H-bridge transformer driver circuit design for isolated power supplies

　　The MAX13256 H-bridge transformer driver provides a simple solution for building isolated power supplies up to 10W. The device operates from a wide 8V to 36V DC supply range and provides up to 300mA of current drive to the primary winding of the transformer. The output voltage is set by the turns ratio of the secondary to the primary of the transformer, which can generate an isolated output of any voltage. The device has an adjustable current limit, which indirectly limits the secondary load current. The current limit threshold of the MAX13256 is set by an external resistor. Once the device detects an overtemperature or overcurrent fault, the /FAULT output is immediately triggered. In addition, the device also has a low-power mode that reduces the overall supply current to 0.65mA (typical) when the driver is not in operation. The device has an internal oscillator that supports autonomous operation; an external clock input can synchronize multiple MAX13256 devices and accurately set the switching frequency. Internal circuitry ensures a fixed 50% duty cycle and ensures that no DC current flows through the transformer when any clock source is used. The device is available in a small 10-pin (3mm x 3mm) TDFN package and operates over the -40°C to +125°C automotive temperature range.