| 摘要 |
PURPOSE:To reduce mixing of switching noises generated in chopper operation to video signals by synchronizing period of a chopper with a horizontal synchronizing signal and making at least one of rising or falling action in the blanking time of the horizontal synchronizing signal. CONSTITUTION:When a horizontal synchronizing signal is supplied to an input terminal at time 52, an AND circuit 3 takes the logical product of a direct signal from an AND circuit 32 and a signal delayed by a delay circuit 34, and generates a single pulse synchronized with rising of the horizontal synchronizing signal, and a transistor 37 becomes on. Consequently, a transistor 14 also becomes on, an output voltage V0 rises from a time t2. When the output voltage Vo becomes higher than the set voltage Vref of a reference voltage source 26, transistors 37 and 14 become off. Thus, on/off-control of the transistor 14 is made synchronously with the horizontal synchronizing signal, and specified DC current Vo can be obtained.
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