TOP232Y datasheet(18/36 Pages) PAM

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TOP232-234

7/01

In addition to using a minimum number of components,

TOPSwitch-FX provides many technical advantages in this

type of application:

1. Extremely low power consumption in the off mode: 80 mW

typical at 110 VAC and 160 mW typical at 230 VAC. This

is because in the remote/off mode the TOPSwitch-FX

consumes very little power, and the external circuitry does

not consume any current (M pin is open) from the high

voltage DC input.

2. A very low cost, low voltage/current, momentary contact

switch can be used.

3. No debouncing circuitry for the momentary switch is required.

During turn-on, the start-up time of the power supply

(typically 10 to 20 ms) plus the microprocessor initiation

time act as a debouncing filter, allowing a turn-on only if the

switch is depressed firmly for at least the above delay time.

During turn-off, the microprocessor initiates the shutdown

sequence when it detects the first closure of the switch, and

subsequent bouncing of the switch has no effect. If necessary,

the microprocessor could implement the switch debouncing

in software during turn-off, or a filter capacitor can be used

at the switch status input.

4. No external current limiting circuitry is needed for the

operation of the U4 optocoupler output due to internal

limiting of M pin current.

5. No high voltage resistors to the input DC voltage rail are

required to power the external circuitry in the primary. Even

the LED current for U3 can be derived from the CONTROL

pin. This not only saves components and simplifies layout,

but also eliminates the power loss associated with the high

voltage resistors in both on and off states.

6. Robust design: There is no on/off latch that can be accidentally

triggered by transients. Instead, the power supply is held in

the on-state through the secondary side microprocessor.

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