DocID10353 Rev 2

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AN1934

Circuit description

32

1.2

Non-isolated flyback + 5 V/250 mA, + 15 V/200 mA (variant 2)

1.2.1

Circuit operation (variant 2)

The total schematic of the power supply can be seen in Figure 32. Compared to variant 1,

this variant is different, specially the feedback loop. Instead of 5 V output, the 15 V output is

regulated by a simple circuit consisting of a Zener diode D8 and a resistor R11. Since 5 V

output is not well-stabilized by the feedback loop, a linear regulator U3 is used. The linear

regulator requires some input-to-output voltage difference to assure a minimum dropout

voltage. For this reason the number of turns of the secondary windings is slightly different

compared to variant 1.

Figure 33. Schematic diagram of non-isolated flyback converter (variant 2)

1.3

Non-isolated flyback +15 V/200 mA, +5 V/60 mA (variant 3)

Table 5. Operating conditions (variant 2)

Parameter

Value

Input voltage range

90-264 VAC

Input voltage frequency range

50/60 Hz

Main output (regulated)

15V / 200 mA

Second output

5V / 250 mA

Total maximum output power

4.25 W

Table 6. Operating conditions (variant 3)

Parameter

Value

Input voltage range

90 to 264 VAC

Input voltage frequency range

50/60 Hz

Main output (regulated)

15V/200 mA

Second output

5 V/20 mA or 60 mA

Total maximum output power

4.25 W