Supertex inc.
Adjustable Off-Line
Inductorless Switching Regulator
Features
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Efficient operation without magnetics
No high voltage capacitors
Adjustable main output voltage (9V to 50V)
Additional 3.3V or 5V internal regulator
Up to 100mA combined output current
Single BOM for 120VAC/230VAC
Built-in soft start
Less than 200mW standby power
SR086/SR087
Initial Release
General Description
The Supertex SR08x is an inductorless switching regulator
designed to operate directly from a rectified AC line. The
operating principle is to turn on a pass transistor when the
rectified AC is below the output voltage, and to turn it off when
the output voltage reaches a specific level. A linear regulator
supplied by V
OUT
provides an additional fixed 3.3V output
(SR086) or 5V output (SR087). Efficiencies of around 55%
may be realized for loads up to 1W in 120VAC applications,
with around 50% efficiencies for loads up to 800mW in 230VAC
applications.
A logic-level enable input allows the SR08x to be disabled
– useful when the SR08x is employed as a keep-alive power
supply.
WARNING! Galvanic isolation is not provided. Dangerous
voltages are present when connected to the AC line. It is
the responsibility of the designer employing the SR08x
to ensure adequate safeguards are in place to protect the
end user from electrical shock.
Applications
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White goods
Household appliances
Lighting controls
Circuit breakers
Keep-alive supplies
Typical Application Circuit
1.25A
90VAC
to
270VAC
50/60HZ
1.0kV
1A
275V
50A
STGD5NB120SZ
1μF
V
OUT
9-50VDC
@ 100mA - I
REG
470μF
390kΩ
1.1MΩ
GATE
V
IN
100nF
R
1
V
GD
V
OUT
FB
= R
2
⎜
⎛
-
1
⎜
1.25V
⎝
⎝
⎛
V
OUT
SR08x
Enable
EN
GND
V
REG
3.3V or 5V
@ 60mA
100nF
R
2
12.4kΩ
NR040306
Supertex inc.
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1235 Bordeaux Drive, Sunnyvale, CA 94089
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Tel: (408) 222-8888
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FAX: (408) 222-4895
·
www.supertex.com
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SUPERTEX [ Supertex, Inc ]
