TOP232-234
In addition to using a minimum number of components,
TOPSwitch-FX provides many technical advantages in this
type of application:
sequence when it detects the first closure of the switch, and
subsequentbouncingoftheswitchhasnoeffect. Ifnecessary,
the microprocessor could implement the switch debouncing
in software during turn-off, or a filter capacitor can be used
at the switch status input.
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.
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.
2. A very low cost, low voltage/current, momentary contact
switch can be used.
3. Nodebouncingcircuitryforthemomentaryswitchisrequired.
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
6. Robustdesign:Thereisnoon/offlatchthatcanbeaccidentally
triggered by transients. Instead, the power supply is held in
the on-state through the secondary side microprocessor.
B
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ETC [ ETC ]
