sr087 Supertex, Inc., sr087 Datasheet - Page 5

• Manufacturer Part Number: sr087
• Description: Adjustable Off-line Inductorless Switching Regulator
• Manufacturer: Supertex, Inc.

Data Sheet Application Section:
Typical Application Circuit
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
R
REG(max)
OUT
3
2
90VAC to
5
R
(
50/60Hz
270VAC
R
and R
and C
=
3
3
may be adjusted in the range of 9V to 50V*‚ by changing
R
+
V
+ R
6
IN
REG
RMS
R



6
=
1 25
4
3
4
at 12.4k
V
). Use ceramic for C
.
)
is a linear regulator supplied from V
V
with appropriate voltage ratings. For C
according to the R
4
OUT
<
OUT
1 5
Equation:
V
. W
−
−
F
1.00A
2V
1
1
5



5
V
IN
275V
according to the following equation.
or less - it assures a minimum 100µA
2
50A
- V
Z
1
X
2
* Two resistors used in
series for reasons of
high voltage creepage
and resistor voltage
rating.
π
⋅
REG
3
2
25
+R
.
-
or 60mA, whichever is less.
is reduced as V
4
A
V
equation below. Select
X
cos
EN
−
1
D
( )
1.0kV
1A
100k
200k
200k
1
OUT
2
V
R
X
*R
*R
V
IN
7
, the maxi-
1
2
OUT
3
, use a
where V
is in-
2
EN
V
IN
5
1
*R
510k
*R
510k
X
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 400k
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 9V for the SR087, or below 7.3V for the SR086.
V
= V
3
4
RIPPLE P P
REG
GATE
OUT
Q
STGD5NB120SZ
requires at least 4V of headroom. Therefore, V
SR087
1
8
IC
(
GND
+ 15V
−
1
3
V
)
GD
≈
7
RMS
I
OUT
C
100nF
1
OUT
2
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.
f C
for 100mA loads). Effi ciency and output
IN
V
+
V
3
+ I
OUT
REG
I
was sized to provide about 2V
REG
FB
3
6
3
REG
may be increased for lower ripple.
5
4
). For lighter loads, C
or less. Two resistors in series
C
1.0µF
2
3
C
100nF
+R
4
V
5VDC
REG
4
SR086/SR087
equation below. R
C
470µF
3
OUT
3
and R
, including ripple,
R
113k
R
12.4k
3
5
6
may be re-
V
12.6VDC
P-P
4
OUT
NR040306
should
ripple
1
IN
+R
.
2