Very cool, that's super useful for someone just getting started with electrical engineering.
Show HN: I made some transistor animations
21–30 of 35 posts
Re: Show HN: I made some transistor animations
#22Very cool!
Re: Show HN: I made some transistor animations
#23Earlier quoted context omitted.
You can google for "From nand to tetris" or get the book Digital Design and Computer Architecture by Harris to get the idea of how these machines work.
Has anyone made a similar resource for zero-to-hero FPGA programming?
Re: Show HN: I made some transistor animations
#24Do this also for triodes/tetrodes/pentodes. I would like to explore a difference between the current (as in BJT) and the voltage (as in field transistor and valves). Currently the only thing I see is that in field transistor the stream is uninterrupted and in BJT the stream is hopping across the base.
I suppose a pentode or a valve working with the grid current is not easy to demonstrate. And I believe no electrical engineer is a real one until he groks the valve theory.
Re: Show HN: I made some transistor animations
#25Cool! I wonder how different those are to real simulations! Do they treat electrons as point-like, or it's all computation on the fields?
The simulation does calculations on the fields only, so it keeps track of the average electron and hole density at each point in space. There is, however, a one-to-one correspondence between the behavior of the fields and the motion of individual particles, which is what makes these animations possible. What I mean by this is the diffusion equation is satisfied by the probability density of a particle undergoing a ra…
Do the electrons in this visualization also repel each other?
Re: Show HN: I made some transistor animations
#26This would have been invaluable when I did my EEE degree many years ago. I use to draw the charge carries instead.
I think universities are missing a course on writing a simulator of all the things you learned, e.g. Maxwell's equations and semiconductor physics for EE.
Re: Show HN: I made some transistor animations
#27Do this also for triodes/tetrodes/pentodes. I would like to explore a difference between the current (as in BJT) and the voltage (as in field transistor and valves). Currently the only thing I see is that in field transistor the stream is uninterrupted and in BJT the stream is hopping across the base. I suppose a pentode or a valve working with the grid current is not easy to demonstrate. And I believe no electrical…
> between the current (as in BJT) and the voltage (as in field transistor and valves)
The BJT is also much more accurately modeled as a device where the collector current is determined by the input voltage (i.e. base-emitter voltage), exactly like the vacuum tubes and the field-effect transistors.
There are however a few reasons why their description as being controlled by the input current is preferred in popular literature.
One is that the dependence between output current and input voltage is more strongly nonlinear than for vacuum tubes and FETs, i.e. it is exponential instead of being polynomial, so it can be approximated as linear only for very small voltage differences, of a few millivolt.
On the other hand there exists a relatively small current range where the collector current depends linearly on the base current, which is useful for mental approximate computations of a circuit with BJTs. But it must be kept in mind that this approximation is not useful for accurate circuit design, because beta (the ratio between the collector current and the base current) instead of being a constant it drops quickly both at big collector currents and at small collector currents.
Besides the great non-linearity of the output current/input voltage dependence and the approximate linearity of the output current/input current dependence, the other reason why BJTs are frequently described as "current-controlled", instead of the more appropriate "voltage-controlled", is that their input has a great leakage current (i.e. the base current), while the leakage currents of the inputs of vacuum tubes and FETs are so small that they are normally negligible.
In conclusion, one may prefer to use the description of the BJTs as "current controlled", but one must be aware of the serious limitations of this point of view. Even for mental computations, it is more useful to use the beta value of a BJT not for computing a fictive current gain, but to compute the input leakage current of the BJT conceived as a transconductance amplifier (unlike beta, which varies from transistor to transistor, the transconductance gain is the same for all BJTs), to be used for computing voltage drops in input resistor networks.
The animated visualizations are nice, but the only way to easily assess the quantitative differences between various types of BJTs, FETs and vacuum tubes is to draw the families of curves that show the output current from output voltage dependence, having as family parameter the input voltage (and also the family of curves obtained by interchanging the output voltage and the input voltage between graph axis and curve family parameter). (These families of curves being sections of the 3D surface of the graph of the output current as a function of input voltage and output voltage, but a 3D graph does not allow a precise comparison of the values in different points.)
Re: Show HN: I made some transistor animations
#28Some feature requests:
IsYou have an online simulator. It'slinked at the top, but I missed it. It would be nice to add a link in ech example to the example runing in the simulator.
I tried the simulator, but I can't see the moving electrons/holes. Also, in the diode simulation, how do I reverse the battery?
Isit posible to show arrows that show the total current in each electrode? Since electrons and holes have different charge, it's hard to see the current. (IIUC the simulator can show the number, but not draw an arrow. So this may be hard to implement.)
Re: Show HN: I made some transistor animations
#29For people who don't have an EE background, like myself, it would be great if for each animation you could add a small explanation for the layman. Looks very cool.
Re: Show HN: I made some transistor animations
#30Earlier quoted context omitted.
The simulation does calculations on the fields only, so it keeps track of the average electron and hole density at each point in space. There is, however, a one-to-one correspondence between the behavior of the fields and the motion of individual particles, which is what makes these animations possible. What I mean by this is the diffusion equation is satisfied by the probability density of a particle undergoing a ra…
Do the electrons in this visualization also repel each other?
The electrons are repelled or attracted by the electric field, which is in turn determined by the average charge density. So two electrons in the animation don't directly repel each other, but the electrons do influence each other through the field.