NEC LCD1550X-BK, Руководство по обслуживанию

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• Output voltage V
OUT
(specification) V
OUT
= 5.70V (Typ.)
(design value)
= V
REF
• (1+ R1/R2)
* V
REF
= 1.26V
±
2%
V
OUT
= 1.26V • 1+(5.6k
Ω
+750
Ω
)/1.8k
Ω
) = 5.71V
• Output current I
OUT
(specifications) I
OUT
= 0.200A (MAX.)
• Ripple current
∆
I
L
(specifications)
∆
I
L
= 0.171Ap-p
• Choke coil L = (V
IN
- V
sat
- V
OUT
) • V
OUT
/
∆
I
L
• f
s
• V
IN
* V
sat
: internal switch's saturation voltage = 0.9V
L618 =(12V - 0.9V - 5.70V) • 5.70V / 0.171Ap-p • 100000Hz • 12V
=150
µ
H
(Taiyo yuden product NO6DB 151K : Tolerable current 0.48A, direct-current resistance 1.0
Ω
)
• Maximum power consumption P = (5.70V x 0.2A) / efficiency 0.8
= 1.43W
* 80% efficiency is value generally used for DC/DC design
• Maximum input current I
IN
= 1.43W / 12V
= 0.12A
• Output smoothing capacitor C657 : 16V_100M-M F55 (CP182P093A41)
ESR =1.00
Ω
MAX / 20˚C, 100kHz
Tolerable ripple current = 140mArms / 105˚C, 100kHz
* Tolerable ripple current frequency compensation coefficient = 1
5.5V output system
Ripple voltage (specifications)
<
=
200mVp-p
Ripple voltage =
∆
I
L
x ESR (1.00
Ω
) = 0.171Ap-p x 1.00
Ω
= 0.171Vp-p
<
=
200mVp-p OK
Ripple current =
∆
I
L
/2 3 = 0.049Arms
<
=
Tolerable ripple current (140mArms) OK
• Input capacitor C656 : 16V_100M-M F55(CP182P093A41)
ESR = 1.00
Ω
MAX / 20˚C, 100kHz
Tolerable ripple current = 140mArms / 105˚C, 100kHz
* Tolerable ripple current frequency compensation coefficient = 1
Ripple voltage = D
ON
(1-D
ON
) D
ON
= V
OUT
/ V
IN
= 5.7V / 12V =0.48
= 0.48 (1-0.48)
=0.50Arms <
=
Tolerable ripple current (140mArms) OK
• Oscillation frequency = 100kHz
PQ1CZ21H2ZP(IC611) Study of DC/DC step down circuit design
750
Ω
5.6k
Ω
1.8k
Ω
IC611
4
1
PQ1CZ21H2ZP
C657 C656
2
L618
Input voltage V
IN
12V Output voltage V
OUT
(Ch1) 5.70V