I am trying to analyze a circuit using source transformations (converting from a voltage source to a current source). I am trying to understand how they work based on a book, but I keep getting confused based on a simple example.

The book says that it is obvious that V0 is the negative of the ratio of the "feedback" resistor (8k ohms) to the input resistor (2k ohms) multiplied by the voltage the input terminal, thus it is -8 volts.

It may be that my brain is currently fired, but the ratio of the resistors part through me for a loop.

dear sirs
i want to connect 20 leds in parallel.
my source is 2x 4.2v batteries parallel
led voltage white 3.4v 20ma
in the following page i can find that i need 20 resistors 47ohms
http://led.linear1.org/led.wiz

now in other page
http://www.hebeiltd.com.cn/?p=zz.led...tor.calculator
i find out that i need resistor 2ohms 03w
does it mean that i need 1 resistor for all circuit?

HI. I want to know how to choose suitable resistors(value) around transistor.
this contents is from Electronics all in one for Dummies.
Please refer the attached file, and answer the question.

Contents in Book
- R1: 330ohm resistor limits the current through the LED to prevent the LED burning out. You can use Ohm's law to calculate the amount of current that the resistor will allow to flow.

I need to mesure 400V dc from MCU with reference voltage of 5V.

So only way I see is to use voltage divider & use factor of 80.

that is 790K & 10K resistor with it.
This will make 5V when 400V is applied.

1. Is my calculations are correct.
2. Is there any method to do with it.
3.

Hi,
i need urgent help if you can help me. I am working on a project for which i am trying to built a circuit that will automatically compensate for impedance mismatch between two resistors by varying the current provided to each resistor so that the voltage across both different resistors will be the same. I have attached the circuit design.

If a pull up resistor is to make the voltage on an input pin high, how does that work since there is a voltage drop across the resistor? Doesn't that mean the voltage coming into the pin would be near 0v since it dropped when going across the resistor? I'm sure I have something backwards i my head.
Thanks for the help
Brian

Hi,

I found an step motor driver where each motor winding is driven by an output of l298 and it also has a resistor in series ( a picture is attached).

I have seen a lot of posts here where people use resistors to limit the current. The problem is the only power resistors I can find to buy are wire-wound.

Ok so in voltage divider biasing of base of NPN BJT transistor, the voltage divider determines the quiescent voltage. 10k and 10k would put 4.5v across the base. 100 ohm and 100 ohm for R(L) and R(E).

Doesn't current flow from the bias resistors at the base to ground through the emitter? How come the voltage is still 4.5v (-the voltage drop)?