![](https://dianyuan-public.oss-cn-shenzhen.aliyuncs.com/t/community/2018/11/13/1542072737-23007-600.png?x-oss-process=image/watermark,g_center,image_YXJ0aWNsZS9wdWJsaWMvd2F0ZXJtYXJrLnBuZz94LW9zcy1wcm9jZXNzPWltYWdlL3Jlc2l6ZSxQXzQwCg,t_20)
![](https://dianyuan-public.oss-cn-shenzhen.aliyuncs.com/t/community/2018/11/12/1542022236-80488-600.png?x-oss-process=image/watermark,g_center,image_YXJ0aWNsZS9wdWJsaWMvd2F0ZXJtYXJrLnBuZz94LW9zcy1wcm9jZXNzPWltYWdlL3Jlc2l6ZSxQXzQwCg,t_20)
![](https://dianyuan-public.oss-cn-shenzhen.aliyuncs.com/t/community/2018/11/12/1542022275-92574-600.png?x-oss-process=image/watermark,g_center,image_YXJ0aWNsZS9wdWJsaWMvd2F0ZXJtYXJrLnBuZz94LW9zcy1wcm9jZXNzPWltYWdlL3Jlc2l6ZSxQXzQwCg,t_20)
假设这种供电方式成立:
便于计算假设一下几种方式:
1、假设输入为50HZ的方波,且峰值为310V;
2、假设上电是正好处于方波的正半周上升沿;
3、已知IC的去电范围为12-26V,且12V启动;
则:正半周的周期时间为10mS;
该电路VCC处的C4充电,充电电流I约为I=310V/(R1+R3);
C4处要充到12V,所需时间t;
C=Q/U,C=3.3uF,U=12V,而Q=It;
则t=C*U/I;
带入数据后,可得t≈170mS;
要就是说,Vcc处按目前的参数根本就不可能充到12V。因为负半轴C4放电。
负半轴C4会放电吗?回路被DB1整流桥阻断了。