TOP232 datasheet(17/38 Pages) POWERINT

17 / 38 page

Rev. D 10/20

TOP232-234

www.power.com

Processor Controlled Supply Turn On/Off

A low cost momentary contact switch can be used to turn the

TOPSwitch-FX 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 implemen-

tation of this function with very few external components as

shown in Figure 27. 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-FX to SOURCE through a diode (remote on). When

the secondary output voltage VCC is established, the micro-

processor 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 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

M may be needed to prevent noise

coupling to the 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

27). 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.

Figure 27. Remote ON/OFF using Microcontroller.

PI-2561-062615

VCC

(+5 V)

RETURN

CONTROL

High-Voltage

DC Input

TOPSwitch-FX

1N4148

LTV817A

6.8 k

Ω

1 nF

100 k

Ω

6.8 k

Ω

LTV817A

27 k

Ω

1N4148

µF

P1 Switch

Status

Power

Supply

ON/OFF

Control

External

Wake-up

Signal

LOGIC

INPUT

LOGIC

OUTPUT

MICRO-

PROCESSOR/

CONTROLLER

–

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