Voltage Regulators and Heat Issues

[EasyGoing1]

So this is not technically about a power supply but it is about supplying power - I hope i'm posting in the correct forum...

Im working on a project that uses an Arduino, a sensor and a piezo speaker.

The speaker is used as an alarm buzzer and is loudest when i source 24v to it via a MOSFET which is actuated by the micro controller.

Then, I power the Arduino with a 7805 regulator as well as the sensor, then I have a separate 7805 feeding the reference voltage pin for a more stable reference voltage so that i can somewhat guarantee accurate voltage readings from the sensor.

My problem is, if i use a single 24v power supply for the whole project then power the 7805's from that source, the 7805 that supplies the Arduino and the sensor gets REALLY FRIGGIN HOT which I know is caused by the large delta between the 7805's input and output.

My question is ... is there anything I can do to lower the heat output from the regulator? I've got a decent heat sync on it (three times the size of the regulator itself) and the heat sync gets so hot that you can't touch it for more than a second or so ... I'm not OK with my project wasting energy like this.

Thank You for any info you can offer,

[eccerr0r]

Re: Voltage Regulators and Heat Issues

Add other dissipation devices before the 7805 (resistors, preregulators). You could use a 7818, then a 7812, then the 7805, and the heat is distributed among the three.

Else use a switching regulator.

[EasyGoing1]

Re: Voltage Regulators and Heat Issues

Add other dissipation devices before the 7805 (resistors, preregulators). You could use a 7818, then a 7812, then the 7805, and the heat is distributed among the three.

Else use a switching regulator.

But wouldn't adding successive step downs be essentially consuming the same amount of power ... only distributed over the other devices?

and what's a switching regulator? ... time to Google...

[R_J]

Re: Voltage Regulators and Heat Issues

I would agree, 24 volts is near the input limt for a 7805, I would at least put a 7812 between the 24 volts ant the 7805 input, also make sure you have good filtering on the input and output, and its good practice to have a .1µf cap as well as the large filter cap. on the output, these regulators like to oscillate if not filtered properly (and then will run hot)

They make cheap buck regulators to drop from 24 volts down to something lower

If you are drawing too much current you will need a heatsink anyway, How much current are you drawing at 5 volts?

[EasyGoing1]

Re: Voltage Regulators and Heat Issues

How much current are you drawing at 5 volts?

I'd need to check but rough guesstimate would be less than 400ma.

[EasyGoing1]

Re: Voltage Regulators and Heat Issues

Else use a switching regulator.

Like this one?

[R_J]

Re: Voltage Regulators and Heat Issues

Something like this is what I was thinking of, there are other types also https://www.aliexpress.com/item/1PCS...806176585.html
1/2 an amp draw is'nt much, If you have a scope, check the regulator output. What caps do you have on the 7805 regulator now?

[redwire]

Re: Voltage Regulators and Heat Issues

It is common to add an inductor to make a boost converter just for the piezo buzzer. This can make is very loud. It is used in some smoke alarms and battery powered things where you want more than 3V or 5V swing going to the piezo. This is assuming you are not using a complete alarm horn or something, but just the disc element.

You can buy SMPS IC that fit a TO-220 7805 pinout, or I buy the cheap chinese modules 8-35VDC to 5V buck converters/USB chargers using TPS40057 IC.
https://www.aliexpress.com/item/24V-...815527104.html works very well for under $2.

[eccerr0r]

Re: Voltage Regulators and Heat Issues

If you're concerned about power loss as heat, yes you need a switching regulator which is designed for efficiency. The modules with inductors preassembled suggested by redwire and R_J above are your best bet. This is because 400mA with a 24V-5V=19V drop would mean nearly an 8 watt heater, and C7 incandescent night light bulbs don't stay cold forever. This is if you want the simple series dissipative solution.

Ah... piezo element, didn't catch that...looks like that problem is solved already. If that's the case having a 5V switching wall wart would be the simplest way to supply power.

[EasyGoing1]

Re: Voltage Regulators and Heat Issues

Something like this is what I was thinking of, there are other types also https://www.aliexpress.com/item/1PCS...806176585.html
1/2 an amp draw is'nt much, If you have a scope, check the regulator output.

I decided on these at $1.25 each roughly... seems to be a popular IC and i can just throw it onto my own pcb instead of working in a whole module...

What caps do you have on the 7805 regulator now?

Ummmmmmm........ im bread boardin' it at the moment ... havent thought that far ahead yet???

[EasyGoing1]

Re: Voltage Regulators and Heat Issues

Indeed knowing what buzzer you're using would be interesting and whether you're set upon using that device. Then need to figure out how it needs to be powered.

The buzzer consists of 24 volt rated piezo speaker, sourced through a 20N06L from the 24v power source, which is triggered from an Arduino pin using the Arduino Tone command... works well in testing but the volume difference even between 19 and 24 volts is absolutely noticeable... so i don't wanna skimp on that ...

heres a rough schematic of what that looks like.

[EasyGoing1]

Re: Voltage Regulators and Heat Issues

It is common to add an inductor to make a boost converter just for the piezo buzzer.

INTERESTING ... what kind of a boost does the inductor realistically provide the piezo?

[eccerr0r]

Re: Voltage Regulators and Heat Issues

The inductor is the same principle as a boost switch mode power supply, except we don't care about which way the current goes (so the diode isn't needed except perhaps to protect the transistor), AC is perfect for a piezo transducer element.

I was wondering whether the piezo transducer had its own oscillator, then that would be a piezo buzzer if it had the oscillator... was a bit confused earlier.

[redwire]

Re: Voltage Regulators and Heat Issues

Your piezo drive circuit sucks, you need a resistor across it to discharge its capacitance and bring the crystal back. AC drive is best.

With an added inductor, you can get over 5-10X the voltage drive to the piezo element. The 60V mosfet would need a TVS to protect it because spikes will go over that. The method is a narrow pulse to charge the inductor, less than 50/50 duty cycle is used.
It's important the drive frequency is near the piezo mechanical resonance, so a signal generator sweep can be helpful. If your Arduino is making say 2.5kHz but the piezo might be designed for 3.5kHz, it would be much quieter than expected.

[EasyGoing1]

Re: Voltage Regulators and Heat Issues

I was wondering whether the piezo transducer had its own oscillator, then that would be a piezo buzzer if it had the oscillator... was a bit confused earlier.

Does this help?

[EasyGoing1]

Re: Voltage Regulators and Heat Issues

Your piezo drive circuit sucks

I think you should stop holding back and tell people what you really thinK!

you need a resistor across it to discharge its capacitance and bring the crystal back. AC drive is best.

With an added inductor, you can get over 5-10X the voltage drive to the piezo element. The 60V mosfet would need a TVS to protect it because spikes will go over that. The method is a narrow pulse to charge the inductor, less than 50/50 duty cycle is used.
It's important the drive frequency is near the piezo mechanical resonance, so a signal generator sweep can be helpful.

OK - do you have a schematic so i can SEE what you're talking bout here? cause a lot of those words slipped straight through my brain like water and oil ... im trying to chew slower ...

If your Arduino is making say 2.5kHz but the piezo might be designed for 3.5kHz, it would be much quieter than expected.

THAT - I UNDERSTAND...

[eccerr0r]

Re: Voltage Regulators and Heat Issues

Are you sure they are transducers or are they buzzers? Will they beep with just DC connected to them? Now I'm confused again...

[R_J]

Re: Voltage Regulators and Heat Issues

Ummmmmmm........ im bread boardin' it at the moment ... havent thought that far ahead yet???

without putting any caps on that regulator it will oscillate, and when it does it will run hot.

[redwire]

Re: Voltage Regulators and Heat Issues

OK from your picture it's an Ali/fleabay piezo buzzer/beeper, which is a piezo-disc with built-in oscillator. It already has an inductor and 2SC1623-L6 transistor, two resistors inside. Attached pic is one I took apart.
*So nothing can be done to make it much louder, you have to go bigger in size.
Operating Voltage: 3-24VDC, 10mA, Frequency 3,900±500Hz, 95dB
Drive Method: Drive Circuit Built in
B072HRZXLG TMOEC piezo buzzer HYDZ2312

You can also get just the piezo disc, some with two-wires or three-wires (needed for the self-oscillating type) and drive it with pulses from the Arduino. Junk smoke detector ones are best I find, for loud alarms because they have a huge disc.

[EasyGoing1]

Re: Voltage Regulators and Heat Issues

Will they beep with just DC connected to them?

Well now that is a great question ... lets find out ...

Holy crap! It sure does ... it even does Star Trek impersonations ... I zipped it up and attached here...