# Tag Info

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 $3.3\:\text{V}$ (...
• 69k
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-...
• 2,039

### 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 ...
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 ...
• 27.1k
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.
• 70.7k

### 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.
• 5,350

### 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 (...
• 57.5k

### What type of regulator to use for LEDs in a scale model vehicle?

I'll assume you're using a suitable power supply like 5V or 12V. The simple way is to use a current-limiting resistor. You can determine the resistor value in three steps: determine your required ...
• 40.2k

### 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 ...

### Handmade vactrols question concerning ROHS

LDRs generally contain cadmium and are therefore not compliant with RoHS legislation in Europe. For example, this Digikey listing:
• 327k

### 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. ...
• 40.2k

### 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 ...
• 14.6k

### 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.
• 467

### Two power sources and two outputs with one switch

It's possible. Here's the schematic.
• 9,717
Accepted

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,...
• 87.2k

### 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 ...
• 327k

### 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 ...
Accepted

### Identify number of strings in Philips 14.5W LED PCB

Is it possible by just looking at the attached image whether the LEDs are in a single series circuit, or whether they're configured in series/parallel? Follow the tracks and you'll see that two ...
• 16.5k
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 ...
• 2,553
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 ...
• 659
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 ...
• 9,161
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 ...
• 5,350
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 ...
1 vote
Accepted

### 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). ...
• 3,012
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 ...
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/...
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 ...
• 327k
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 ...
• 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 ...
• 327k
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 ...
• 140k

Only top scored, non community-wiki answers of a minimum length are eligible