TOP242R POWERINT [Power Integrations, Inc.], TOP242R Datasheet - Page 25

• Manufacturer Part Number: TOP242R
• Description: TOPSwitch -GX Family Extended Power, Design Flexible, EcoSmart, Integrated Off-line Switcher
• Manufacturer: POWERINT [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 shut-
down procedure that is product specific. For example, in the
case of the inkjet printer, the shutdown procedure may include
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
safely parking the print heads in the storage position. In the
case of products with a disk drive, the shutdown procedure
may include saving data or settings to the disk. After the shut-
down 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
pin 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
100 kΩ
may be needed to prevent noise coupling to the
U3
P1 Switch
Status
LOGIC
INPUT
PROCESSOR/
CONTROLLER
MICRO
OUTPUT
LOGIC
LTV817A
U4
6.8 kΩ
TOP242-250
ON/OFF
Control
Supply
Power
1N4148
Wake-up
External
Signal
PI-2561-033001
RETURN
1/02
(+5 V)
G
V
CC
6.8 kΩ
25