27
votes
Why exactly does maximum power transfer happen at 50 ohms (matched impedance)?
The power delivered to the load is from the Joule heating effect:
\begin{equation}
P=\dfrac{\Big(\dfrac{R_L}{R_L + 50}G\,V_{IN}\Big)^{2}}{R_L}
\end{equation}
So from differential calculus we know ...
- 1,194
25
votes
Accepted
Will this circuit work ? 100 Leds project
No, that's a really bad circuit. You have 100 LEDs, all in parallel. Bad idea.
Since this is a assignment, I'm not going to give you a better circuit outright. However, consider that LEDs want to ...
- 311k
20
votes
Accepted
check if an unsigned binary number is divisible by 15
Do you know how to check for divisibility by 9 in base 10?
Add all the digits using base 10 arithmetic. If the result has multiple digits, repeat the process. Stop when you have one digit. If the ...
- 159k
17
votes
Why exactly does maximum power transfer happen at 50 ohms (matched impedance)?
Intuitively: when you raise the load resistance, you are increasing its share of the voltage (and thus power) versus the other resistance; but you are decreasing the total current (and thus power). ...
- 2,270
12
votes
Combining resistors in a simple network
The ground node has got you confused.
How much current flows in the ground?
Why treat R4 and R5 different to R1 R2 R3?
- 7,652
12
votes
Trouble understanding when voltages get split
Just re-draw the schematic, slightly:
simulate this circuit – Schematic created using CircuitLab
(Note that your confusion about "Would the 9V be split between these two resistors?" completely ...
- 77.2k
12
votes
How can I calculate the current flowing through this diode?
but I'm just not good at solving diodes in parallel circuits
So, in general for problems like this (which you do hit in real life if you're doing circuit design, so it's not just academic), you start ...
- 45.1k
12
votes
Problem with equivalent resistance
simulate this circuit – Schematic created using CircuitLab
Here's the circuit redrawn. R1 and R2 form a voltage divider, as do R3 and R4. Since the ratios are the same for each voltage divider,...
- 15.1k
12
votes
Accepted
How to calculate current at one circuit node in a textbook exercise
Maybe a little visual drawing will help.
You can easily calculate the currents in each resistor using Ohms Law.
Then using Kirchhoff's current law, all the currents in a node must sum to 0.
Note: The ...
- 7,333
12
votes
Accepted
Inverting op-amp problem
Your simulation won't work unless you connect the op-amp's power supply voltage sources to ground on the other side! Also, the source of negative supply will need to be non-zero.
Besides that, another ...
- 28.2k
10
votes
Design a 8 - 6 - 4 - 2 - 0 - 1 - 3 - 5 - 7 - 9... Counter
Given it is an assignment, I'm not going to work through the logic. However in all such questions you can boil it down to a circuit with two steps:
You have a binary ...
- 63.8k
10
votes
Accepted
Calculate total harmonic distortion
The amplitude distortion plot you showed is in dB, dBV specifically (dB's relative to 1 V). So you need to take those dB values and covert them into volts before putting them into your formula.
For ...
- 9,737
10
votes
Accepted
how to solve this op-amp circuit?
Your circuit doesn't have negative feedback: -
Therefore it acts as a comparator with hysteresis and hence, the output changes state when the input voltage passes the hysteresis threshold points ...
- 437k
10
votes
Accepted
Circuit analysis homework - LTspice results are different from calculations
Check your complex arithmetic:-
@100Hz
I get
Za = 4.7000e+03 + 6.2832e+01i
Zb = 2.2000e+03 - 3.3863e+04i
Zc = 1.0000e+03 - 1.5915e+05i
Zp = Za || Zb = 4.5887e+03 - 5.6789e+02i
Vo = 4 * Zp/(Zp + Zc) = ...
- 379k
8
votes
Accepted
Input and Output Impedance parameters of two port network
For the input impedance, expand the matrix equation and then use the output condition: \$Z_L=-\large \frac{V_2}{I_2}\$
Similar approach for the output impedance.
- 7,505
8
votes
Am I on the right path to solve this RLC-Circuit? (Need to find the voltage at the resistor)
Yes, your analysis is correct.
It would have been quicker to solve for the resistor current and then multiply through by \$\small R\$ to get the resistor voltage, \$v_R\$, as below (I've used \$\...
- 7,505
8
votes
How can I calculate the current flowing through this diode?
You should really simplify stuff before launching into the math. For instance: -
Can you see how much easier this is to simplify following the standard source transformation I did above? Do you know ...
- 437k
7
votes
Accepted
Design a 8 - 6 - 4 - 2 - 0 - 1 - 3 - 5 - 7 - 9... Counter
It sounds like you are expected to solve this with a state-machine type circuit, however it can also be done using a classical counter circuit.
The key to this problem is recognizing that for half ...
- 46.4k
7
votes
Am I on the right path to solve this RLC-Circuit? (Need to find the voltage at the resistor)
As you could figure out, your source is expressed as a phasor, hence we can assume safely the solution can be expressed with phasors and impedances, in consistency with the requirement of ignoring ...
- 1,409
7
votes
Diode stack circuit
Perhaps the easiest way to see is to re-draw the schematic. If there is one thing I try to do, over and over again, it is hammer at this with everyone I reach out to. I recommend early and continual ...
- 77.2k
7
votes
Design a class AB audio amplifier
For 10 watts into 8 ohm speaker, you can do this system design
P = Vrms * Vrms / Rload
10 watts = V * V / 8
10 * 8 = V * V thus Vrms_out ~~ 9 volts RMS, or 2.828 * 9 peakPead
You will need ...
- 33.7k
7
votes
Accepted
Transfer function of an RLC filter
Your numerator in this:
$$
v_{o}=v_{oi}\frac{R}{Ls+R_{L}+\frac{R(\frac{1}{Cs})}{R+\frac{1}{Cs}}}
$$
Should be \$Z_R || Z_C\$. That is,
$$
v_{o}=v_{oi}\frac{R || Z_C}{Z_L+R_{L}+(R||Z_C)}
$$
- 4,897
6
votes
Effects of using voltmeter w/ 20 kΩ impedance across 35 kΩ resistor?
Instead of claiming you can't do this, stop and actually think about it.
Draw the schematic of the circuit without the voltmeter. Then draw the schematic with the voltmeter. To the circuit, the ...
- 311k
6
votes
Finding the current in a parallel circuit
Start by labelling your circuit. You should know that in a series circuit, the current is the same at any point in the circuit.
simulate this circuit – Schematic created using CircuitLab
We ...
- 11.8k
6
votes
Accepted
Calculate peak input current of switch mode power supply
First thing to notice is that you have a a very small output capacitor, which is used to supply the load during the on phase (when the inductor is being charged and there is no power transfer between ...
- 3,539
6
votes
I can’t seem to understand the preference of the flyback converters for the reason given below
When you talk about the differences between a flyback and or forward converter, you could say the following:
the flyback converter is usually suited for low to moderate output power (100-150 W as a ...
- 20.5k
6
votes
Current across a diode?
You are asked to find the operating point such that the small-signal resistance is 5 ohms, i.e.
$$\frac{dv_d}{di_d} = 5\,[\Omega]$$
You can obtain this by both sides of the given equation relating ...
- 18.1k
6
votes
Accepted
Strange Nodal Analysis
Your mistake is again the current direction.
For \$V_1\$ node you have wrote:
$$+12A + \frac{V_1 - V_2}{2\Omega}....= 0$$
As we can see from a circuit diagram the \$12A\$ current is entering the node(...
- 13.8k
6
votes
Transfer function of an RLC filter
These are the kinds of questions that should be brought here more often. I see that ErikR has correctly identified the flaw in your writing and that you've selected the answer. Great!
So I won't ...
- 77.2k
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