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DI-27

更新时间: 2022-04-23 23:00:11
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帕沃英蒂格盛 - POWERINT /
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2页 51K
描述
3 W AC Adapter: <10 mW No-load Consumption

DI-27 数据手册

 浏览型号DI-27的Datasheet PDF文件第2页 
®
Design Idea DI-27  
TinySwitch® 3 W AC Adapter:  
<10 mW No-load Consumption  
Topology  
Flyback  
Device  
Power Output  
Input Voltage  
Output Voltage  
Application  
Adapter  
3 W  
85-265 VAC  
TNY254  
12 V  
consume <100 mW at no-load. However, by providing  
external bias, the internal high voltage current source, which  
normally powers the IC from the DRAIN pin, is disabled and  
a further reduction in consumption is therefore achieved.  
Design Highlights  
• Extremely low no-load power consumption (<10 mW at  
115/230 VAC input)  
• Simple RC snubber/clamp reduces EMI  
• Low cost, low component count solution  
The bias winding should provide enough current to fully  
disable the internal current source. Figure 2 shows that the  
bias winding and choice of C5 and R3 should provide  
250 µA to 300 µA at no-load to minimize consumption.  
Zener VR3 is required to clamp the BYPASS pin voltage.  
Operation  
The TinySwitch flyback converter in Figure 1 generates an  
isolated 12 VDC, 3 W output from 85 VAC to 265 VAC input.  
Typical applications include wall mounted AC adapters for  
consumer products.  
The output Zener VR2 is not biased, minimizing the  
secondary circuit consumption. A low current Zener there-  
fore provides the best output voltage tolerance.  
The key performance characteristic of the circuit shown is  
extremely low no-load consumption of <10 mW. A linear  
transformer adapter of similar rating will typically consume  
1 W to 4 W at no-load. At $0.12/kWh, the TinySwitch can  
therefore reduce energy costs by $1 to $4 per year.  
Components R2 and C3 provide a low cost clamp and also  
help reduce EMI by softening switching edges. This type of  
snubber increases switching losses and would therefore  
normally be avoided in low consumption circuits. However,  
with TinySwitch, these losses are negligible at no-load as  
switching frequency is so low. This is illustrated in Figure 3  
where replacing R2 and C3 with a Zener clamp across the  
primary winding reduces consumption by <0.25 mW.  
The no-load performance is achieved using a transformer bias  
winding as a low voltage source for TinySwitch operating  
current. Even without this winding, a TinySwitch circuit will  
C8  
2.2 nF Y1  
D6 UF4003  
+12 VDC  
1
10  
L1  
1.0 mH  
L2  
Ferrite  
Bead  
C7  
C6  
180 µF  
16 V  
49T  
100 µF  
16 V  
D1 & D2  
1N4007  
28 AWG  
9
3
223T  
36 AWG  
D5 1N4148  
RTN  
RF1  
8.2  
R1  
4.7 kΩ  
C5  
100 µF  
10 V  
30T  
x2  
37 AWG  
R3  
4.7 kΩ  
2
4
L
VR2  
BZX79B11  
85 - 265  
VAC  
TinySwitch  
R2  
1.5 k  
1/2 W  
C1 & C2  
3.3 µF  
400 V  
U1  
TNY254P  
D
EN/UV  
N
BP  
D3 & D4  
1N4007  
S
VR3  
BZX79-  
B6V2  
U2  
PC817A  
C3  
68 pF  
1 kV  
U2  
C4  
0.1 µF  
50 V  
PI-3011-091802  
Figure 1. 3 W AC Adapter with <10 mW No-load Consumption.  
September 2002  
DI-27  
www.powerint.com  

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