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.
Last edited: