IR IRS2500 80W PFC开关电源解决方案
Many offline applications require power factor correction circuitry in order to minimize transmission line losses and stress on electrical generators and transformers created by high harmonic content and phase shift. Appliances often incorporate switching power supplies (SMPS) which include capacitive filter circuitry followed by a bridge rectifier and bulk capacitor supplying a load.
Without power factor correction circuitry a SMPS draws a high peak current close to the line voltage peak and almost no current over much of the cycle, resulting in a power factor of around 0.5 and a high total harmonic distortion.
Power factor correction circuitry is added which enables the appliance to draw a sinusoidal current from the AC line with negligible phase shift and very low harmonic distortion. This allows optimization of the load seen by the power grid such that power can be supplied without creating additional conductive losses in transmission lines or additional burden on transformers and generators. Costs to electricity providers are therefore reduced, which are hopefully passed on to the consumer.
Although not explicitly specified in standards such as IEC 61000-3-2 relating to power factor and line current harmonics, it is generally a requirement for the total harmonic distortion (THD) of the line input current supplying a PFC pre-regulator to be as low as possible. As is normally the case a tradeoff exists between cost and performance where more expensive high end products rated at higher power typically incorporate active power factor correction circuits, while low cost passive circuits often suffice in cheaper consumer products.
This is a market trend in power supplies used in a variety of appliances as well as electronic lighting ballasts for Fluorescent, high intensity discharge (HID) lamps and LED lighting.
For a product incorporating active power factor correction a THD of less than 20% over a wide input voltage range, normally 100VAC to 305VAC is expected.In many cases THD can be less than 10% over much or all of this voltage range.
The IRS2500 based PFCpre-regulator does not provide galvanic isolation of the output from the line input. Therefore if the system is supplied directly from a non-isolated input, an electrical shock hazard exists.The DC output voltage is highenough to produce a potentially lethal electrical shock!
It is recommended that for laboratory evaluation that the IRS2500PFC board be used with an isolated AC or DC input supply. The IRS2500 series Boost topology is suitable only for front end applications where isolation is either not necessary or provided elsewhere in the system.