High-power ultrasonic welding requires a power amplifier circuit that can achieve high-power amplification. High-power ultrasonic transmitting circuits mainly use bridge switching power amplifiers because they are simple, stable and reliable to implement. . Bridge switching power amplifiers can be divided into two types: half-bridge and full-bridge. In order to reduce the switching loss of field effect tubes under high-frequency working conditions, the high-power ultrasonic drive circuit uses a full-bridge switching amplifier with an auxiliary network [5]. The preliminary design circuit is as shown in the figure?
This circuit structure solves the traditional problem of The problem of zero voltage switching (zvs) PWM circuit transformer is small leakage inductance and lagging bridge arm making it difficult to achieve ZVS. At the same time, based on the current enhancement principle, this circuit structure can achieve zero-voltage switching in any load and input voltage range, greatly reducing duty cycle loss. It is worth noting that a diode is connected in reverse parallel to each field effect transistor. This is because the field effect transistor structure itself forms a parasitic diode 6 (not shown), which forms an integral whole with the field effect transistor. But because the reverse breakdown voltage of this parasitic diode is very small, when the load circuit returns, the diode will be broken down, causing the field effect transistor to fail. Therefore, in order to avoid this phenomenon, the field effect transistor is connected in reverse parallel. A diode with a larger reverse breakdown voltage can ensure that the parasitic diode of the field effect transistor is not broken down, thus ensuring the normal operation of the field effect transistor. The model of this diode can be MUR3020PT or FR series fast diode. It mainly plays a protective role. It only needs to be protected from breakdown