1. What is the basic operating principle of the power supply?
Answer: the higher AC voltage (AC) input will be converted into the lower DC voltage (DC) required by PC operation through working high-frequency switching skills.
2. What is the operation flow of power supply?
A: when the mains power enters the power supply, first remove the high-frequency clutter and disturbing signals through choke coil and capacitor filtering, and then obtain high-voltage DC power through rectification and filtering. Then, the DC is converted into high-frequency pulsating DC through the switching circuit, and then sent to the high-frequency switching transformer for voltage reduction. Then filter out the high-frequency AC part, so as to output relatively pure low-voltage DC for computer use.
3. What is the primary effect of EMI circuit?
A: the effect of EMI circuit is to filter out all kinds of disturbing signals from the power grid and prevent the high-frequency disturbing power grid composed of power switch circuit. EMI is an important part of CCC certification.
4. What is a high voltage rectifier filter circuit?
A: the high-voltage rectifier filter circuit is composed of a rectifier bridge and two high-voltage electrolytic capacitors. The effect is to convert 220V AC mains power into 300V DC power.
5. What are the general types of high voltage electrolytic capacitors?
A: there are generally two high-voltage electrolytic capacitors we generally call large capacitors. Because of their high withstand voltage value, they are very large. According to the capacity, high-voltage electrolytic capacitors generally have 330uf, 470uf, 680uF, 820uf, 1000uf, 1200uf, etc. the withstand voltage value is generally 200V and the temperature resistance is 85 degrees.
6. What is the principle of switching circuit?
A: the principle of the switching circuit is that an oscillation circuit is composed of a switching tube and a PWM (pulse width modulation) control chip to generate high-frequency pulses. The high-voltage DC generated by the high-voltage rectifier filter circuit is transformed into high-frequency pulse DC, which is sent to the main transformer for voltage reduction and becomes low-frequency pulse DC.
7. What is the principle of low voltage rectifier filter circuit?
A: low frequency pulsed DC is rectified by diode and then filtered by electrolytic capacitor. In this way, the output is a stable current with different voltages. Because the voltage here is now very low, although the capacitance capacity is large, generally 1000uf, 2200uf, etc., the capacitance volume is very small because it does not require a high withstand voltage value.
8. What effect does the auxiliary circuit have?
Answer: 300V DC becomes pulse current through the auxiliary power switch tube. Two sets of AC voltage are output through the auxiliary power transformer. One way is stabilized by rectifier and three terminal voltage regulator, and + 5VSB is output and added to the main board as standby voltage; The other way is rectified and filtered, and the output assists the 20V power supply to supply PWM and other chip operations. With the auxiliary circuit, the computer can complete the software startup and shutdown.
9. What is PFC?
Answer: PFC (power factor correction), namely "power factor correction", is mainly used to characterize the application power of electronic products to electric energy. The higher the power factor, the higher the utilization power of electric energy. It is necessary to add PFC circuit for computer power supply certified by CCC. The azimuth is after the second layer filtering and before the full bridge rectifier circuit. There are two types of PFC: passive PFC (also known as passive PFC) and active PFC (also known as automatic PFC).
10. What are the characteristics of automatic PFC?
A: the input voltage of automatic PFC can range from 90V to 270V; The power factor is higher than 0.99, and has the benefits of low loss and high reliability; It can be used as auxiliary power supply instead of auxiliary power transformer; The output DC voltage ripple is very small, so the automatic PFC power supply does not need to select a large capacity filter capacitor.
11. What are the characteristics of passive PFC?
A: passive PFC generally adopts inductance compensation method to improve the power factor by reducing the phase difference between the fundamental current and voltage of AC input. The power factor of passive PFC is not very high, it can only reach 0.7 ~ 0.8, and the calorific value is relatively large.
12. What is the software startup and shutdown function of the power supply completed through?
A: the software startup and shutdown function of the power supply is completed through pw-ok circuit. During standby, pw-ok outputs a zero level power self-test signal to the host, and the host stops operation and is in standby state. After controlled startup, pw-ok will delay for hundreds of milliseconds after the output voltage of switching power supply is stable, jump from level 0 to + 5V, and output high-level signal to the host. This signal is equivalent to at power supply
PG signal. The host machine starts the system after detecting the signal of no shortage of pw-ok power supply. In case of mains power failure or shutdown during the operation of the host, the pw-ok output signal disappears hundreds of milliseconds ahead of the ATX switching power supply + 5V output voltage, notifying the host trigger system to automatically close before the power supply is cut off, so as to prevent the hard disk head from scratching the hard disk in case of sudden power failure.
13. What is conduction annoyance?
A: conducted annoyance is a concept used to measure the electronic annoyance signal sent by electronic products to the whole power grid in the working process. All electronic products will announce annoyance signals to the power grid when using electricity. If the annoyance signal is too large, it will affect the power quality of the whole power grid and annoy the normal work of other electrical appliances. Therefore, most countries have a rigid regulation on the transmission annoyance target of electronic products to stop the production and sale of products with excessive transmission annoyance.
14. What are the more important items in power supply inspection?
A: there are mainly cross load, surge, input voltage, ripple noise, output short circuit, over power, conversion power, power factor, response time, timing, noise, conducted radiation, leakage current, high and low temperature inspection, etc.
15. What is surge current?
A: surge current refers to the peak current flowing into the power supply equipment at the moment of power connection. Because the input filter capacitor charges rapidly, the peak current is much greater than the steady-state input current. The power supply shall limit the surge level that AC switch, rectifier bridge, fuse and EMI filter equipment can withstand. Repeat the switching loop. The AC input voltage should not damage the power supply or cause the fuse to blow out.
16. What is conversion power?
A: because the power supply is in operation, some electric energy is converted into heat and lost. Therefore, it is necessary to minimize the heat loss of the power supply. Conversion power is the percentage of output power divided by input power. Version 1.3 power supply requires a small conversion power of 70% under full load. Version 2.0 has increased the recommended conversion power to 80%.
17. What is the difference between power factor and conversion power?
A: Although power factor and conversion power refer to the utilization rate of power supply, there are great differences. In short, the loss caused by power factor is borne by the power department, while the loss of converted power is borne by the user. The power factor of national power grid can be seen.
18. What is rated power?
A: the rated power refers to the large load of the power supply under stable and continuous operation. The rated power represents the real load ability of a power supply. For example, the rated power of a power supply is 300W, which means that when the operation is continued 24 hours a day and 365 days a year, the sum of all loads cannot exceed 300W. But in fact, the power supply has certain redundancy. For example, the power supply with rated power of 300W can operate safely and normally at 310W, but try not to use it beyond the rated power, otherwise it may cause the power supply or other computer components to be burned due to overcurrent.
19. What is overpower maintenance?
A: in addition to the rated power, there is another data called "overload maintenance" and "OPP" in English. Overload maintenance means that the load of the power supply continues to rise. When it reaches a certain point, the power supply will automatically cut off, so as to avoid overcurrent damaging the power supply or other parts of the computer. The OPP value is generally about 1.3 times of the rated power. Some manufacturers set the OPP too high, which is actually unsafe. There will be an interval between the rated power and OPP, for example, the rated power of the new cold drill is 300W and the OPP is 370W, so the area between 300-370w is a "blind area". Suppose you stay in this interval for a long time (generally
Continue for tens of seconds), which is likely to cause the power supply or other parts of the computer to burn.
20. What is the principle of temperature control power supply?
A: the temperature control circuit is mainly completed by thermistor. When the power supply starts working, the power supply voltage of the electric fan is 7V. When the temperature in the power supply increases, the thermistor resistance decreases, the voltage gradually increases, and the speed of the electric fan also increases. In this way, the temperature in the casing can be maintained at a low level. In the case of light load, it can complete the mute effect. When the load is large, it can ensure heat dissipation.
