Apr 22, 2012

Make this Amplifier Short/Overload Protection Circuit

While working with high power amplifier designs, two things become crucial, the protection of the amplifier and the protection of the speakers from an accidental over current influx.


Especially when the amplifier design involves costly mosfets, the design becomes specifically vulnerable to short circuits at the outputs.

A short circuit at the output may be caused due to mishandling or ignorance from the part of the user.

Whatever might be the reason, the end results in the destruction of the precious mosfets inside the amplifier box.

The above mishap can be prevented by adding a small circuit for detecting a short circuit conditions at the outputs of an amplifier.

The given amplifier short/overload protection circuit diagram, shows an inexpensive design using just a single transistor for implementing the intended feature.

Normally a low value resistor is usually employed at the output of mosfet amplifiers, the current developed across this resistor can be well exploited for tripping a relay in case it exceeds the safe maximum current value.

The current threshold across the above resistor is sensed by an LED inside an optocoupler, which lights up the moment a short or overload conditions is sensed.

This instantly triggers the opto transistor which in turn switches ON the transistor driver and the associated relay mechanism.

Since the relay coils support the amplifier connection with the speaker output, disconnects the amplifier from the output connection, preventing the amplifier devices from a possible damage.

The capacitor at the base of the transistor keeps the transistor switched for a few seconds so that the relay does not oscillate randomly.





29 comments:

  1. see, talk of ingenuity this is one of them, it obviously agreed with my slogan "simple and functional" keep it on.

    ReplyDelete
  2. HI
    this diagram seems not complete how does the relay power up?where is the source of its power?

    ReplyDelete
    Replies
    1. Hi,
      yes by mistake the positive connection is not shown in the diagram, a separate +12V should be connected to the link that connects the relay coil and the opto transistor.

      Delete
  3. have you built and tested this project/the project is impressive does this protection also include d.c currents against the speakers?

    ReplyDelete
    Replies
    1. not tested, but i am sure about it.

      yes it would also handle DC shorts across the speaker

      Delete
  4. Useful but I want the number of opto couple

    ReplyDelete
  5. OK it is useful circuit I want to know the number of opto couple
    Thank-you

    ReplyDelete
  6. Say the value of resistance 0.5 ohm iam not able to get in india

    ReplyDelete
  7. Sir thank you for reply but in India only 1 omhs is available can I use that one
    Thanks again

    ReplyDelete
    Replies
    1. saravanan, please tell what is the max wattage limit do you prefer to implement? the resistor value will depend on this

      Delete
  8. 100 Watts 5.1 amplifier system it is designed by MOSFET IC I have changed my speaker for more than 8 times in 2 years
    Thankyou

    ReplyDelete
    Replies
    1. for 100 watt you can use the following formula

      100/V = current

      therefore R = 1.5/current

      here V is your amp supply voltage

      Delete
  9. Sorry I can't understand which voltage
    Input to transformer is 220 volt and the output of the transformer is 24 volt the transformer current rateing is 5 amps
    Mean while I get only 1 ohmes in India
    Thank-you

    ReplyDelete
    Replies
    1. the 0.5 ohm shown in the diagram will need to be calculated as explained using the formula in the previous comment.

      If your amplifier operating volatge is 24V then

      100/24 = 4.16

      R = 1.5/4.16 = 0.36 ohms

      wattage of resistor will be = 1.5 x 4.16 = 6.24 or a 10 watt will do.

      if you are getting 1 ohm then use two in parallel, in place of the indicated 0.5 ohm

      Delete
    2. .....two 1 ohm in parallel will do in place of 0.36 ohm

      Delete
  10. Thank you sir so I want to ready 6 circuit for 5.1 amplifier

    ReplyDelete
  11. This circuit is new it OK can we use in4148 diode

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  12. This comment has been removed by the author.

    ReplyDelete
  13. Does anyone have a COMPLETE working circuit (including missing +12V to relay and opto) with all parts IDENTIFIED? Has anyone tested or built this circuit?

    ReplyDelete

Swagatam Majumdar
Swagatam MajumdarHi Friends, Welcome to my site, a place where you will discover a massive collection of electronic circuit ideas, mostly requested by the dedicated readers and exclusively designed by me for their customized application needs. I have posted more than 1100 circuit designs in this site, if you have a personalized circuit requirement you may feel free to request it through the comment box, if it seems feasible to me then surely you may find it published here with your credentials attached in the post, thanks and please keep reading



 
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