Figure 35 : P.C. Board and Component Layout of the Circuit of fig. 34 (1:1 scale)

SELECTION OF COMPONENT VALUES (see fig. 34)

Component

Recommended

Value

Purpose

Allowed Rage

Notes

Min.

Max.

R1

R2

–

100 k

Ω

Set Input Voltage

Threshold for Reset.

–

220k

Ω R1/R2

5

− 1

If output voltage is sensed R1 and

R2 may be limited and pin 12

connected to pin 10.

R3

4.3 k

Ω

Sets Switching Frequency

1 k

Ω

100k

Ω

R4

10 k

Ω

Pull-down Resistor

22k

Ω May be omitted and pin 6 grounded

if inhibit not used.

R5

15 k

Ω

Frequency Compensation

10k

Ω

R6

Collector Load For Reset

Output

0.05A

Omitted if reset function not used.

R7

R8

–

4.7 k

Ω

Divider to Set Output

Voltage

–

–

–

1k

Ω

R7/R8 =

-

–

Sets Current Limit Level

7.5k

Ω

the current limit is internally fixed.

C1

10

µF

Stability

2.2

µF

C2

2.2

µF

Sets Reset Delay

–

–

Omitted if reset function not used.

C3

2.2 nF

Sets Switching Frequency

1 nF

3.3nF

C4

2.2

µF

Soft Start

1

µF

–

Also determines average short

circuit current.

C5

33 nF

Frequency Compensation

C6

390 pF

High Frequency

Compensation

–

–

Not required for 5 V operation.

C7, C8

L1

100

µF

300

µH

Output Filter

–

100

µH

–

Q1

Crowbar Protection

The SCR must be able to withstand

the peak discharge current of the

output capacitor and the short

circuit current of the device.

D1

Recirculation Diode

L296 - L296P

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