AN557 Datasheet, PDF (49/52 Pages) STMicroelectronics – EASY APPLICATION DESIGN WITH THE L4970A

AN557 APPLICATION NOTE
higher than 1A maintaining an elevated efficiency of the system.
Such outputs must have a good precision and stability and must be protected from short circuiting.
With the application circuit suggested below, one the aime is to satisfy the performance listed above, and
to contributing to the simplification of the power trasformer, both at 50Hz and at high frequency.
It’s important to remember not to exceed the absolute maximum voltage ratings of the device. In this case
the differential voltage applied to the device is the sum of the maximum input voltage (positive) and of that
controlled output negative.
Figure 68.
220nF
12V<Vi≤50V
11
1000
µF
8
L4974A
5,6
17 18 15,16
1
20
9
7
15K
150µH SB560
Vo=18V/3A
12K
56nF
Dz
20V
4.7K
3x
100µF
EKR
Figure 69. Circuit for negative output voltage
D93IN008A
220nF
12V<Vi≤35V
11
1000
µF
8
L4974A
5,6
17 18 15,16
1
20
9
7
100µH
SB560
15K
6.2K
4.7K
-12V
470µF
D93IN009
Linear low drop post regulation
In some application it becomes necessary to generate stable, precise fixed or adjustable output voltages
at high efficiency and with a truly negligible output ripple. Summarizing a regulator that offers the quality
of a linear type of control with the efficiency of a switching regulator. The fig. 70 shows the diagram of a
swithcing preregulator at high efficiency followed by one or more series regulators of the type very "low
drop", or in the case of elevated current, by a discret low drop solution.
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