BCM352 x 125 y 300A00
3.0 POWER, VOLTAGE, EFFICIENCY RELATIONSHIPS
Because of the high frequency, fully resonant SAC topology,
power dissipation and overall conversion efficiency of bus
converters can be estimated as shown below.
OUTPUT
POWER
INPUT
POWER
Key relationships to be considered are the following:
1. Transfer Function
a. No load condition
PR
OUT
PNL
VOUT = VIN • K
Eq. 1
Figure 15 — Power transfer diagram
Where K (transformer turns ratio) is constant
for each part number
b. Loaded condition
VOUT = Vin • K – IOUT • ROUT
Eq. 2
2. Dissipated Power
The two main terms of power losses in the
BCM™ bus converter are:
- No load power dissipation (PNL) defined as the power
used to power up the module with an enabled power
train at no load.
- Resistive loss (ROUT) refers to the power loss across
the bus converter modeled as pure resistive impedance.
~
~
PDISSIPATED
P
NL + PROUT
Eq. 3
Therefore, with reference to the diagram shown in Figure 15
POUT = PIN – PDISSIPATED = PIN – PNL – PROUT Eq. 4
Notice that ROUT is temperature and input voltage dependent
and PNL is temperature dependent (See Figure 15).
The above relations can be combined to calculate the overall module efficiency:
POUT
PIN
PIN – PNL – PROUT
VIN • IIN – PNL – (IOUT)2 • ROUT
PNL + (IOUT)2 • ROUT
h
=
=
=
= 1 –
Eq. 5
(
)
PIN
VIN • IIN
VIN • IIN
BCM® Bus Converter
Page 12 of 18
Rev 1.7
vicorpower.com
800 735.6200
1/2013
VICOR [ VICOR CORPORATION ]
