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Output
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How the circuit works .. The main component of this circuit is the BFY51 transistor (the BC 637 is a close equivalent). It has three connections as shown: The base (b) The circuit works in the same way as module P1. The base is at its input side, the collector at its output side and the emitter being common to the collector and base circuits. When a voltage greater than approximately 0.6 volts, is applied to the base, current is allowed to flow into the transistor's collector and out of its emitter. This current originally flows from the + power rail, through the output device ( eg. Motor, Lamp etc.) and then into the collector. The output device is being sinked by the transistor (see OP1). The transistor is acting as a current switch. (The 1K resistor on the base, is there to prevent too much current entering the transistor.) |
Circuit Diagram
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Extra information.... The BFY51 transistor is an npn medium power semiconductor. It is a low cost device chosen for its output power. Its gain specification can be found by looking for its hFE characteristics in an electronic components supplier's catalogue. Its value is 40. Other specifications/ details are also given. Gain = Collector current (Ic) / Base current (Ib) Emitter Current (Ie) = Base Current (Ib) + Collector Current (Ic)
The maximum output current (Ic) = 1 amp Alternative transistor.... The BC 637 is a popular substitution for the BFY51 as it is approximately half the cost and has a very similar specification. Please note the leg connections in the diagram above.
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