![]() You might also look at a triac or IGBT or a solid-state relay - they have (in effect) several transistors combined into a convenient package. Should be able to hook you up with several kinds of transistors that meet that criteria. You'll need to use transistors that can handle voltages higher than your average mains voltage and also currents higher than your average load current. (See Wikipedia: TRIAC and Wikibooks: Power Electronics: Triac). Then connect them in antiparallel so the combination acts as a triac. You can build two SCRs out of a pnp and npn transistor each. (See the Wikipedia SCR dimmer schematic). Then you can use a bunch of diodes to steer the current so the SCR can turn on and off both the positive and negative half-cycles. You can put a pnp and a npn transistor together so the combination acts identical to a SCR. This approach may be simplest to understand, but in practice other AC switches have lower net cost. The "neutral" line and the emitter of each transistor are all connected, and the CPU power supply and the gate of each transistor stay within a few volts of neutral. Normally the CPU would either turn both transistors on, or both transistors off. (zero electrons flow through this diode+transistor connection when the transistor is off, or during the positive half-cycles). You can put a diode in series with the collector of another (pFET or pnp) transistor that conducts when the "hot" line of the mains is negative relative to "neutral", so when the CPU turns on that transistor, the transistor turns on the light bulb during the negative half-cycles. (zero electrons flow through this diode+transistor connection when the transistor is off, or during the negative half-cycles). You can put a diode in series with the collector of one (nFET or npn) transistor that conducts when the "hot" line of the mains is positive relative to "neutral", so when the CPU turns on that transistor, the transistor turns on the light bulb during the positive half-cycles. The above circuit was implemented in Proteus.Yes, there are several ways to build an "AC switch" entirely out of transistors. ![]() The current is diverted through the RED LED D2 instead of damaging the entire circuit. The current now flows through RED LED D2, which is now ON and passes through the short circuit path (the closed switch) and through the ground terminal. Transistor Q2 also stops conducting as its collector voltage also dropped to 0V and it too, is not biased anymore. Q1 stops conducting as its base voltage is 0V now and it is no longer biased. Now the switch is closed i.e The circuit is ‘shorted’, the output voltage drops to 0V as there exists no potential difference. As long as the green light is on, there is no short circuit. During this time Red LED D2 remains off as there is no flow of current through it. The current flows through the green LED D1 and it turns ON. When the power supply is ON, transistors Q1 and Q2 get biased and start conducting. The circuit is shorted when the switch is closed.Ĭurrent chooses the path that offers the least resistance. A switch is used to replicate the shorting of the circuit. LEDs are connected in order to identify the flow of current and the presence of a short circuit. The circuit is powered by a 5V DC supply. The circuit discussed here uses two simple transistors to protect the circuitry from short circuit. A short circuit protection circuit can be built using relays, transistors and even basic diodes. ![]() There are many ways to override the short circuit. The short circuit protection circuit discussed below plays the same role of a fuse in the household electric circuits. Hence, using circuits that protect the circuit from short circuiting are important. A short circuit can cause significant damage to the components such as ICs, rendering them useless. We might make wrong connections or connect the wrong terminals i.e., anything can go wrong. Similarly, while working with smaller circuits, we are always at the risk of a short circuit. A fuse is used to stop the surplus current. A surplus of current then flows through the appliances and can damage all the other household appliances if not stopped. We often encounter short circuits in our daily life too! Electrical appliances stop working after a sudden spark sometimes, this is due to short circuits in their internal circuitry. Short circuits are common while working with electricity.
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