AN-32
Step 5. Set current waveform parameter KP for desired
mode of operation and current waveform: KP ≡ KRP for KP
≤ 1.0 and KP ≡ KDP for KP ≥ 1.0 (Figures 9 and 10)
IR
IP
KP ≡ KRP =
• For KP ≤ 1.0, KP ≡ KRP, continuous mode (see Figure 9)
I
R
Primary
I
IR
P
KP ≡ KRP
=
where IR is primary ripple current and IP
IP
is primary peak current.
• For KP ≥ 1.0, KP ≡ KDP, discontinuous mode (see Figure 10)
(a) Continuous, K < 1
P
VOR × (1−DMAX
)
KP ≡ KDP
=
I
I
P
Primary
R
(VMIN −VDS ) × DMAX
• For continuous mode design, set
KP = 0.4 for universal input
(b) Borderline Continuous/Discontinuous, K = 1
P
0.6 for 230 VAC or 115 VAC with doubler.
PI-2587-011400
• For discontinuous mode design, set KP = 1.0.
• KP must be kept within the range specified in Table 5.
Figure 9. Continuous Mode Current Waveform, KP ≤1.
(1-D) x T
=
KP ≡ KDP
t
T = 1/fS
Primary
D x T
(1-D) x T
t
Secondary
(a) Discontinuous, K > 1
P
T = 1/fS
Primary
D x T
(1-D) x T = t
Secondary
(b) Boarderline Discontinuous/Continuous, K = 1
P
PI-2578-011800
Figure 10. Discontinuous Mode Current Waveform, KP ≥1.
B
12/02
9
ETC [ ETC ]
