Abstract: Introduced one kind of novel power factor adjusts (PFC) the chip. Its main feature enhanced time the underloading power factor and improved electric circuit’s dynamic property. The experiment indicated: This kind of novel PFC control chip has realized these functions.
Key word: Power factor adjustment; Dynamic property; Electric current compensation
Introduction
Along with power quality standard’s carrying out, the power factor adjusts (PFC) the technology to become in the electric power electron domain the research hot spot, the PFC converter more and more has applied in the switching power supply, the frequency conversion velometer and in the fluorescent lamp exchange electron ballast. In the last few years, along with the PFC technology’s development, the PFC control chip also had the very big development. According to electric circuit’s working pattern, the PFC control chip may divide into 3 kinds:
1) makes and breaks control chip;
2) electric current critical continual control chip;
3) electric current continual control chip.
This article introduced one kind of novel electric current continual control chip NCP1650, it improved the PFC electric circuit’s dynamic property, and the strict control PFC electric circuit peak power output, simultaneously it also enhanced under the underloading power factor. This article has manufactured a 100W PFC circuitry prototype by this kind of novel control chip, has carried on the analysis to the chip, finally has given the experiment profile.
1 NCP1650 function introduction
NCP1650 uses 16 foot SOP seal, pin disposition as shown in Figure 1, Table 1 has given the pin function. It is one kind of mean current pattern control chip, it may apply in makes and breaks with in the electric current continual pattern PFC electric circuit. Because its interior has used the precise part, electric circuit’s output and the electric current may limit precisely, therefore regarding the same power rank’s PFC electric circuit, may enable in electric circuit’s power component’s rank to achieve is smallest.
Table 1 NCP pin function table
| Pin | Name | Function |
| 1 | Vcc | Power source power supply |
| 2 | Vref | Voltage reference |
| 3 | ACCOMPAC | Compensation |
| 4 | ACREFAC | Datum |
| 5 | ACINPUTAC | Input |
| 6 | FB/SD | Feedback/separation |
| 7 | LOOPCOMP | Compensated loop |
| 8 | PCOMP | Power compensated loop |
| 9 | Pmax | Maximum work rate limit |
| 10 | Iavg | Electric current proportion |
| 11 | Iavg-fltr | Filter electric capacity |
| 12 | Is- | Negative sampling current input |
| 13 | RAMPCOMP | Slope compensation |
| 14 | CT | Fixed time electric capacity |
| 15 | GND | Earth |
| 16 | OUTPUT | Actuation output |
NCP1650 has the soft start, the output overvoltage protection, the instantaneous current limit, the input low pressure protection, functions and so on output maximum work rate limit.
1.1 electric current compensatory function
Regarding the output scope wide PFC electric circuit, receives the varying degree in the underloading time power factor the limit, but has the strict request in the industrial field to electric circuit’s power factor, therefore everybody pays attention to this question more and more. NCP1650 may solve this problem.
NCP1650 will act according to the actual input current the size, for a sampling electric current signal corresponding compensation, like this may enhance when the underloading the power factor. Figure 2 has given the electric current compensator schematic diagram. In the chip electric current sampling compensator is one has the differential input wide scope band width amplifier. It inputs the level by a differential, a high-frequency current mirror image and a low frequency mirror image constitution. And the low-frequency current mirror image has 3 out-ports, gives the AC error amplifier separately, the power multiplier and the electric current compensator.
Figure 4
The NCP1650 base pin 12 are negative electric current sampled signal inputs. Therefore this kind of control chip’s electric current sampling compensator’s input voltage signal is a negative voltage signal. And the base pin 12 also (resistance number for 1kΩ) dock with the internal electric current diverter. When chip work, in the electric current diverter’s voltage by the transformation is electric current (i1), this electric current will actuate the high-frequency current mirror image. This electric current mirror image’s output (i1) becomes the proportion with the PFC electric circuit’s in inductance instantaneous electric current, if the type (1) shows.
i1=Vis-/1kΩ (1)
At the same time, this high-frequency current mirror image provides a voltage signal through a 15kΩ resistance to the buffer amplifier; Moreover, this high-frequency current mirror image’s PWM output provides a signal directly to the PWM generator, like this may control switching valve’s driving signal. When PFC electric circuit work underloading, 12 gives a chip corresponding voltage signal through the base pin, it promptly will actuate the high-frequency current mirror image, will thus carry on the compensation to the sampling voltage signal, has increased this sampled signal, like this may track the reference signal well, will enhance under the underloading the PFC electric circuit’s power factor.
1.2 dynamic property adjustment functions
Regarding the PFC electric circuit, the dynamic property is the question which very difficult to solve. When input voltage or output change can cause the output voltage very big change, like this will reduce electric circuit’s life greatly, will give the following DC/DC electric circuit to bring the very tremendous pressure.
In Figure 3 has given the solution dynamic response schematic diagram. When the output voltage changes is high, the voltage feedback signal also correspondingly increases, when achieves some setting value will give a PWM generator signal, will control the driving signal. Reduces regarding the output voltage is also same. Because the NCP1650 interior has established the voltage feedback datum maximum value and the minimum value, therefore the feedback signal can only change in this scope, like this works as the input voltage or the output change, the output voltage change’s scope will not be big, also improved the dynamic property.
2 experimental results
The PFC main circuit chart see also Figure 4, its main parameter is as follows: Input voltage AC90~265V; Frequency 47~63Hz; The output voltage is DC400V; Output maximum work rate 100W; The biggest switch operating frequency is fmax=100kHz.
The experimental result had proven NCP1650 has solved when well the underloading the PFC electric circuit’s power factor, simultaneously the dynamic property was also improved. Figure 5 has given input voltage 115V, time the output 20W input current profile; Figure 6 has given input voltage 115V, time the output 100W input current profile; Figure 7 has given input voltage 230V, time the output 20W input current profile;
Figure 8 has given input voltage 230V, time the output 100W input current profile; Figure 9 and Figure 10 has given the output separately from the underloading to the full load and from the full load to the underloading time output voltage.
3 conclusions
Take NCP1650 as the core design PFC electric circuit, enhanced time the underloading power factor, like this when underloading reduced to electrical network’s pollution; Simultaneously it improved in the output change time dynamic property. Therefore, it may apply is being quite high to the dynamic property request and the output scope quite wide situation.
