AUTOMATIC DIAPHRAGM CONTROL CIRCUIT FOR CCTV AUTOMATIC DIAPHRAGM LENS

摘要

PROBLEM TO BE SOLVED: To protect a whole automatic diaphragm control circuit including a stabilized power source circuit from a thunder surge by inserting a surge absorber between a power source line and a ground line at the input side of the stabilize power source circuit, and inserting a low impedance resistance element between the surge absorber connection and the stabilized power source circuit of a power source line at the input side. SOLUTION: This automatic diaphragm control circuit of a CCTV automatic diaphragm lens is provided with a stabilized power source circuit II for stabilizing a power source supplied form the outside, an input signal detecting circuit III, and output circuit IV, and a middle point power source circuit V, and a diaphragm driving signal is obtained from a picture signal or a pseudo signal outputted from a CCTV camera so that the opening and closing of a diaphragm can be controlled by an iris servo meter VI. Then, a surge absorber is inserted between a power source line P1 and a ground line at the input side of the stabilized power circuit II, and a fixed resistance R1 of a low impedance is serially connected between the surge absorber of the power source line P1 and a reserve connection protecting diode D1 of the stabilized power source II.