AN938 datasheet(27/33 Pages) STMICROELECTRONICS

Part #	AN938

Description	The L4973 family is a 3.5 A monolithic DC-DC converter

PDF	33 Pages

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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27 / 33 page

AN938

Applications

Doc ID 5410 Rev 10

27/33

Applications

4.1

Mains transformer power supply with output adjustable from

0 V to 24 V

Figure 37 shows a power supply including mains transformer working at 50 Hz 220Vac or 60

Hz 110Vac, bridge rectifier and filtering capacitor. The output voltage is adjustable from 0 to

24 V.

Figure 37.

Typical adjustable 0-24 V power supply

The formula to evaluate the output voltage is:

Equation 21

Figure 38 shows the formula plot in which it is possible to program the output voltage from 0

V to 24 V using a 10 k

Ω potentiometer as R4. R5 is fixed at 4.3 kΩ and R3 is 47 kΩ.

Output capacitors have to be chosen with low ESR to reduce the output ripple voltage and

load transients.

AM03519v1

L4973V3.3

3 x

C12

47K

10K

4,5,6

13,14,15

7,8

2,3

R5 4.3K

220VAC

28VAC

3.336

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⎝⎠

⎛⎞

5.1

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⋅

–

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