Electronic Load of the LED Power Supply Test

The CV mode loading of electronic loads is the basis for LED power supply testing. CV is a constant voltage, but the load is only a device that pulls current and cannot provide a constant voltage by itself. Therefore, the so-called CV only uses a voltage negative feedback circuit to servo the changes in the output current of the LED power supply, so that the charge on the LED output capacitor balance to achieve the purpose of constant voltage. Therefore, there are two core factors that determine CV accuracy: load bandwidth and LED power supply output capacitance value.Today qihe smt pick and place machine sharing the electronic load of the LED power supply test.

When the ripple frequency of the output current of the LED power supply is very high, if the load bandwidth is insufficient, it will not be able to servo the current change, causing oscillation. When oscillation occurs, the load input voltage changes sharply, and the LED output capacitor will undergo frequent high-current charge and discharge. , the current ripple detected at this time will be much larger than the actual current ripple when the LED power supply is working in a steady state.

When the load bandwidth is insufficient, if the output capacitance of the LED power supply is large enough, the oscillation amplitude can be controlled within an acceptable range. However, the price competition of LED power supplies is very fierce, and the output capacitance capacity is generally insufficient. Therefore, the LED power supply needs to be Testing has very strict requirements on load bandwidth.

The bandwidth index of the load will not be directly marked by the manufacturer. You can only refer to another index: the full-scale current rise time. Obviously, the smaller the full-scale current rise time, the higher the load bandwidth; the higher the load bandwidth, the better the LED. The lower the requirements for the power supply output capacitance. Generally speaking, a load with a full-scale current rise time of 10uS can meet the testing needs of most LED power supplies, but in theory, any load may oscillate in CV mode. , when the LED output capacitance remains unchanged, the higher the load bandwidth, the smaller the oscillation amplitude, and the higher the confidence of the test results. Therefore, users must pay close attention to the load input voltage ripple when using electronic loads for testing. Once Vpp changes beyond the range, the entire test result is no longer credible, which is very important.

In CV mode, the voltage is constant, and the current ripple is usually very large. In order to improve the test efficiency, the load often has a higher data refresh frequency, so the data jumps greatly. Many users use this to determine whether the load is suitable for LED testing. Testing, in fact, this is a very serious misunderstanding. Whether the data is stable or not is actually very easy to achieve. You only need to increase the time measurement of data filtering to achieve a very short low-end electronic load.

Because the measurement accuracy is low, it must not be Not filtering on a large time scale is a blessing in disguise, making the data appear to be more stable. In fact, this is an illusion. To achieve accurate measurement, the fundamental method can only be to increase the sampling rate. If the sampling rate is not increased, the confidence level of such measurement results will be very low and may cause serious quality accidents.

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