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VD997为18V稳压管,在正常工作状态下,该保护电路均处于截止状态,当因某种原因导致各种输出电压升高(超值高出额定值的15％～20％)时,原15.5V输出电压将会超过18V,此时VD997反向击穿,使V474饱和导通,其集电极呈现低电平,使V904(C1815)基极处于低电平而截止,这便相当于遥控开机信号被短路到地,V903饱和导通,N902(“光耦器”)
VD997 18V regulator, under normal working conditions, the protection circuit are in the cut-off state, when for some reason led to a variety of output voltage increases (value higher than the rated value of 15% to 20%), the original 15.5V output voltage will exceed 18V, at this time VD997 reverse breakdown, V474 saturated turn-on, the collector presents a low level, so V904 (C1815) base is low and cut off, which is equivalent to the remote control Power-on signal is shorted to ground, V903 is fully on, N902 (“Optocoupler”)