如果用PWM芯片 UC38XX 系列它是两个，辅助电源5V一个，主电路一个，使用TL494就是三个，多一个驱动变压器。输出12V，5V，3.3V。

　　输入不知道你测它有什么用，一般是高频脉冲电，可以用频率表量，大约是20KHZ一35KHZ之间。输出波型好的是四方波，有些设计差的用料不足可能是三角波或梯形波。

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　　电脑电源是开关电源，一般来说，台式机ATX电源内有3个变压器，分别是主电源变压器、副电源变压器、主电源开关管推动变压器，副电源的结构和一般的手机充电器电路结构类似，只是功率更大些，原边一端接市电整流后的直流电源，对地（电路中的地）电压约310V，另一端接尖峰吸收电路和开关管，电压未知。副边经过半波整流直接输出，副电源输出电压为5V。主电源变压器的原边是半桥推挽结构，副边各组电源经过全波整流后输出，波形不知道没测过。推动变压器用于开关管与电源振荡电路之间的信号耦合，应该是方波。