Diodes and resistors in parallel

Thread Starter

PJB

Joined Oct 24, 2019
4
Hello,

Why would you place these components together in parallel, what's going on here, can someone explain ?

PJ.
 

MisterBill2

Joined Jan 23, 2018
4,061
Here is a guess based on no additional information. A diode and resistor of a higher value in parallel will follow ohm;s law in the reverse biased direction, while in the forwarsd direction the voltage drop will be about the same as a diode forward voltage drop in the forward direction. That can be useful in nmany instances.
 

MisterBill2

Joined Jan 23, 2018
4,061
Here's another more complicated schematic. What is the purpose of each diode in this circuit ?
View attachment 189657
Since current flows in both directions in the connection between the discharge and trigger connections, the diode D2 with resistor R2 allows a lower current to flow during the discharge portion of the cycle. D1 provides a much faster charge with a charging current limited by R1.
This looks a lot like a homework assignment.
In addition, the whole appearance of the blog looks different, and I am wondering if it is caused by the last microsoft update, or is there a change in the AAC website that I am not aware of? And in the information about posters there is no longer an "occupation" section, which I had found very interesting. So, What Happened???
 

Reloadron

Joined Jan 15, 2015
4,593
In addition, the whole appearance of the blog looks different, and I am wondering if it is caused by the last microsoft update, or is there a change in the AAC website that I am not aware of? And in the information about posters there is no longer an "occupation" section, which I had found very interesting. So, What Happened???
Didn't you get the memo? :)

Take a lookie at some of these threads. The AAC forums just went through some major changes. Check out the link.

Ron
 

MisterBill2

Joined Jan 23, 2018
4,061
Didn't you get the memo? :)

Take a lookie at some of these threads. The AAC forums just went through some major changes. Check out the link.

Ron
NO, I am not aware of any memo posted where I would see it. Of course I have been rather busy with a lot of work in the more physical world, spending much less time in cyberville. So I probably missed a flash post. That happens more frequently these days.
 
This site got new software a few days ago then I could not log-in because half a year ago I changed my e-mail address. You cannot change an e-mail address on most forums so I needed to register as a new user with my new name as "Audioguru again".
 

DarthVolta

Joined Jan 27, 2015
149
A lot of times in SMPS with opto-couplers, they will have a resistor across the photodiode side, and they call it the basis resistor, it's usually 100's -1,000's of Ohms.

The calulation for that whole section was big, so IDK what they are trying to do really.

In the basic small signal model of a diode, it just gives an equivalent resistance to the diode, so then it would just be 2 resistors in parallel.
 

MisterBill2

Joined Jan 23, 2018
4,061
A resistor across the LED in an opto-coupler does two different things, depending on the applied voltage. For a switching application it tends to reduce the sensitivity a bit, which reduces the effect of leakage currents from the driver circuit. It also provides a path for reverse voltages. Above the turn-on voltage that resistor tends to reduce the current through the LED, providing a bit of protection and an adequate load for the driver. For application in linear modes, the shunt resistor tends to reduce the non-linear current/voltage effect of the diode as it transitions from a high impedance off state into the forward conduction state, which makes the load on the driver less variable.
 

MisterBill2

Joined Jan 23, 2018
4,061
I had a similar problem. PM @jrap he can help you get it straightened out.
I have read both of those books. Both do require a degree of the suspension of disbelief. And both are well written. "Atlas shrugged" certainly is a long tome promoting the writers personal agenda, with no attempting to hide it at all. The concept of persona responsibility for the results of one's actions is fine, but the focus on the virtues of personal greed are rather tedious. The movie seems to be quite different from the book, but that is to be expected. "The Lord of the Rings" especially the second version, is clearly a tale intended to be engrossing and entertaining. I have not seen any of what I would say was pushing some personal agenda even after reading it a few times. And much of it is more believable.
 

shortbus

Joined Sep 30, 2009
7,091
I have read both of those books. Both do require a degree of the suspension of disbelief. And both are well written. "Atlas shrugged" certainly is a long tome promoting the writers personal agenda, with no attempting to hide it at all. The concept of persona responsibility for the results of one's actions is fine, but the focus on the virtues of personal greed are rather tedious. The movie seems to be quite different from the book, but that is to be expected. "The Lord of the Rings" especially the second version, is clearly a tale intended to be engrossing and entertaining. I have not seen any of what I would say was pushing some personal agenda even after reading it a few times. And much of it is more believable.
You seem to have missed the essence of my tag line. It is the fact that many adults still use Atlas Shrugged as their meaning of life, and that is absurd. It is a work of fiction by a failed author that in her last days of life used the system and it's help, that she railed against in the book. A total hypocrite that some people tend to put on a pedestal.
 

MisterBill2

Joined Jan 23, 2018
4,061
You seem to have missed the essence of my tag line. It is the fact that many adults still use Atlas Shrugged as their meaning of life, and that is absurd. It is a work of fiction by a failed author that in her last days of life used the system and it's help, that she railed against in the book. A total hypocrite that some people tend to put on a pedestal.
Well Yes, That is true. I think Bob Seger used a useful descriptor in one of his songs, Pseudo-intellectual, as in "long-haired Pseudo-intellectual" . (from Back in 72). and this also proves that just because somebody writes well does not mean that they are smart or wise. So I offer no argument to your assertions. I found them to be interesting works of fiction, and like all fiction, not examples of reality.
 

MisterBill2

Joined Jan 23, 2018
4,061
You should really try to explain that to a couple of members here.
I try to avoid telling people over the age of 5 how to run their lives, unless they ask for my advice. A very few do, and the rest do not, and I am happy to just present a good example. At this site it is a bit different because most thread starters ARE asking questions. And here I am OK with handing out good advice for free. I used to get paid quite well to give good advice, since it worked well with machines and controls.
 
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