AN2872 datasheet(13/23 Pages) STMICROELECTRONICS

13 / 23 page

AN2872

Experimental results

Doc ID 15305 Rev 1

13/23

Experimental results

4.1

Load regulation and output voltage ripple

The 12 V output is affected by the load due to the effects described in Chapter 3.1.2 and

3.2. The real load regulation of the 12 V output (linear regulator U2 is not assembled) for

different input voltages is visible in Figure 6.

Figure 6.

12 V output load regulation for different output loads and input voltage levels (linear

regulator U2 not assembled)

The flatness of the load characteristic can be influenced mainly at light load by setting

a fixed load (a resistor instead of Zener diode D2) or assembling a linear regulator to

represent light load. The behavior of the load characteristic can be influenced by the value

of the auxiliary capacitor C8 and total value of resistance of R3 and R4.

The output voltage ripple is very low and presents a good opportunity to use smaller

capacitors with higher ESR and lower capacitance. The data measured with the

demonstration board are shown in Figure 7. It is possible to see the higher 100 Hz ripple at

90 VAC on the input. This ripple can be avoided by increasing the capacitance of the input

capacitors.

10.5

11.5

12.5

13.5

14.5

-20

100

120

140

160

IOUT (mA)

VOUT (V)

500 V AC

400 V AC

230 V AC

120 V AC

90 V AC

AM00362

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