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Offline LED Driver susceptible to noise problems?

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eem2am

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Hello,

I have just simulated an Offline LED Driver in LTSPice, the free downloadable simulator.

Anyway, the output is isolated, and I have to use an opto-coupler for feedback.
Unfortunately, there are no low_reference_voltage_Opto_Drivers on the market, ………-the only ones available have a reference voltage of 2.5V.

Therefore, I have had to bias up the current sense voltage with a current source involving a simple 5V regulator and a few resistors.

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My Question is simply:-
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Will this method of sensing the LED current result in an over-susceptibility to noise?……since the resistors used may turn noise currents into high noise voltages which will give noise problems at the high impedance inputs of the IC’s?


Anyway, here is the whole schematic:-

XXXXXXXXXXXXXXXXXXXXXX

Here is a close-up of the LED current sense circuitry:-

XXXXXXXXXXXXXXXXXXXXXX
 

FvM

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Current sense operation is effectively cancelled for higher frequencies by C14, in so far there's no noise problem.
It's a different question, if C14 introduces meaningful loop behaviour.

Generally, there should be a current feedback circuit involving less effort.
 

eem2am

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thankyou FvM,

Unfortunately, with LED circuitry being so immature at present, there are no isolated feedback chips available with the required low feedback reference voltage...so the above is genuinely as simple as it gets.......malheuresement.
 

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