TNY290PG Datasheet, PDF (5/26 Pages) Power Integrations, Inc. – Energy-Efficient, Off-Line Switcher With Line Compensated Overload Power

TNY284-290
Enable Function
TinySwitch-4 senses the ENABLE/UNDERVOLTAGE pin to
determine whether or not to proceed with the next switching
cycle. The sequence of cycles is used to determine the current
limit. Once a cycle is started, it always completes the cycle
(even when the ENABLE/UNDERVOLTAGE pin changes state
half way through the cycle). This operation results in a power
supply in which the output voltage ripple is determined by the
output capacitor, amount of energy per switch cycle and the
delay of the feedback.
The ENABLE/UNDERVOLTAGE pin signal is generated on the
secondary by comparing the power supply output voltage with
a reference voltage. The ENABLE/UNDERVOLTAGE pin signal
is high when the power supply output voltage is less than the
reference voltage. In a typical implementation, the ENABLE/
UNDERVOLTAGE pin is driven by an optocoupler. The collector
of the optocoupler transistor is connected to the ENABLE/
UNDERVOLTAGE pin and the emitter is connected to the
SOURCE pin. The optocoupler LED is connected in series with
VEN
CLOCK
DCMAX
VEN
CLOCK
DCMAX
IDRAIN
IDRAIN
VDRAIN
Figure 7. Operation at Near Maximum Loading.
VEN
CLOCK
DCMAX
IDRAIN
VDRAIN
PI-2749-082305
Figure 8. Operation at Moderately Heavy Loading.
VEN
CLOCK
DCMAX
IDRAIN
PI-2667-082305
VDRAIN
Figure 9. Operation at Medium Loading.
www.powerint.com
VDRAIN
PI-2377-082305
Figure 10. Operation at Very Light Load.
PI-2661-082305
5
Rev. A 09/12