斩波电路的控制方式有( )。<br>·保持开关周期T不变,调节开关导通时间<img src="/lqwvjeImg/da/da3aefd3c34125927eb43bd1ceaeefbf.png"style="width:27px;height:23px;">,称为脉冲宽度调制<br>·保持开关导通时间<img src="/lqwvjeImg/da/da3aefd3c34125927eb43bd1ceaeefbf.png"style="width:27px;height:23px;">不变,改变开关周期T,称为频率调制或调频型<br>·<img src="/lqwvjeImg/da/da3aefd3c34125927eb43bd1ceaeefbf.png"style="width:27px;height:23px;">,和T都可调,使占空比改变,称为混合型。<br>·<img src="/lqwvjeImg/da/da3aefd3c34125927eb43bd1ceaeefbf.png"style="width:27px;height:23px;">,和T都不可调,使占空比改变,称为混合型。