LM340-12MDC National Semiconductor Corporation, LM340-12MDC Datasheet - Page 9

• Manufacturer Part Number: LM340-12MDC
• Manufacturer: National Semiconductor Corporation

Equivalent Schematic
Application Hints
The LM340/LM78XX series is designed with thermal protec-
tion, output short-circuit protection and output transistor safe
area protection. However, as with any IC regulator, it be-
comes necessary to take precautions to assure that the
regulator is not inadvertently damaged. The following de-
scribes possible misapplications and methods to prevent
damage to the regulator.
Shorting the Regulator Input: When using large capacitors
at the output of these regulators, a protection diode con-
nected input to output (Figure 1) may be required if the input
is shorted to ground. Without the protection diode, an input
short will cause the input to rapidly approach ground poten-
140AK-5.0, I
Line Regulation
OUT
= 1A, T
A
= 25˚C
00778105
9
tial, while the output remains near the initial V
the stored charge in the large output capacitor. The capacitor
will then discharge through a large internal input to output
diode and parasitic transistors. If the energy released by the
capacitor is large enough, this diode, low current metal and
the regulator will be destroyed. The fast diode in Figure 1 will
shunt most of the capacitors discharge current around the
regulator. Generally no protection diode is required for val-
ues of output capacitance ≤ 10 µF.
Raising the Output Voltage above the Input Voltage:
Since the output of the device does not sink current, forcing
the output high can cause damage to internal low current
paths in a manner similar to that just described in the “Short-
ing the Regulator Input” section.
140AK-5.0, V
Line Regulation
IN
00778107
= 10V, T
A
= 25˚C
OUT
www.national.com
because of
00778106