Here is an example of an isolated DC/DC converter using the MAX256 transformer driver. The MAX256 enables designers to quickly implement a simple isolated DC/DC converter. This diagram shows a typical application circuit with the MAX256. Each part of the circuit is divided into separate colored sections for clarity. Starting from the left in the resistor section, the oscillator frequency can be configured between 100kHz to 1MHz depending on the value of the external resistor that is connected to CK_RS and ground. If left unconnected, the oscillator defaults to 100kHz. In this example, 47kΩ will yield a frequency of 380 kHz typical. There is a graph provided in the datasheet that shows oscillator frequency versus RS. The Capacitors section shows a couple of capacitors for decoupling VCC from the input power supply noise. Also, the MODE pin is tied high to VCC or +5V in this case to enable the internal oscillator. Connecting the MODE pin to GND enables external clock signals to be used and an internal flip-flop divides the external clock by two. In the Transformer Driver section, the two GND pins are tied to ground and the ST1 and ST2 pins are connected to the transformer’s two primary windings. For the transformer section, there are a few things to keep in mind when selecting a transformer: the isolation level, turns ratio for the desired output, and most importantly, the ET product. The ET product is the maximum area of pulse which a given transformer can transmit. Choosing the right transformer with sufficient ET constant will ensure it will not saturate the magnetic core, resulting in large currents that can damage the transformer. The ET product formula is VCC/(2*switching frequency). Using a maximum supply voltage of 5.5V and frequency of 380kHz, the ET product is 7.24Vµs. The transformer in this example has a turns ratio of 1:1.3, an ET product of 7.24 Vµs, and an isolation voltage of 4.5kVrms. For the diodes section, ordinary silicon diodes can be used for current levels less than 50mA, but use Schottky diodes for higher current levels to improve efficiency, making sure the current rating of the diodes are higher than maximum load current. For the output capacitor, a standard ceramic 0.1 µF capacitor is sufficient where ripple is not critical, otherwise use capacitors with low ESR.