Transistor to toggle amplifier

Using Arduino General Electronics
#1

I am using this cheap amplifier board at 12v with Arduino, for sound effects in my truck:

TDA2030A

It works good. When my project wakes from sleep mode, I would like to toggle a transistor to power the 12v power source for the audio amplifier. I believe it may peak at 2 amps, 18 volts - however, the battery will probably only provide up to 14.4 volts.

The 2n2222 transistor I tried seems to distort the audio, and is not strong enough to provide the full power to the audio amp.

Can someone advise a better more efficient mosfet or other circuit? I have tip-120's that handle 5 amps, I was going to use. They probably are not efficient with the power, but the device should not be on when the vehicle is idle, to avoid draining the battery (as I have found in my previous projects).

#2

but the device should not be on when the vehicle is idle, to avoid draining the battery (as I have found in my previous projects).

Your truck should already have an accessory power bus/connection that's off whenever the ignition is off. For example, the radio (and almost everything else) is powered-off when you turn off the key. In fact, if you expect to automatically turn-off the amplifier you'll have to "sense" the accessory power anyway.

The 2n2222 transistor I tried seems to distort the audio, and is not strong enough to provide the full power to the audio amp.

A 2N2222 shouldn't have any more voltage drop than any other transistor (if you turn it on "hard" with enough base current) but it will probably burn-up with the current of an audio amp.

A transistor will have a (small) voltage drop across it, and that's not desirable with an audio amp. A MOSFET will have a smaller voltage drop. I'm not sure how much current your amplifier needs, but if you decide to use one, get a "power" MOSFET that's rated for at least a couple of amps.

BTW- The TIP-120 is a Darlinginton transistor so it's got a LOT more current gain and there's a chance it will saturate (fully turn-on) in the same circuit as the 2N2222, but I don't know anything about your 2N2222 circuit.

#3

The project is more complicated, I summarized to avoid confusion. It must stay on to receive wireless signal that will trigger relays to start & shut down the truck. The relay that toggles accessory on, is actually controlled by Arduino.

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The circuit I am using, was a 2.3k resistor to the base from Arduino pin. The amplifier was connected to power 12+v, and ground tied to the collector pin, base tied to ground. Simple. Tip 120 I would wire it the same way, if I can't find a better suitable circuit to do the job.

#4

I agree with the previous post. Get a power MOSFET (more precisely - a logic level MOSFET) like the IRLD024 (2 Amperes) or the IRF640 (10 Amperes) and they can be directly controlled with a digital output connected to their gate through a 10k resistor. These would provide low side drive, connecting between the ground of your radio and power ground (Drain to radio; Source to main ground). Also, power MOSFETs can be easily paralleled to get higher current ratings (source to source, drain to drain, and gate to gate). The transistor you mentioned is never going to handle any significant amount of current and bipolar power transistors need a lot of base current to function as high current switches. MOSFETs make bipolar transistors look like dinosaurs for this application and power MOSFETs are really the way to go. Voltage at their gate controls current and next to zero current is drawn from the gate driver (your Arduino output). There are also some new high side solutions from Infineon (BTS50015-1TAD) if low side won't work for you. Check with Mouser for those.

#5

Ok thanks, I'll try out the Mosfets.

BTS50015-1TAD $6.00 at mouser. They also sell a nice shield for $38.00. Other mosfets are a fair price around $1.00 each

#6

Trexo: Get a power MOSFET (more precisely - a logic level MOSFET) like the IRLD024 (2 Amperes) or the IRF640 (10 Amperes) and they can be directly controlled with a digital output connected to their gate through a 10k resistor. These would provide low side drive, connecting between the ground of your radio and power ground (Drain to radio; Source to main ground).

Three mistakes here.

1) The IRF640 is not a logic level mosfet, and should not be used with Arduino's 5volt logic.

2) A 10k resistor between Arduino pin and gate is generally a bad thing. It slows switching.

3) Switching the ground of an amplifier may not be possible if there is something connected to the amp input. Leo..

The amp should be switched high-side (the supply). Google "high-side switch". You will need a P-channel mosfet and a small (2n2222) level shifter. Leo..

#7

Wawa: I have no experience working with mosfet. I don't know how many different channels there are and what difference between the levels. I am sure it's something I can learn in time. I would just look up an example circuit, pray the person who wrote it knows what they're doing and test to see if it works.

#8

See what you understand on this page.

http://www.gammon.com.au/motors

You need diagram#3 if the supply is ~12volt, and diagram#4 if the supply is more than that. The "load" can be anything. A motor, relay/solenoid, or your amplifier.

Come back with questions if needed. Leo..

#9

Well, because I practice it doesn't mean I'm any good at it. I am sure you can probably find at least one other thing on Wikipedia that was invented, that I don't know how to use. Does this information help you to advise me with using a mosfet on this tread? Or would you like me to elaborate more on some mental disfunctions and learning disorders?

#10

Wawa: See what you understand on this page.

You need diagram#3 if the supply is ~12volt, and diagram#4 if the supply is more than that. The "load" can be anything. A motor, relay/solenoid, or your amplifier.

Come back with questions if needed. Leo..

I think I need to check my eyes. I looked up and down the posts on the thread and can't find any diagrams, or links to anything with diagrams on them.

#11

Sorry, must have forgotten the link. Added it to the original post. Leo..

#12

Ok, thanks for the link update. The article helps to explain.

#13

Wawa: Three mistakes here.

1) The IRF640 is not a logic level mosfet, and should not be used with Arduino's 5volt logic.

2) A 10k resistor between Arduino pin and gate is generally a bad thing. It slows switching.

3) Switching the ground of an amplifier may not be possible if there is something connected to the amp input. Leo..

The amp should be switched high-side (the supply). Google "high-side switch". You will need a P-channel mosfet and a small (2n2222) level shifter. Leo..

1) You are correct in stating the IRF640 is not a logic level MOSFET but it will almost fully saturate at +5V gate voltage for low currents so it can be used with Arduino outputs. For higher currents it may drop excessive voltage. Try an IRL3303 if that's a problem. It's rated at 4 milliohms with a +5V gate to source voltage, handling 17 Amperes. 2) For this application (switching power) speed isn't important. Use a 1k for that matter but 10k provides a bit more protection for the Arduino output. Speed will be determined by the gate resistor and the gate input capacitance of the MOSFET and is still pretty good with 10k. 3) It depends on what the amplifier input configuration is. In many cases, it won't matter but you are correct in saying high side switching is preferred. That's why I included further references to those types of devices although the level shifter you mentioned will work fine. It's always nice to have all that in a single package.

#14

Am I reading this right? IRL3303, quick search on eBay they are like $2.50 - $5.00 each. That's more than the cost of all the circuits used in the audio amplifier board itself.

#15

Trexo: 1) You are correct in stating the IRF640 is not a logic level MOSFET but it will almost fully saturate at +5V gate voltage for low currents so it can be used with Arduino outputs. For higher currents it may drop excessive voltage. Try an IRL3303 if that's a problem. It's rated at 4 milliohms with a +5V gate to source voltage, handling 17 Amperes.

You can't say that, it won't be saturated, it will be somewhere in the triode region, and with the manufacturing spread of threshold voltage being 2V..4V, different devices will have wildly different on-resistances.

The typical plateau voltage for an IRF640 is 6.5V.

#16

How about an AOI510? http://www.digikey.com/products/en?keywords=AOI510 http://www.digikey.com/Web%20Export/Common/icons/datasheet.png Although I like Wawa's solution better.