We don't need to power the chip at 12V nor do we need to supply 120mA.
10mA is good enough for this application, thank you.

 

We are not talking about 10mA, we are talking about the fact that the 555 cannot supply 200mA at any reasonable output voltage.
Show me one circuit on the web that uses the 555 at 5v and delivers 200mA?
Of course you can drum up unrealistic capabilities and confuse the beginner into thinking the 555 is good for "all applications."

 

I build my knowledge via different means, empirically, and from manufacturers' data sheet, and not from a nitwit on the internet. I have no interest in carrying on a debate with you.

 

@Colin55 - Many of your claims are in opposition to demonstrated results, thus are demonstrably wrong.

No one has claimed that the 555 is good for "all applications" -- that is a straw man of your own invention.

 

What use is an output voltage of 3.5v ? You could only use it to power the motor on an electric bike at 20mph.
Test the chip at 12v and 15kHz and feel the heat. At 120mA you can just keep your finger on it and 200mA "blows you away."

You sure about that? The ‘Lil Professor says the junction temp is about 80C with 25C ambient. About 1/2 watt dissipated in the output typ. Not counting discharge pin dissipation but that’s pretty small. I couldn’t find ‘blows you away’ in the datasheet but the numbers are nicely under Absolute Max Ratings.

 

You sure about that? The ‘Lil Professor says the junction temp is about 80C with 25C ambient. About 1/2 watt dissipated in the output typ. Not counting discharge pin dissipation but that’s pretty small. I couldn’t find ‘blows you away’ in the datasheet but the numbers are nicely under Absolute Max Ratings.

No. I am just making everything up. I just burnt my finger and all the skin has just peeled off.

How is it that: when you load the 555 with 100R on 12v, the output is 10v and the current is 100mA from the supply and the output is 50:50 The load is only getting an average of 50mA? Where is the other 50mA going?
This is the sort of questioning that no-one has ever thought of.
That's why the chip gets so incredibly hot.

 

You sure about that? The ‘Lil Professor says the junction temp is about 80C with 25C ambient. About 1/2 watt dissipated in the output typ. Not counting discharge pin dissipation but that’s pretty small. I couldn’t find ‘blows you away’ in the datasheet but the numbers are nicely under Absolute Max Ratings.

No. I am just making everything up. I just burnt my finger and all the skin has just peeled off.

How is it that: when you load the 555 with 100R on 12v, the output is 10v and the current is 100mA from the supply and the output is 50:50 The load is only getting an average of 50mA? Where is the other 50mA going?
This is the sort of questioning that no-one has ever thought of.
That's why the chip gets so incredibly hot.

The supply current isn't a continuous 100 mA. How can it be?

You also need to properly segregate the current in the timing components and, correspondingly, the power dissipated in them.

 

That's why I use a simple $5.00 moving coil ammeter that shows the average or "actual" current-flow and I measure between battery and 1,000u so the electro takes up all the irregularities.

 

How is it that: when you load the 555 with 100R on 12v, the output is 10v and the current is 100mA from the supply and the output is 50:50 The load is only getting an average of 50mA? Where is the other 50mA going?

It isn't "going" anywhere. the second "50" is the percentage of time when the output is low and there is almost zero current into a ground-connected load. No current = no power dissipation.

This is the sort of questioning that no-one has ever thought of.

I completely agree.

ak

 

It isn't "going" anywhere. the second "50" is the percentage of time when the output is low and there is almost zero current into a ground-connected load. No current = no power dissipation.

You completely missed the point.

 

It isn't "going" anywhere. the second "50" is the percentage of time when the output is low and there is almost zero current into a ground-connected load. No current = no power dissipation.

You completely missed the point.

May be. So I’ll ask - where’s the other 50mA going? The chip will be hot in either case so we should dispense with that as an indicator.

I’m not trying to provoke an argument but I am kind of a specs and numbers guy and I’m interested in how those are off by 100%.

 

I’m not trying to provoke an argument but I am kind of a specs and numbers guy and I’m interested in how those are off by 100%.

I haven't done the math, but I believe with the right timing components (namely, a big capacitor and a low ohms resistor), you could drive substantial current into them at higher frequencies. This would be current from the supply not appearing in the output.

 

I haven't done the math, but I believe with the right timing components (namely, a big capacitor and a low ohms resistor), you could drive substantial current into them at higher frequencies. This would be current from the supply not appearing in the output.

I guess so but I was thinking more along the lines of a good design. Burning 40-50ma in a 15KHz timing RC says more about the designer than whether the chip is suitable for the task. And no, I am neither a fan nor an advocate of 555s. I just never experienced that level of internal power consumption when I did use them so I'm curious about that and want to ensure that questions get good answers.

 

Why should the 555-timer chip get hot?

Test #1
LM555 @ 5V supply, 15kHz 50% duty cycle, 15Ω load at pin-3 to ground.
High voltage = 3V
Assuming average power is 50%
power through load resistor = 0.3W, temp = 40°C
power through IC = 0.2W, temp = 30°C

Test #2
LM555 @ 12V supply, 15kHz 50% duty cycle, 56Ω load at pin-3 to ground.
High voltage = 10V
Assuming average power is 50%
power through load resistor = 1W, temp = 70°C
power through IC = 0.2W, temp = 30°C

(Temperatures measured with IR thermometer.)

 

I guess so but I was thinking more along the lines of a good design. Burning 40-50ma in a 15KHz timing RC says more about the designer than whether the chip is suitable for the task. And no, I am neither a fan nor an advocate of 555s. I just never experienced that level of internal power consumption when I did use them so I'm curious about that and want to ensure that questions get good answers.

The current in the timing RC circuit is not the same current at the pin-3 output.
The chip supply current is 3 to 5mA @5V while the output can source or sink 200mA.
The current in the RC circuit will depend on the timing resistors and can easily be less than 1mA.

 

Why should the 555-timer chip get hot?

Test #1
LM555 @ 5V supply, 15kHz 50% duty cycle, 15Ω load at pin-3 to ground.
High voltage = 3V
Assuming average power is 50%
power through load resistor = 0.3W, temp = 40°C
power through IC = 0.2W, temp = 30°C

Test #2
LM555 @ 12V supply, 15kHz 50% duty cycle, 56Ω load at pin-3 to ground.
High voltage = 10V
Assuming average power is 50%
power through load resistor = 1W, temp = 70°C
power through IC = 0.2W, temp = 30°C

(Temperatures measured with IR thermometer.)

How about at "high" frequency, something over 100kHz?

 

How about at "high" frequency, something over 100kHz?

I don't think there will be any difference but I will check tomorrow.

 

Sorry for the late reply, unfortunately didn't have the chance to follow up on this one. But thanks for all the inputs. I will review and see what I can come up with Great support

 

So to answer the question about the phone+amplifier- yeah, i want to have this as a standalone solution.
So basically what I gathered from your discussion I could consider the following options:

1. 555+amplifier+tweeter. I could just build it and see if it blows up, cuz that's the fun way
   
2. build the oscilator circuit manually (?)+amplifier+tweeter.

I wanted to do this with a piezzo, but as mentioned i couldn't find one for the frequency.

 

Just wondering, is the 90db SPL requirement at 30 cm or 1m?