Ten Causes and Diagnostic Methods of LED Driver Failure
As a key component of LED lighting, the quality of the LED driver directly affects the reliability and stability of the entire lamp. This article starts with related technologies such as LED driving and customer application experience, analyzes and analyzes many errors in the design and application of lamps and lanterns:
1. Did not consider the LED lamp beads Vf range of changes, resulting in low lamp efficiency, or even unstable
If the maximum output voltage of the selected LED driver is lower than VoH, the maximum lamp power may not reach the actual required power at low temperatures. If the minimum voltage of the selected LED driver is higher than VoL, the output of the driver may exceed the operating range at high temperatures. Unstable lighting may flash.
However, considering the overall cost and efficiency, blind pursuit of the ultra-wide output voltage range of LED drivers is impossible: because the driver voltage is only within a certain range, the driver efficiency is the highest. Out of range, efficiency and power factor (PF) will decrease. At the same time, the output voltage range of the driver is designed to be too wide. As a result, costs increase and efficiency cannot be optimized.
2. Did not consider the power margin and derating requirements
Under normal circumstances, the rated power of the LED driver refers to the data measured under rated conditions and rated voltage. Considering that different customers have different applications, most LED driver suppliers will provide power derating curves according to their product specifications (common load and ambient temperature derating curves and load versus input voltage derating curves).
3. Do not understand the operating characteristics of the LED
When designing requirements, LED driver users should first understand the operating characteristics of the LED, and avoid putting forward some indicators that do not meet the principle of the working characteristics, and avoid indicators far beyond the actual requirements to avoid excessive quality and cost.
4. The test failed
The correct test method is to adjust the voltage regulator to the LED driver’s rated operating voltage range, and then connect the driver to the boot test. Of course, the technically improved design can also avoid the problem of malfunction caused by this type of test misoperation: The startup voltage limit circuit and the input undervoltage protection circuit are set at the input of the driver. When the input does not reach the driver’s set start voltage, the driver does not operate; when the input voltage drops to the input undervoltage protection point, the driver enters the protection state.
5. Different loads, different test results
When the LED driver is used to test the LED driver, the result is normal and when using an electronic load for testing, the result may not be normal. Usually this phenomenon has the following reasons:
(1) The instantaneous output voltage or power of the driver exceeds the operating range of the electronic load meter. (Especially in CV mode, the maximum test power should not exceed 70% of the maximum power of the load, otherwise the load may temporarily exceed the protection function during the loading process, causing the drive to fail to work or load.)
(2) The characteristics of the electronic load meter used do not apply to the measurement of the constant current source, and the jump of the load voltage level occurs, causing the driver to fail to operate or load.
(3) Since there is a large capacitance inside the input of the electronic load meter, the test is equivalent to connecting the large capacitor in parallel with the output of the driver, which may cause the current sampling operation of the driver to be unstable.
Since the LED driver is designed to meet the operating characteristics of the LED lamp, the test method that is closest to actual and practical application should be to use LED lamp beads as the load and string the ammeter and voltmeter on the voltmeter to test.
6. The following situations often occur will lead to LED driver damage:
(1) The AC output is connected to the DC output of the driver, causing the driver to malfunction;
(2) AC is connected to the input or output of the DC / DC driver, causing the driver to malfunction;
(3) The constant current output is connected to the dimming lamp, causing the driver to fail;
(4) Connect the phase wire to ground, resulting in no output from the driver and energized enclosure;
7. The out of phase
Usually outdoor engineering applications are three-phase four-wire systems. Taking the national standard as an example, the rated working voltage between each phase line and the neutral line is 220Vac, and the voltage between the phase line and the phase line is 380Vac. If the operator connects the driver input to two phases, the LED driver input voltage exceeds the standard and the product fails after power is turned on.
8. The fluctuation range of the power grid exceeds a reasonable range
When the wiring of the same transformer power grid branch is too long and there are large-scale power equipment in the branch, when the large-scale equipment starts or stops, the voltage of the power grid fluctuates violently, even leading to instability of the power grid. When the instantaneous voltage of the grid exceeds 310Vac, the driver may be damaged (even if there is a lightning protection device, since the lightning protection device responds to pulse spikes of several tens of us levels, the grid fluctuation may reach tens of milliseconds or even hundreds of milliseconds).
Therefore, special attention must be paid to the large-sized motors on street lighting branching grids. It is better to monitor the amplitude of power grid fluctuations or to supply power to independent grid transformers.
9. The line tripping
Too many lights on the same branch will lead to a period of power overload, and uneven power distribution between phases, resulting in frequent tripping of the line.
10. The drive cooling
When the driver is installed in a non-ventilated environment, the driver’s housing should be in contact with the lamp housing as much as possible. When conditions permit, a thermally conductive adhesive or thermal pad is applied on the contact surface between the housing and the lamp housing to increase the heat dissipation performance of the driver, thereby ensuring the performance of the driver. Life and reliability.
In summary, the LED driver has many details in practical application, which needs analysis and adjustment in advance to avoid unnecessary failures and losses!