27
votes
Accepted
What is negative current?
understand that voltage is relative to ground,
I prefer to disagree. A voltage is against a reference point. Often that reference point is ground but not always.
Taken the above into account your ...
- 14.7k
25
votes
Accepted
How do you interpret/draw out the simplified circuits in Sedra's Microelectronics?
It doesn't matter where the arrows go because they are separated from the circuit of interest by current sources.
For a more practical approach you may consider the arrows pointing up to a more ...
- 188k
19
votes
Accepted
How does an SR Latch get started
It is true that the latch will "wake up" in an unknown state. In the real world, given a little time, the latch will have a valid state with either Q=0 or Q=1.
You make the latch "get started" by ...
- 31.8k
18
votes
Accepted
LED Fails to illuminate, what am I not seeing in my configuration(s)?
Classic beginner's breadboard mistake.
Figure 1. We somehow expect the green connections to be zero ohms while the red one is an open-circuit!
All five sockets in a row are the one terminal strip. ...
- 188k
16
votes
How can a circuit not have a neutral?
The two sides are out of phase with each other. When one side is high, the other is low, and vice versa.
This is a 240 V outlet.
- 9,693
16
votes
Do capacitors waste power as heat or whatever on AC?
There would be power loss because with real life capacitors, there are parasitic losses, this means that the capacitor can not act as a pure capacitive load in real life, this is mainly because of the ...
- 886
15
votes
Accepted
Understanding this circuit with op. amps
I'll let someone else do the sums formally/generally, but there is an easy approach here that will allow you to solve it by inspection.
As you know, the op-amp inputs are both going to be 0V at ...
15
votes
Accepted
What role does this diode play?
This diode is to surpress any back-EMF caused when the motor is switched off. In general, when one has an inductive load such as a motor, or an electromagnet's solenoid, when you switch it on, there ...
- 377
14
votes
Accepted
Is there a simpler solution for this kind of priority switch? (a teaser for the holidays)
I have made a design using 4 switches. It functions as you said.
Case 1: When you turn ON SW1 first, Lamp 1 will glow. Thereafter, if you turn ON SW2, both Lamp 1 and Lamp 2 will glow.
Case 2: When ...
13
votes
Accepted
Why is it called Wired-OR when it is functioning as Wired-NOR?
This is a historic convention.
The preferred active level in many 5V TTL circuits was low as the noise immunity at the input was higher (3V as opposed to 0.8V in ...
- 22.9k
13
votes
How do I determine whether a switch can handle the power/current in a circuit?
Current and voltage ratings do not neccessarily apply at the same time and in a single operating point.
A switch is a pretty good example for this:
it must not conduct a current higher than the rated ...
- 3,217
13
votes
Accepted
Voltage drop over open circuit
The meter has some high resistance across its terminals (in the megaohm range for a DMM, about 10k to 50k for an analog meter type) so a slight current will flow through it, the LED and the resistor.
...
- 64k
13
votes
Accepted
Can an opamp have a negative gain?
The term "negative gain" can be ambiguous. It could mean "attenuation", and it could also mean amplification but with reversal of polarity.
If a gain is given the units of decibels,...
- 34.6k
13
votes
Accepted
Putting an Ammeter in Parallel with a Wire but Still Having Series-Resistors
You're basically right, but analyzing this ammeter as being "in parallel" with anything isn't really a helpful way to look at it; it's just shorted out. Because an ammeter's burden voltage ...
- 46.8k
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,...
- 29.2k
11
votes
Accepted
My textbook claims that base kW = base kVA, but doesn't this equality break down when power factor isn't zero?
You are correct that KW only equals KVA when power factor is 1. They are not suggesting otherwise.
The text is just telling you that the base for \$\mathrm{KW}_{\mathrm{pu}}\$ and \$\mathrm{KVA}_{\...
- 3,720
11
votes
Why did current increase when voltage decreased?
Instantaneous increase in current with lower input voltage is only possible with power electronics with regulation. For example a TV will adjust the duty cycle of the SMPS to keep all DC rail ...
- 18.1k
10
votes
Accepted
What's the rationale behind these warnings about extension cords?
Let's say you're extension cables are 1 mm² cross-sectional area.
The loop resistance is 33.6 mΩ/m.
A 25 m cable will have a loop resistance of 840 mΩ.
The voltage drop at 11 A will be given by V = ...
- 188k
10
votes
Accepted
why does a fuse break when a wire is connected to ac socket directly
A Mixer has much higher impedance than a piece of wire - limiting the current which can flow and thus not melting the wire or tripping the breaker.
Your battery can't supply enough current to melt ...
- 2,103
10
votes
How does an SR Latch get started
When you power on a bi-stable element like a NOR SR latch (with inputs at 0) it will start at to some state. That is not necessaraiy a 'binary' state, the the outputs can for instance be halfway ...
- 48.9k
10
votes
LED Fails to illuminate, what am I not seeing in my configuration(s)?
My students often made this mistake. So I forced myself to make this image of a similar board with drawn connecting lines.
Also, I removed (with great difficulty) the adhesive pad from the underside ...
- 21.3k
10
votes
Circuit that turns two LEDs off/on depending on switch
From another thread, here is a non-standard approach that works very well. SW1 can be replaced with a small n-channel MOSFET such as a 2N7000, or a small NPN transistor with a base resistor.
When the ...
- 26.3k
9
votes
How can a circuit not have a neutral?
tl; dr: You should install a NEMA 14-50 (4-wire: L1/L2, Neutral and Ground) instead of NEMA 6-50 for best flexibility. NEMA 14-50 is the standard 'dryer' plug now, and it's what a car charger uses too....
- 64k
9
votes
Do capacitors waste power as heat or whatever on AC?
There are three loss mechanisms within the capacitor, all of which are fairly minor, and one that it causes to the power supply, which depending on how you're billed for your electricity, may or may ...
- 186k
9
votes
How is he not shocked?
WARNING : WHAT THIS GUY DOES IS VERY DANGEROUS
The voltage is very low (<2V), so there is no risk of being shocked (at least not on the secondary side, the 120V on the primary side are plenty ...
- 9,601
9
votes
How is he not shocked?
Two important points:
Voltage is relative, and must be measured between two points.
A circuit must be completed for current to flow.
The thing about #2 that's easy to forget is that if a point has a ...
- 3,954
9
votes
Accepted
Help me understand BJTs better. Resistance of Base Emitter on BJT
The base-emitter junction is a diode. Like all diodes, it has a highly nonlinear V-I characteristic, so trying to measure its resistance with a tool meant to measure linear resistors is essentially ...
- 46.8k
8
votes
Accepted
How do I find the equivalent resistance of a circuit with a node between each resistor?
Keyword Y-Δ-transformation:
You can transform the Y-configuration at R3, R4, R5 into a Δ-configuration Ra, Rb, Rc and then see that there are three parallel configurations (R1 || Ra, R2 || Rb and R6 |...
- 16.6k
8
votes
How is a series resistor limiting the voltage for a diode?
The resistor is not limiting the voltage for the diode, the voltage on a diode can be considered as constant:
Source: Tutorialspoint.com
As you can see in the diagram, the voltage of a diode is kind ...
- 10.3k
8
votes
Basic BJT current mirror : ... so the collector-base voltage of Q2 is also zero?
Without getting too involved in the details, there are typically two very important and one slightly less important (usually) details to keep track of with respect to a simplified BJT model. (Ignoring ...
- 79.7k
Only top scored, non community-wiki answers of a minimum length are eligible