大多数开关电源都依赖于通过电压反馈来控制的PWM(脉宽调制)输出。555定时器IC可以实现PWM,而且花钱不多。图1电路示出了仅仅利用一个简单公式就可将一个555PWM电路变成一个开关电源的方法。该电路使用2个555 IC。以非稳态模式工作的IC_1触发以PWM模式工作的IC_2。在高占空因子下,IC_1设定的振荡频率约为60kHz。IC_1的输出只是在触发PWM电路的大约2.5μS内为低电平,而在周期的其余时间内为高电平。PWM电路的最大脉宽约为 Most switching power supplies rely on PWM (Pulse Width Modulation) outputs that are controlled by voltage feedback. 555 timer IC can achieve PWM, but not much money. The circuit in Figure 1 shows a way to turn a 555PWM circuit into a switching power supply using only a simple formula. This circuit uses two 555 ICs. IC_1 operating in unsteady mode triggers IC_2 operating in PWM mode. At high duty cycle, IC_1 sets the oscillation frequency to about 60kHz. The output of IC_1 is only low for approximately 2.5 μs that triggers the PWM circuit and high for the rest of the cycle. The maximum pulse width of PWM circuit is about