TOP242 Power Integrations Inc., TOP242 Datasheet - Page 25

• Manufacturer Part Number: TOP242
• Description: Family Extended Power/ Design Flexible/Integrated Off-line Switcher
• Manufacturer: Power Integrations Inc.

Processor Controlled Supply Turn On/Off
A low cost momentary contact switch can be used to turn the
TOPSwitch-GX power on and off under microprocessor control
that may be required in some applications such as printers. The
low power remote off feature allows an elegant implementation
of this function with very few external components as shown in
Figure 45. Whenever the push button momentary contact
switch P1 is closed by the user, the optocoupler U3 is activated
to inform the microprocessor of this action. Initially, when the
power supply is off (M pin is floating), closing of P1 turns the
power supply on by shorting the M pin of the TOPSwitch-GX
to SOURCE through a diode (remote on). When the secondary
output voltage VCC is established, the microprocessor comes
alive and recognizes that the switch P1 is closed through the
switch status input that is driven by the optocoupler U3 output.
The microprocessor then sends a power supply control signal to
hold the power supply in the on-state through the optocoupler
U4. If the user presses the switch P1 again to command a turn
off, the microprocessor detects this through the optocoupler U3
and initiates a shutdown procedure that is product specific. For
example, in the case of the inkjet printer, the shutdown procedure
may include safely parking the print heads in the storage
Figure 45. Remote ON/OFF using Microcontroller.
High Voltage
+
-
DC Input
U4
U3
1N4148
P1
1 nF
C
M
D
S
CONTROL
M
TOPSwitch-GX
F
27 kΩ
U1
C
47 µF
position. In the case of products with a disk drive, the shutdown
procedure may include saving data or settings to the disk. After
the shutdown procedure is complete, when it is safe to turn off
the power supply, the microprocessor releases the M pin by
turning the optocoupler U4 off. If the manual switch and the
optocouplers U3 and U4 are not located close to the M pin, a
capacitor C
when it is open.
The power supply could also be turned on remotely through a
local area network or a parallel or serial port by driving the
optocoupler U4 input LED with a logic signal. Sometimes it is
easier to send a train of logic pulses through a cable (due to AC
coupling of cable, for example) instead of a DC logic level as
a wake up signal. In this case, a simple RC filter can be used to
generate a DC level to drive U4 (not shown in Figure 45). This
remote on feature can be used to wake up peripherals such as
printers, scanners, external modems, disk drives, etc., as needed
from a computer. Peripherals are usually designed to turn off
automatically if they are not being used for a period of time, to
save power.
U2
M
LTV817A
may be needed to prevent noise coupling to the pin
100 kΩ
U3
P1 Switch
Status
August 8, 2000
LOGIC
INPUT
PROCESSOR/
CONTROLLER
MICRO
OUTPUT
LOGIC
LTV817A
U4
6.8 kΩ
TOP242-249
ON/OFF
Control
Supply
Power
1N4148
Wake-up
External
Signal
PI-2561-033001
RETURN
7/01
(+5 V)
V
E
CC
6.8 kΩ
25