Newbie: 2.4Mhz piezo oscillator circuit - Page 1
Forum section: electronics / projects

author: dteck
author_rank: Contributor
timestamp: July 01, 2014, 04:20:57 pm
content: Hi everyone,I'm going to preface this by saying I'm still pretty new to this hobby. So I apologize if I'm making a stupid mistake, but I'm having trouble driving a 2.4Mhz piezo transducer. The manufacturer (fujicera) has a standard circuit they recommend for driving it, and I tried to replicate it. But when I put it all together I'm not getting the excitation I expected. Attached are some pictures of the provided standard circuit, my eagle files, the assembled unit, and simple testing tools.It is meant to be powered off 24vac but I want to use it with a 24vdc SMPS and this is being tested with a dc bench top power supply.When ramping up the power some voltages do seem to make the piezo hum -slightly- but at 24vdc the piezo should be nebulizing the water, sadly however all that happens is that I'm dumping about 0.4a into nothing. The transistor gets nice and toasty and if you don't have the piezo under a bit of water it will also warm up pretty quick.All I have in the way of test gear is a cheap multimeter. (been hanging around ebay lately looking for a deal on an old scope)I'm hoping someone who has some actual EE skills can look this over and tell me where I'm going wrong.Notes about the board I used 2 and 3 watt resistors and the 2.2ohm resistor gets very hot to the touch. the surface mount parts are 0603 (excluding the inductors). Also I skipped the diodes and just used jumper wire. For testing I placed the Piezo between two pieces of dead soft silicone and placed a small length of pvc over the top and filled it with water. The silicone should have plenty of give for the piezo to flex.Thanks in advance.

author: mij59
author_rank: Frequent Contributor
timestamp: July 01, 2014, 04:50:20 pm
content: Hi,Your circuit can't be powered by 24 Vdc, build according to the original circuit diagram.

author: dteck
author_rank: Contributor
timestamp: July 01, 2014, 05:02:26 pm
content: Quote from: mij59 on July 01, 2014, 04:50:20 pmHi mij59,I'm curious why It cant be powered with DC. I thought that since the original has the AC go through a diode bridge I could just skip that bit and power it directly from DC.

author: mij59
author_rank: Frequent Contributor
timestamp: July 01, 2014, 05:12:14 pm
content: Quote from: dteck on July 01, 2014, 05:02:26 pmThe signal after the diode bridge is just a rectified sine wave, there is no filter cap in the circuit to make it a dc voltage.

author: dteck
author_rank: Contributor
timestamp: July 01, 2014, 05:45:45 pm
content: Quote from: mij59 on July 01, 2014, 05:12:14 pmThanks mij59 I hadn't even thought of that. I guess Ill pick up a transformer and a rectifier and see how things go from there

author: mij59
author_rank: Frequent Contributor
timestamp: July 01, 2014, 05:57:15 pm
content: Thanks mij59 I hadn't even thought of that. I guess Ill pick up a transformer and a rectifier and see how things go from thereOr if you want to use a dc power supply you will need a different circuit, check the manufacturer site.

author: dteck
author_rank: Contributor
timestamp: July 01, 2014, 07:21:41 pm
content: Quote from: mij59 on July 01, 2014, 05:57:15 pmSadly all the example circuits I saw on the fuji cera site were AC.But I'm open to suggestions if anyone has any on how to drive it from dc.I thought this would be a good use for the spare 24vdc SMPS I had laying around.

author: mij59
author_rank: Frequent Contributor
timestamp: July 02, 2014, 11:39:48 am
content: But I'm open to suggestions if anyone has any on how to drive it from dc.Found this on Google searching for 2.4Mhz piezo transducer.Notice that the oscillator is not on 100% of the time, don't know why this is.

author: bktemp
author_rank: Super Contributor
timestamp: July 02, 2014, 01:03:37 pm
content: I think the piezo needs a minimum amount of power to operate properly. But this power level is too high for continous operation and would overheat the piezo transducer. Therefore it is pulsed using short bursts.

author: dteck
author_rank: Contributor
timestamp: July 02, 2014, 07:16:35 pm
content: Quote from: mij59 on July 02, 2014, 11:39:48 amFound this on Google searching for 2.4Mhz piezo transducer.Notice that the oscillator is not on 100% of the time, don't know why this is.I did see this on the fujicera example circuit page, but unfortunately its for a different piezo element and a different frequency. That circuit is for driving a 30mm disk at 1MHz. Google is a little misleading showing it but i think its because fujicera put all their diagrams on one page. so scrolling down gets you to the 2.4MHz circuit i started with.

author: dteck
author_rank: Contributor
timestamp: July 04, 2014, 06:15:45 am
content: I picked up a 24v transformer and a rectifier.My cheapo meter shows it giving 25v after the rectifier.When I turn it on I can hear the transistor humming, and the piezo does seem to move -a little-.but I'm still not getting the nebulization That I should be getting.And the 2.2ohm resistor still gets too hot to touch.

author: mij59
author_rank: Frequent Contributor
timestamp: July 04, 2014, 06:45:50 am
content: Quote from: dteck on July 04, 2014, 06:15:45 amIf you remove the piezo does R5 still get hot ?Measure the voltage across R5.

author: dteck
author_rank: Contributor
timestamp: July 05, 2014, 01:15:38 pm
content: Quote from: mij59 on July 04, 2014, 06:45:50 amI hooked it up without the piezo and R5 does not get hot. The transistor started heating up pretty quick, but there was no hum.I measured about 0.2 to 0.55v across R5

author: mij59
author_rank: Frequent Contributor
timestamp: July 05, 2014, 01:22:50 pm
content: Quote from: dteck on July 05, 2014, 01:15:38 pmThere must be a short in the piezo transducer.

author: dannyf
author_rank: Super Contributor
timestamp: July 05, 2014, 01:44:03 pm
content: QuoteI would suggest that you understand the circuit before attempting to build it. There is a reason for them to power the circuit with rectified DC, rather than DC: so the oscillation is modulated by a 100Hz signal.

author: dteck
author_rank: Contributor
timestamp: July 06, 2014, 07:54:29 pm
content: Quote from: mij59 on July 04, 2014, 06:45:50 amI tried hooking up a different piezo element and got the same results.I actually also tried a third one where I soldered the piezo as a short (both leads on the same metalized area). That burned out the 25uh inductor.Quote from: dannyf on July 05, 2014, 01:44:03 pmI wont argue that understanding how a thing works before building it is good advice, and probably a key part of being good at this. But I've always tried to work above my level of experience and understanding. I always naively think things wont be that difficult. Here I though that since there was a standard circuit provided it would be a simple follow the recipe kind of thing. And when It wasn't working I though that perhaps it was just me missing something simple (like a bad board layout). That said now that Ive learned that I cant run I guess I should learn how to walk. If you have any recommendations for places that would help a newbie learn about oscillation circuits like this I would be happy to read them.

author: dannyf
author_rank: Super Contributor
timestamp: July 06, 2014, 10:36:15 pm
content: The circuit is an oscillator, modulated by the rectified ac.There is substantial amount of current going through the transistor under 35vdc power supply, north of 500ma peak. The transistor dissipates on average 1w and 10w+ peak. So it needs some fairly serious cooling.

author: mij59
author_rank: Frequent Contributor
timestamp: July 07, 2014, 04:17:55 am
content: Quote from: dteck on July 06, 2014, 07:54:29 pmThe transducer is capacitor, measure the resistance between the leads.

author: dteck
author_rank: Contributor
timestamp: July 08, 2014, 05:39:08 pm
content: Quote from: mij59 on July 07, 2014, 04:17:55 amI tried two different piezos and both show openI'll add a picture of the piezo that I shorted as well. It obviously shows short.I'm also attaching the spec sheet for the piezo elements I'm using. (this was where I got the standard circuit)

author: bktemp
author_rank: Super Contributor
timestamp: July 08, 2014, 06:19:57 pm
content: Try connecting the piezo to the driver circuit using much shorter wires and twist them to decrease the parasitic inductance as much as possible.

author: dannyf
author_rank: Super Contributor
timestamp: July 08, 2014, 07:30:12 pm
content: Piezo's are capacitors so they should show open on a meter.Also, the soldering on the first piezo is correct and the soldering on the 2nd piezo is incorrect / weird.

author: dteck
author_rank: Contributor
timestamp: July 08, 2014, 09:40:51 pm
content: Quote from: bktemp on July 08, 2014, 06:19:57 pmI tried trimming the leads and twisting the cables. It didn't seem to make much difference.When I turned it on the transistor got nice and warm, R5 however did not. There was no hum and the water didn't seem to move at all.Quote from: dannyf on July 08, 2014, 07:30:12 pmThe second picture was of one that I had soldered as a short. It was intentional for testing, but you're right its not how it should be.

author: mij59
author_rank: Frequent Contributor
timestamp: July 09, 2014, 03:48:50 am
content: Quote from: dteck on July 08, 2014, 09:40:51 pmPlease check the transistor, it may be damaged by shorting the transducer.It's best to remove the transistor, check the diode form base to collector and the diode from base to emitter. ( positive lead on base)I'm wondering if the value of R5 is correct, in an other circuit the value is 22 Ohm.

author: mij59
author_rank: Frequent Contributor
timestamp: July 10, 2014, 02:41:56 am
content: There is a problem with your schematic, C3 is connected to the emitter of the transistor, it should be connected to the C2.

author: dteck
author_rank: Contributor
timestamp: July 10, 2014, 12:55:55 pm
content: Quote from: mij59 on July 09, 2014, 03:48:50 amI checked the transistor and it showed as open on the base to collector and base to emitter.Ill get some 22ohm resistors and try them out.Quote from: mij59 on July 10, 2014, 02:41:56 amYou're rightI fixed this with a bit of jumper wire.And I tested it out. The piezo seemed to move a bit. it wasn't nebulizing the water but there was some movement. And the transistor got very hot very quick.

author: mij59
author_rank: Frequent Contributor
timestamp: July 10, 2014, 01:15:03 pm
content: Quote from: dteck on July 10, 2014, 12:55:55 pmDoes R5 still get very hot ?

author: dteck
author_rank: Contributor
timestamp: July 10, 2014, 01:34:27 pm
content: Quote from: mij59 on July 10, 2014, 01:15:03 pmR5 did not seem to get hot but I also didn't have it on very long.

author: mij59
author_rank: Frequent Contributor
timestamp: July 10, 2014, 01:50:56 pm
content: Quote from: dteck on July 10, 2014, 01:34:27 pmPlease don't replace R5 with 22 Ohm, i think it is not necessary.If the transistor gets too hot, try a bigger heat sink.

author: miguelvp
author_rank: Super Contributor
timestamp: July 11, 2014, 02:06:13 am
content: Do you have the part number of your piezo, once you get the circuit working you need to hit the right frequency or not much will happen, for that you'll need the datasheet for the piezo in question.Edit: nevermind the frequency is in the title, but the part number will still be nice to know.

author: dteck
author_rank: Contributor
timestamp: July 11, 2014, 04:33:24 pm
content: Quote from: miguelvp on July 11, 2014, 02:06:13 amA few posts back I added the spec sheet for the piezo element that I got from the manufacturer, but here are a few particulars.Its a Fuji Ceramic:2.4Z20D-QS (C-204)Frequency:2.4MHz+- 100KHzImpedance:<3ohmCapacitance:1850pf+- 20%Rated voltage:24VrmsRated Current:0.6Arms(in standard circuit)Life:5000 hoursbefore 15% reduction (in standard circuit)

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 12, 2014, 04:59:39 am
content: Rather than using a self oscillating driver (surprisingly complex on the inside), what about use a more conventional oscillator (7400 series logic or a really fast 555) driving a MOSFET switching an inductor with the piezo in parallel? Make the oscillator adjustable in frequency so that you can tune it for best performance and you can keep the output stage voltage low for testing. Later on, you can even use a PLL to automatically tune the frequency.

author: dteck
author_rank: Contributor
timestamp: July 12, 2014, 06:23:27 pm
content: Quote from: NiHaoMike on July 12, 2014, 04:59:39 amgiven how little progress I've been making even with Mij59's help I might do this. I've also considered dropping the 2.4MHz piezo and switching to a 1.7MHz piezo and then using the Linear "LT3572 - Dual Full-Bridge Piezo Driver with 900mA Boost Converter". The specs say it can go up to 2.25MHz, but I'm wondering if I could drop the resistance value on the RT pin and push it up to 2.4MHz. The characteristics page shows 2.25Mhz as typical but with +-0.35MHz. I might get some samples and try it. then if it doesn't work I could use them for the 1.7MHz transducers.I'm also working on getting some proper test gear. putting in bids for used scopes and better multimeters. My $16 Chinese special isn't cutting it anymore for the kinds of projects I want to do.

author: mij59
author_rank: Frequent Contributor
timestamp: July 13, 2014, 04:07:52 am
content: Quote from: dteck on July 12, 2014, 06:23:27 pmThe LT3572 is only a driver, you'll still have to generate the resonance frequency.The RT pin set the frequency of the power supply part, it is not used to drive the piezo.The piezo transducer is a ceramic resonator with a narrow frequency response, as @miguelvp stated driving the piezo with a slightly higher or lower frequency will have no effect.You could "tune in" the resonance frequency, but it's no a practical solution.You might consider dropping the project completely, without the proper test gear it's almost impossible analyse the circuit.Maybe you could buy a new or used ultrasonic humidifier and hack it.A better multimeter is a good idea, but won't help ( in this case ), the "brains" are not in the the meter.

author: dteck
author_rank: Contributor
timestamp: July 13, 2014, 12:23:09 pm
content: Quote from: mij59 on July 13, 2014, 04:07:52 amwhoops you are absolutely right the adjustable frequency is for the boosting switch mode power circuit.Maybe I could use a signal generator to put out a square wave at 2.4MHz and pump that into the PWM pins on the lt3572...But you are right I was perhaps a bit overly ambitious in this and should shelf it until I get some better equipment (and learn to read more carefully).Thanks for all your help.

author: bobwidlar
author_rank: Contributor
timestamp: July 13, 2014, 03:15:31 pm
content: Have you tried to trim the 5k pot, to find a good biasing point of the transistor? (you probably did). I also notice that you use a half-wave rectifier instead of a full one, though I don't think it should matter.Hmm, the best advise I can give is to probe different nodes. Especially base-emitter voltage of the transistor.

author: dteck
author_rank: Contributor
timestamp: July 15, 2014, 06:52:46 pm
content: Quote from: mij59 on July 13, 2014, 04:07:52 amI picked up a used Tektronix TDS320 (thanks ebay). And fair warning its my first scope and Ive had it about half a day so I cant say I know how to use it very well. But I did hook it up to the circuit and I can see a bit of a problem. Its not putting out 2.4MHz its more or less putting out 480-500KHz. I didnt have the piezo itself hooked up while probing it, and the R4 68Ohm resistor got super hot.I tried it with both the rectified AC and a bench top DC supply.I'm still putting this project on hold since I'm going to be moving soon. So I don't have much time to work on it. but I did want to check back in and show everyone how completely wrong the output is.Quote from: bobwidlar on July 13, 2014, 03:15:31 pmI did try turning the trimpot. It wasn't making any real difference.

author: mij59
author_rank: Frequent Contributor
timestamp: July 16, 2014, 03:24:46 am
content: Very nice, now we can see what's going on !The frequency of the circuit is determent by the piezo, without the piezo it won't oscillate at 2.4 MHz.

author: masterx
author_rank: Newbie
timestamp: March 10, 2016, 03:14:31 pm
content: Hi,have any one tested thishttp://www.fujicera.co.jp/product/e/03/image/ap_002.gif?Does it work? I have 1 MHz piezo disc with 20 mm diameter. I guess it should work. I do not know it's parameters, I do not have any datasheet.I have spend a lot of time in research, building and testing. I still did not get any result.I have arduino Mega and I'm using it as generator of square wave 50% Duty Cycle impulse. I was using different approach for several circuits but non of them did not work as they should.If anyone have generated 1 MHz and it works just let me know. I would build it.Thanks!