Power Factor Correction Introduction

PFC English called “Power Factor Correction”, meaning “power factor, power factor correction”refers to the effective power and total power consumption (apparent power) between, that is the effective power divided by the total power consumption (apparent power ratio). Basically the power factor can be measured by the degree of effective utilization of power when the power factor, the greater the value of, on behalf of its power utilization rate is high. A computer switching power supply, power factor correction is a capacitor input type circuit, the phase difference between thecurrent and voltage will cause the switching power loss, at this time we need to improve the power factor of PFC circuit. PFC currently has two kinds, one kind of passive PFC (also known as passiveand active PFC (PFC) also known as active PFC). 1 passive PFC passive PFC are generally classified “inductance compensation type” and “the valley fill circuit (Valley Fill Circuit)” “inductance compensation method” is to make the AC input voltage phase difference between the fundamental current and reduced to improve the power factor, passive PFC includes mute type is PFC and nonsilent passive PFC. Power factor can only passive PFC reach 0.7 ~ 0.8, it is generally in the vicinity of the high voltage filter capacitor. “The valley fill circuit” is a new type of passive power factor correction circuit, which is characterized by a rectifying bridge behind the valley fill circuit tosubstantially increase rectifier conduction angle, by fill valley point, make the input current from thepeak pulse becomes close to sinusoidal waveform, the power factor is increased to 0.9 right and left, obviously reduce the total harmonic distortion. Compared with the traditional inductive passive power factor correction circuit, the utility model has the advantages of simple circuit, power factor compensation effect is remarkable, and does not require the use of large volume weight heavyinductor in the input circuit. 2 active PFC and active PFC by the inductor and capacitor and electronic components, small volume, through a special IC to adjust the current waveform, thephase difference between current and voltage compensation. Power factor more active PFC can achieve a higher — typically up to 98%, but the cost is relatively high. In addition, active PFC can also be used as an auxiliary power supply, therefore the use of the active PFC circuit, often do not require standby transformer, and active PFC DC output voltage ripple is small, the power supplyneed not filter capacitor using great capacity. 1) PFC main circuit schematic diagram
clip_image001
Figure PFC main circuit schematic as lossless absorption principle diagram of the PFC main circuitshown in figure. Figure B1 bridge rectifier, L1 PFC boost inductor, D1 as a blocking diode, S1 as the switch tube, C1, C2, D2, D3 and D4, L2 composed of lossless absorption network, C3 is the output filter capacitor. Analysis of the specific process is as follows: when S1 is disconnectedbefore, in C2 through D5 and L2 energy transfer to the C1, the C2 voltage is below 0. The polarity of the C1 as shown in figure 1. When the S1 is off, C2 is initially zero voltage, current in L1 to charge C2 through D3, until D1 conduction so far. And D4, D5 clamp to the output voltage by C2potential. At the same time C1 through D2 to load discharge, can inhibit the S1 drain voltage rise time, so as to fully guarantee the S1 turn off at zero voltage condition. When the S1 is closed, the left end of the C1 through the S1 grounding, a charge capacitor C2 through the D5, L2 to C1.When the switch is off again, repeat the above process. 2) three-phase PFC matrix converter circuit topology and principle of Figure 1 shows the three-phase PFC matrix converter topology. Switch of the matrix converter is composed of two back-to-back IGBT. The turn-on and cut-off current switchof this component can be to the positive and negative direction of two voltage and two positive and negative directions, so the switch has the function of [1] four quadrant. On the diagonal of every H bridge two bidirectional switches off can be complementary, such as volt second area is bipolar voltage pulse is transferred to the secondary output of the high-frequency transformer. Each switchwidth by adjusting plate through the simulation of AC voltage uphase, output voltage feedforwardfeedback uout and primary current sampling value IPRI as input, and then obtained by the PFC chip UC3854BN simulation arithmetic of adjusting plate. Comprehensive DSP CPLD simulation plate,adjusting plate input, sends 6 pulse width modulation wave driving 6 bidirectional switches VQ1 toVQ6.

Over-load protection of switching power supply

Abstract: in the output short-circuit or overload protection to the power supply or load, which isreferred to as the overcurrent protection, over-current protection. This paper introduces severaltypes of over-current protection, e.g., font, constant current, constant power type, and compared.
Power supply as the power supply equipment of all electronic products, in addition to meet theperformance requirements of power supply products, protection measures of its own is also very important, such as over-voltage, over-current, over temperature protection. Once the electronicproduct failures, such as open circuit electronic product input side short circuit or the output side,the power must close its output voltage, in order to protect the power of MOSFET and output sideequipment not to be burnt, or it may cause further damage to electronic products, and even causethe operator of electric shock and fire phenomena, therefore, switch the power supply over-current protection function must be perfect.
Overcurrent protection mode of 1 commonly used in switching power supply
Over current protection in various forms, as shown in Figure 1, can be divided into the rated currentdroop type, namely, font; constant current; constant power type, the majority of current. Currentsetting value is typically 110% to 130% of rated current. Usually it will be automatically renewed type.
In Figure 1 the current droop type, the representation of the constant current, constant power typerepresentation.

Pic1 over-current protection performance

dc to dc convertor

DC / DC converter is a DC electric transform a voltage into another or several voltage DC power equipment.
DC / DC converter with parallel and non parallel two.
1, parallel DC DC converter with high frequency pulse width modulation edge resonant technology advanced, greatly enhanced the efficiency. With high voltage stabilizing accuracy, strong anti-interference ability, low output noise, fast dynamic response, wide range of working temperature etc..
2, non Paralleled DC / DC converter adopts imported DC-DC module, has the advantages of high voltage stabilizing accuracy, low output noise, strong anti-jamming ability, and has the advantages of small size, light weight.
DC converter is generally one-way, in some places will also use bidirectional DC / DC converter to work.
The Chinese liquid crystal display panel of the power module working state, also can visually display the data such as voltage and current; various protection functions module module built-in charging, complete; float switch circuit, and a choice of manual or automatic control. The monitoring interface can be operating state monitoring module, can switch machine control, are floating control, and is equipped with automatic current sharing bus interface, charging bus interface. Intelligent machines equipped with RS485 interface, can be matched with the monitoring module, PC machine, PLD and other intelligent devices connected, complete remote monitoring, realize the power supply system of the four remote function.