Talking about the winding of high frequency transformer

2019-04-09 14:51:01 JuKe Technology (DongGuan) Co., Ltd. Read

Talking about the winding of high frequency transformer

 This article is mainly about the introduction of high-frequency transformers, and focuses on the winding of high-frequency transformers.
High frequency transformer

The high-frequency transformer is a power transformer with a working frequency exceeding the intermediate frequency (10 kHz). It is mainly used for high-frequency switching power supply transformers in high-frequency switching power supplies, and also for high-frequency inverters in high-frequency inverter power supplies and high-frequency inverter welding machines. Variable power transformer. According to the working frequency, it can be divided into several grades: 10kHz- 50kHz, 50kHz-100kHz, 100kHz~500kHz, 500kHz~1MHz, 10MHz or more.

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 working principle

A transformer is a device that converts alternating voltage, current, and impedance. When an alternating current is passed through the primary coil, an alternating magnetic flux is generated in the core (or core) to induce a voltage (or current) in the secondary coil.

The transformer consists of a core (or core) and a coil. The coil has two or more windings. The winding connected to the power supply is called the primary coil, and the other winding is called the secondary coil. [1]

Design principle

In the design of high-frequency transformers, the leakage inductance and distributed capacitance of the transformer must be minimized because the high-frequency transformer in the switching power supply transmits a high-frequency pulse square wave signal. During transmission transients, leakage inductance and distributed capacitance can cause inrush currents and spikes, as well as top oscillations, resulting in increased losses. Usually, the leakage inductance of the transformer is controlled to be 1% to 3% of the primary inductance.

The leakage inductance of the primary coil—the leakage inductance of the transformer is caused by the fact that the magnetic flux between the primary and secondary coils is not fully coupled between the layers and between the layers.

Distributed Capacitor----Between the windings of the transformer windings, between the upper and lower layers of the same winding, between the different windings, the capacitance formed between the winding and the shielding layer is called the distributed capacitance.

Primary winding----The primary winding should be placed in the innermost layer, so that the length of the primary winding of the transformer can be minimized, so that the entire winding is minimized, which effectively reduces the distribution of the primary winding itself. capacitance.

The secondary winding----the primary winding is wound, and the (3~5) layer of insulating pad is added to rewind the secondary winding. This reduces the capacitance of the distributed capacitance between the primary winding and the secondary winding, and also increases the dielectric strength between the primary and secondary, meeting the insulation withstand voltage requirements.

The bias winding—the bias winding is wound between the primary and secondary, or the outermost layer, and the switching power supply is adjusted based on the secondary voltage or the primary voltage.
Talking about the winding of high frequency transformer

1: Using the dedicated transformer design software PIXls Designer and PI TRANSFORMER Designer, will take the required parameters, such as input voltage range, output voltage requirements, bias voltage magnitude, transformer estimated power, power factor, rated load, primary coil layer, times The parameters of the number of turns of the coil are input. The PI software will give a reasonable transformer parameter according to the parameters input by the user. Then the designer can wind the transformer according to the given parameters. The software will give the following parameters: Primary coil The number of layers of the feedback coil, the secondary coil, the number of turns, the size of the wire, the direction of winding, the size of the air gap, the number of layers of the tape between the coil and the coil, the type of the skeleton, the type of the magnetic core, the requirements for the immersion paint, and the like.

2: With these parameters, you can wind the transformer. Before winding the transformer, first assign a number to the foot of the skeleton. For example, we need to wind an input voltage of +24V, output 1 is +9V, and output 2 It is a +15V transformer, and the power output of the 2 output terminals is 1.5W. Then the winding method of this transformer is as follows:

The winding method of the primary coil: starting from the lead 2, using the enamelled wire with a wire diameter of 0.19 mm to wrap around the frame for 53 turns, it is estimated that there are two layers, and the winding should be as flat as possible. At the end of pin 1, after winding, wrap two layers with insulating tape.

Winding method of the bias coil: starting from the lead 5, use the enameled wire with a wire diameter of 0.13 mm to wrap around the frame 27 to the end of the pin 4. After winding, wrap two layers with insulating tape and wrap it with a layer of insulating tape. All but the pins have exposed coils.

9V end coil winding method: wrapped in 7-foot and 6-foot bottom with insulating tape, using enameled wire with a diameter of 0.35 mm, starting from 7 feet and ending with 20 to 6 feet, wrapped in two layers with insulating tape. Wrap the windings other than the 7-pin 6-pin with an insulating tape.

15V coil winding method: wrapped in 10 feet and 9 feet with insulating tape, using enameled wire with a wire diameter of 0.19 mm, starting from 10 feet and ending with 34 to 9 feet, wrapped with two layers of insulating tape, and then loaded with two fast magnetic The core is placed with 0.3 mm thick paper (ie, air gap, about 4 layers of white paper thickness) between the two cores. After flattening, the core and the skeleton are wrapped with tape. (Insulation tape refers to 4KV insulation)

3: Test transformer output and load capacity

Test method: Install the wound transformer on the test board that has been tested successfully, and test the circuit output and load capacity. If the output end and load capacity are normal, the transformer withstand voltage capability can be tested.

4: Test transformer withstand voltage capability.

The transformer withstand voltage test is divided into three groups, namely the primary end (1, 2 feet), the 9V end (6, 7 feet), and the 15V end (9, 10 feet). Add 3KV AC voltage to any two groups for 20 seconds (any clip of each end of the clip can also be fully clipped). If the voltage tester alarms, the transformer will be unqualified and will not pass the alarm.