SR087SG-G Supertex, SR087SG-G Datasheet - Page 5

• Manufacturer Part Number: SR087SG-G
• Description: Switching Converters, Regulators & Controllers 5.0V Adjust Off-Line Switching Regulator
• Manufacturer: Supertex

Specifications of SR087SG-G

• Output Voltage: 50 V
• Output Current: 100 mA
• Output Power: 1 W
• Input Voltage: 120 V to 230 V
• Operating Temperature Range: - 40 C to + 125 C
• Mounting Style: SMD/SMT
• Package / Case: SOIC-8
• Number Of Outputs: 2
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Output Voltage*
V
feedback resistor R
Leave R
load required for the proper operation of the SR087. Change
R
C
low ESR capacitor with an adequate ripple current rating
(800mA
Since V
mum current available from V
creased due to power considerations.
I
Input Voltage
To reduce standby power for 230VAC-only applications,
or for supply voltages less than 90Vrms, R
be changed according to the R
should remain at 400kΩ or less. Two resistors in series
are employed to ensure adequate creepage distances for
230VAC operation. For 120VAC-only applications, single re-
sistors may be employed.
Output Ripple*
Storage capacitor C
at 100mA load (I
duced. Conversely, C
Use a low ESR capacitor with an adequate ripple current
rating (800mA
current capability may drop with increased capacitance be-
cause of a smaller conduction angle associated with lower
ripple. Due to feedback hysteresis, ripple cannot be reduced
below 4%.
*V
must not fall below 9.0V.
Line Transformer
During initial testing it is tempting to use an isolation
transformer or a variable transformer on the AC line. However,
the high inductance of the transformer (frequently in the
REG(max)
OUT
3
2
REG
R
(R
and R
and C
3
3
may be adjusted in the range of 9V to 50V*‚ by changing
requires at least 4.0V of headroom. Therefore, V
+ R
+ R
= 1.5W / (V
REG
RMS
R
V
6
4
RIPPLE(P-P)
5
4
3
) <
at 12.4kΩ or less - it assures a minimum 100µA
= R
). Use ceramic for C
is a linear regulator supplied from V
with appropriate voltage ratings. For C
according to the R
4
Supertex inc.
Equation:
√ 2V
6
RMS
[(V
OUT
≈ (I
IN
for 100mA loads). Efficiency and output
OUT
OUT
2
5
3
+ I
- V
according to the following equation.
OUT
was sized to provide about 2V
/ 1.25V) - 1]
- 5.0V), or 60mA, whichever is less.
3
π • 25µ
REG
X
may be increased for lower ripple.
+ I
2
). For lighter loads, C
- V
REG
X
) / 2f
cos
REG
3
2
+R
.
3
+R
-1
is reduced as V
IN
4
●
4
C
equation below. Select
√2 • V
1235 Bordeaux Drive, Sunnyvale, CA 94089
equation below. R
3
V
X
IN
3
OUT
and R
, including ripple,
OUT
3
may be re-
, the maxi-
where V
OUT
P-P
3
4
, use a
should
ripple
is in-
1
+R
X
2
= V
5
mH’s) interferes with the normal operation of the SR087 and
should not be used. This is not a concern with the normal
inductance of the AC line or for AC line filters.
The SR087 draws current from the AC line in short, high
current pulses. The transformer’s high inductance tends to
limit the current pulse. Furthermore, inductive kickback on
the falling edge of the current pulse can create high voltage
spikes which must be absorbed by the transient protector.
EMI Capacitor
The use of a small-value capacitor from circuit common to
earth ground prevents the SR087 from operating and should
not be employed.
EMI
The SR087 circuit as depicted on Page 1, (Typical Application
Circuit), meets FCC Class B and CISPR 14-1 (household
appliances) requirements for conducted emissions, for
combined loads of less than 20mA (I
Fuse
Although the average current drawn from the AC line is
low, the RMS current is fairly high due to the current being
drawn in short, high-current pulses. Since a fuse is basically
a resistor with a power dissipation given by I
must be sized for the RMS current, not the average current.
For a 1.0W load and 120VAC the RMS current is 700mA
and for a 0.5W load at 230VAC it is 360mA
Load
Total load on the SR087 is the total load current drawn from
V
OUT
OUT
+ 15V
(I
OUT
) and, since the linear regulator is supplied from
AC Line
●
Tel: [phone]
AC Line
Use the minimum anticipated RMS value for V
Take resistor tolerance into account, selecting the
next lower standard value. Choosing a lower value
has no effect other than higher standby power.
ground
earth
●
www.supertex.com
SR087 &
Circuitry
common
circuit
OUT
Circuitry
SR087
+ I
REG
RMS
RMS
).
.
2
SR087
R, the fuse
IN
RMS
.
,