In power supply design, we often hear the word leakage inductance. So what is leakage inductance and what impact does it have on the power supply?

1. What is leakage inductance?

In a transformer or coupled inductor, it is generated by the primary winding and cannot be coupled to Part of the magnetic flux in the secondary winding is called leakage inductance.

2. What about leakage inductance? Test

To test leakage inductance, you need to short-circuit all other coil legs except the two legs of the primary winding, and then test the primary winding inductance. The measured inductance value becomes leakage inductance. value. As shown in the picture below, short-circuit pins 3, 4, 5, and 6, and then test the inductance of pins 1-2. The leakage inductance value will be obtained.

3. Leakage inductance pair What is the impact of power supply

Leakage inductance is distributed in the entire coil of the transformer and is in series with the winding, because its energy cannot be released to the secondary side. Therefore, a large voltage spike will occur when the switch is turned off. It increases the voltage stress and heat of the switching tube, and also worsens the overall EMI performance.

4. How to reduce Leakage inductance

The leakage inductance of the transformer is proportional to the square of the number of primary turns. Reducing the number of turns can reduce the leakage inductance. In addition, the primary can be placed on the inner and outer layers and the secondary pole is sandwiched in the middle (sandwich winding). If there are too many primary layers, the leakage inductance will also increase, and the direct distributed capacitance of the layer will increase, causing the high frequency to be directly coupled, making the leakage inductance of the high frequency part larger, and also causing instantaneous oscillation of the switch, increasing the Losses in transformers and switching devices.