LED Backlight driver output current / voltage

Nov 26, 2014 5 Replies
B

Our LCD has 10 series white LEDs for backlight with total Vf of 15V and cur rent of 40ma. The backlight circuit is designed with SC4509. As per the dat asheet its recommended output voltage is 20V and output current of 30ma. T his translates to 20V * 30ma = 600mW. Our design also 15V * 40ma = 600m W. So is it correct assumption that the IC can be used in this design sinc e the total power remain with in the limit? or the output current has to be less than 30ma irrespective of the output voltage? The max switch current limit of SC4509 is 500ma.


Thanks if Advance



-bj


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J

According to the data sheet, you can get no more than 30mA. If your Vf is 15V, then you cannot get more than 450mW output power.

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B

Thanks but the switch max current limit 500ma. So can't we get 30ma + 10ma more ?

-bj

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J

The data sheet says 30mA max LED current. Go ahead and try it.

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S

Am Mittwoch, 26. November 2014 14:00:02 UTC+1 schrieb snipped-for-privacy@gmail.com:

urrent of 40ma. The backlight circuit is designed with SC4509. As per the d atasheet its recommended output voltage is 20V and output current of 30ma. This translates to 20V * 30ma = 600mW. Our design also 15V * 40ma = 60

0mW. So is it correct assumption that the IC can be used in this design si nce the total power remain with in the limit? or the output current has to be less than 30ma irrespective of the output voltage? The max switch curre nt limit of SC4509 is 500ma.

Sometimes is the thermal power dissipation from the internal switch resista nce is the limiting factor. In this case the output voltage is not important, only the current counts. If you take the bigger package (MLPD-W8) with better thermal disspation and a good layout, you would have a better chance.

The datasheet in not clear about the limitations, if it is internally limit ed, then it would not help you.

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M

I'd like info/source for the 1.5V LEDs that you're using. Thanks,

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