The main parameters of luminous semiconductor elements (LEDs) include their rated current and operating voltage. These data are usually given in data sheets or in the technical data sheet for the product. The situation is more complicated when an LED falls into the hands, by its appearance it is impossible to determine its belonging to a certain brand.
At the same time, there are no documents for him either.
Analytical method
To determine the operating voltage of an unknown LED, an analytical approach is used, which consists in evaluating its properties based on physical characteristics.
You can judge whether a product belongs to one type or another by the following parameters:
- Radiation color.
- Body type and dimensions.
- Its shape.
If the LED body is made of a transparent compound, it is very easy to determine the color of its glow. To do this, it is enough to ring it with an ordinary multimeter.
Touching the legs of the LED with the probes of the device in direct polarity, you can see a slight glow, which can be attributed to a certain type.
The fact is that the glow color indicates that this element belongs to one or another class of emitting structures. In this case, the operating voltage for this category of semiconductors has a fixed value (see table).
Knowing the nature of the glow of an unknown LED, you can find in this table data on semiconductors of a similar design and the same color. This will help determine the approximate amount of voltage supplied to it. The analytical method allows you to obtain only indicative information, for the confirmation of which practical actions are required.
Experimental method
For practical confirmation of the information obtained theoretically about the LED, the following additional elements and devices will be required:
- A resistor with a nominal resistance of about 590-620 ohms (more is possible).
- Power supply with adjustable output voltage.
- Multimeter.
After they are prepared, you need to assemble the diagram below.
It can be seen from it that the resistor limits the current limit through the LED, and the potential drop in the forward direction is monitored by a multimeter.
Checking in this case is reduced to a smooth increase in voltage from zero to a certain (threshold) value at which the LED element starts to glow. With a further increase in the test voltage, the brightness of its glow will reach the nominal value, and the readings on the multimeter display will stop changing.
This means that the semiconductor pn junction has opened completely (its saturation has occurred), and all excess voltage from the power supply will "drop" across the limiting resistor.
The reading read from the screen of the measuring device is the sought-for nominal voltage for this LED sample. In conclusion of the experiments, it remains only to check the new data with the previously obtained theoretical results.