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.





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28 comments

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May 27, 2013 at 3:26 AM delete

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

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Anonymous
September 26, 2013 at 11:36 PM delete

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

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September 27, 2013 at 7:12 PM delete

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.

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Anonymous
October 1, 2013 at 1:11 AM delete

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

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October 1, 2013 at 1:37 PM delete

not tested, but i am sure about it.

yes it would also handle DC shorts across the speaker

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March 18, 2016 at 11:29 AM delete

Useful but I want the number of opto couple

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March 18, 2016 at 11:32 AM delete

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

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March 18, 2016 at 12:09 PM delete

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

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March 21, 2016 at 12:25 PM delete

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

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March 21, 2016 at 12:28 PM delete

Can I use MCT2E instead of 4N35

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March 21, 2016 at 9:19 PM delete

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

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March 21, 2016 at 9:49 PM delete

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

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March 22, 2016 at 8:33 AM delete

for 100 watt you can use the following formula

100/V = current

therefore R = 1.5/current

here V is your amp supply voltage

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March 22, 2016 at 10:22 AM delete

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

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March 22, 2016 at 7:02 PM delete

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

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March 22, 2016 at 7:21 PM delete

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

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March 22, 2016 at 7:57 PM delete

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

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March 23, 2016 at 7:11 AM delete

you are welcome, yes that's right!

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March 23, 2016 at 10:59 PM delete

This circuit is new it OK can we use in4148 diode

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March 24, 2016 at 3:00 PM delete This comment has been removed by the author.
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