MC7918CT Fairchild Semiconductor, MC7918CT Datasheet - Page 9

• Manufacturer Part Number: MC7918CT
• Description: Linear Regulators - Standard TO-220 1A Neg Volt
• Manufacturer: Fairchild Semiconductor

Specifications of MC7918CT

• Polarity: Negative
• Number Of Outputs: 1
• Output Type: Fixed
• Output Voltage: - 18 V
• Output Current: 1 A
• Line Regulation: 360 mV
• Load Regulation: 360 mV
• Dropout Voltage (max): 2 V
• Input Voltage Max: - 35 V
• Maximum Operating Temperature: + 125 C
• Minimum Operating Temperature: 0 C
• Package / Case: TO-220
• Mounting Style: Through Hole
• Output Voltage Tolerance: +/- 4 %
• Voltage Regulation Accuracy: 4 %
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

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
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 mF or larger tantalum,
mylar, or other capacitor having low internal impedance at
high frequencies should be chosen. The capacitor chosen
should have an equivalent series resistance of less than
0.7 W. The bypass capacitor should be mounted with the
shortest possible leads directly across the regulators input
terminals. Normally good construction techniques should be
When a boost transistor is used, short circuit currents are equal to the sum of the
series pass and regulator limits, which are measured at 3.2 A and 1.8 A respectively
in this case. Series pass limiting is approximately equal to 0.6 V/R
beyond this point to the peak current capability of the MC7905C is possible if the
regulator is mounted on a heatsink; otherwise thermal shutdown will occur when
the additional load current is picked up by the regulator.
The MC7900 Series of fixed voltage regulators are
In many low current applications, compensation
*Mounted on heatsink.
−10 V
Input
Gnd
10 mF
+
(−5.0 V @ 4.0 A, with 5.0 A Current Limiting)
MJE200*
or Equiv
Figure 9. Current Boost Regulator
0.56
0.56
0.56
5.6
+
1.0 mF
2N3055*
or Equiv
MC7905*
APPLICATIONS INFORMATION
+
SC
1.0 mF
. Operation
http://onsemi.com
MC7900 Series
−5.0 V
Output
Gnd
9
used to minimize ground loops and lead resistance drops
since the regulator has no external sense lead. Bypassing the
output is also recommended.
The MC7905, −5.0 V regulator can be used as a constant current source when
connected as above. The output current is the sum of resistor R current and
quiescent bias current as follows.
The MC7815 and MC7915 positive and negative regulators may be connected as
shown to obtain a dual power supply for operational amplifiers. A clamp diode
should be used at the output of the MC7815 to prevent potential latch−up problems
whenever the output of the positive regulator (MC7815) is drawn below ground with
an output current greater than 200 mA.
The quiescent current for this regulator is typically 4.3 mA. The 5.0 V regulator was
chosen to minimize dissipation and to allow the output voltage to operate to within
6.0 V below the input voltage.
Gnd
+20 V
−20 V
Input
Input
0.33 mF
−20 V
Gnd
Input
Figure 10. Operational Amplifier Supply
+
Figure 8. Current Regulator
1.0 mF
+
+
1.0 mF
1.0 mF
I
O
MC7905
(±15 @ 1.0 A)
=
5.0 V
R
MC7815
MC7915
+ I
B
1.0 mF
1.0 mF
+
1.0 mF
10
+
+
R
or Equiv
1N4001
I
−
V
O
O
= 200 mA
Gnd
≤ 10 V
+15 V
Output
Output
−15 V
Gnd