dSPACE DS1103, Hardware Installation And Configuration Manual

Page: 206 / 302

Influences on Board Performance Using AutoBox/Tandem-
AutoBox
Starting from the description of the design of the AutoBox/Tandem-
AutoBox power supply, power supply’s influence on the I/O board
performance is explained.
The guidelines below apply to AutoBox through Version
3.0 and Tandem-AutoBox through Version 4.0. They are
not relevant for later versions.
Objective
The picture below shows a block diagram of the AutoBox/Tandem-
AutoBox power supply. It is a two-stage switched mode supply. The
first stage is a SEPIC converter translating the 8 V … 60 V input
voltage range from the car battery into a constant 24 V for the
following push-pull converter stages. These stages perform the
galvanic isolation and provide the +5 V and ±12 V for the ISA bus, i.e.
for the dSPACE boards.
Design of
AutoBox/Tandem-AutoBox
power supply
Car
battery ISA-bus
power
Pi filter SEPIC stage Secondary stage
PWM
DC
DC
+
–
Compared to a switched mode power supply operated from the
mains voltage, the input voltage of the SEPIC converter is low,
requiring much higher input currents for the same output power. At a
low input voltage, the input current can be up to 30 A. The amount
of noise generated by a PWM stage is directly related to the switching
current involved. The operating voltage has only minor impact. A
mains
‑
operated PWM power supply with a similar input current
would supply several KW output power and would generate a similar
amount of noise.
Comparison to mains
operated power supply
s
General Notes and Tips on Signal Conditioning
t
206
s
DS1103 Hardware Installation and Configuration November 2014