AN2451 datasheet(37/55 Pages) STMICROELECTRONICS

37 / 55 page

AN2451

Board description

Doc ID 12791 Rev 3

37/55

In the input stage, an EMI filter is implemented (C1-L2 plus C3-L3-C2) for both differential and

common mode noise, in order to fit the requested standard.

The blocking diode D2 and the clamping network (R2-C4) clamp the peak of the leakage

inductance voltage spike, assuring reliable operation of the VIPer12AS-E. D2 must be very

fast recovery and very fast turn-on to avoid additional drain overvoltage. The clamp

capacitor C4 must be low-loss (with polypropylene or polystyrene film dielectric) to reduce

power dissipation and prevent overheating, since it is charged with high peak currents by the

energy stored in the leakage inductance.

A Leading Edge Blanking (LEB) circuit for leakage inductance spikes filtering has also been

implemented (Q1 - C5 - R3). It blanks the spike appearing at the leading edges of the voltage

generated by the self-supply winding, greatly improving short circuit behavior.

The output rectifiers have been selected to take the maximum reverse voltage and the RMS

secondary current into account. A STPS1H100 Power Schottky rectifier has been chosen

for this purpose.

A LC filter has been added on the output (consisting of L4, C9 and C29) in order to filter the

high frequency ripple without increasing the output capacitors size or quality.

The transformer used for this application has three windings, since one of them is needed to

supply the VIPer12AS-E. The primary inductance has been chosen as 2.7 mH and the

reflected voltage has been set to 80 V.

A layer type has been chosen with EF12.6 or E13/7/4 core.

The characteristics are listed in Table 11.

Some significant waveforms are represented in the following figures. Figure 33 and

Figure 34 show typical waveforms in both open-load and full-load conditions.

Table 10.

SMPS specifications

Parameter

Value

Input voltage range, Vin

85-265

Vac

Output voltage, VOUT

12 V

±10%

Peak output current, IOUT(MAX)

500 mA

Table 11.

SMPS transformer specifications

Parameter

Value

Core geometry

SRW12.6ES or E13/7/4

Primary inductance

2.7 mH±10%

Leakage inductance

180

μH max

224 turns – 0.1 mm

NAUX

39 turns – 0.1 mm

NSEC

31 turns – 0.2 mm (TEX-E wire)

Withstanding voltage

4 kVRMS

AN2451 Datasheet(PDF) 37 Page - STMicroelectronics

AN2451 Datasheet(HTML) 37 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 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55

Datasheet Download

Link URL