Key points for checking transformer saturation

qwqwqw2088

Key points for checking transformer saturation [Copy link]

The explanation here is about "transformer saturation"

Transformer Saturation

The saturation of transformer T1 is related to the primary winding and secondary winding that control the flyback operation. T1 has a third winding (pins 4 and 5) that generates the power supply VCC of the power IC. Regarding this, it is necessary to check whether VCC is generated as designed.

First, the saturation of the transformer. The magnetic materials (iron, ferrite, etc.) used in the transformer have the characteristics of saturation magnetic flux density. As the current flowing to the primary winding of the transformer increases, the magnetic field strength will increase. The magnetic flux density does not increase infinitely. After reaching the saturation point, the magnetic flux density will hardly increase with the increase of current. This state is called saturation magnetization, and the magnetic flux density at this time is the saturation magnetic flux density.

When the saturation point is exceeded, the state of saturation magnetization is called transformer saturation. This is the same as inductance. When a transformer is saturated, the magnetic flux density does not increase, but the inductance value decreases sharply.

When the inductance value decreases, the resistance to DC becomes only the resistance of the transformer winding. In other words, a large current will flow when the transformer is saturated. This is the cause of the transformer saturation problem in power supply design. This is the same as for inductance.

The waveform data on the right is the transformer switching the Ids of the built-in MOSFET on the primary side. The green line is normal, that is, the transformer is not saturated. In contrast, the red dotted line shows the typical waveform when the transformer is saturated.

As mentioned above, once the transformer is saturated, a large current will flow through it, causing a peak current in Ids, which means a sharp increase in current. When the current is too large, the MOSFET may be destroyed.

When designing a transformer, the maximum current Ippk on the primary side is calculated to design the transformer appropriately. If an Ids current waveform like the above waveform data is observed, the transformer must be redesigned.

The following summarizes the key points for checking transformer saturation and the condition settings.

Key points for checking transformer saturation

• Observe the current waveform of the drain current Ids using an oscilloscope or current probe.
• When the transformer is saturated, the Ids rise amplitude will change, and Ids will rise sharply.
• The current increase may cause the destruction of MOSFET etc.
• When confirming the saturation of the transformer, please confirm the actual status of related factors such as Ippk
• Depending on the situation, the transformer design may need to be redesigned.

Setting the inspection conditions

• Input voltage: minimum value, maximum value (when power is turned on, when normal)
• Load current: Maximum
• Ambient temperature: upper and lower temperature limits of temperature conditions

led2015

Advantages of saturation phenomenon:

1. Protective circuit: Through the saturation phenomenon, it can limit the current in the circuit, thereby protecting the circuit from being burned by overload.

2. Control voltage: Saturation can change the impedance in the circuit, thereby controlling the output voltage of the circuit.

3. Reduce losses: Saturation can reduce the current in the circuit, thereby reducing the losses in the circuit.

Disadvantages of saturation phenomenon:

1. Impact on output voltage stability: Due to the saturation phenomenon, the output voltage is difficult to increase, which may make the output voltage unstable and affect the normal operation of the equipment.

2. Reduced efficiency: Saturation will increase the energy loss of the transformer, thereby reducing the conversion efficiency.

3. Shortened life: Saturation will increase the temperature of the transformer, thereby shortening the life of the equipment.

maychang

led2015 Published on 2023-6-4 20:40 Advantages of saturation phenomenon: Protecting the circuit: Through the saturation phenomenon, it can limit the current in the circuit, thereby protecting the circuit from over-current...

【Advantages of saturation phenomenon】

Who summarized the three advantages of magnetic saturation? Can magnetic saturation also limit current?

xutong

The inductor transformer is saturated, and the current waveform is observed under what conditions to show obvious changes.

You can watch it with limited flow, which is safer