Power integrations InnoSwitch3 User Manual

Rev. A 10/18
8
Application Note AN-72
www.power.com
• Higher VOR reduces the voltage stress on the output diodes and SR
FETs, which in some cases may allow a lower voltage rating for
higher efciency.
• Higher VOR increases leakage inductance which reduces power
supply efciency.
• Higher VOR increases peak and RMS current on the secondary-side
which may increase secondary side copper, diode and SR FET losses
thereby reducing efciency.
It should be noted that there are exceptions to this guidance
especially for very high output currents where the VOR should be
reduced to obtain highest efciency. Higher output voltages
(above 15 V) should employ a higher VOR to maintain acceptable
peak inverse voltage (PIV) across the output SR FET.
Optimal selection of the VOR value depends on the specic
application and is based on a compromise between the factors
mentioned above.
Mode of Operation, K
P
K
P
is a measure of how discontinuous or continuous the mode of
switching is. K
P
> 1 is said to be in discontinuous operation (DCM),
while K
P
< 1 denotes continuous operation (CCM).
Ripple to Peak Current Ratio, K
P
Below 1 (indicating continuous conduction mode), K
P
is the ratio of
ripple to peak primary current (Figure 5).
Table 6. Suggested Values for VOR.
Figure 5. Continuous Mode Current Waveform, K
P
≤1.
Output
Voltage
Suggested VOR
Value
Suggested
Range
5 V 55 V 45 V - 60 V
9 V 85 V 80 V - 90 V
12 V - 20 V 110 V 100 V - 120 V
K
P
≡ K
RP
=
(a) Continuous, K
P
< 1
(b) Borderline Continuous/Discontinuous, K
P
= 1
I
R
I
P
I
PI
R
I
P
I
R
PI-2587-103114
Primary
Primary
K
P
≡ K
DP
=
T = 1/f
S
T = 1/f
S
(1-D) × T
(1-D) × T = t
t
D × T
D × T
(b) Borderline Discontinuous/Continuous, K
P
= 1
(a) Discontinuous, K
P
> 1
Primary
Secondary
Primary
Secondary
PI-2578-103114
(1-D) × T
t
Figure 6. Discontinuous Mode Current Waveform, K
P
≥1.

Power integrations InnoSwitch3 Specifications

General

Brand	Power integrations
Model	InnoSwitch3
Category	Switch
Language	English