AN3276 datasheet(9/22 Pages) STMICROELECTRONICS

9 / 22 page

AN3276

The new ST solution - BC2: energy recovery circuit

Doc ID 17975 Rev 1

9/22

2.2.1

Phase before t0

Figure 8.

Equivalent circuit before t0

Before t0, the BC

2 circuit has the same behavior as the conventional boost converter. The

boost diode DB conducts to send the main inductor energy through the output bulk

capacitor.

2.2.2

Phase t0 to t1

Figure 9.

Equivalent circuit t0 to t1

At t0, the power MOSFET turns on and the current in DB is equal to I0. At t0+, the current soft

switching occurs, that is to say, the voltage across the power MOSFET decreases to 0 volt

under a zero current and no switching losses appear. After t0, the current flowing in L

increases linearly until it reaches the input current I0 added with the recovery diode IRM,

whereas the current flowing in DB decreases linearly down to -IRM.

Figure 7 shows the behavior of these currents taking account of the m2 transformer ratio.

The simplified dI/dt expression in transistor TR and the boost diode DB can be estimated

using,

and

At t0 +, the COSS capacitance of the power MOSFET is discharged in its RDS(on). Unlike

standard PFC circuits, the voltage applied across the drain is lower because the reflected

Coss

Vmains

NS2

NS1

V OUT

Coss

mains

NS2

NS1

V OUT

NS2

out

−

≈

(

mains

out

−

AN3276 数据表(PDF) 9 Page - STMicroelectronics

AN3276 数据表(HTML) 9 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

数据表下载