Need guidance

[epilot]

Hello,

Some days ago I made a circuit like the picture to increase the input voltage of an ultrasonic sensor used as a range finder, the source voltage was 12V and the designer of this diagram according to wave forms wanted to increase the voltage on the ultrasonic sensor by factor 2 , there is a 180 degree phase shifting between output pins.
Ok the question is that how this is possible getting 24V from a simple inverter circuit?
My confusion is because there should be a complex circuit to get a NEGATIVE voltage but as you can see in the pic we have nothing more than few inverter gates,
Well, we have a 12V source and it has a +12V and a 0V, I think ideally we will have a +12V on one output pin of the gate and a 0V on another pin at a moment, there is no else component to generate a NEGATIVE voltage, so what is the problem with my understanding of this circuit?
I have this problem with bridged amplifiers too.

Thanks for any input.

 

[Dr.EM]

Bridged amplifiers do have dual polarity supplies, so it makes sense. This however, does not. I agree that a maximum of 12v can appear accross the sounder.

 

[Nigel Goodwin]

No Dr. EM, there's no need for dual supplies on a bridged amplifier, and they effectively provide double the HT supply to the load - that's the whole reason for them!. With a 12V supply the simple bridged circuit shown above will provide 24V p-p to the load (minus the usual losses in the circuit of course).

Perhaps you're being confused by the scope picture on the output?, there's actually no ground reference point on the bridged output.

 

[JimB]

epilot

Think about it like this:

Connect the supply to the speaker and the speaker cone is pushed out.
Disconnect the supply, reverse the polarity and the speaker cone is pulled in.

Twice the amount of movement from the speaker, with the same supply.

Make sense?

JimB

 

[AllVol]

Doesn't the output waveform simply rotate about the operating point established by the inverter pair?

 

[audioguru]

Doesn't the output waveform simply rotate about the operating point established by the inverter pair?

Think about a "normal" single-ended amplifier with one wire of the speaker effectively at half the supply voltage (capacitor-coupled or a dual-polarity supply). The amplifier then drives the speaker's other wire to the supply voltage or to ground. The supply voltage peak-to-peak.
Now connect the speaker to a bridged amplifier pair and one side of the speaker will be driven to the positive supply and the other speaker wire will be driven to ground. Double the supply voltage peak-to-peak.

 

[mramos1]

Nigel is correct, I had a piezo curcuit (connected to a microcontroller) and I need more voltage to it. Nigel and Ron H told me to take the ground pin, tie it to another IO pin on the microcontroller, and pulse one high and the other low and flip them back and forth.

It was a 6V supply and sure enough, much louder. I even pulled out the scope, a nice 12Vp-p squarewave from a 6VOLT supply.

 

[epilot]

Perhaps you're being confused by the scope picture on the output?, there's actually no ground reference point on the bridged output.

Yes Nigel, I was confused with the waveforms in the picture,
it make sense now, the positive and ground are reversed according to input signal and with this trick we can get a double voltage.

But as this circuit is a a bridged amplifier let me know if the freq response of a bridget amplifier is double than its Configuration as a common amplifier?
For example if I have an amplifier IC with a freq response from 50Hz to 15kHz if I configure it as a bridged amplifier the will I have a freq response from 25Hz to 30kHz too?

 

[audioguru]

The frequency response of a bridged amplifier isn't doubled, it is the same or could even be 3/4'd if each amplifier is in series for one of the outputs.

 

[Nigel Goodwin]

But as this circuit is a a bridged amplifier let me know if the freq response of a bridget amplifier is double than its Configuration as a common amplifier?
For example if I have an amplifier IC with a freq response from 50Hz to 15kHz if I configure it as a bridged amplifier the will I have a freq response from 25Hz to 30kHz too?

It will just be the same, or perhaps slightly worse depending how you bridge it, it can't ever be better.

 

[epilot]

epilot

Think about it like this:

Connect the supply to the speaker and the speaker cone is pushed out.
Disconnect the supply, reverse the polarity and the speaker cone is pulled in.

Twice the amount of movement from the speaker, with the same supply.

Make sense?

JimB

The problem is that for a common single ended amplifier we have a ground pin and an output pin that reverse from positive to zero and when it is zero we have no sound in the speaker but in a bridged amplifier when this pin goes to zero the other pin goes to positive and we will have a sound!!!?
That is not correct but how know what is the problem with my understanding about these kind of circuits?

 

[epilot]

It will just be the same, or perhaps slightly worse depending how you bridge it, it can't ever be better.

The frequency response of a bridged amplifier isn't doubled, it is the same or could even be 3/4'd if each amplifier is in series for one of the outputs.

Ok thanks,

So which one of these IC's are THE BEST choice for 50 or 60kHz freq, bridged or common mode no difference so?
TDA2005, TDA2003, TDA1557, LM3875T
I have these IC's in my hands at the moment and want to configure them for that freq.

 

[audioguru]

The problem is that for a common single ended amplifier we have a ground pin and an output pin that reverse from positive to zero and when it is zero we have no sound in the speaker but in a bridged amplifier when this pin goes to zero the other pin goes to positive and we will have a sound!!!?
That is not correct but how know what is the problem with my understanding about these kind of circuits?

A single-ended amplifier with a single supply uses a coupling capacitor to block DC but pass the audio to the speaker.
The AC from the amplifier passes through the coupling capacitor and causes the speaker to vibrate at the frequency of the AC. The DC output voltage of the amplifier is at half the supply voltage without a signal and swings up and down from there. The DC voltage at the speaker is 0V due to the coupling capacitor and swings positive and negative from there. When the output voltage of the amplifier swings to the supply voltage then the speaker's voltage swings to half the supply voltage. When the output voltage of the amplifier swings to ground then the speaker's voltage swings to a negative voltage that is half the supply voltage.

 

[audioguru]

Do you have anything that will vibrate at 50kHz or 60Khz? Why?
The ultrasonic piezo transducers that I have seen vibrate at about 40kHz and don't work at higher frequencies.

Look at the datasheets for the amplifiers to see how difficult or easy they are to bridge and their max frequency response. I go to www.datasheetarchive.com .

 

[Nigel Goodwin]

Yes, you need to provide more details - so far we don't have a clue what you're trying to do, and it doesn't sound hopeful?.

 

[audioguru]

Yes, you need to provide more details - so far we don't have a clue what you're trying to do, and it doesn't sound hopeful?.

His 1st post mentioned an ultrasonic rangefinder.

 

[Nigel Goodwin]

His 1st post mentioned an ultrasonic rangefinder.

Yes, but now he's mentioning strange frequencies?.

 

[epilot]

Do you have anything that will vibrate at 50kHz or 60Khz? Why?
The ultrasonic piezo transducers that I have seen vibrate at about 40kHz and don't work at higher frequencies.

Look at the datasheets for the amplifiers to see how difficult or easy they are to bridge and their max frequency response. I go to www.datasheetarchive.com .

Oh sorry I forgot to say that I found 2 ultrasonic transducers (used for cleaning), just like the big transducer in the pic.It seems the freq response is between 50 or 60kHz(I am not completely sure yet) they are 50mm in diameter they need a high amplitude signal and I want to use a power amplifier for them but it seems the companies write the freq response of sound no ultrasonic level for their IC's in the data sheets so most are writing a freq range between 20 or 50Hz to the upper level of a human hearing that is 20kHz so i was not able to found out which one is good for that range??

Some of amplifier IC's get hot even without any load in the output,this means more and more power but I need for an IC that does not get hot when there is no load....

Sorry I have to go to the bed,I am not able to write more for now.

 

[audioguru]

they need a high amplitude signal

How many volts p-p?

which one is good for that range??

Your piezo transducers don't need a power amp.

Some of amplifier IC's get hot even without any load in the output.

You looked at high power amplifiers that have a high current output therefore don't have a very good high frequency response. Your piezo transducers don't need much current.

The amplifier ICs waste power and get hot to minimise crossover distortion. Your transducers don't care about distortion.

Why not use an opamp that drives a complimentary emitter follower? It will have a low idle current, go to 100kHz and drive the capacitance of the transducers perfectly. Make bridged amplifiers to double the drive voltage if the transducers can handle it.

 

[epilot]

How many volts p-p?


Why not use an opamp that drives a complimentary emitter follower? It will have a low idle current, go to 100kHz and drive the capacitance of the transducers perfectly. Make bridged amplifiers to double the drive voltage if the transducers can handle it.

I want to start with 24 or 30V P-P for now.

I am not sure if my op amps will deliver a 30V P-P or not. here are the opamps I have at the time:
LF411N, LF356N
Do you think that they can deliver 3A at 30V?

i think a class D power amplifier is the best choice because i want to use both my transducers in parallel with the amplifier, perhaps a class D bridget amplifier is the best choice.

i am getting confused now about which kind of amplifier I should use?