The MAX5003 high-voltage switching power-supply controller has all the features and building blocks needed for a cost-effective flyback and forward voltage-mode control converter. This device can be used to design both isolated and nonisolated power supplies with multiple output voltages that operate from a wide range of voltage sources. It includes a high-voltage internal start-up circuit that operates from a wide 11V to 110V input range. The MAX5003 drives an external N-channel power MOSFET and has a current-sense pin that detects overcurrent conditions and turns off the power switch when the current-limit threshold is exceeded. The choice of external power MOSFET and other external components determines output voltage and power. The MAX5003 offers some distinctive advantages: soft-start, undervoltage lockout, external frequency synchronization, and fast input voltage feed-forward. The device is designed to operate at up to 300kHz switching frequency. This allows use of miniature magnetic components and low-profile capacitors. Undervoltage lockout, soft-start, switching frequency, maximum duty cycle, and overcurrent protection limit are all adjustable using a minimum number of external components. In systems with multiple controllers, the MAX5003 can be externally synchronized to operate.