UCC25706D

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The UCC25706D device is an integrated offline switcher for offline AC-DC power conversion. The device provides a cost-effective solution for low-power offline power supplies, allowing designers to reduce component count and design time. Incorporating an insulated flyback power stage, frequency jitter and peak current mode control, the device offers programmable primary over-voltage protection, primary current sense redundancy and output voltage accuracy of ±3%.

Application Field

The UCC25706D is mainly used in a range of isolated and non-isolated AC-DC applications with power levels of up to 200 Watts, including use in offline power supplies for consumer, office and industrial applications, non-isolated dc-dc converters, adapters and battery chargers. With its integrated primary side components, advanced operating modes, low RDS(ON), noise immunity, and other features, it enables a compact transformer size, excellent power density and high efficiency. Additionally, the device offers advanced power-saving features such as low standby power, as well as programmable start-up over-current protection and secondary side overload protection. It also has integrated features such as programmable brown-in/out protection and open-loop fault protection.

Working Principle

The UCC25706D uses a peak current mode control method that operates in fixed frequency and provides improved output voltage regulation by varying the average inductor current. The device is an integrated insulated flyback power stage with auto-restart capability. It includes a N-MOSFET switch, a programmable primary peak current limit, an oscillator, an over-voltage protection (OVP) circuit, protection logic, and output voltage sense. The power stage utilizes the primary Peak Current Mode Operational Amplifier (PMOA) to regulate the average inductor current, which results in different average power from the output of the device, thus providing improved output voltage regulation. The PMOA then drives the switch to control the power switch current that limits the peak current in the switch. The peak current is set by an external resistor.

The device operates in fixed frequency mode, with the oscillator frequency programmed by an external resistor. The internal OVP circuit monitors the output voltage, and when the output voltage exceeds a predetermined level, the OVP will turn off the switch and no average current will flow. The device is protected by an open loop fault protection circuit, which trips when the MOSFET switch is on for more than 25ms. This prevents high switch current and high frequency current signal generation, which can cause damage to the transformer and affect system safety. Additionally, the device uses Brown-In/Out protection to prevent excessive inrush and/or overcurrent events during start-up. The UCC25706D is also equipped with a programmable start-up over-current protection feature, which limits the inrush current during start-up, thus improving system reliability.

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