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TOP250P- Datasheet(PDF) 24 Page - Power Integrations, Inc. |
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TOP250P- Datasheet(HTML) 24 Page - Power Integrations, Inc. |
24 / 52 page TOP242-250 M 12/04 24 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, which 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 V CC is established,themicroprocessorcomesaliveandrecognizesthat 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 detectsthisthroughtheoptocouplerU3andinitiatesashutdown 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 productswithadiskdrive,theshutdownproceduremayinclude savingdataorsettingstothedisk. Aftertheshutdownprocedure 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 toAC 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. U1 U2 U4 U3 CM P1 P1 Switch Status Power Supply ON/OFF Control External Wake-up Signal PI-2561-081204 VCC (+5 V) RETURN CONTROL MICRO- PROCESSOR/ CONTROLLER LOGIC INPUT LOGIC OUTPUT High Voltage DC Input TOPSwitch-GX D M S F C 1N4148 U4 LTV817A 6.8 k Ω 1 nF 100 k Ω 6.8 k Ω U3 LTV817A 27 k Ω 1N4148 47 µF + Figure 45. Remote ON/OFF using Microcontroller. |
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