38k<RZCD<42k

25/ 40

200V/255V

40k



25.7k<RZCD<28.3k

220VAC

Disable

27k



17.1k<RZCD<18.9k

110VAC

40/ 55

100V/128V

18k



10V

9.5k<RZCD<10.5k

25/ 40

66V/100V

10k



RZCD<6.3k

110VAC

Disable



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