New answers tagged

1 vote

Ring oscillator not oscillating

The 1Meg resistors are so high that the current gain of a typical BJT won't give a net gain around the loop of over unity, so no oscillation. MOSFETs don't have a problem with this high resistance. To ...
user avatar
  • 13
2 votes

Weird PWM signal if powered by AC/DC source

The funny waveform is explained by the scope probes being connected to incorrect places for what you are trying to measure. You are trying to measure voltage waveform of the LED from the LED terminals,...
user avatar
  • 87.1k
0 votes
Accepted

To decouple or not to decouple these LEDs/drivers?

The first device is a simple analog circuit and does not depend on supply impedance (including the need of bypass capacitors). The second one seems to have more active circuitry inside it, but also ...
user avatar
8 votes
Accepted

Why is capacitor discharge time higher when an LED is included?

The short answer is the "voltage drop" of the diode, but the longer answer is the non-linear I-V characteristic of the diode. In hand-wavy engineering we resort to a simplified piecewise-...
user avatar
  • 2,009
5 votes

Why is capacitor discharge time higher when an LED is included?

If you’re putting the LED in series with the resistor then the discharge current will be significantly lower, and will drop almost to zero when the capacitors discharge to the forward drop of the LED.
user avatar
  • 5,340
0 votes

Possible damage to LED or driver from PWM power source and flickering?

Driving a CC regulator for LEDs with external PWM might blow the external fuse or exceed the internal current limit to cut off and retry thus flicker. So I would say this is incompatible with PWM ...
user avatar
0 votes

How to calculate the total power of a LED using solid angle?

Vishay has published how to measure light density and intensity at a conical distance in a document from the datasheet page you posted. "General Information Measurement Techniques" ...
user avatar
1 vote

Connect different "blinking LEDs" in parallel

The following in not exact but will get you close enough. The voltage drop of LEDs varies by chemistry which controls color. The following is in order from low to high voltage drop. Laser diode: ~1.5V ...
user avatar
  • 2,553
2 votes

Connect different "blinking LEDs" in parallel

These are blinking LEDs, they contain the circuitry to make them blink and current-limiting circuitry. So they don't need (or want) series resistors. The bad news is that you must give them a voltage ...
user avatar
4 votes

Connect different "blinking LEDs" in parallel

Those are not simply LEDs. They are LEDs with an integrated circuit in an LED housing. They are meant to operate on 5V. Your 3V power supply is not enough. Without the motor, the battery voltage is (...
user avatar
  • 57.4k
1 vote

Alternative to individally addressable LEDs

Another option: there are various LED driver ICs that are basically a shift register with output stages to drive LEDs, e.g. TLC6C5912, see the data sheet They can be driven from an SPI interface, and ...
user avatar
  • 659
3 votes

Alternative to individally addressable LEDs

One of many solutions: get a microcontroller with 44 pins – cheapest you can find, and drive the LEDs using an NPN transistor as a buffer. Some microcontrollers may be able to drive all those LEDs ...
user avatar
5 votes
Accepted

Alternative to individally addressable LEDs

You want led matrix driver or multichannel led pwm driver ics. Most can handle the pwm and dot control themselves as well. You may need a microcontroller locally depending on your setup.
user avatar
  • 70.7k
2 votes

LED forward current vs forward voltage

Don't I determine the current of the LED by my resistor value? I assume you're thinking about the simplified model where you assume that the voltage drop across the LED is some constant, which you ...
user avatar
0 votes

How does this tone generator circuit work?

In general, this is called a 'relaxation oscillator'. These work by using feedback to create a toggling (astable) non-linear circuit. The feedback path for this circuit is the 20nF 'whistle chip' that ...
user avatar
  • 40.2k
1 vote

LED Current Draw Questions

LEDs generally have a rather steep resistance curve, in other words a small change in voltage results in a large change in current. When you insert your ammeter in series with one LED it’s current ...
user avatar
  • 5,340
1 vote

Driving a LED with a potentiometer in parallel, electronic basics

In comment, you cleared up what "perfect LED" meant. If it has a threshold voltage Vth, then your circuit can be replaced by simulate this circuit – Schematic created using CircuitLab ...
user avatar
1 vote

Driving a LED with a potentiometer in parallel, electronic basics

Your circuit is: simulate this circuit – Schematic created using CircuitLab with example values filled in. Recognise that D1 is piecewise: conducting or not conducting (not open or closed). ...
user avatar
  • 2,985
1 vote

LED forward current vs forward voltage

It is amazing how it is possible to show so many practical considerations for the humble LED "flashlight". Obviously, in this world, a lot of complexities are hidden behind every simple ...
user avatar
2 votes

Two power sources and two outputs with one switch

It's possible. Here's the schematic.
user avatar
  • 9,658
1 vote

Driving a LED with a potentiometer in parallel, electronic basics

Your Prof. possibly described the ideal diode as a current switch at a certain threshold voltage. We usually call it a Current Rectifier and in the old days the schematic would define them as CR1, CR2 ...
user avatar
7 votes

LED forward current vs forward voltage

All batteries have ESR resistance and LEDs can be modelled with an ESR of 1/2Pmax minimum = 1/2(0.1W) = 5 Ohms Vf = 2.6+ I*5 ohms, when using rated current of 20 mA. But the tolerance on that can be ...
user avatar
23 votes
Accepted

LED forward current vs forward voltage

The resistor limits current and the LED curve is right When I mentioned that both are right, I mean it this way: Assuming, for example, that your voltage source is a low-impedance \$3.3\:\text{V}\$ (...
user avatar
  • 68.8k
2 votes

LED forward current vs forward voltage

LEDs drop a voltage when you pass a current through them, and that's given by the curve you have reproduced. The curve is for the LED alone. The voltage across your resistor will be the supply ...
user avatar
  • 14.6k
2 votes

LED forward current vs forward voltage

It is the IV curve of a LED.Due to the fact that the LED is a semiconducting device you cannot use Ohm's law to determine the current inside a LED by its voltage drop.
user avatar
-2 votes

UL/CE/CSA certification for low voltage electronics/LED product?

Answer here for quebec: https://www.rbq.gouv.qc.ca/domaines-dintervention/electricite/interpretations-techniques/approbation-dappareillage-electrique-de-30-v-et-moins.html Regards
user avatar
6 votes
Accepted

Two power sources and two outputs with one switch

Here's a schematic diagram which includes a double-pole single-throw (DPST) switch that should, as @Eugene commented, do what you need: simulate this circuit – Schematic created using ...
user avatar
  • 27k
0 votes
Accepted

How to wire multiple LED lights to an AC outlet

Unfortunately I don't know enough about electronics to come up with the proper circuit diagram for this. You don't need to. These thing are a cheap commodity that is everywhere. And anyway, it would ...
user avatar
-3 votes

How to wire multiple LED lights to an AC outlet

Here is an inexpensive power supply capable of driving up to 100 LEDs in parallel. Adjustable so you can dim the light intensity if desired. If you want a cheaper unit choose one that do not have ...
user avatar
0 votes

Keep a 12V led strip on for a few seconds

70mA times 5 seconds is 350mC (milli-Coulombs). Let's assume your LED strips can drop from the normal 13.2V down to 11.2V (2 volt drop) and that's still an okay brightness for you. Then the ...
user avatar
  • 6,386
1 vote

Keep a 12V led strip on for a few seconds

It's probably not worth the trouble to protect the huge inrush current from blowing a fuse then make it large enough in Farads using a Ultracap to sustain some Amps for low sag in voltage. C = Ic Δt/...
user avatar
0 votes

Power injection LED strip: best method art instalation?

C would be ideal, b second, and A the minimum for a decent installation. C provides a low resistance to both sides of the bars, which means the far end of the bar doesn't see a voltage droop from high ...
user avatar
  • 70.7k
1 vote

Dual LED Configuration

You can buy a 4-pin (most likely only SMT) dual red/green LED and make either of the two possible anode-cathode connections yourself. Or connect them as common anode or common cathode. There are many ...
user avatar
0 votes

Addressable LEDs (WS2815): power and data in a multicore cable

No, there won't be any crosstalk like that. You can use appropriate wires for each task. So the signal line can be any modest size of data wire, e.g. 0.2 mm2. The power wires, however, are a whole ...
user avatar
0 votes

Controlling 90 LEDs using one WS2811

this is official diagram for driving higher currents. I don't know if you still need it but I will leave it for anyone reading this in the future
user avatar
1 vote

Finding replacement LED while measuring power source

Electrically you can replace those dead diodes with any modern, similar package size LED with the same forward voltage and a current rating of at least 20mA (which should be simple to find). As long ...
user avatar
  • 10.4k
1 vote

What are the names of screens used in "Basic calculators"?

They are segment (as opposed to graphic) LCD displays (Liquid Crystal Display displays). There are two basic types, static and multiplexed. Static types have single common pin and the segment pins are ...
user avatar
2 votes

What are the names of screens used in "Basic calculators"?

Liquid Crystal Displays, or LCDs, use a material (the ‘liquid crystal’) which can be polarized in segments by an applied voltage. The display glass is made up of several layers and mirror on the back. ...
user avatar
  • 40.2k
0 votes

What are the names of screens used in "Basic calculators"?

Many calculators use LCD displays which are low power.
user avatar
  • 3,745
1 vote

Handmade vactrols question concerning ROHS

The LDR that you link to is probably not RoHS. The only thing that says it's RoHS is the marketplace listing. How reliable are those? I don't know whether you've ever bought, for instance, LiPo ...
user avatar
  • 140k
1 vote

Handmade vactrols question concerning ROHS

Vactrols and LDRs are not going to be RoHS, due to their containing either CdS or CdSe. You can get a RoHS, isolated, current controlled, variable resistor. Here is one type, with R versus current, ...
user avatar
  • 140k
2 votes

Handmade vactrols question concerning ROHS

LDRs generally contain cadmium and are therefore not compliant with RoHS legislation in Europe. For example, this Digikey listing:
user avatar
2 votes

Independently control LEDs in series with intermediate point

One half of this LED bar looks just right for 3-pin charlieplexing: That will only work if the supply voltage is not enough to light two LEDs in series, though. For red LEDs on 3V3, it's alright. To ...
user avatar
  • 57.5k
0 votes

Is there anything to limit LED output dimming 50% while the wall dimmer controls 50% to 0%?

On the front page of the datasheet it tells you that the fixture supports 0-10V dimming. So for 50% dimming you need to set the dimming control input to about 5V. 0-10V dimming fixtures typically ...
user avatar
  • 13.2k
0 votes

Water level indicator LEDs one by one

An optical prism water sensor is 'on' by default (dry) and 'off' when immersed. Sounds like exactly what you're looking for, and you avoid the hassle of passing electricity through water. More about ...
user avatar
  • 40.2k
3 votes

Why does this LED have three PCB pads in the data sheet?

it's a leveling pad to support the lens part of the LED to make sure the led lays on its side at 90 degrees instead of leaning downwards towards the PCB. As there's a possibility of this pad ...
user avatar
  • 26.6k
2 votes
Accepted

Capacitor discharging after power supply is turned off

What am I missing? The capacitor is discharging quickly into the power supply, if the power supply is turned off while it is still connected. That is why... I noticed that the LED actually remains ...
user avatar
  • 16.5k
0 votes

DC motor as a generator

An unloaded DC motor with a certain applied voltage will generate a back emf that is about 90 % of the applied voltage. A (red) LED requires about 1.7 V to start to light. So, if you apply 2 V to the ...
user avatar
  • 12.4k
1 vote

DC motor as a generator

Yes, you can but note that a motor creating electrical power is more difficult to turn than a motor with the leads disconnected. Make sure your air motor can turn the motor when the leads are ...
user avatar

Top 50 recent answers are included