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Topic: Using logic level FET TK5Q60W with a 8R speaker (Read 2192 times) previous topic - next topic

boylesg

How would you go about hooking this up to an arduino pin?

I tried the simple approach with just the FET and the speaker but all it seems to do is heat up the speaker.

Unclear how to go about it.

slipstick

Unclear what you're trying to achieve with it. What's happening on the pin that you think a speaker will be interested in?

Steve

boylesg

#2
Nov 05, 2017, 02:00 pm Last Edit: Nov 05, 2017, 02:01 pm by boylesg
Sorry...using the Tone library and this sort of circuit minus the resistors.
And 5V rather than 12V while I am testing.


slipstick

Well for a start the TK5Q60W isn't a logic level MOSFET. The giveaway is that all the timing figures in the datasheet use a Vgs of 10V to switch it on fully. So driven from an Arduino it's in it's linear zone which is why it's getting hot.

And I'd prefer to see the circuit that you're using. A circuit that you are not using isn't very helpful. If you have no resistors at all that's not a good idea.

Steve

jremington

"8 Ohm" is the nominal speaker impedance at 1 kHz. The resistance is much less.

DVDdoug

#5
Nov 05, 2017, 07:03 pm Last Edit: Nov 05, 2017, 07:05 pm by DVDdoug
Quote
I tried the simple approach with just the FET and the speaker but all it seems to do is heat up the speaker.
Are you saying you didn't get any sound?   If the speaker is heating-up with no sound, that means your putting DC across the speaker...  Either something is wrong with your electronics, or your writing a digital-high.    (Or, it's possible that you're sending ultrasonic signals.)

Power is V2/R.    So 5VDC would be 3 Watts which is a fair amount of heat from a small speaker.   A 5V square wave is 2.5V average, so that's a little less than 1W.   

Note that a 10W speaker is rated for 10W audio peaks and it can only handle about 1W continuously.   So, you could possibly burn-up a small speaker.

I would assume that the output goes low when tone() stops, but you might want to check that or write a low after turning the tone off.   ...With no sound, there should be no current and the speaker cone should be in it's neutral/resting position (if the speaker is not enclosed and you can see the cone).     You can also put a capacitor in series with the speaker to block DC (maybe 1000uf depending on the frequency of the tones.)




boylesg

I managed to find the following circuit from this post: https://forum.arduino.cc/index.php?topic=22678.0


Will try this unless anyone thinks it is inappropriate.

Grumpy_Mike

Check what size of negitave voltage that FET gate can take. Make sure it is more than the positive signal you feed into it. Otherwise put a reverse diode across the gate pull down resistor.

boylesg

#8
Nov 06, 2017, 10:31 am Last Edit: Nov 06, 2017, 10:32 am by boylesg
Check what size of negitave voltage that FET gate can take. Make sure it is more than the positive signal you feed into it. Otherwise put a reverse diode across the gate pull down resistor.
What about this circuit, extrapolating form the previous one to get 12V on to a TO220 fet gate?


Grumpy_Mike

The value of R2 means the BC548 will take 1A and fry it. Change it to 1K.

Assuming L1 is the speaker then it is fine but not the best of designs. The circuit will take 1A peak current can your power supply cope? It seems a bit brutal to me. Also R4 will get hot it will be dissipating 12 watts max. If you have a square wave then that will average out a 6W but that is still a chunky resistor you need, probably one rated at 10W.

However, you can remove C1 and D1

boylesg

#10
Nov 06, 2017, 12:04 pm Last Edit: Nov 06, 2017, 12:05 pm by boylesg
The value of R2 means the BC548 will take 1A and fry it. Change it to 1K.

Assuming L1 is the speaker then it is fine but not the best of designs. The circuit will take 1A peak current can your power supply cope? It seems a bit brutal to me. Also R4 will get hot it will be dissipating 12 watts max. If you have a square wave then that will average out a 6W but that is still a chunky resistor you need, probably one rated at 10W.

However, you can remove C1 and D1
Oh bugger....forgot about that. Was focused on pushing 1A into the fet gate.

Oh well I could up it to BC337.

What would you recommend for adequate current into an average TO220 fet gate?

But this involves only audio frequency so I guess I don't really need the FET to switch FAST.


boylesg

#11
Nov 06, 2017, 12:18 pm Last Edit: Nov 06, 2017, 12:40 pm by boylesg
How about this:


Grumpy_Mike

#12
Nov 06, 2017, 02:06 pm Last Edit: Nov 06, 2017, 02:07 pm by Grumpy_Mike
You still don't need to be so brutal with the driver transistor. Yes you have got it down to 250mA but even that is way too high. Replace R2 with 1K and remove R5 altogether.

R4 is still way too low and that resistor will get very hot.

boylesg

#13
Nov 06, 2017, 02:26 pm Last Edit: Nov 06, 2017, 02:31 pm by boylesg
Bugger again.....5 / 50 = 0.1A

Should have been 12 / 0.1 = 1.2k

I do have rather a lot of metal oxide resistors I could use.

Trying to get the sound loud. What resistor would you suggest for small 3-4cm diameter speaker.

Grumpy_Mike

Quote
Trying to get the sound loud.
Then I would suggest that you use a class B amplifier instead of that circuit. That circuit is in effect a class A amplifier and can only ever be 25% efficient.

As it is only a square wave then a H-Bridge would act as a class B amplifier. 

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