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4.为适应宽电源(AC90～270V),增加了一路正反馈电路——恒流激励电路该电路由开关变压器T803⑨～⑦绕组、⑦～⑧绕组、射级跟随器VQ820、R822、R823、VD828等组成。该电路具有双重作用:一是当输入交流市电较高时,T803⑨～⑦绕组⑨端输入脉冲电压增高,当高于VD828的齐纳击穿电压时,VD828击穿导通,使VQ820基极电压被钳位在VD828稳压值(7.5V)上,致使其集电极电流保持恒定不变,为开关管VQ83提供恒定的激励电流,增加了输出电压的稳定性;二是当AC输入电压低于160V以下时,开关变压器T803⑨～⑦端正反馈绕组⑨端输出脉冲电压幅度低于
4. To meet the wide power supply (AC90 ~ 270V), an increase of all the positive feedback circuit - constant current excitation circuit The circuit consists of switching transformer T803 ⑨ ~ ⑦ winding, ⑦ ~ ⑧ winding, shooter follower VQ820, R822, R823, VD828 And so on. The circuit has a dual role: First, when the input AC mains is high, T803 ⑨ ~ ⑦ end of the winding input pulse voltage increases, when the voltage higher than VD828 Zener breakdown, VD828 breakdown conduction, so VQ820 base The voltage is clamped at the regulated value of VD828 (7.5V), resulting in a constant collector current, providing a constant excitation current for the switching tube VQ83 and increasing the stability of the output voltage. Second, when the AC input voltage is low Below 160V, the switching transformer T803 ⑨ ~ ⑦ positive feedback winding ⑨ end of the output pulse voltage amplitude below