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TNY274P 参数 Datasheet PDF下载

TNY274P图片预览
型号: TNY274P
PDF下载: 下载PDF文件 查看货源
内容描述: 高能效,离线式开关具有更大的灵活性和扩展功率范围 [Energy Efficient, Off-Line Switcher with Enhanced Flexibility and Extended Power Range]
分类和应用: 开关
文件页数/大小: 24 页 / 1604 K
品牌: POWERINT [ Power Integrations ]
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TNY274-280  
loadisproportionaltotheprimaryinductanceofthetransformer  
and peak primary current squared. Hence, designing the supply  
involves calculating the primary inductance of the transformer  
for the maximum output power required. If the TinySwitch-III  
is appropriately chosen for the power level, the current in the  
calculated inductance will ramp up to current limit before the  
DCMAX limit is reached.  
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 EN/UV  
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.  
Enable Function  
TinySwitch-III senses the EN/UV pin to determine whether or  
The EN/UV pin signal is generated on the secondary by  
comparing the power supply output voltage with a reference  
voltage. The EN/UV pin signal is high when the power supply  
output voltage is less than the reference voltage.  
V
EN  
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  
withaZenerdiodeacrosstheDCoutputvoltagetoberegulated.  
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.  
CLOCK  
DC  
MAX  
I
DRAIN  
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.  
V
DRAIN  
PI-2749-082305  
Figure 6. Operation at Near Maximum Loading.  
V
V
EN  
EN  
CLOCK  
CLOCK  
DC  
DC  
MAX  
MAX  
I
I
DRAIN  
DRAIN  
V
DRAIN  
V
DRAIN  
PI-2377-082305  
PI-2667-082305  
Figure 8. Operation at Medium Loading.  
Figure 7. Operation at Moderately Heavy Loading.  
E
2/06  
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