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LED modulation circuit design problem

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rocsavi

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dear all,

i have to design a simple LED Modulation circiut...
Moudulation input is RF sine wave having frequency = 10KHZ, and 20mV peak to peak amplitude...
RF signal have DC bias-offset of 20 Volts...
LED used is ordinary type RED color LED having forward current in the range of 50mA..
How can drive the LED from above mentioned RF signal?? Any suggestion please...RF signal INPUT IMAGE IS ATTCHED FOR REFERENCE...PLEASE REPLYsine.JPG
 

KlausST

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Hi,

I don't know what you mean...

To drive a LEDfrom a voltage source you need a current limiting resistor.

Because the bias voltage is high in relation to a LED forward voltage the output (light) will be about proportional to input voltage.

Klaus
 

rocsavi

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Hi,

I don't know what you mean...

To drive a LEDfrom a voltage source you need a current limiting resistor.

Because the bias voltage is high in relation to a LED forward voltage the output (light) will be about proportional to input voltage.

Klaus
Klaus,
i means that, i have to design a voltage to current converter( using op-amp or BJT... ), so that with that current can driven LED..can u give me a suggestion for voltage to current conveter??
 

FvM

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The problem specification isn't very clear. Do you want a low (0.1%) modulation according to the input signal offset? Or reduce the offset to get maximal modulation depth?
 

KlausST

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Hi,

A bit more information please.

Why Opamp/bjt solution?
Is it because power dissipation, linaerity, precision?

An R is a simple voltage to current converter. Do you bother because of the forward voltage of the Led?

Klaus
 

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