45 - 23/May/97
2.1.2 Soft Start
Figure 2.2 shows a current limit circuit for a standard configuration (1 Power Supply and 3
modules): it is not strictly necessary for the system operation, though it is recommended to
limit the current through R-S-T phases on power up, as filter capacitors at power supply input
are uncharged and can require very high instantaneous current.
The three limit resistors must be short-circuited after 150 to 200 ms. They must be of high
energy type (to charge/uncharge capacitors) and must be rated 10 to 20
Ω
, 100W.
The delay can be achieved by a timer (CR2 in Fig. 2.2) or by the circuit marked CR1 in
Fig. 2.2. In this case the component list is as follows:
Cc
: capacitor 0.1
µ
F, 250V
Cd
: electrolytic capacitor 20
µ
F, 250V
F1, F2 : fuse 315 mA,- 250V
K1
: bridge rectifier 1A, 400V
Rc
: resistor 22
Ω
, 5 W
Rd
: resistor 10 k
Ω
, 5 W
T2
: relay SPST 5A, 220V, coil 110 V, 10 k
Ω
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