AP1694AEV11 查看數據表（PDF） - Diodes Incorporated.
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AP1694AEV11 Datasheet PDF : 10 Pages
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AP1694AEV11 User Guide
230VAC Triac Dimmable GU10 LED Driver
WHY USE DIODES TAPPED TRANSFORM STRUCTURE
The traditional Buck converter turn on time is inverse proportion with input voltage.
Vo = D x Vin. The duty cycle will be getting smaller when the input voltage goes higher.
Example: Vo=12V, Vin= 120VAC, Fs= 75kHz.
D= Vo/Vin * = 12V/120V * 1.414 = 0.07
Ton=D/Fs = 0.07/ 75kHz =0.933µs. T=1/Fs =13.33µs
Since the Ton time is too short in the duty cycle; therefore there is not enough current passing
through the LEDs and charging the inductor. In result, it caused the efficiency to be lower.
In order to solve this issue ‐ use the Diodes tapped transformer to boost the output current &
increase the Ton time in the duty cycle.
With the “new tapped” transformer, the Duty cycle will be:
D is original duty cycle = Vo/Vin*1.414, n = NA+Np/NA & L = Lp + LA,
Vo/Vin = D’/(D’ +n(1‐D’)), If NA=40Ts, Np=100Ts, n=3.5
D’ = nVo/(Vin+(n‐1)Vo) = 0.21 The duty cycle almost increased by 3 times.
The Efficiency will increase about 4 to 5% (before the Efficiency was about 72% now is 77%)
comparing with the “none tapped” transformer.
AP1694AEV11 Rev2
July 2015
www.diodes.com
Page 2 of 10
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