Abstract: The NCP1601 power factor adjustment controller may work in the continuous signal pattern (DCM) and the critical conduction pattern (CRM) under two kind of working patterns. In the article introduced that NCP1601 the structure and the characteristic, narrate its principle of work in detail and give one kind of model application electric circuit.
Key word: Power factor adjustment controller DCM/CRM principle integrated circuit
1 outline
The Anson US Semiconductor Company promotes the NCP1601 power factor adjusts (PFC) the controller to be able to conduct the pattern not continuously (DCM) and the critical conduction pattern (CRM or BCM) under works, it has at the same time two kind of working patterns the merit. Because fixed frequency DCM may limit the highest turn-on frequency, thus limit pollution system environment conduction radiation and EMI noise. But does not decide frequency CRM to be possible to limit pressure-rise MOSFET, the diode and inductor’s maximum current, reduces the cost, enhances electric circuit’s reliability. NCP1601 unifies DCM and the CRM merit and the high secure protection characteristic, suits in the electronic ballast, the AC adapter, TV and the command in and so on low power power source PFC pre-regulator application.
May under DCM and CRM the work be the NCP1601 main innovation spot. NCP1601 other characteristics are as follows:
· can provide the simple voltage pattern feedback under the voltage working pattern;
· starting current (typical value for 17μA) and closure electric current (typical value for 24μA) low;
· The DCM turn-on frequency is programmable;
· may the synchronized pattern work (the OSC foot be possible to receive the exterior digital signal);
· has the protection (OVO) the function, its threshold level is the PFC level output voltage normal value 107%;
· owes the protection through it (UVP) the function to be possible when the output voltage drops to the normal adjustment level below 92%, automatic shut-off;
· has the programmable current protection (OCP);
· the overheated closure (OTSD) the function may when the junction temperature surpasses 140℃ until IC and, when the junction temperature drops to 95℃ below makes the component to resume the work;
· satisfies the IEC1000-3-2 standing operating procedure the input current overtone limit request.
MCP1601 has NCP1601A and the NCP1601B two kind of models, the two’s Vcc undervoltage locking (UVLO) the lag voltage is different. NCP1601A UVLO has the 4.75V lag, but the NCP1601B UVLO lag is 1.5V.
2 basic structures and pin arrangement
NCP1601 uses 8 pin PDIP and 8 pin SO seal (junction temperature scope for - 40℃~ 125℃), pin arrangement as shown in Figure 1.
Various pins’ function is as follows:
Foot 1(FB): The feedback/closes the foot. This foot may receive in proportion to PFC electric circuit output voltage feedback electric current IFH. IFB earth materials for internal reference electric current Iref (typical value is 200μA) when 107%, OVP is activated, on foot Drv actuation output closure; But when IFB<0.08Iref, the component enters the low power loss shutting down pattern.
Figure 2
Foot 2 (Vcontrol): Control end. On this foot the voltage uses in the positive governing input impedance and the electric circuit power factor. This foot exterior capacitor limit voltage Vcontrol band width. In order to obtain the power factor to adjust, control voltage’s band width should be lower than 20Hz. This foot exterior electric capacity Control typical value is 0.1μF.
Foot 3 (Ramp): The connection may use in this foot exterior capacitor Cramp establishing the pitch signal, this capacitor immediate influence PFC electric circuit’s input impedance and biggest power input.
Foot 4 (CS): Electric current sensing foot. This foot may provide uses in OCP and zero electric current examination (ZCD) electric current Is, this Is decided on the pressure-rise inductance electric current and this foot’s offset voltage. When Is>200μA, carries out the OCP, IC actuation output closure; When Is<14μA, carries out the OCP, IC actuation output closure; When Is<14μA, electric circuit examination zero electric current.
Foot 5 (Osc): Vibration/synchronization end. In the oscillation mode, this foot exterior connects capacitor Cosc, may establish DCM the oscillator frequency. In the synchronized pattern, this foot meets the external drive signal. When carries on the DCM operation, actuation output along by synchronization to exterior negative along on. When the switching period ended, if the inductance electric current were not a zero, the output actuation will not allow the breakover to forbid to conduct the pattern (CCM) to work continuously, caused its work at the CRM pattern.
Foot 6 (GND): IC place.
Foot 7 (Drv): Uses in exterior MOSFET the actuation output.
Foot 8 (Vcc): The supply voltage, the operating region is 9~18V. The NCP1601A start threshold is 13.75V, but the NCP1601B start threshold is 10.5V, two kind of component’s closure threshold Voc(off) is 9V.
3 NCP1601 DCM and CRM principle of work
The PFC pressure-rise converter’s inductance electric current breakover way may divide into 3 types, namely continual electric conduction pattern (CCM), not continual electric conduction pattern (DCM2) and critical electricity pattern (CRM or BCM-Boundary Conduction Mode). And CCM is suitable in 300~3000W compares the high efficiency PFC, this electric circuit’s structure is quite complex; But DCM and CRM are suitable for 75~300W low power PFC, its circuit structure is relatively quite simple.
The CCM work besides AC sinusoidal voltage cross zero, in any time, the pressure-rise inductance electric current is not zero. This kind of fixed frequency mean current pattern CCM control plan’s switching period maintains invariable, but the dutyfactor is the change. The NCP1601 internal structure and exterior part connection as shown in Figure 2.
CRM is the turn-on frequency change specially, and in sinusoidal voltage zero crossing time the frequency is highest, is lowest in the sinusoidal voltage peak value’s place turn-on frequency. Once in the pressure-rise inductor’s electric current eliminates is zero, the new switching period then starts, but does not have the electric current dead area. The CRM shortcoming has attached in the sine wave zero crossing the turn-on frequency is quite high, EMI is quite serious. This causes is may limit the maximum current stress and may use light-sized and the inexpensive MOSFET pressure-rise diode and the pressure-rise inductor.
The DCM characteristic is the turn-on frequency is fixed, and between two switching period inductance electric current existence dead area. Its principal advantage is can limit the biggest turn-on frequency, front end causes the EMI filter design simplification. But, under the similar average input current, DCM needs the high peak value inductance electric current, thus needs to select the enlargement the power component.
Innovation NCP1601B the PFC controller may works in CRM and under the DCM two kind of patterns, and will not cause the power factor to degenerate, its current waveform as shown in Figure 3.
Figure 4
4 model application electric circuit and test data
Pressure-rise pre-regulator electric circuit as shown in Figure 4 based on NCP1601B 130W PFC. This PFC the pressure-rise converter’s AC input voltage may from 90Vac to 260Vac. Under the 230Vac input voltage, its output voltage Vout=391V, the power factor (PF) is 0.973, joint current harmonic distortion THD=9%, efficiency η=96.4%. When inputs Vin=90~180Vac, PF≥0.99, THD≤6%, may achieve the ultra low THD level. Table 1 arranges in order is under the 90~250Vac input voltage test result.
Table 1 test data
| Vin(Vca) | Pin(W) | Vout(V) | Iout(mA) | PF | THD(%) | Eta (%) |
| 90 | 143.4 | 327 | 400 | 0.998 | 4 | 91.2 |
| 110 | 161.1 | 373 | 400 | 0.997 | 6 | 92.6 |
| 130 | 160.5 | 378 | 400 | 0.996 | 6 | 94.2 |
| 150 | 160.9 | 382 | 400 | 0.993 | 7 | 95.0 |
| 180 | 161.6 | 386 | 400 | 0.990 | 6 | 95.5 |
| 190 | 161.7 | 387 | 400 | 0.986 | 8 | 95.7 |
| 210 | 162.0 | 389 | 400 | 0.980 | 8 | 96.0 |
| 230 | 162.2 | 391 | 400 | 0.973 | 9 | 96.4 |
| 250 | 162.8 | 393 | 400 | 0.929 | 16 | 96.6 |
5 concluding remark
NCP1601 may works under CRM and DCM and has two kind of pattern merits. It uses the DCM control plan nearby the AC line input voltage zero crossing, because this time has carried on the limit to the turn-on frequency, therefore moves solves the EMI problem. But nearby the sine wave peak value, to avoid the big peak value inductance electric current, the electric circuit uses the CRM control method, like this may use the small inductor, MOSFET and the pressure-rise diode, thus not only reduced the cost, moreover enhanced system’s reliability. NCP1601 will work under DCM and CRM will not have the power factor to drop, will thus be one kind of innovation control plan.
