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How to prevent the load usage of Voltage Stabilizer?

2020-07-23

In actual production industry and daily life, in order to improve the performance of the voltage stabilizer , it is generally recommended that you use a three-loop EMI filter (dual CM + single DM). There are many differences in the effects of filters in practical applications, especially under heavy load conditions. The main reason for this problem may be that the inductance devices in the filter saturate under heavy load and full load, especially filters with differential mode inductance. Because the differential mode inductance has to flow through all the working currents in the live or neutral line of the power supply, if the differential mode inductance is improperly designed and the current is large, it is easy to saturate, and unsaturated iron powder cores can be used. The working principle of the filter is to form a large characteristic impedance discontinuity on the transmission path of the radio frequency electromagnetic wave, and reflect most of the energy in the radio frequency electromagnetic wave back to the source. The performance of most filters is measured under the condition that the source and load impedances are both 50, and the performance of the filter cannot reach the best under actual conditions. Two or more stages of filters can keep the internal contacts at a relatively stable impedance, so the impedance of the load and source is not very dependent, and it can provide performance close to 50/50. Regardless of the product, reliability is extremely important, which is directly related to the cost of maintenance. In order to ensure the high reliability of the voltage regulator, a current-limiting protection circuit is required when designing. This is to prevent long-term damage to the voltage regulator due to excessive load.


There are 2 methods for general current limiting protection measures:

1. Limit the output current to the maximum value. The disadvantage of this method is the large internal loss.

2. While reducing the voltage, the output current is also reduced. The advantage is that the energy consumed during work is small, but the limitation is not obvious, and there is still current passing through, which will accelerate the aging of the device.


In view of this situation, it is recommended that you improve the lower short-circuit protection circuit on the basis of current limit, and disconnect the power MOS tube under the condition of ensuring a short circuit. This will have an effect. In this circuit design, VMP is the power MOS tube of the linear regulator. When a short circuit occurs, when the voltage stabilizer realizes the short-circuit protection, the VM1 tube will be cut off to reconstitute the current mirror. The role of the transistor is to Ensure that the circuit can input the voltage normally during the short circuit period, thereby ensuring that the voltage is always in a low voltage state, and improving the reliability of the circuit. On the basis of the current-limiting circuit, after improvement, the high reliability of the voltage regulator can be ensured, and the loss can be reduced, which is well applied in power management!


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