Diode protection or tvs

Discussion in 'The Projects Forum' started by barg, Feb 25, 2016.

  1. barg

    Thread Starter New Member

    Dec 23, 2015
    22
    0
    Hi,

    I am using a 3 n ch fets for a load of 2A each, source is 12v. i would like to protect this circuit but not sure which diode is the best fit to do that - schotky or tvs or both?

    Also not sure which values, if for tvs, will a break down value of 12v is right? and if to use a 1 dirrection or two dirrectios tvs diode? can a 1 dirrection tvs protects from reverse voltage connection?

    As for the schotky is it enough for 1A?

    Appreciat your assistance!

    Thanks,
     
  2. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    5,005
    745
    Are you trying to protect the D/S of the fets from spike damage due to induction devices, like coils or motors, if so use shottkey or ultrafast diodes.
    A tvs diode behaves like a zener.
     
  3. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,546
    1,252
    The two diodes protect different things in different ways. Without more information about the loads there is no clear advice. Using D1 only is series protection, and will protect the DC power source by disconnecting it from load transients. However, it will let any load turn-of positive voltage inductive kicks go to their full peak value, which can let relays and solenoids release more quickly. But the diode will need a rating of hundreds of volts and the spikes can generate significant radiated and conducted noise. D2 is shunt protection, and clamps or limits both the positive and negative peak voltages of any turn-off transients. Depending on the load, the transient current can be significant but the voltages are low. If you read the TVS datasheets you will see that the actual clamp voltage can be several volts higher than the diode rating, so choose carefully. If you must choose only one, I'd start with D2.

    ak
     
  4. barg

    Thread Starter New Member

    Dec 23, 2015
    22
    0
    Thank you Dogydave and AK,

    load is 3 leds each 2A feeds from 12v wall switch adapter, Purpose of diode/s is to protect from high voltage and load kicks for the mosfets s/d and leds and the circuite which has also other 12v components.

    Question is if tvs diode protects from reverse voltage like simple diode do? and is a 12v breakdown voltage for this tvs, can fits to this circuite?
     
  5. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    5,005
    745
    If you're protecting the fets D/S use shotky or ultrafast diodes across the d/s terminals, or use mosfets with built-in diodes, like Irfz44n, IRF540
     
    Last edited: Feb 25, 2016
  6. barg

    Thread Starter New Member

    Dec 23, 2015
    22
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    you mean that a schotky diode will protect from over voltage spikes?

    I dont understand why to use 3 diodes for each fet terminal, instead of 1 schotky in the vin entry?
     
  7. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    5,005
    745
    the correct way for spike suppresion, is to put the diode across the load, which is the led in your case, not across the supply, so three fets means three diodes,
     
  8. barg

    Thread Starter New Member

    Dec 23, 2015
    22
    0
    Ok, in addition to this 3 diodes, if i will put a rectifier diode in the entry of 1A, for reverse current protection, will that will be enough?
     
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