LED indicator circuit

LED indicator circuit.
1. General DC voltage indicator circuit.
The circuit is as above, generally LED + current limiting resistor. As an indicator light, the LED current does not need to be very large, generally 1-2ma. The smaller the current, the more durable the LED light is. It can be calculated according to the current, power supply voltage, and conductivity voltage drop. The resistance value of the current-limiting resistor is also measured, and the output power of the current-limiting resistor is also measured, and the appropriate packaging is selected.
Calculation method of LED current-limiting resistance: current-limiting resistance ω = (power supply voltage V-LED turn-off voltage drop V) / current A.
The voltage drop of the light-emitting diode: basically around 1.2~2V. Different manufacturers have different color pressure drops. As long as the diode is turned off, the voltage drop is basically clear, but the voltage drop will rise slightly as the operating voltage rises:
High Brightness LED Voltage Drop:
The key has three colors, but the voltage drop of the three LEDs is different. The actual standard value of the voltage drop is as follows:
The voltage drop of the bright red LED is 2.0-2.2V.
The voltage drop of the light yellow LED is 1.8-2.0V.
The voltage drop of the emerald green LED is 3.0-3.2V.
The rated current is about 20mA when everything is lit properly.
SMD LED voltage drop:
The red voltage drop is 1.82-1.88V, and the current is 5-8ma.
The emerald green voltage drop is 1.75-1.82V, and the current is 3-5ma.
The orange voltage drop is 1.7-1.8V, and the current is 3-5ma.
The voltage drop of the basket color is 3.1-3.3V, and the current is 8-10ma.
The milky white voltage drop is 3-3.2V, and the current is 10-15m.
Second, 220V AC indicator circuit.
The general 220V AC current LED indicator circuit is the same as the above circuit, that is, LED + current limiting resistor, this type of circuit is used for general power sockets. The maximum working voltage of 220V AC current reaches 310V. If the current of the LED indicator is limited to within 1ma, it is best to choose a current limiting resistor of more than 300K, within 1M. The larger the selected internal resistance, the smaller the current, the smaller the current limiting resistance and the heating of the LED, and the more durable the LED indicator will be.
LED indicators are often very easy to be damaged in daily power sockets, the reason may be that the LED penetrates in the opposite direction and is damaged or the current limiting resistor is ignited (generally, the resistor is too small or the output power selection is not suitable).
The above simple indicator circuit is applied in 220V communication, because the breakdown voltage of the LED in the reverse direction is generally only a few volts. In the negative half cycle of the AC current, the LED is in the reverse direction of penetration, but because of the existence of the current limiting resistor , the current is small, generally not easy to damage the LED, but some LEDs are very easy to damage after penetration, long-term penetration will reduce the service life of the LED, the solution is to connect ordinary diodes on both sides of the LED or connect high voltage diodes in series (such as 1N4007 ),generally). For better cost savings, it is not easy for manufacturers to add additional diodes. In addition, they can also increase the resistance of the current limiting resistor plus the current limiting resistor to reduce the penetration current, but if the current limiting resistor is too large, the LED chromaticity will be reduced.
In addition, the current limiting resistor can also be replaced by a power capacitor, so that the resistance wire heating problem is not possible. The capacity of the power capacitor is measured according to the circuit current. Current=220V/capacitive reactance, capacitive reactance XC=1/2πFC. Power capacitors generally choose a voltage resistance above 400V. Because high-voltage capacitors are much more expensive than resistors, such circuits are generally not used.