Mistakes of Electronic Load in LED Power Supply Test and Solutions

Want to improve the efficiency of LED power supply test, the quickest and easiest way is to select the appropriate electronic load. If the knowledge of the electronic load is not familiar enough, or proficiency is not enough to grasp, it may even result in test results of the confidence of the decline, thus affecting the quality of the product, serious accidents can also lead to. This article describes the principle of electronic load CV, and LED power supply test some of the errors introduced.

 

Electronic load CV mode with load, is the basis for LED power test. CV, is a constant voltage, but the load is only the current load of the device itself can not provide a constant voltage, so the so-called CV, only through the voltage negative feedback circuit to servo LED power output current changes, the LED output capacitor Of the charge balance, and thus achieve the purpose of constant voltage. Therefore, the core factors that determine CV precision are two:

 

Load bandwidth

 

LED power output capacitor size

 

When the LED power supply output current ripple frequency is high, if the load bandwidth is insufficient, it can not servo current changes, and cause shock, when the shock occurs, the load input voltage changes rapidly, LED output capacitor will be frequent high current charge and discharge , At this time the current ripple detected will be much larger than the steady-state LED power supply when the actual current ripple.

 

When the load bandwidth is insufficient, if the LED power supply output capacitance is large enough, then the shock amplitude can be controlled within an acceptable range, but unfortunately, LED power supply price competition is fierce, the output capacitance is generally insufficient, LED power supply for testing, the load bandwidth requirements are very harsh.

 

Load bandwidth indicators, manufacturers are not directly marked, can only refer to another indicator: full-scale current rise time, it is clear that the smaller the full-scale current rise time, indicating the higher the bandwidth of the load. The higher the load bandwidth, the lower the LED power output capacitor requirements, in general, 10uS full-scale current rise time load, to meet most of the LED power supply test needs, but in theory, any load in CV mode The higher the load bandwidth, the smaller the amplitude of the shock, the higher the confidence of the test results, therefore, the user in the use of electronic load (such as the use of electronic load), the use of electronic load When testing, pay close attention to the load input voltage ripple Vpp changes, once its out of range, the entire test results will no longer credible, this point is very important, the user must bear in mind.

 

In the CV mode, the constant voltage, and current ripple is usually very large, and the load in order to improve test efficiency, data refresh rate is often high, so the data beating very large, many users to determine whether the load is suitable for LED test, in fact, this is a very serious misunderstanding, the data is stable or not, in fact, is very easy to achieve, only need to increase the data filter time measure can be achieved, very short low-end electronic load, because the measurement accuracy is low, So have to filter a large time scale, but instead of a blessing in disguise, so that the data seem more stable, in fact, this is an illusion. To achieve accurate measurement, the fundamental method is to increase the sampling rate, not to improve the sampling rate, such a measurement on the confidence level is very low, may lead to serious quality accidents.

 

Comprehensive analysis of the above, LED power supply test, the load has a harsh requirements, mainly the following points:

 

Full-scale current rise time, is to ensure accurate load with the fundamental, the lower the value the better;

 

Data sampling rate, is to ensure accurate measurement of the fundamental, the higher the value the better;

 

Vpp real-time display, is to determine whether the measured data is the fundamental;

 

Filter speed adjustment function, is able to get a stable means of small current data;

 

Finally, to draw attention to the market there are some load, known as the LED power supply test dedicated electronic load, in fact, is a general electronic load from a face-lift made, and are generally not the bandwidth and sampling rate of the electronic load test requirements converted from, its And bandwidth is not increased, because bandwidth is the core technology of the load, and costs are closely related, it is difficult to improve, it is often improved through three ways to make the current data more stable, but also more credible.

 

The easiest way is to increase the filter strength and force the data to stabilize. Simple use of this method, easily lead to misjudgment, triggering quality accidents.

 

Adjust the voltage feedback loop, the voltage feedback signal for strong filtering to reduce the current amplitude of shock. This method in the opposite direction, and further reduce the load bandwidth, so that the situation does not shock with a substantial shock situation, have become smaller amplitude of the shock.

 

This method can suppress the occurrence or amplitude of the oscillation, but the measured current ripple will be much smaller than the actual ripple, but it is helpful to test the DC operating point. But the load rated voltage is generally high, so the price of high-voltage capacitors and size is a very serious problem, it is difficult to increase to the ideal situation, and often with the second method of comprehensive use. There is also a problem is that this situation, which tend to use relatively inexpensive high-voltage electrolytic capacitor, will bring a lot of parasitic problems.

 

This paper introduces the principle of electronic load, especially the electronic load in the LED measurement errors in the process of focusing on. In addition, some feasible solutions are proposed in this paper in order to obtain more stable current data. Hope that everyone after reading this article can be harvested.

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