- v2 + in .NET Creation Code 128 Code Set C in .NET - v2 +

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- v2 + use visual .net code 128 printing tocompose code-128b with .net GS1 General Specifications + V3 T Pi I /1 /2. :"il Figure 1 0 - 1 visual .net barcode 128a 2 Three bias states of the p-n-p-n diode: (a) the forward-blocking state; (b) the forward-conducting state; (c) the reverse-blocking state..

10 . junction. In a barcode 128a for .NET normal p-n diode, the n region is terminated in an ohmic contact, so that the supply of electrons required to match recombination (and injection into p) is unlimited.

In this case, however, the electron supply is restricted essentially to those electrons generated thermally within a diffusion length of j2. As a result, the current passing through the j \ junction is approximately the same as the reverse saturation current of /2. A similar argument holds for the current through /3; holes required for injection into n2 and to feed recombination in p2 must originate in the saturation current of the center junction j2.

The applied voltage v divides appropriately among the three junctions to accommodate this small current throughout the device. In this discussion, we have tacitly assumed that the current crossing /2 is strictly the thermally generated saturation current. This implies that electrons injected by the forward-biased junction / 3 do not diffuse across p2 in any substantial numbers, to be swept across the reverse-biased junction into n\ by transistor action.

This is another way of saying that a2 (for the "n-p-n transistor") is small. Similarly, the supply of holes to p2 is primarily thermally generated, since few holes injected at j1 reach j2 without recombination (i.e.

, ax is small for the "p-n-p"). Now we can see physically why Eq. (10-5) implies a small current while cq + a 2 *s small: Without the transport of charge provided by transistor action, the thermal generation of carriers is the only significant source of electrons to ti\ and holes to p2.

. 10.4.5 Conducting State The charge tran visual .net code 128b sport mechanism changes dramatically when transistor action begins. As o^ + a 2 approaches unity by one of the mechanisms described, many holes injected at j \ survive to be swept across j2 into p2.

This helps to feed the recombination in p2 and to support the injection of holes into n2. Similarly, the transistor action of electrons injected at y3 and collected at j2 supplies electrons for tiv Obviously, the current through the device can be much larger once this mechanism begins. The transfer of injected carriers across j2 is regenerative, in that a greater supply of electrons to ti\ allows greater injection of holes at /j while maintaining space charge neutrality; this greater injection of holes further feeds p2 by transistor action, and the process continues to repeat itself.

If 04 + ot2 is large enough, so that many electrons are collected in nt and many holes are collected in p2, the depletion region at j2 begins to decrease. Finally, the reverse bias disappears across j2 and is replaced by a forward bias, in analogy with a transistor that is biased deep in saturation. When this occurs, the three small forward-bias voltages appear as shown in Fig.

10-12b. Two of these voltages essentially cancel in the overall v, so that the forward voltage drop of the device from anode to cathode in the conducting state is not much greater than that of a single p-n junction. For Si, this forward drop is less than 1V, until ohmic losses become important at high current levels.

We have discussed the current transport mechanisms in the forwardblocking and forward-conducting states, but we have not indicated how. High-Frequency and High-Power Devices switching is in Code 128 Code Set A for .NET itiated from one state to the other. Basically, the requirement is that the carrier injection at /j and j2 must somehow be increased so that significant transport of injected carriers across j2 occurs.

Once this transport begins, the regenerative nature of the process takes over and switching is completed..
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