Using Portable Power Boost in the Isolated Flyback Application
Some electronic devices need power from an axillary power supply, through a low voltage adapter. Examples include relay controls and MOSFET drive-circuits. The problem is, it is difficult to find isolated controllers that work at such voltages. However, there is a solution.
You can control and operate such flyback power stages by using boost converters on low power. Take, for example, a device getting power from a 5 V transformer, requiring an isolated 500 mA, 5V axillary power supply. The input voltage lies somewhere between 3V and 6V. Note that smaller size is more important than efficiency.
In this case, a flyback power stage becomes an obvious choice because of its isolation and low-output power. Considering the size limitations and the application, an embedded engineer may consider a boost controller with integrated FET ideal for this application.
There are many low power boost converters in the market that meet these specifications. Note that you may have to use a custom power supply to power such applications. The switching frequency of the converter may extend to 2.2 MHz. This also translates into smaller input/output filter components smaller transformer.
Look for a converter with a high integration current mode. The peak FET current should be limited to 3A. So the controller will be better off if it uses continuous conduction mode. Note that there will be switching losses. This can be countered by using a 1 MHz operating frequency for the current. Another advantage is, it will reduce the size of the transformer and its physical size.