Electronics > Beginners

Ripple current / voltage, what is too much?

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cowana:

--- Quote from: r0d3z1 on October 24, 2018, 10:21:53 am ---it's a good question, the LED don't like ripple but it will be hard to find such a parameters in the DS

--- End quote ---

LEDs are perfectly happy being driven with PWM, which could be considered as 100% ripple.

The datasheet will state the maximum allowed current (usually in continuous, average and pulsed cases) - from there it is just a matter of considering the IV characteristics to convert that into a ripple specification.

FriedMule:
My knowledge is wary poor so I'd trust the smart people, like you on this forum and Mr. EEV:-)
My circuit is inspired from this EEV video: https://youtu.be/wopmEyZKnYo?t=633

Since I am new and don't have any lab gear yet, could anybody please tell me if my circuit will work at all and if so how much ripple it delivers?

T3sl4co1l:
You've drawn it with a MOSFET, which doesn't multiply capacitance at all.  Or, actually, following the same design motivation, it still is, but the ratio is nearly infinite; but that's absurd, and in practice, that means the description breaks down and it's better called just a filtered source follower.

You aren't apparently filtering anything the LM317 won't handle, so I don't get the point in the first place.

How does an opto fit into this?

Tim

FriedMule:
Dave it talking about the advantages of using a N-FET in that circuit in his video, don't know if I have misunderstood.

The Opto arrives for two reasons, first I can't find out how to read max ripple for a component, don't know what to look for and the Opto is something I want to use in a smps.

mvs:

--- Quote from: FriedMule on October 25, 2018, 02:19:34 pm ---Dave it talking about the advantages of using a N-FET in that circuit in his video, don't know if I have misunderstood.

--- End quote ---
Large gain of MOSFET is advantage for this circuit, but it comes together with a large voltage drop.
MOSFETs are usually enhancement mode devices with VGS(th) >2V. Single silicon BJT or Sziklai pair will drop only 0.6V.


--- Quote --- Since I am new and don't have any lab gear yet, could anybody please tell me if my circuit will work at all and if so how much ripple it delivers?
--- End quote ---
You can get some SPICE simulator (LT-SPICE, PSPICE, TINA-TI, etc.) and simulate your circuit or at least parts of it.
LT-SPICE calculates around 1.2mV peak-tp-peak ripple after your capacitor multiplier for 10V 60Hz AC input and 10 Ohm load (please see attachment).

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