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MC7905C View Datasheet(PDF) - ON Semiconductor

Part NameDescriptionManufacturer
MC7905C 1.0 A Negative Voltage Regulators ON-Semiconductor
ON Semiconductor ON-Semiconductor
MC7905C Datasheet PDF : 16 Pages
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MC7900 Series
APPLICATIONS INFORMATION
Design Considerations
The MC7900 Series of fixed voltage regulators are
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.
In many low current applications, compensation
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
used to minimize ground loops and lead resistance drops
since the regulator has no external sense lead. Bypassing the
output is also recommended.
−20 V
Input
MC7905
10
IO = 200 mA
R
VO 10 V
+ 1.0 mF
Gnd
1.0 mF
+
Gnd
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.
5.0 V
IO = R + IB
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.
Figure 8. Current Regulator
−10 V
Input
0.56
0.56
0.56
MJE200*
or Equiv
2N3055*
or Equiv
MC7905*
−5.0 V
Output
10 mF
5.6
Gnd +
1.0 mF
+
1.0 mF
+
Gnd
*Mounted on heatsink.
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/RSC. Operation
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.
Figure 9. Current Boost Regulator
(−5.0 V @ 4.0 A, with 5.0 A Current Limiting)
+20 V
Input
0.33 mF
Gnd
−20 V
Input
MC7815
+
1.0 mF
+
1.0 mF
+
1.0 mF
+
1.0 mF
MC7915
+15 V
Output
1N4001
or Equiv
Gnd
−15 V
Output
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.
Figure 10. Operational Amplifier Supply
(±15 @ 1.0 A)
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