The MCP1012 is used as a primary-side start-up IC for starting an offline auxiliary switching supply working in conjunction with a secondary-side controller. The MCP1012 does not linearly regulate the power converter, but rather a secondary-side controller (digital and/or analog) accurately linear regulates using sophisticated adaptive control schemes that enhance performance and efficiency. The primary function of the MCP1012 are to provide startup of the flyback converter using an internal open-loop, peak current-mode current regulator. It does this by accepting PWM commands via an isolation medium (s.a. a pulse transformer, opto, or other) from a secondary-side controller. It integrates various protection features, including an undervoltage lockout (UVLO) and overvoltage lockout (OVLO) protection, and overtemperature protection (OTP.) Additionally, the MCP1012 provides peak cycle-by-cycle current limiting both when under control of its internal current regulator or under control of the secondary-side controller.