Page 1
SR037DB1
measurements.
e
Inductorless Switching Power Supply
Introduction
The Supertex SR037 is an inductorless switching power
supply controller intended for 120/240VAC line operation.
The operating principle is to activate a pass element
between line and load only when the input voltage is lower
than a certain value. Thus conduction only occurs with a
low voltage drop across the pass element, resulting in more
efficient operation compared to a standard linear regulator.
The SR037DB1 demo board contains all the circuitry
needed to supply a low-current (<40mA) load. Included is
input protection circuitry, a full wave bridge rectifier, a pass
element, and output capacitors.
Board Layout and Connections
Z
1
AC
IN
F
1
Specifications
AC Input 24VAC to 264VAC
O
utput Voltages
V
O
utput Current
I
UNREG
Efficiency
ACIN=120VAC 60Hz, IU=40mA, IR=0mA
D
1
IC
1
C
2
UNREG
V
REG
Q
1
C
+ I
1
REG
40Hz to 100Hz
12V to 22V
5.0V ±10%
4
0mA @120VAC
30mA @ 240VAC
40% typ
WARNING!!!
Do not connect to scope ground or to the ground of other
earth-grounded instruments. Doing so will short the AC line,
resulting in damage to the circuit and/or instrument. Either
use an isolation transformer on the AC line, use a differential
probe, or use a floating, battery-powered instrument to make
ACIN
Connect to the AC line. The AC input is protected by a 400V
transient voltage suppressor and a 250mA fuse.
GND
Circuit common.
Note that since galvanic isolation is not provided, connecting
this point to an earth-grounded instrument (such as an
oscilliscope) will short the AC line, resulting in circuit and/or
instrument damage.
Also note that GND may be at a higher potential with respect
to earth ground, even if the AC is switched off. Use caution!
Do not connect to earth ground. This ground must
remain floating when supplied from the AC line!
V
GND
V
R
UNREG
EG
WARNING!!!
No galvanic isolation. Dangerous voltages ar
present when connected to the AC mains.
V
UNREG
The unregulated output. Nominal output voltage is 18 volts.
This output will have a certain amount of 120Hz ripple,
depending on load.
Do not connect to earth-grounded loads.
V
REG
The regulated output. 5.0V nominal output voltage.
Do not connect to earth-grounded loads.
22MAR02 1
Page 2
120/240VAC
50/60Hz
250mA
P6KE400CA
Inductorless Switching Power Supply
SR037 Schematic
V
N2460
220DF
SR037DB1
V
U
NREG
S
R037
Parts List
Desig Desc Part Number
F
Z
D
IC
Q
C
C
Fuse, 3AG, 250mA, 250V
1
Transient voltage suppressor, 400V P6KE400CA
1
Diode bridge, 1A, 600V
1
HV Supply Controller Supertex SR037SG
1
MOSFET, 600V N-channel Supertex VN2460N8
1
Capacitor,alum, 220DF, 35V
1
Capacitor, cer, 1DF, 16V
2
1DF
V
REG
Modifications
The SR037DB1 may be modified to provide higher output current. Remove Q1 and replace with a D-Pak N-channel MOSFET with
a voltage rating appropriate for the input voltage. The on resistance of the replacement FET is not as important as the gate
threshold voltage – the lower the threshold voltage, the more efficient the converter.
To reduce ripple at the higher output current, C1 may be replaced with a higher value capacitor.
22MAR02 2
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