In analogue circuits, the tripolar tube will never be bypassed, while the pnp-type tripolar tube will always be confused by many newcomers. When i first painted the board, i used the pnp pipe as npn, and it turned out to be unguided, and i ran it all afternoon. Since then, i've understood that learning triodes can't just go back to the junction, but it's just going to have to eat the direction of the current and the fluid movement。
This article is about the pnp triodeRationaleAnd basic applications. I do not intend to list the formulas, but rather to tear apart the internal structure of the pnp, the conditions of bias, the current relationship, the typical application of the circuits, and the pits that are easily pedaled during selection. Whether it's a student in electronics, a new hardware engineer, or a self-student, as long as you have to deal with the triode, it's worth ten minutes of patience。
Pnp-type tripolar tube structure and circuit symbol, with a background set first 1. 1 from a “sweed” point: the internal structure of the pnp
The pnp-type tripolar tube is structurally composed of two p-type semiconductors with a single n-type semiconductor, each of which produces an electrode in three areas corresponding to the launch zone, base zone, and catchment area. You think of it as a sandwich: the two-level top-down package is the p-type, the middle ham is the n-type, and that's a lot to remember。
Here is a detail that can easily be ignored: although both the launch area and the catchment area are semiconductors of the p type, there is a marked difference in their mixing concentration and physical size. The highest levels of mixing are found in the launch area, which is designed to efficiently inject the drops into the base area; the largest area is in the catchment area, which is due to the need to absorb greater effort and to collect the drops through the base area; and the base area is very thin and has the lowest mixing concentration. The very thinness of the base region is central. If the base area is too thick, the probability of the fluid compounding during the crossing increases sharply, leading to a significant loss of magnification capacity and even to no work。
This led to the formation of two pn knots: between the launch zone and the base zone, and between the catchment area and the base zone. For the pnp tube, the firing knot is the closure of p-zone to n-zone, while the collection is the closure of n-zone to p-zone. The rationale for follow-up analytical work would be much smoother if the bias between the two knots was understood。
1. 2 in the direction of the polar arrow, why is it in the middle
The pnp-type tripolar circuit symbol contains an arrow on the line that fired the pole, pointing in the direction of the pole, i. E. From the outside. A lot of beginners are stuck here: why is the npn's arrow going out, and the pnp going in? The arrow actually means the actual direction of the current when it is launched. The pnp tube launch area is a p-type semiconductor, the hollow is the majority of the flow, and the positive current flows from the launch pole into the tube, so the arrow points to the interior。
Remember the simplest way to judge: the arrow is the direction of the current. When the pnp tube is functioning, the discharge of the electrode is flowing into the tripolar tube, so the arrow is directed in; when the npn tube is functioning, the discharge of the electrode is flowing and the arrow is directed out. You just keep this in mind, you don't turn the pipe back when you draw the circuit。
There is also a practical little technique: using a binary binary stage of a universal watch, a red pen to launch the pole, a black pen to base the pole, and if it shows a pn knot with a positive guidance barometer (usually between 0. 5 and 0. 7 v), it means that it is a pnp tube, and you have found its launch pole and base. I'll talk about it later in the exercise。
2. Central to the rationale for triodes: how the pnp is channeled and amplified 2. 1 differing conditions: two sentences to clarify the conditions for the pnp's guidance
For the pnp tripolar tube to be in a state of magnification, the condition of bias can be summarized in two sentences: the launch is positive and the charge is negative. For pnp tubes, this will be achieved by launching a polar level above the base level, while the base level is higher than the aggregate level. In other words, the voltage relationship is the firing of a polar voltage greater than a base voltage greater than a collectivity voltage greater than vb greater than vc。
And here i repeat, because this is where countless beginners are: the current direction of the pnp tube is from the launch pole to the base pole and from the launch pole to the collector pole, that is, from the launch pole to the tube and from the base pole and the collector. The npn tube, on the other hand, flows from the base poles and the collectors, and from the launching poles. If you get used to npn analysis, you'll probably reverse the direction, and the entire circuit analysis will be completely confused。
The direction of the launch means that a large number of holes in the launch area will cross the fuse into the base zone, while the reverse of the charge will ensure that these holes can be efficiently collected in the area. These two
