MC7806 Motorola, MC7806 Datasheet - Page 14

• Manufacturer Part Number: MC7806
• Description: THREE TERMINAL POSITIVE FIXED VOLTAGE REGULATORS
• Manufacturer: Motorola

Design Considerations
designed with Thermal Overload Protection that shuts down
the circuit when subjected to an excessive power overload
condition, Internal Short Circuit Protection that limits the
maximum current the circuit will pass, and Output Transistor
Safe–Area Compensation that reduces the output short
circuit current as the voltage across the pass transistor is
increased.
capacitors are not required. However, it is recommended
that the regulator input be bypassed with a capacitor if the
regulator is connected to the power supply filter with long
14
The MC7800 Series of fixed voltage regulators are
In many low current applications, compensation
Input
The MC7800 regulators can also be used as a current source when
connected as above. In order to minimize dissipation the MC7805C is
chosen in this application. Resistor R determines the current as follows:
For example, a 1.0 A current source would require R to be a 5.0
10 W resistor and the output voltage compliance would be the input
voltage less 7.0 V.
The MC7800 series can be current boosted with a PNP transistor. The
MJ2955 provides current to 5.0 A. Resistor R in conjunction with the V BE
of the PNP determines when the pass transistor begins conducting; this
circuit is not short circuit proof. Input/output differential voltage minimum is
increased by V BE of the pass transistor.
R Source
10 F
0.33 F
Input
Figure 9. Current Boost Regulator
XX = 2 digits of type number indicating voltage.
MJ2955 or Equiv.
I B
Figure 7. Current Regulator
R
1.0 F
^
3.2 mA over line and load changes.
I
O
MC7805
+
0.33 F
5.0 V
R
MC78XX
MC7800, MC7800A, LM340, LM340A Series
)
I
B
I O
R
Constant
Current to
Grounded
Load
APPLICATIONS INFORMATION
1.0 F
Output
,
wire lengths, or if the output load capacitance is large. An
input bypass capacitor should be selected to provide good
high–frequency characteristics to insure stable operation
under all load conditions. A 0.33
mylar, or other capacitor having low internal impedance at
high frequencies should be chosen. The bypass capacitor
should be mounted with the shortest possible leads directly
across the regulators input terminals. Normally good
construction techniques should be used to minimize ground
loops and lead resistance drops since the regulator has no
external sense lead.
Input
Input
The addition of an operational amplifier allows adjustment to higher or
intermediate values while retaining regulation characteristics. The
minimum voltage obtainable with this arrangement is 2.0 V greater than the
regulator voltage.
R Source
The circuit of Figure 9 can be modified to provide supply protection against
short circuits by adding a short circuit sense resistor, R SC , and an
additional PNP transistor. The current sensing PNP must be able to handle
the short circuit current of the three–terminal regulator. Therefore, a
four–ampere plastic power transistor is specified.
10 F
Figure 8. Adjustable Output Regulator
0.33 F
Figure 10. Short Circuit Protection
R
1.0 k
MC7805
XX = 2 digits of type number indicating voltage.
MOTOROLA ANALOG IC DEVICE DATA
or Equiv.
2N6049
R SC
1.0 F
V O = 7.0 V to 20 V
V IN = V O 2.0 V
6
or Equiv.
MJ2955
4
7
MC1741G
2
3
0.33 F
F or larger tantalum,
MC78XX
10 k
Output
0.1 F
Output