Dear Sir,

I am designing a buck converter using to light laser diode which has forward voltage of 4.7v. It have feedback voltage reference as 0.25v, which i used to set the constant current. i have used two 0.33ohm resistors in parallel to get a constant current of 1.5A.

Vin = 8.4v

Vout = 4.7v (laser diode forward voltage)

Iled = 1.5A

Frequency = 314Khz

I ripple = 20% of Iled = 0.3

L= (VIN – VOUT ) × D × T / Iripple

=((8.4-4.7) x (4.7/8.4) x (1/314000) / 0.3 ) x 1000000 uH

= 21.977uH

I have selected 22uH. but when i finished the board and tried to check if i am getting 1.5A constant current. I failed, I am only getting 1.1A~1.2A. What am i doing wrong. i have selected 10uf capacitor for input and output. and C3 as 0.1uf.

I am designing a buck converter using to light laser diode which has forward voltage of 4.7v. It have feedback voltage reference as 0.25v, which i used to set the constant current. i have used two 0.33ohm resistors in parallel to get a constant current of 1.5A.

Vin = 8.4v

Vout = 4.7v (laser diode forward voltage)

Iled = 1.5A

Frequency = 314Khz

I ripple = 20% of Iled = 0.3

L= (VIN – VOUT ) × D × T / Iripple

=((8.4-4.7) x (4.7/8.4) x (1/314000) / 0.3 ) x 1000000 uH

= 21.977uH

I have selected 22uH. but when i finished the board and tried to check if i am getting 1.5A constant current. I failed, I am only getting 1.1A~1.2A. What am i doing wrong. i have selected 10uf capacitor for input and output. and C3 as 0.1uf.

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