Buffered rectifier bridge solution based on ST STD80N10F7 + thermistor

With the continuous improvement of people's production and living standards, people's awareness of environmental protection has become stronger and stronger, and the slogan of energy-efficient and green travel has long been deeply rooted in people's hearts, and has prompted people to actively practice it.

As a member of the global village, the face of global warming trend, we have an obligation to make some efforts to curb it, even if it is a small move.

When it comes to warming, we have to talk about energy, because it is the excessive use of energy by humans that has led to the current warming.

The interpretation of energy overuse actually has two meanings, one is the irrational use of energy, and the other is the inefficient use of energy. Throughout the global energy system, coal, oil, and natural gas are still the three most dominant energy sources in the world, but all three are non-renewable energy sources, and once they are mined out, they are gone.

Caught in this situation, we have to find new alternative energy sources and new energy-saving road, thus the term "new energy" is emerging!

People's understanding of new energy is renewable, environmentally friendly, low-cost, high security, such as commonly used solar, water, wind, and even small nuclear energy. The final form of these new energy sources will actually be transformed into electricity, in the form of electricity used by people.

Electricity is the most widely used energy source, people's clothing, food, housing and transportation are all inseparable from electricity, the emergence of electricity can be said to have overturned an era, intensified the great changes of the times, to people's production life with great convenience and advanced, so that human civilization proudly took a big step forward!

Based on the absolute advantage of electric energy, human beings can no longer go back to the primitive period of slash-and-burn farming, so we have to look forward and consider the problem of sustainable use of electric energy. In terms of the science and technology that human beings have mastered so far, it is no longer a problem to go to heaven and earth, and energy is naturally not a big problem.

However, as we have said before, coal, oil and natural gas are non-renewable renewable energy sources, and they will be exhausted one day, so the development of new energy sources and energy saving is the road to sustainable development.

The use of electricity is evaluated by energy efficiency, and appliances with high energy efficiency are more energy-efficient and relatively more friendly to the environment. For power supplies, we divide energy efficiency into five levels: Bronze, Silver, Gold, Platinum, and Titanium, with higher efficiency going forward, which also means more energy efficiency.

In order to design and develop a more efficient power supply, we need to figure out the loss of power supply, which places are large losses to try to optimize which places, for example, we developed our own 200W LLC switching power supply to solve a big loss problem, but also a big pain point of switching power supply.

Power supply for safety reasons, there is a limit on the size of the boot current, people hope that the smaller the boot current the better, in order to reduce the inrush current when the power supply is turned on. If the inrush current is too high, it will produce some uncontrollable dangerous factors, such as the fire problem. The reason for the inrush current when the power supply is turned on is that the large capacitor C1 has a charging process, and the instantaneous charging will have a large current.

In order to limit the power supply start-up current, the general solution is to add a thermistor RT1, using the thermistor's high impedance at room temperature to limit the charging current of large capacitor C1. We did a comparison test between the power supply start-up current with the thermistor and without the thermistor, and the start-up current with the thermistor was 10A, while the start-up current without the thermistor reached 18A.

Therefore, many current power supply products in order to limit the inrush current when the power is on, are simply add a thermistor to solve. But we also need to recognize the downside of doing so - reducing power supply efficiency! This is contradictory to the above talk about energy saving and power reduction, that is, adding a thermistor will be more power consumption, very detrimental to energy saving and emission reduction.

For this pain point, we developed and designed a new buffer rectifier bridge, we use a low-voltage MOS tube to solve this problem.

The model of Q1 in the figure is STD80N10F7, a low-voltage MOS with a withstand voltage of 100V, and at both ends of the thermistor RT1. We do a delay on the MOS opening, and wait for the large capacitor C1 full charge before opening.

The ingenuity of this circuit is that the thermistor is playing a current-limiting role when the power is on, and it will be short-circuited by the MOS tube after the power is on, thus solving the problem of thermistor consumption. From the test data, if not add MOS tube, the thermistor will consume more than 1W of power on the thermistor, and the temperature reached 138 ℃, while the addition of MOS tube there is no loss.

Some people will be concerned that the use of an additional MOS will not increase the cost? In fact, it does not increase the cost, because the low-voltage MOS is very cheap, but also reduces the operating temperature of the power supply as a whole, can improve the life of the power supply, the overall calculation is actually more cost-effective.

►Scene application diagram

Scene application diagram