The effect of series and parallel connection of LED lamps on lamp life
The arrangement of the LEDs on the commonly used light source boards is basically in these four modes. Below we explain the relationship and influence of the series-parallel arrangement structure circuits of these LEDs and the life of the whole lamps.
The circuit shown in Figure 1
Advantages: The circuit design is simple, the current distribution of the LED is even, the working current of the LED lamp is equivalent to the output current of the power supply. The Vf of the LED does not need to be considered. According to the output range of the power supply voltage, as long as there is not a large number of LED short circuits, the lamp can ensure the lighting, only the brightness reduce.
Disadvantages: There is an LED open circuit damage, the whole lamp is not bright, causing serious consequences of turning off the lights. Moreover, the driving output voltage is relatively high, and the insulation requirement for the aluminum substrate is relatively high.
The circuit shown in Figure 2
Advantages: The power supply output voltage is relatively low and the production process is simple. When several strings of Vf are in the same state, the whole lamp works normally, and the operating current of the LED does not change.
Disadvantages: The Vf requirements for LEDs are more stringent. If the Vf difference is large, the current distribution is not even. When the Vf of a string is relatively low, the operating current of the string increases sharply, the temperature is too high, and the light decay is severe. If there is a single LED breakdown, the current of the string increases sharply, and the LED will open the current. At this time, the current of the drive output is all distributed on the other LEDs. All the LEDs will work in the overcurrent state, and the Vf is relatively low. A series of currents will be larger, resulting in the result that all LEDs are overheated and damaged, the entire lamp is extinguished, and almost all LEDs are severely degraded, with no rework value. If there is an LED open circuit, it will also produce the same result.
The circuit shown in Figure 3
Advantages: The shunt constant current mode is adopted, and the Vf of the LED is not considered. If there is a single breakdown damage, it will not affect the normal operation of other LEDs. If there is a single LED open circuit, the string does not light, and the other strings can work normally. The current is stable, does not affect the normal operation of other strings, and will not cause serious consequences of turning off the lights. The function expansion is convenient, and the additional functions of the constant current module can be used for secondary development, and various protection functions such as temperature control, time control, and dimming can be added.
Disadvantages: The circuit is relatively complicated, the quality requirements for workers are relatively high, and the cost is slightly increased.
The circuit shown in Figure 4
Advantages: If the Vf of the LED is relatively close, the circuit works relatively stable. The more paralleled, the higher the stability of this circuit.
Disadvantages: If the Vf of one LED is relatively low, the operating current of this LED will be relatively large, causing light decay or overcurrent open circuit, which has less impact on other LEDs. The parallel column of the same column current increases slightly after the distribution. It can cause serious consequences of turning off the lights.
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