Current operating vs voltage operating electronic devices

[fisico30]

Hello Forum,
I have heard of current operating devices, like LEDs, and voltage operated devices...

What is the difference?
It seems to me that all electronic devices, once provided a certain voltage, draw the current they need...so what is this distinction between current operating and voltage operating?

thanks
fisico30

 

[milesyoung]

This isn't a very precise definition (you could probably find a rigorous one with a little Googling) but it seems to me to have to do with functionality.

If you want a LED to emit light you have to drive a current through it. You naturally apply a voltage across the LED to produce the current, but I think it's reasonable to say that the current is the direct cause of the LED emitting light, not the voltage.

Other popular examples are BJT/FET's where a base current or gate voltage, respectively, controls the V/I characteristics of the transistor.

 

[Abstr7ct]

You need a voltage source to be able to push current through an electronic device. It all comes down to Ohm's law V=IR. Electronic devices are rated according to the voltage and current required for proper operation. If you can represent a device as a load, then you can find the current drawn by that device using Ohm's law, simply by dividing the operating voltage value over the load which has the unit of ohm.

As far as I know, there's nothing called current/voltage operating device, because you can't get current going through a device without a voltage source to push that current through it. Any electronic device has resistance, which according to it, the electronic device draws a certain level of current.

LEDs, for example, don't have a known constant resistance value, so it has come with practice that we connect a resistor in series with an LED to limit the current that goes through it. You can directly connect a 2~3 volt power supply, which is the usual operating voltage for an LED, to an LED and you get a proper function (illumination) but it will get hotter with time and may burn eventually.

 

[cabraham]

Some devices are better when driven with constant current & the voltage is incidental, like LEDs, bjt's, SCRs, triacs, Hall effect devices/sensors, etc. Others are better suited to being driven with constant voltage with current being incidental, such as incandescent light bulbs (which also can be current driven but usually voltage drive is preferred for reasons i will not go into), FETs, integrated op amps (voltage feedback type), vacuum tubes, etc.

An LED cannot be driven by a voltage source, please do not attempt to do so. If an LED is driven with a 10 mA current source & the forward voltage is measured at 2.2 volts, one should not attempt to drive the LED with a 2.2 volt constant voltage source. The result is thermal instability. An LED is built from a semiconductor material which has a conductivity that increases w/ temp (resistivity decreases w/ increasing temp.

A voltage source across an LED, even the "right value of voltage" will produce thermal runaway. An LED must be current driven. If no constant current source is available, a voltage source can be used with an appropriate valued series resistor. The resistor prevents thermal runaway & limits the current.

With linear devices, i.e. a linear resistive heating element, it can be driven from constant voltage or constant current. No reason one would be better than the other.

Claude

 

[alphysicist]

I can provide some clarification on the difference between current operating and voltage operating electronic devices.

Current operating devices, such as LEDs, are designed to operate at a specific current level. This means that the device will function properly when a certain amount of current is flowing through it. On the other hand, voltage operating devices are designed to operate at a specific voltage level. This means that the device will function properly when a certain amount of voltage is applied to it.

The distinction between these two types of devices lies in their internal circuitry and design. For example, an LED has a specific current level that is required for it to emit light, so it is designed to operate at that current level. If the current is too low, the LED will not light up, and if it is too high, it may burn out.

In contrast, a voltage operating device, such as a computer or phone, has a specific voltage level that it needs to function properly. The internal circuitry of these devices is designed to operate at a specific voltage, and if the voltage is too low, the device may not turn on, and if it is too high, it could potentially damage the device.

Overall, both current operating and voltage operating devices are important in the world of electronics and serve different purposes. It is crucial to understand the difference between the two in order to properly use and maintain electronic devices. I hope this helps to clarify the distinction between current operating and voltage operating devices.