Driving the atomizer Low frequency - Page 1
Forum section: electronics / projects

author: LakshmiN
author_rank: Contributor
timestamp: May 26, 2021, 01:49:14 pm
content: Hi,I've 113KHz piezo transducer @113KHz,I'm trying to drive using esp32 PWM.The circuit is like belowhttps://drive.google.com/file/d/1zhKuv2c7sNym4U4FlQH316Y0FW0GAKf_/view?usp=sharingI don't see any signal at the output to the transducerFew more imagesa) PWM from esp32https://drive.google.com/file/d/1zLPTC6ox9OqzUcqnJMl8KPpZIdXz3_eB/view?usp=sharingb)Drain output-https://drive.google.com/file/d/1zXeZokUjRW-X_52eC5odotq2L2ZdSLxO/view?usp=sharingc)Drain out without the supply-https://drive.google.com/file/d/1zNONu02OX0GQwbQ5JtSl-IeuvYcmWs1S/view?usp=sharingI'm out of ideas here on what's going wrong here.

author: Marco
author_rank: Super Contributor
timestamp: May 26, 2021, 02:25:46 pm
content: You should just bump your old thread.Any way, you have a working driver board ... figure out what exactly you are doing different. For one thing they are driving it at a different frequency, since they have a working circuit and you don't, use their frequency (though their circuit might be self resonant, not fixed frequency). If that's not enough, use the exact same passives around the piezo they did (the single MOSFET driver works like a boost circuit and the passives have to be somewhat matched to the transducer).

author: LakshmiN
author_rank: Contributor
timestamp: May 26, 2021, 02:37:13 pm
content: I've used the same components as the driver board except that mosfet. apart from that circuit is very similar.I've observed the signal which is coming through driver board but in my case i do not see.

author: Marco
author_rank: Super Contributor
timestamp: May 26, 2021, 04:56:26 pm
content: Something is different, because the driver is working and your circuit isn't.Threshold voltage for that MOSFET can be up to 4V ... don't care what inductor you used, when that MOSFET turns you would see it on the drain voltage. Either the MOSFET is dead or your Vgs is too low.PS. well your Vgs is too low period obviously, a bit over the threshold voltage would at least give you something but it still wouldn't be turning on properly. That MOSFET is intended to be driven with a 10V gate voltage.

author: LakshmiN
author_rank: Contributor
timestamp: May 27, 2021, 01:44:46 am
content: Though the TK22E10N1,S1X N-channel vgs(thr, min) is 2V-4Vmax,esp32 PMW Out is 3.4V level.The one on the driver circuit PWM level is 5V level and is usinghttps://www.onsemi.com/pdf/datasheet/fqu2n60c-d.pdfN-channel.

author: ace1903
author_rank: Regular Contributor
timestamp: May 27, 2021, 07:58:05 am
content: Maybe MOSFET is fried. Temporary replace inductor with LED + resistor combination and observe illumination at lower frequency.Circuit relies that transducer is connected and driven at resonant frequency, otherwise energy stored into inductor will cause voltage spike that will destroy the MOSFET.post schematic or picture of the working driver board. Usually transducer are driven by simple oscillator that has frequency dependent of the load and automatically adjust its frequency.This driving by simple PWM at 107KHz looks wrong to me.

author: ace1903
author_rank: Regular Contributor
timestamp: May 27, 2021, 09:24:45 am
content: Probably inductor is driven into saturation when using 24V and MOSFET with several milliohms Rdson.On semi part has Rdson in range of 4,7Ohms which limits current through the inductor.

author: LakshmiN
author_rank: Contributor
timestamp: May 27, 2021, 09:30:07 am
content: Mosfet is fine. I do read vsd to be 0.5V.Driver board circuit is similar to one in explained in this video-

author: ace1903
author_rank: Regular Contributor
timestamp: May 27, 2021, 10:17:42 am
content: 0.5V over several milliohms says that inductor is deeply into saturation.Put 4,7 ohm resistor in series with inductor and check again.

author: LakshmiN
author_rank: Contributor
timestamp: May 27, 2021, 11:10:40 am
content: Not that I meant ..I measured the source to drain diode drop to check whether MOSFET is dried or not.yes I do have two 10Ohm parallel at the drain to the inductor

author: Marco
author_rank: Super Contributor
timestamp: May 27, 2021, 03:18:12 pm
content: The drain voltage is a rock steady 30V ... it's not turning on, so either it's dead or you're not driving it hard enough.To test if it's dead just replace the inductor with a high value resistor and drive the gate with 10V.