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PRODUCT SPECIFICATION
RC4195
6
Brownout Protection
The RC4195 is one of the most easily applied and trouble-
free monolithic ICs available. When used within the data
sheet ratings (package power dissipation, maximum output
current, minimum and maximum input voltages) it provides
the most cost-effective source of regulated
±
15V for power-
ing linear ICs.
Sometimes occasions arise in which the RC4195 ratings
must be exceeded. One example is the "brownout". During a
brownout, line voltages may be reduced to as low as 75
V
RMS
, causing the input voltage to the RC4195 to drop
below the minimum dropout voltage. When this happens, the
negative output voltage can go to positive. The maximum
amount of current available is approximately 5 mA.
In general this is not enough current to damage most ICs
which the RC4195 might be supplying, but it is a potentially
destructive condition. Fortunately, it is easy to protect
against. As shown in the typical application circuit, a diode,
D, can be connected to the negative output.
If a small signal silicon diode is used, it will clamp the nega-
tive output voltage at about +0.55V. A Schottky barrier or
germanium device would clamp the voltage at about +0.3V.
Another cure which will keep the negative output negative
all times is the 1 m
W
resistor connected between the +15V
output and the Comp– terminal. this resistor will then sup-
ply drive to the negative output transistor, causing it to satu-
rate to -1V during the brownout.
Heatsinking
When operating these devices near their extremes of load
current, ambient temperature and input-output differential,
consideration of package dissipation becomes important to
avoid thermal shutdown at 175
°
C. The RC4195 has this fea-
ture to prevent damage to the device. It typically starts affect-
ing load regulation approximately 2
°
C below 175
°
C. To
avoid shutdown, some form of heatsinking should be used or
one of the above operating conditions would need to be
derated.*
The following is the basic equation for junction temperature:
Equation 1
where
T
J
= junction temperature (
°
C)
T
A
= ambient air temperature (
°
C)
P
D
= power dissipated by device (W)
q
J-A
= thermal resistance from junction to ambient air
(C/W)
The power dissipated by the voltage regulator can be detailed
as follows:
Equation 2
where
V
IN
= input voltage
V
OUT
= regulated output voltage
I
O
= load current
I
Q
= quiescent current drain
T
J
T
A
P
D
q
J
A
–
+
=
P
D
V
IN
V
OUT
–
(
)
I
O
V
IN
I
Q
′
+
′
=
Figure 10. Typical Application Circuit
4195
10
μ
F
+V
S
–V
S
Comp–
+V
OUT
–V
OUT
65-3467-03
Gnd
10
μ
F
+18V To +30V
-18V To -30V
1M
+15V at 100 mA
-15V at 100 mA
Balanced Output (V
OUT
=
±
15V)
D
———————————————
*In allowing for process deviations, the user should work with a maximum allowable function temperature of 150
°
C.
**The current drain will increase by 50
m
A/V
OUT
on positive side and 100
m
A/V
OUT
on negative side