Transformer selection & Design considerations
The transformer specification and design is probably the most critical part of successfully applying the LT8300. Since the voltage on secondary side of the transformer is inferred by the voltage sampled on the primary-side, the turns ratio must be tightly controlled to ensure a consistent output voltage.
Linear Technology has worked with leading magnetic component manufacturers to produce pre-designed flyback transformers for use with the LT8300. Table 1
shows an abbreviated list of recommended off-the-shelf transformers from Wurth Elektronik, Pulse Engineering and BH Electronics. A complete listing is shown in the LT8300 data sheet. These transformers typically withstand a 1,500VAC breakdown voltage for one minute from the primary to secondary. Higher breakdown voltages and custom transformers can also be utilized.
Table 1: LT8300 off-the-shelf transformers
An LT8300 circuit can be modeled using any of the transformers listed in Table 1
by downloading a free copy of the LTspice software at www.linear.com/LTspice
. This simulation produces realistic results to help further ease and confirm the design of such converters. The simulation circuit includes information on how the circuit starts up and its reaction to load steps for different input voltage. It is easy to make changes and see the impact to its circuit performance.
Power supply isolation can be utilized in medical systems to get off a noisy supply voltage and is also needed in distributed power architectures for safe operation. A LT8300 based circuit simplifies the design of an isolated flyback converter by eliminating the need for an optocoupler, secondary-side reference voltage and extra third winding off the power transformer. This device maintains primary to secondary isolation with only one part crossing the isolation barrier. Readily available off-the-shelf transformers prevent the need for a custom transformer. The LT8300 operates from a 5V to 100V input voltage range with up to 2 watts of output power making it well suited for a wide range of medical, industrial, telecom and datacom applications.
About the author:
Bruce Haug is Senior Product Marketing Engineer, Power Products, at Linear Technology Corp.
See related links:
Improving medical imaging with direct radiography
Smart devices are key for medical gear makers
Using clinical observation to facilitate medical device commercialization
An embedded solution for medical device interoperability
[Get a 10% discount on ARM TechCon 2012 conference passes by using promo code EDIT. Click here to learn about the show and register.]