![]() ![]() The device has good amplifying factor and also the gain is almost linear making 2N3055 one of best solution for power amplifiers. 2N3055 is also used in audio power amplifiers.2N3055 is one of the basic transistors available in the market for cheap and with features being suited for many applications. I have tried unsuccessfully to locate the image of the three devices, which showed the TO-5, TO-66 and TO-3 cans. 2N3055 is preferred when you want a simple switching device for medium power loads. It advertised the 2N3053, 2N3054 and 2N3055 as a 'new range of power transistors' from RCA.The diode D is a trick to force the reference voltage to be a Vbe drop higher. If you see the pass transistor as an emitter follower amplifier (where the load is not shown), you see that the output voltage will be just the 7812 voltage minus a Vbe drop. This pushes the reference voltage of the 7812 regulator up by 0.7V giving roughly 12.7V at the output. In this case the 7812 is used as just the voltage reference for the 2N3055 pass transistor. If you add a silicon diode from the GND pin to your circuit ground, there is a voltage drop of 0.7 ish volts across the diode when conducting. If the voltage at the load were to go up the transistor would limit the current as Vbe would drop (turning the transistor off - well slightly more off) which would cause the voltage to drop back down.īy using a 7812, it regulates to 12V at Vout relative to its GND pin. ![]() If the voltage across the load were to drop the transistor would have to compensate and pull it back up to maintain 0.7V Vbe. So if you apply 12.7V to the base, you should get about 0.7V less at the emitter - so 12V at the emitter in this case.Īs long as there is a load attached, and there is sufficient voltage at the input of the regulator, the transistor will always be driven on, so there will be 0.7V Vbe. When an NPN Bipolar transistor is on, there is roughly 0.7V to 1V Vbe (voltage at base relative to emitter). 2N3055 TRANSISTOR USES DRIVERSThey can carry an impressive 15 Amps of collector current making them ideal for high power switching applications such as motor drivers for use in power inverters. ![]() This is more than a bare 7812 can handle without going into thermal shutdown, so you will also need a heatsink here as well, although not nearly as big as on the 3055. 2N3055 (NPN), MJ2955 (PNP): Complementary silicon power transistors are designed for general-purpose switching and amplifier applications. To provide 150 mA of base current at a supply voltage will dissipate. Also note that, due to the low gain at high currents, the 7812 will dissipate significant power. If you build this, you must provide a fairly beefy heat sink for the transistor. So the power dissipated will be about 3 amps times 14 volts, or roughly 40 watts. 2N3055 TRANSISTOR USES FULLAt full output and a 24 volt supply, The 2N3055 will be dropping about 13-14 volts, and will be carrying most of the current (at least 95%). The other thing you need to watch out for is power dissipation. This is not a very good circuit (but it is simple and cheap). At 3 amps, something in the vicinity of 10.5 volts, or maybe a bit lower. The base current supplied by the 7812 will be multiplied by the gain ($h_fe$ or $\Beta$) of the 3055, so the 7812 does not have to provide an enormous amount of current, although at maximum current the gain will drop, so you might expect a gain of 20 or so, for a base current requirement from the 7812 of 150 mA.įor an open circuit (no load), you can expect about 12 volts from this circuit. For 3 amps you should expect a voltage drop in the range of 1.5 to 1.6 volts. However, that number really only applies at currents around 1 to 10 mA. Since this is a silicon transistor, the usual number is a voltage drop of ~0.7 volts. With the base held at 12 volts, the voltage drop of the base-emitter junction will determine the exact output voltage. In effect, the added diode is intended to compensate for the transistor base-emitter voltage drop. Apply this as appropriate to the following. Combining the two suggests that the base voltage will be in the range of 12.1 to 13.3 volts. I was also ignoring the fact that 7812s have a nominal output in the range of 11.4 to 12.6 volts. If the 7812 output is at 12 volts, then depending on the current levels at the load the output voltage will be less than 12 volts, and possibly a good deal less.ĮDIT - As Russell McMahon pointed out, I was ignoring the diode in the linked circuit. In fact, the output is not held at exactly 12 volts. ![]()
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