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The Importance of Power Factor Correction in Off-line Power Supplies
Power Factor Correction (PFC) is utilized to shape the input current of off-line power supplies to maximize the real power available from the mains. Ideally, the input current would be a perfect in-phase replica of the input voltage, reducing the current draw from the mains and thus minimizing losses and costs associated with the distribution and generation of the power. This, along with minimized interference thanks to freedom from harmonics, enables the design of highly efficient power supplies that comply with today’s every-expending regulatory requirements.
onsemi offers PFC Controllers implementing innovative CCFF, VSFF, and FCCrM methods that provide significant light load efficiency improvements. In addition, these methods enable the use of a smaller transformer when compared to the traditional Critical Conduction Mode (CrM) approach. For example in a 100W application with similar performance a CrM implementation requires a ~450 µH transformer whereas applications using ON Semiconductor solutions would require only ~300 µH. The smaller size and improved light load efficiency make them a good fit for products required to meet new industry efficiency standards.
Current Controlled Frequency Fold-back (CCFF)
CCFF reduces frequency when the instantaneous line current is below a present level, where switching losses are dominant. Frequency decay rate is controlled for optimized efficiency.
50% Load (115 V rms)
Valley Synchronized Frequency Fold-back (VSFF)
With VSFF, the frequency is reduced when the control signal is below a preset level by adding a constant dead-time over the sinusoid.
50% Load (115 V rms)
Frequency Clamped Critical Conduction Mode (FCCrM)
FCCrM firmly limits the frequency at a preset level.
50% Load (115 V rms)
A full suite of evaluations boards along with users manuals, schematics, layout files, and BoMs are available to evaluate the efficiency and features of the devices for your application. The graph below demonstrates the dramatically improved light-load efficiency observed with the evaluation boards.
Evaluation Board |
PFC Controller |
Description |
Mode |
NCP1615 |
120W High Efficiency |
CCFF |
|
NCP1611 |
160W Low Profile |
CCFF |
|
NCP1612 |
160W Low Profile |
CCFF |
|
NCP1602 |
160W Low Profile |
VSFF |
|
150W Adapter |
VSFF |
||
NCP1602 |
240W All-in-One |
VSFF |
Device |
Package |
HV Start-up |
pfcOK Pin |
Mode |
PSM |
Average Efficiency |
Light Load THD |
NCP1615 |
16-pin |
Yes |
Yes |
CCFF |
Yes |
Best |
Good |
8-pin |
No |
No |
CCFF |
No |
Best |
Good |
|
10-pin |
Yes |
Yes |
CCFF |
No |
Best |
Good |
|
6-pin |
No |
No |
VSFF |
No |
Good |
Best |
|
16-pin |
Yes |
Yes |
FCCrM |
No |
Good |
Good |
Click on the devices above for RS offer