Metal Switch Glows Tough
Robust stainless steel switch with back lit ceramic actuator resists
scratches, abrasions and chemicals
- Momentary action
Figure 3: Isolation barriers
The capacitors connected between the line or neutral and ground are
specifically rated to fail safe. They also provide a path to harness and control
conducted emissions that are present in switching power supplies due to the
voltage being switched at high frequencies. A Class II device does not have this
capacitive path and, therefore, great care must be taken by the design engineer
in circuit design.
The result is that the power supply design engineer must pay careful attention to the circuit to ensure isolation and EMC compliance. The block diagram
in Figure 3 illustrates the isolation barriers for the system.
The optimized power solution will take into consideration many factors,
including power, input voltage, and output voltage. These factors will influence
the topology selected and switching frequency. Regardless of those choices, the
key component will be the transformer.
Transformer design is crucial for all power designs. In isolated converters, it
becomes an important barrier from primary to secondary. Topology, switching frequency, power, and form factor will all influence the design decision.
Techniques to optimize required isolation and tight magnetic coupling include
approved triple insulated wire, multi cavity bobbins and split winding techniques. In all cases, the goal is to maintain the required creepage and clearance
distances while achieving tight magnetic coupling.
Technology advances provide the opportunity to enhance people lives.
Standards are designed to support the use of technology in a safe manner.
Power supply designers and integrators must pay particular attention to ensure
the design provides the isolation voltage, leakage current, and all the elements
necessary to support the medical device market. The introduction of the 60601-
1-11 collateral standard is an important step to facilitate the introduction of
advanced technology in a safe manner.