# IRF520 replacement

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#### bogdanfirst

##### New Member
i have a schematic that uses a IRF520(or 530 or 540) MOSFET to drive a 4...16R speaker. the circuit is powered from 12V so the max. current wil be 3A. the thing is that the IRF520 is designed for 9.2A and i dont need that much current, and it is quite expensive as well. and i was looking for a replacement wich will hold less current, since i am going to use a 8R speaker, 2A is enough. so i need a FET with about the same electrical characteristics and to be easily available and cheap, @2-3A. can anybody help me?

#### Chippie

##### Member
A mosfet from the BUZ brigade perhaps ? BUZ11......

#### Pilot

##### New Member
Why not try the IRF 510?

The main problem seems to be "easily available & cheap".

We tend to forget that while such parts are available and cheap here in the UK, and in the USA, the same cannot be said for some countries. This gives the problem of not knowing what is available near you.

Re: the IRF510, if they are suitable but not available, pm me.

#### bogdanfirst

##### New Member
Wich one from the BUZ series?
about the IRF510, 5.6A is still too much. considering that it drives a speaker of 4...16Ohm from a 12V power suply...i dont understand those people that designed the circuit.

#### Chippie

##### Member
Chippie said:
A mosfet from the BUZ brigade perhaps ? BUZ11......

BUZ11 or BUZ11A 8)

#### bogdanfirst

##### New Member
seems that i am not getting it.....
http://www.chipcenter.com/questlink/searchResult.jhtml;$sessionid$5XAH5BAAAKJDUQSNDISSFEQ
as i see ...lots more amps then i need(2-3)

#### Chippie

##### Member
bogdanfirst said:
i have a schematic that uses a IRF520(or 530 or 540) MOSFET to drive a 4...16R speaker. the circuit is powered from 12V so the max. current wil be 3A. the thing is that the IRF520 is designed for 9.2A and i dont need that much current, and it is quite expensive as well. and i was looking for a replacement wich will hold less current, since i am going to use a 8R speaker, 2A is enough. so i need a FET with about the same electrical characteristics and to be easily available and cheap, @2-3A. can anybody help me?

I re- read your post........max current draw by the speaker is 12/4 amps..3 in this case....however you are intent on using a speaker with an impedance of 8 ohms.....so the current is then 12/8 amps or 1.5A

I'd be inclined to go with something with a slightly higher current rating than your choice, based on the impedance of the speaker is measured at 1kHz, therefore its impedance could be much higher at a different frequency, so current would change(higher) ok this may be a peak......Using a semiconductor in its SOAR isnt good practice.....imho

I'd still go with the higher rating.....As to cost I cant comment, not knowing how much they are in Rumania, but here in the UK semi prices are reasonable.....How about importing them to your coucntry ? :lol:
Just a thought.....

#### bogdanfirst

##### New Member
well, the price is not that big, but the thing was that there was no point in bying a 9.2 A FET when i need less then 1/3 of its capacity. also i domt know why the person that designed the circuit used such a high power. i found a BUZ'i dont know what number' at 5.6A, and i think that i will choose this one. and you are right about the impedance, considernig that the sound is similar to a police siren, i htink that the frequency is not that high, so the impedance will not modify so much....but still....

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