CA3140, CA3140A

FN957 Rev.10.00

Page 15 of 24

Jul 11, 2005

A small heat sink VERSAWATT transistor is used as the series

pass element in the fold back current system, Figure 17, since

dissipation levels will only approach 10W. In this system, the

D2201 diode is used for current sampling. Foldback is

provided by the 3k

 and 100k divider network connected to

the base of the current sensing transistor.

Both regulators provide better than 0.02% load regulation.

Because there is constant loop gain at all voltage settings, the

regulation also remains constant. Line regulation is 0.1% per

volt. Hum and noise voltage is less than 200

V as read with a

meter having a 10MHz bandwidth.

Figure 18A shows the turn ON and turn OFF characteristics of

both regulators. The slow turn on rise is due to the slow rate of

rise of the reference voltage. Figure 18B shows the transient

response of the regulator with the switching of a 20

 load at

20V output.

FIGURE 16. REGULATED POWER SUPPLY

FIGURE 17. REGULATED POWER SUPPLY WITH “FOLDBACK”

CURRENT LIMITING

5V/Div., 1s/Div.

FIGURE 18A. SUPPLY TURN-ON AND TURNOFF

CHARACTERISTICS

Top Trace: Output Voltage;

200mV/Div., 5

s/Div.

Bottom Trace: Collector of load switching transistor, load = 1A;

5V/Div., 5

s/Div.

FIGURE 18B. TRANSIENT RESPONSE

FIGURE 18. WAVEFORMS OF DYNAMIC CHARACTERISTICS OF POWER SUPPLY CURRENTS SHOWN IN FIGURES 16 AND 17

1

3

75



3k



100



2

1k

 1k

D2201

CURRENT

LIMITING

ADJUST

2N6385

POWER DARLINGTON

2

1k



1

3

8

2N2102

1k



+30V

INPUT

4

CA3140

7

1

6

5

100k



2

3

180k



56pF

1k



82k



250

F

+

-

0.01

F

100k



14

10

6

9

8

50k



13

5

F

+

-

12

CA3086

2.2k



3

1

5

4

62k



VOLTAGE

ADJUST

10

F

+

-

2.7k



1k



11

7

2

HUM AND NOISE OUTPUT <200

(MEASUREMENT BANDWIDTH

LINE REGULATION 0.1%/V

LOAD REGULATION

(NO LOAD TO FULL LOAD)

<0.02%

OUTPUT

0.1

 24V

AT 1A

1

2

1k

 200

D2201

“FOLDBACK” CURRENT

LIMITER

2N5294

3k



8

2N2102

1k



+30V

INPUT

4

CA3140

7

1

6

5

100k



2

3

180k



56pF

1k



82k



250

F

+

-

0.01

F

100k



14

10

6

9

8

50k



13

5

F

+

-

12

CA3086

2.2k



3

1

5

4

62k



VOLTAGE

ADJUST

10

F

+

-

2.7k



1k



11

7

2

HUM AND NOISE OUTPUT <200

(MEASUREMENT BANDWIDTH

LINE REGULATION 0.1%/V

LOAD REGULATION

(NO LOAD TO FULL LOAD)

<0.02%

OUTPUT

 0V TO 25V

25V AT 1A

3

100k



“FOLDS BACK”

TO 40mA

100k

