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2016August

The power dissipation of 4mW low duty cycle LED flash

From: www.szbako.com Data:10/08/2016

battery powered equipment usually has a power indicator light. But this indicator may not consume a small power. The appropriate prompts the state of starting, this case can be described in this paper is used simple circuit are provided by using a low duty cycle of the flash. A miniature single Schmitt trigger logic inverter is

SN74AHC1G14 />, plus two resistors and a Schottky diode and a capacitor, it constitutes the flash timing generator, as shown in the figure. Output waveform cycle about for

/> is to speed up the charging time of the capacitor, C, to shorten high output time TL. implementation method is to increase the resistance of RCH and no more than 200 mV positive pressure drop of Schottky barrier diodes in series D1S.D1S and can be neglected. LED time of the light is about (1 /100) & times; TL≈ 5ms.

LED drive comprises constitutes a PNP bipolar transistor Q1 and a NPN bipolar transistor Q2.Q1 and Q2 a convertible current source of . When logic high electricity at ordinary times, led by a constant current, current value of about IO≈ 0.7V/RS. The circuit for 10mA.

series silicon diodes D1 and D2 provide the powerful nonlinear negative feedback functions the Schottky diode D2S cathode. If for any reason, the voltage drop on the resistor RS is increased, and the connection of the D1 to the D2 will force the Q2 emitter voltage to produce nearly the same lift. This increase reduces the Q2 collector current, so it also reduces the Q1 base current, forming a closed loop. The final result is to reduce the Q1 collector current, so that it maintains a constant value.

note, when the output of the IC1 is low, the current through the D2S and the resistor RB can be ignored. This is because, when the IC1 output is low, the base of the Q2 is kept low, so that it is shut off from the current source. When the current source is turned off, led was extinguished, at this time only microampere level leakage current through the D2S and Rb. If the surface mounted component, the circuit can do in a less than 16mm× 16mm board.

this work has been supported by the Slovakia research and development department, the contract number is APVV-0062-11s.

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