How to distinguish the quality of switching power supply?

How to judge the quality of switching power supply?

I have experience in switching power supply maintenance, give you some suggestions, I hope it will help you: the two aspects of switching power supply are most concerned about: 1, power; 2. Efficiency.

For power, you are the purchasing department, considering the cost, so choose the right one for your production needs, followed by the efficiency problem, in fact, the calculation of efficiency is very simple, let the switching power supply work, measure its input and output power (p=ui), let the percentage of output and input division is efficiency. According to the above points, it should be possible to roughly determine the switching power supply you want to purchase.

1. Measure the resistance between the poles. Place the multimeter in the R 100 or R 1K position and test it with six different connections for the red and black watch pens. Among them, the forward resistance values of the transmitting junction and the collector junction are relatively low, and the resistance values measured by the other four connection methods are very high, ranging from several hundred thousand ohms to infinity.

However, regardless of whether it is low or high resistance, the interpolar resistance of silicon transistors is much greater than that of germanium triodes.

2. The value of the penetration current of the transistor ICO is approximately equal to the product of the multiple of the tube and the reverse current ICBO of the collector junction. ICBO grows rapidly with the increase of ambient temperature, and the increase of ICBO will inevitably lead to the increase of ICEO. The increase of ICEO will directly affect the stability of the pipe, so the small ICEO tube should be used as much as possible.

The most commonly used IC model for power PWM control circuits is UC3842 (or KA3842). The following is a brief introduction to the judgment method of UC3842:

After replacing the damaged components on the periphery, do not install the switch tube first, power up and measure the voltage of the 7 pins of UC3842, if the voltage fluctuates between 10-17V, and the rest of the pins also have fluctuating voltages, it means that the circuit has vibrated and UC3842 is basically normal; If the voltage of pin 7 is low, and the rest of the pins have no voltage or do not fluctuate, the UC3842 is damaged.

In UC3842 between the feet of the addition of about +17V DC voltage, if the measurement of 8 pins has a voltage of +5V and the feet also have different voltages, then UC3842 is basically normal, the working current is small, and it is not easy to damage itself The most common reason for its damage is that after the short circuit of the power switch tube, the high voltage is added from the G pole to its 6 pins and it burns out and some models omit the protection diode of G pole grounding, then when the power switch tube is damaged, the current limiting resistor of UC3842 and G pole external connection must be broken At this time, it can be replaced directly.

It should be noted that the source (S pole) of the power switch tube is usually connected with a small resistance value and a high-power resistance as an overcurrent protection detection resistor The resistance value of this resistance is generally between, and if it is greater than this value, it will not be able to carry the load (that is, the subpolar voltage is low).

Nowadays, the use of MOS power tubes in low-power switching power supplies has become increasingly popular. Taking the TO-220 encapsulated MOS power tube as an example, the method of estimating the quality of the tube with an ordinary multimeter is introduced. When the pins are not clear, the source and drain are determined according to the characteristics of the damping diode in the tube package.

Then dial the multimeter to the RX10K gear, connect the black watch pen to the drain D, connect the red watch pen to the source pole S, and use a metal tweezer to short-circuit the S, G pole. Note that the tweezers should first contact the source S, and then contact the G pole, and when the tweezers are released, the G pole should be released first, and then the S pole should be released, and the resistance value indication should be about 10m ohms. Then use tweezers to short-circuit the G pole and the D pole, and the resistance value indication is less than 50K ohm, and the gauge needle can be stable and unchanged, indicating that the tube is basically normal.

You directly use the tired knife to try to boot on the motherboard, to see if you can light up the computer, if you can, but you use the switch to turn on, that is, the switch is broken.

Measure its resistance with a multimeter.

1. Select the brand of the switch. Try to buy high-quality sockets that have passed the test of time and the market, for example, the brand of CHINT switch socket that we often use is the selection of raw materials through research and development, and this product has undergone a perfect and strict quality assurance system.

2. Look at the material of the switch and socket. If you choose a good switch and socket panel, the materials used are flame retardant, insulation, impact resistance, etc., it can be said that it is subject to national standards in terms of technical indicators.

3. There are many materials for the shell of the switch socket, for example, the PC imported from Bayer in Germany is relatively better, flame retardant and high temperature resistant. Then you can use a lighter to test whether it can be flame retardant and high temperature resistant when you choose.

4. Look at the socket conductor material. Good socket brands are made of tin phosphor bronze. Tin phosphor bronze sheet has good elasticity, anti-fatigue and is not easy to oxidize.

High-precision tin phosphor bronze has good electrical conductivity and elasticity, so that the material can effectively ensure the passage of large currents. The integrally molded phosphor bronze has higher precision and better quality.

5. See if the switch and socket have safety guarantees. The socket is designed with a safety door, if there is a belt, this design can effectively prevent the baby at home from accidentally plugging in the electric shock, and it is also a great improvement in the safety of the socket. It also prevents pests and dust from entering.

You can find a key that is just wide enough to insert and insert it into a single hole, if you can't easily break through the barrier of the protective door, then it means that you can really protect the safety of your family.

6. Look at the reasonable spacing of the socket hole distance. The hole spacing of 15mm is already a reasonable spacing for general household five-hole sockets, and if 19mm can easily cope with various special plugs, the practicality will be relatively high.

Top 10 switch brand rankings.

First place: Legrand, Legrand has won wide acclaim from customers at home and abroad by virtue of its excellent products and high-quality service, and its brand awareness, reputation and market share are in the forefront of the domestic high-end switch and socket industry.

Second place: Simon, Simon's exquisite products and high-quality service have also won the favor of a large number of well-known domestic real estate developers and key projects, while Simon has continuously improved the process, selected new materials, and quickly occupied a place in the market.

Third place: Futina Foton Electric, as a 20-year-old brand, its first Foton point switch sales in 2016 are still hot, generally recognized by the majority of users, launched a variety of suitable for a variety of home decoration styles of Foton point switch, especially Foton solid wood point switch series by villas, hotels and other high-end places favored. I hope to continue to sit firmly in the future, continue to occupy the market advantage, and win glory for domestic brands.

Fourth place: Siemens, the cost performance of Siemens switches is obvious to consumers, and its products have been deeply loved by consumers, and the brand image of high quality and good quality is deeply rooted in the hearts of the people.

No. 5: ABB, headquartered in Zurich, Switzerland, is a global leader in power and automation technology for industrial and power industry solutions. The quality of ABB switches is reliable, and the appearance is simple and fashionable, safe and reliable, but the ** is relatively high.

Sixth place: Schneider, this brand is mainly due to the long-term accumulation of popularity of low-voltage professional products, and has also benefited a lot in the field of wall switches.

Seventh place: Philips switch, Philips switch is not too prominent switch brand, but its switch quality is still worthy of the trust of consumers and close to the people** is also one of the reasons for the list.

Eighth place: opple opple lighting, the old brand is trustworthy, the product is finely made, but the design of the product still lacks the shortcomings of the fashionable taste, and has recently won a lot of consumer eyeballs and choices in the transformation of smart home and smart lighting.

No. 9: Belkin, founded in 1983 in the United States, is one of the world's fastest-growing companies, the world's leading provider of connectivity solutions, and one of the fastest-growing private companies in the United States.

No. 10: Breakthrough Electric, Breakthrough Electric specially for modern homes and offices to develop and produce wiring board socket products, the development and production of lightning protection wiring board socket and other power socket products have been highly recognized and praised by civil, scientific research, office, finance, communications, medical and other fields.