Historically, 12 volt power supplies have been the most common and in demand. They are both safe for human health and reliable. The on-board electrical systems of cars also have a twelve-volt power supply in most cases. Practice shows that connecting an LED to 12 volts, as well as to a power source with a different voltage, is simple if you know some rules and laws of electrical engineering.
Content
- LED characteristics
- Power supply overview
- Algorithm of actions when connecting
LED characteristics
All light-emitting diodes have passport characteristics, of which the rated forward current and voltage drop are important for their connection. According to the current-voltage characteristic, which has a non-linear character, a slight excess rated voltage sharply increases the current flow, and this leads to the failure of all element.
Light emitting diodes are usually have low reverse voltage (about 5 volts). It is recommended to check that the polarity is correct before connecting the element to the electricity source.
To protect against polarity reversal, together with the LED, a conventional diode with a high reverse voltage should be installed in parallel with it.
Power supply overview
The best option is to connect the LED to 12 volts through a current stabilizer. But some manufacturers save on this element and produce current sources without stabilizing it.
Most common transformerless IPequipped with a damping capacitor and an output with a current setting resistor. Such a circuit is not protected from voltage surges in the network, but due to its low cost and compact design, it is used in many devices, including LED light sources.
When using a battery to supply power to the LED, it is enough to add a limiting resistor with the correct power and resistance to the circuit. The on-board network of cars also has 12 volts in most cases, but its voltage surges are quite significant under different operating modes. Therefore, a stabilizer (driver) is required to connect the LED to the power supply from the car electrical system.
Sometimes you can find a power supply unit without a stabilizer with a transformer. Such elements are connected in series in them.:
- transformer;
- diode bridge for current rectification;
- capacitive filter (conventional capacitor).
Any jump in the power supply from such a power supply will be transmitted to the LEDs, and this will affect their performance. Such power supplies are justified to use in cases where the network has stable parameters.
Power supplies that provide alternating electricity cannot be used to connect LEDs. They, at least, need to be supplemented with a rectifier and a capacitor, and at best, also a stabilizer.
Algorithm of actions when connecting
The entire procedure consists of five steps, performed sequentially.
The algorithm of actions is as follows:
- Determination of the type of power supply unit and its operating parameters.
- Determination of power consumption, nominal current and voltage drop of the LED.
- Calculation of the number of LEDs that can be safely connected to the existing PSU, and calculation of the resistor, if required.
- Installation of the circuit, during which the elements are connected taking into account the polarity.
- Checking the soldering of contacts and their insulation.
Information on the parameters of the supplied current by the power supply can be found in the technical data sheet or the nameplate on the case. The characteristics of the LEDs necessary for calculating the resistor can be found in reference books or technical documentation, if available.
The formulas for calculating the power and resistance of a resistor are based on Ohm's Law. 
Power is defined as follows: P = (Upit - (Uled1 + Uled2 +… + Uledn)) * Iled.
And the required resistance can be found using a similar formula, only at the end the voltage is not multiplied by the current strength, but is divided by it. In both formulas, Uledn is the voltage drop across each LED, Usup is the power supply voltage, and Iled is the LED rated current.
Depending on the conditions, the brightness of the COB matrices can be adjusted by changing the current strength. For this, their circuit is equipped with a driver. Each COB matrix has its own parameters of the operating current and the approximate voltage drop, which are indicated in the passport for the element.
Using a 12 volt power supply to power the COB matrix is not entirely correct. Even with a voltage drop of about 12 volts, a limiting resistor is required for its operation. As a result, the operating current is lower than the nominal value and the glow of the element occurs with less efficiency. The way out is to use a low-voltage-to-current converter in the circuit.
