Published in issue 292, October 2000
Loss-free switching, using a Field Effect Transistor (FET) and a capacitor‘s discharge function, is the base theme of this elementary circuit.The one-minute light circuit shown in Figure 1 consists of six components, whose functions are easy to point out. The power source is a 6-volt battery, paralleled to the branch point with a lamp and transistor, acting an on/off switch.Likewise, parallel to the battery is a node linking a pushbutton switch coupled to a very high ohmic valued resistor. The BUZ10 is a Field Effect Transistor (FET), which differentiates itself from a normal transistor, in so much that almost no base current is needed for it to switch on — instead, a voltage at the Gate pin is required. Thus switching without performance loss is possible, which is extremely practical for battery switching circuits.
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