STEVAL-ISA007V1 Datasheet, PDF (2/5 Pages) STMicroelectronics – High power 3-phase auxiliary power supply evaluation board Based on L5991 and ESBT STC08DE150HV

Reference design general description
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Reference design general description
STEVAL-ISA007V1
A dedicated reference design with ESBT has been developed, featuring the high power wide
input range requirement of a highly demanding industrial market.
The maximum output power is 150W. Generally speaking, the necessity to handle both high
output power and wide input voltage leads to the design of a fly-back stage working in mixed
operation mode: continuous and discontinuous:
The continuous current mode introduces a right half plan zero in the loop-transfer function
which makes the feedback stabilization difficult. At the input voltage range, and after a brief
description of the differences between continuous and discontinuous mode, it will soon be
clear that it is very difficult and inconvenient to design a fly-back converter working in
discontinuous mode. Finally, referring to the power spec of our demo, it is clear that
discontinuous mode cannot be used because it would determine a very high primary and
secondary peak current with a higher cost of all the main components involved: power
transistor, secondary diode and output capacitor.
Thanks to the adoption of the PWM L5991, the converter is able to operate in mixed mode.
For higher power levels with a switching frequency close to 90kHz, the converter operates in
Continuous Current Mode (CCM), while in stand-by and for power levels lower than 25W,
the converter works in Discontinuous Current Mode (DCM) at a switching frequency of
about 35kHz.
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