SR036 Supertex Inc, SR036 Datasheet - Page 6

• Manufacturer Part Number: SR036
• Description: Inductorless / Dual Output Off-Line Regulators
• Manufacturer: Supertex Inc

Applications Information, continued
The circuit shown in Figure 4 uses the SR036 to supply a
regulated 3.3V for the logic control circuitry while the unregu-
lated voltage is used to drive a 12V relay coil. The operating
voltage for a 12V relay coil is typically very wide and can
therefore operate directly from the unregulated line.
The circuit shown in Figure 5 uses the SR037 to supply a
regulated 5.0V for the logic control circuitry while the unregu-
lated voltage is used to drive a 5.0V coil relay. To overcome the
voltage variation of the unregulated line, a bipolar transistor is
Figure 4: Driving 12V Relay Coils
Figure 5: Driving 5V Relay Coils
120VAC
240VAC
120VAC
240VAC
or
or
Fuse
Fuse
R =
= 100
5.0V -
Ω
40mA
40mA
β
VN2460N8
VN2460N8
HV
HV
1K - V
IN
IN
Ω
Gate
Gate
SR037
SR036
be
GND
GND
6
,
Source
Source
where V
V
V
OUT
OUT
used to drive the coil with a constant current. The resistor value
from the emitter to ground sets the desired coil current. For an
arbitrary coil current of 40mA, the resistor value can be calcu-
lated as:
3.3V
5.0V
be
220µF
1µF
1µF
220µF
= 0.6V and
Unregulated Voltage
Unregulated Voltage
Control
Control
Circuit
Circuit
Logic
Logic
β
= 100
1N4001
1KΩ
1N4001
VN2110K1
2N3904
100Ω
12V Coil
Relay
5V Coil
Relay
SR036/SR037