TNY274_09 POWERINT [Power Integrations, Inc.], TNY274_09 Datasheet - Page 5

• Manufacturer Part Number: TNY274_09
• Description: Energy-Effi cient, Off-Line Switcher With Enhanced Flexibility and Extended Power Range
• Manufacturer: POWERINT [Power Integrations, Inc.]

In a typical implementation, the EN/UV pin is driven by an
optocoupler. The collector of the optocoupler transistor is
connected to the EN/UV pin and the emitter is connected to the
SOURCE pin. The optocoupler LED is connected in series with
a Zener diode across the DC output voltage to be regulated.
When the output voltage exceeds the target regulation voltage
level (optocoupler LED voltage drop plus Zener voltage), the
optocoupler LED will start to conduct, pulling the EN/UV pin
low. The Zener diode can be replaced by a TL431 reference
circuit for improved accuracy.
Figure 6.
www.powerint.com
DC
V
I
Figure 8.
CLOCK
DRAIN
DRAIN
DC
MAX
V
I
V
CLOCK
DRAIN
EN
DRAIN
MAX
V
Operation at Near Maximum Loading.
EN
Operation at Medium Loading.
PI-2749-082305
PI-2377-082305
ON/OFF Operation with Current Limit State Machine
The internal clock of the TinySwitch-III runs all the time. At the
beginning of each clock cycle, it samples the EN/UV pin to
decide whether or not to implement a switch cycle, and based
on the sequence of samples over multiple cycles, it determines
the appropriate current limit. At high loads, the state machine
sets the current limit to its highest value. At lighter loads, the
state machine sets the current limit to reduced values.
Figure 9.
Figure 7.
V
DC
I
CLOCK
DRAIN
DRAIN
DC
V
MAX
I
CLOCK
DRAIN
V
DRAIN
EN
MAX
V
EN
Operation at Moderately Heavy Loading.
Operation at Very Light Load.
TNY274-280
PI-2661-082305
PI-2667-082305
Rev. I 01/09
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