43
votes
Accepted
Are LEDs better than we think?
Yes, this is widely known. Anyone who has tested it knows that. The die manufacturers certainly know it.
They don't specify LEDs for more than 5V reverse voltage because it would not measurably ...
35
votes
Why has my tweeter speaker burned up?
Your linked description shows that the tweeter is intended to be used with a woofer for music reproduction. The description doesn't cover use of the tweeter as a specialist ultrasonic transducer on ...
- 4,433
32
votes
Accepted
When is it okay to exceed the absolute maximum rating on a part?
Its never safe to exceed the maximum ratings. Even operating at a point within the ratings can result in failures if for example the manufacturing process has drifted out of spec (I've had power ...
- 3,774
25
votes
Are LEDs better than we think?
If you stand under a tree in a lightning storm and you survived, does that mean anything significant? This is somewhat like reverse biasing an LED > -5V.
Graph , courtesy of This shows the ...
- 148k
23
votes
Accepted
Where Does VDD+0.3V Input Limit Come From on IC chips?
Most likely there is an ESD protection diode connected between the input pin and the VDD net on the chip, in such a way that it is normally reverse biased (A schematic showing the configuration is ...
- 134k
21
votes
When is it okay to exceed the absolute maximum rating on a part?
Exceeding absolute maximum ratings is a bad idea.
In some very limited circumstances, carefully pushing something past the limits might be worth the risk. This might apply to one-off situations ...
- 315k
21
votes
Why has my tweeter speaker burned up?
It appears that the problem lies with the power ratings of loudspeaker components being the power rating of the system and not that of the individual component.
For example, in the 1970s, Philips were ...
- 19.2k
19
votes
Accepted
Relay contact (switching) voltage
Since the maximum switching voltage is 250VAC/25A, can I use this
relay to switch 380VAC/1A load?
You can't horse-trade current rating and voltage rating on a relay contact.
What is the ...
- 473k
18
votes
When is it okay to exceed the absolute maximum rating on a part?
I once came across Atmel App Note AN2508 - AVR182: Zero Cross Detector (not TI, I know - still interesting) that condones such a construction... For zero-cross sensing on mains!
To protect the device ...
- 2,624
18
votes
Where Does VDD+0.3V Input Limit Come From on IC chips?
This is due to the input protection diodes.
A typical input looks like this (CMOS inverter shown):
simulate this circuit – Schematic created using CircuitLab
The diodes in newer parts are ...
- 22.6k
18
votes
Accepted
Is it a problem to use a capacitor at or near its rated DC voltage?
It depends. Capacitors are fairly complex components, despite their appearances, and quite a bit of consideration goes into applying them such that they last a long time. The below covers only a few ...
17
votes
125 mW resistor subjected to 600 mW dissipation in professional safety system
From the data you provide, this indeed seems like a bad design. I also get about 600 mW dissipation in R1 in the circuit you show.
The fact that the resistor is getting really hot is direct ...
- 315k
17
votes
Accepted
Can a switch's rated voltage/current be too great for a given application
Can a switch be rated too highly for an application? as in can it be
too beefy?
Yes it can. Many switches that are designed for low currents will operate cleanly (well, switches are never that clean) ...
- 473k
15
votes
125 mW resistor subjected to 600 mW dissipation in professional safety system
Well, you're kind of guessing on a lot of things, yet you seem very sure that an 0805 resistor, which you think these are, is rated for 125mW.
There are 1W-rated (at 70°C) 0805 resistors. Of course ...
15
votes
Why does a battery have a limit for current in amperes?
The electrochemical reactions in the battery can only take place so fast. With some batteries the current should be artificially limited to protect the battery from self-destruction. It may be able to ...
14
votes
Relay contact (switching) voltage
When you're dealing with voltages that high, the biggest challenge for a relay is snuffing the arc. The arc is proportional to voltage.
As a relay opens, voltage will arc across the contacts. ...
13
votes
Accepted
Do FETs have a Maximum Gate-Drain voltage?
First of all, the oxide layer that separates the drain/source from the gate in the source/drain-to-gate overlap regions1 is not thicker than the oxide layer over the substrate (i.e. where channel ...
- 5,367
12
votes
Accepted
How to determine the nominal current of an LED?
It has several unmarked white SMD LEDs ...
... without marking you cannot get a datasheet and without datasheet there you don't have a chance of finding out the real current.
However there is a ...
- 1,186
12
votes
Accepted
Why do contactors have lower withstanding current for signaling than power circuits?
(Trying to state more clearly what KASPAROLDENDORFF already said)
This contactor has two sets of contacts:
Power circuit, consisting of 3 normally open contacts.
Signalling circuit (also called ...
- 9,666
12
votes
Why does a battery have a limit for current in amperes?
An ideal voltage source can supply whatever current the load wants, unlimited.
But a battery is not an ideal voltage source. So, it can't.
A battery can be modeled as a voltage source plus a series ...
- 25.7k
11
votes
Accepted
Push Button with Voltage Rating (AC) : 125V, Only having power supply of 3.5 or 5V
Your question is wisely asked. In general, an AC-rated switch should be derated for DC use. AC ratings are usually higher than the DC rating, if available, for the exact same switch. There's a reason ...
- 78.8k
11
votes
Are LEDs better than we think?
Exceeding absolute maximums from data sheets does not necessarily mean immediate catastrophic failure. It means that you've gone into a region for which the manufacture no longer sees fit to ...
- 30.6k
11
votes
Where Does VDD+0.3V Input Limit Come From on IC chips?
The 0.3V drop comes from the Schottky clamping diodes used to protect the pins of the chip. These diodes typically connect between each pin and the two power rails. If they are forward biased by more ...
- 178k
11
votes
Why has my tweeter speaker burned up?
I'm afraid that you are another Amazon victim. I note that you have linked to an Amazon ad rather than a manufacturer's datasheet which would explain how the device is rated and expected operating ...
- 181k
11
votes
Why has my tweeter speaker burned up?
The power ratings for audio equipment are often completely bogus. Check out the amount of copper in a 350W motor (and note that a speaker is also essentially a motor, only the motion is linear instead ...
- 26k
10
votes
How serious is the 125 °C limit on an NTC thermistor?
Absolute maximums are not an absolute physical limitation; they are a statement from the manufacturer that performance and reliability beyond that value is not guaranteed.
If you exceed an absolute ...
- 34.9k
9
votes
How to determine the nominal current of an LED?
VERY approximately:
LED power rating = bulb_ratinf/number_of_LEDs.
So if eg 5W bub with 15 LEDs.
LED power ~= 5W/15 = 1/3 Watt per LED.
LED forward voltage is typically ~= 3V.
So LED current ~= ...
- 152k
9
votes
Accepted
Is there a reason why we don't use higher rated voltage capacitors?
Part of the order contained two 10uF electrolytic capacitors but at different ratings, one at 1000V and one at 630V (for what it's worth, the voltage I'm working with here is ~440V).
If you're sure ...
- 82k
9
votes
Accepted
Operating above maximum characteristic supply voltage, but below absolute maximum voltage
No one can tell for sure in general, except the manufacturer.
Providing those two sets of values is industry standard. The rationale behind is that beyond absolute maximum ratings the manufacturer ...
8
votes
125 mW resistor subjected to 600 mW dissipation in professional safety system
Typical general purpose SMD resistors are usually of the thick film type.
This type of resistor is not designed for long term overload (indeed, none are), but the effect of overstressing the part ...
- 22.6k
Only top scored, non community-wiki answers of a minimum length are eligible