Basic design knowledge of high frequency transformer

High-frequency transformer is different from the power transformer, the high-frequency transformer is an integral part of the amplifier in the working amplifier circuit. Moreover, it works in the frequency band with a certain bandwidth, and its parameters are related to the amplifier circuit parameters. Therefore, when analyzing and designing the high-frequency transformer, it must be combined with the amplifier circuit and determine the electrical parameters according to its characteristics.

1. The main role of high-frequency transformer

The main function of the high-frequency transformer is to convert the impedance of a certain value into another value, so that the impedance match between the two circuits or the amplifier to obtain the best load impedance. The impedance obtained by using a transformer is different from a specific resistance, which is a network including the transformer’s own parameters (self-inductance, leakage inductance, distributed capacitance, copper resistance), and its reactance component changes with the frequency. In various circuits at different frequencies, the transformer can be equivalent to a specific network, called the equivalent circuit. Figure 8 is the equivalent circuit of the high-frequency transformer. The difference between it and the equivalent circuit of the power transformer is that the internal resistance Ri of the power supply is supplemented, and the primary and secondary leakage inductance are combined and represented by LS, which is defined as the primary total leakage inductance.

2. Impedance matching

Transform the signal voltage, so that the front and back amplifiers achieve impedance matching, to ensure that the signal is not distorted, efficient transmission.

Step 3 Isolate

The two circuits can be isolated using a high-frequency transformer.

4. Multiple signal superposition or decomposition

The transformer can be used to superimpose two or more signals, or to divide a signal into several signals to transmit to the load.

5. Phase reversal

By changing the polarity of the transformer, the phase of the output signal is opposite to that of the input signal; Or become two equal and opposite signals.

6. Equivalent circuit of high-frequency transformer