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四、保护电路 1.过压保护电路:当取样、误差放大或脉宽调整等电路发生故障时,就会使开关管V501导通时间过长,而引起输出电压U_0的大幅度上升;另外如果负载开路的话,也会使输出电压大幅度上升。U_0上升过大就会使负载(尤其是行输出管)或电源开关管V501因过载而损坏,为此本机内设置有过压保护电路。过压保护电路由可控硅V505、D512、D517、R525、R526、R527、C522、C523等元件组成。取样绕组上的电压经过R523、R524分压后加至稳压管D517和可控硅V505的触发极与阴极之间。在输出电压U_0正常时,该电压不足以使稳压管导通,故可控硅截止,保护电路不起作用;当U_0高于正常值时取样绕组上的电压亦升高,R523两端的电压也随之升高,当U_0为175V时,R523两端电压高于稳压管的稳定电压6.2 V,使稳压管D517导通,于是可控硅得到触发电流而导通。由于C523在可控硅导通前已经被充电到6.17V(V505的
Fourth, the protection circuit 1. Over-voltage protection circuit: When sampling, error amplification or pulse width adjustment circuit failure, it will make the switch V501 conduction time is too long, which led to a substantial increase in output voltage U_0; the other if If the load is open, the output voltage will also increase drastically. If U_0 rises too much, the load (especially the line output tube) or the power switch tube V501 will be damaged due to over-load. Therefore, an over-voltage protection circuit is provided in the unit. Over-voltage protection circuit by the SCR V505, D512, D517, R525, R526, R527, C522, C523 and other components. Sampling winding voltage after R523, R524 partial pressure added to the regulator D517 and thyristor V505 between the trigger pole and cathode. When the output voltage U_0 is normal, the voltage is not enough to turn on the regulator, so the SCR is turned off, the protection circuit does not work; when the U_0 is higher than the normal sampling voltage on the winding also rises, the voltage across R523 Also will be increased. When U_0 is 175V, the voltage across R523 is higher than the steady voltage of the regulator, 6.2 V, so that the regulator D517 is turned on, so the SCR can be triggered current and turn on. Since C523 has been charged before the thyristor is turned on to 6.17V (V505’s