TPS92200D1EVM: How to turn off LED instantly?

future chang1

Part Number: TPS92200D1EVM
Other Parts Discussed in Thread: TPS92200

Hi Expert:

In the following diagram,the green line is the LED-290+ which is the output of the TPS92200.

I send zero voltage to DIM pin of TPS92200.

So the output voltage of TPS92200 start to turn off.

The voltage of LED anode down slowly.

I wonder this voltage will not turn off the LED totally.

LED is still a little on.

How could I turn off the LED instatly (when I send 0 to the DIM pin)?

best regards

0 future chang1 over 2 years ago

Hi expert :

The UV LED Vf is 6V at 50mA=> I set 100mA maximum current

According to the inductor calculation :

L=(6*(8.7-6)) / (8.7*0.2*0.05*1MHz)= 186uH

Because the LED current is small.

So I need to choose very large inductor ?

The lower the LED current, the larger the inductor ?

best regards

0 Yuting Shao over 2 years ago in reply to future chang1

Hi Chang,

If you want to shut down the output more quickly, smaller output capacitor may help. But it will lead to a little lager output ripple.

For 100mA, considering of 50% inductor ripple, inductor larger than 6.8uH is enough.

Robin

0 future chang1 over 2 years ago in reply to Yuting Shao

Hi Yuting :

For the L calculation

Vout=6V, Vin max=8.7V, K=0.2, Lled=0.05A,Fsw=1MHz

L=(6*(8.7-6)) / (8.7*0.2*0.05*1MHz)= 186uH

Do I calculate correctly ?

best regards

+1 Yuting Shao over 2 years ago in reply to future chang1

Hi Chang,

Sorry for my mistake. Pls use the below tool for detailed calculation.

Robin

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