May 10, 2010 - 200W PFC of Only 1mm Thickness

Soft switching employs parasitic inductances and capacitors to reduce switching losses. Ideally, you get a huge benefit with intelligent control without the need to add components. Why not using the internal output capacity of a power MOSFET for elimination of switching losses? Figure 1 shows such a PFC rectifier topology with zero voltage switching.

 
Fig. 1: Topology of interleaved bridgeless PFC rectifier employing zero voltage switching for a 200W converter with 1mm thickness. 

Unfortunately the internal capacitors of the MOSFETs shown explicitly in Fig. 1 are highly non-linear (Fig. 2) which makes analysis difficult. To make the topology work it is essential to fully consider the non-linearity in the time domain analysis. Figure 3 shows what happens if the non-linear capacitor would be replaced by an equivalent constant capacitor. Simplifying with a constant capacitor does not work in this case!

 
Fig. 2: Voltage-dependency of a non-linear capacitor as modeled in GeckoCIRCUITS. The characteristic shows the internal output capacity Coss(UDC) of the power MOSFET IPB60R385CP from Infineon. 

 
Fig. 3: (a) Transient simulation of the switching behaviour employing the nonlinear voltage-dependent MOSFET output capacitor Coss = Coss(u) from Fig. 2. (b) Employing the equivalent constant time-related MOSFET output capacitor Coss = 340pF from the datasheet.  

Simulation with non-linear capacitors (and inductors) is very easy with GeckoCIRCUITS. Just open the parameter dialog of a capacitor, activate 'Non Linear Behavior', open the dialog, and set voltage - capacitor values (see online example).

We publish a paper on this issue including the example of the zero voltage switching PFC rectifier with experimental verification and all details at the IPEC 2010 (ECCE-Asia) in Sapporo, Japan, in June.

The rectifier shown in Fig. 1 is employed to realize a 200W PFC of a total thickness of only 1mm ("Power Sheet"). The topology has beneficial properties concerning EMI noise (EMI filter not shown in Fig. 1). Switching frequency is between 400kHz and 600kHz, and efficiency is close to 97%. Send an email to request more information!

 
Fig. 4: (a) Simulation with GeckoCIRCUITS employing non-linear capacitor characteristic. (b) Experimental verification.