The main purpose of the power supply is to convert the rectified AC Input to DC regulated current for 6 LEDs. The power supply provides protection for the LEDs, limits the transient input voltage and protect against inrush current at plug in. The overall power supply conformity (e.g. mains harmonics (EN), mains interference, international safety standards etc.) are not approved for all the applicable European Norms (EN).
This application note describes the design of a tiny AC or DC Flyback power supply.
It�s main purpose is to convert the rectified AC or DC Input to DC regulated output voltage. The power supply provides protection for this supply voltage, isolates the rest of the network from the output, limits the transient input voltage and protects against inrush current at plug in. The board fully complies to the EN55022 norm (Conductive average) and international safety standards. The secondary side is regulated at 3.3V. The controller is switching with a fixed frequency of 250 kHz. The heart of the power supply is the controller LM3481 current mode PWM from National Semiconductor.
The advantage of the proposed solution is using a standard off the shelf transformer, small solution size and high ambient operating temperature up to 85�C (105�C possible).
Based on the presented solution higher output power up to several Watt can also be achieved using the LM3481.
Features
Input RangeOutput
| LM3481 | Min 8.9 VDC
or 24 VAC | 3.3 VDC |
Max 40 VDC
or 24 VAC | 100 mA |
The LM3481 integrates many features to simplify the Flyback converter implementation:
- Hysteretic under-voltage shutdown protects the power stage from excessive stress if the input voltage is below the required minimum operating level.
- Current mode control allows for simple type 2 control and protects the power MOSFET from over-current
- Integrated 1A capable gate drive to provide rapid switching of the power MOSFET.
- Internal soft start
- Pulse skipping at light load