Everest CORE - Product Manual |
Application Guide
INGENIA | 08/01/2019
24
DC Bus input stage
Everest CORE is a switched power regulator using a very fast state-of-the art switching technology. This allows
Everest CORE to be extremely efficient, but at the cost of requiring a relatively more sophisticated input stage to
avoid transmitting a "sharp" ripple voltage through the power supply lines. This is of an special importance when
sharing the DC bus with other sub-systems or when targeting EMC-related certifications, as CE marking. The most
suitable solution will strongly depend on the requirements of the target market or environment (industrial,
medical, domestic, automotive...), and the specific dynamics of the load, but in most cases it will consist in 4
elements:
•
Input power filter
•
Earth decoupling
•
DC bus bulk capacitors
•
Sourge / ESD protections
The 2 first elements can be resolved by means of a line filter. A 1-stage line filter might be enough in some cases,
but in most cases a 2-stage would make it to pass the conducted emissions tests. However, a line filter might be
expensive and very bulky compared to the Everest CORE, so the on-board discrete solution can be the best trade-
off. Here, only very basic and raw indications are given by the following schematic:
The basic protection to fulfill the minimum requirements of most industrial-grade EMC certifications would consist
in a power filter targeting the common mode of the DC bus. The input and output capacitors are separated into 1-
decade pairs to extend their effectiveness to higher frequencies (this could be done up to 2 decades or even more).
The selected values just pretend to be indicative of this. This capacitors should be of X-type ceramic and their
voltage must be carefully selected to match the application under a "safety" criteria: keep in mind that
capacity of
ceramic capacitors experience a strong derating over voltage
. Decoupling capacitors to Earth C9 and C10 are of
crucial importance. They must be of Y-type and rated to safety standards, specially when it comes to have its failure
mode guaranteed.
For more demanding EMC requirements, like certifications framed in domestic or automotive standards, an
additional filter targeting the differential mode might be required. Here a CLC or Pi filter is suggested, although
many others may be valid. This filter is intended to reduce the voltage ripple in the DC bus caused by the fast
commutation of the Everest CORE, as it propagates through the cables affecting both the conduced and radiated
frequency ranges. This is strongly related to the load, as inductance and current ratings of the motor directly affects
the DC bus voltage ripple, but DC bus bulk capacity plays a notable role in reducing this effect (see below). In any
case, selecting an L1 small enough might be demanding, specially when rated to withstand the current ratings of
the Everest CORE.
for further help on this topic.
Second, the
DC bus bulk capacity
plays a crucial role in the EMI response, but also in the motion control. As a
dummy rule of thumb, the greater the installed capacity, the better, but at the same time capacitors are big and
expensive, so optimising the number and type of the capacitors included in the design is usually something to take
care of. Typically, having this capacitors will respond to 3 purposes:
