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  • 5V 3W Flyback Power Supply

  • Created: Dec 06, 2016

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This reference design is 5V, 3W offline flyback power supply. It features the ICE3RBR4765JG current mode controller used as a flyback controller. It has a built-in 650V CoolMOS as the main switching component, as well as the startup cell. This design operates in Discontinuous Conduction Mode (DCM), running at 65KHz switching frequency. Its output is a single 5V at 600mA generated by secondary side regulation. Active Burst Mode (ABM) operation provides very low standby power consumption; less than 13mW over input voltage range 180Vac to 265Vac. Also, low Electromagnetic Interference (EMI) is achieved by built-in frequency jitter and soft start operation.

When the input voltage is applied, the ICE3RBR4765JG starts to charge its VCC capacitor through the built-in startup cell. The startup cell is activated if the VCC voltage is below the undervoltage threshold level of 10.5V. The VCC charge current is controlled to 0.9mA by the startup cell. The startup cell remains active until the VCC voltage exceeds the on-threshold of 18V, when the ICE3RBR4765JG starts to operate and the startup cell is turned off. In order to achieve the lowest power consumption, VCC is set as low as possible within a defined range. Due to the tolerance of the ICE3RBR4765JG, especially the undervoltage lockout level, a safe margin for VCC is taken into account when the transformer auxiliary winding is determined. Capacitors C4 and C5 are selected to be sufficient to keep VCC above this safe margin during the discharge phase, when the IC is not in a steady state. The VCC capacitance must not be unnecessarily large with respect to the startup time. In steady state conditions, VCC is stable as the IC is supplied from the auxiliary winding.

Mostly, operations that need a reliable power supply with low standby power consumption are the target application. Like the Internet of Things (IoT); its standby power supply, power supply for microcontrollers, sensors, actuators, and etc. that is embedded in each of the devices stay connected to the network at all times.



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