How can I drive a 120 W piezoelectric transducer with a high-voltage transformer stage, and do I need frequency control because its impedance changes?
Drive the piezo with a transformer-coupled push-pull amplifier, because the transformer steps the voltage up and the transducer is not a plain 20-ohm resistor [#21669323][#21669327] Use two MOSFETs with inverted drive or a square-wave oscillator/timer interrupt around 42–47 kHz, keeping the frequency within the piezo’s rated tolerance [#21669323][#21669325] A real PWM/feedback loop is optional: it can stabilize the output if you sample the secondary, but a fixed oscillator such as a 555 or CMOS source can work if the frequency is correct [#21669325] The reply also suggested an IRFZ840 should be suitable, with about 5 V gate drive [#21669325][#21669329] For a 120 W design, the estimate given was roughly 65–67.5 V on the secondary and about 1.75 A, with the primary current much lower because the primary can look almost open-circuit at 42 kHz [#21669327][#21669329]
Hi All who can help me? i am trying to drive a Piezoelectric Transducer , but there are 2 question. first, in many document i read,mentioned that for driving this transducer and for getting 120 watts power, we have to use high voltages about 400 volt,and my question is how we can use 400 volts for radiation resistance about 20 ohms??i thing one thing is wrong here,what is wrong???? 2nd, in these documents mentioned that the frequency is changing because of changing impedance,is it necessary to use a frequency control circuit or we can drive the transducer without using this circuits??? please help me
Amigo do u know what is consideration for driving this transducer? i found ou that we need to use a transformer after power amplifier and in last step for increasing voltage and isolation. acctually i wanna produce a pulse signal by AVR and then use that for driving transducer, but i dont know what i need for doing this work can u help me , plz?
It shows you how to wind the transformer for achieving this application then apply the coding that you would in a pic micro to atmel cpu or in your case what you call the arduino Its All roughly the same thing
So you want pwm out one channel driving one of the fets and inverted on the other output driving the other Fet for a signal frequencey of 42khz to 47khz depending on what ever your piezo element is rated at
Lets see how you would work this out If you know your instruction time then one port will be high for x cycles instruction time and the other port pin will be low during that period
To complete one cycle the you would have to use period = 1/f which is 1/ 42000
So lets see period for 42khz is 23.81us which constitutes one cycle 11.9 us On 11.9us OFF
You would use possibly a timer interupt and then invert the state of the ports every 11.9us
Preloading the timer with a value so that every 11.9us it overflows and calls the on interrupt routine
The on interrupt routine would simply alter the state of the ports ie if Invert port pin state ie low to high or high to low
i.e Port.pin = NOT (port.pin ) // invert state
C syntax would be something like this
Inside your interrupt call back PORTD = PORTD ^ B00100100; // invert bit 5 , 3 (digital pin 5, digital pin 4), leave others untouched
Or not having worked with ardiuno reading through it appears you may do this ISR(TIMER1_COMPA_vect) { digitalWrite(PORTPINA, !digitalRead(PORTPINA)); digitalWrite(PORTPINB, !digitalRead(PORTPINB)); }
Thats how I would approach this Then if you need to check your output with a simulator or a Scope
You would have to alter the value in the timer to account for other instyruction times to get far greater accuracy on your final frequency out
You are using a form of pwm by changing the pin sates with the use of a timer interrupt although not true pwm it is essentially a square wave oscillator with two pins You could use real pwm to ensure correct V out stabilized if you were using adc to check output voltage sampled from your secondary of the TX but you don’t really need to be that accurate Your frequency out how ever does need to be reasonably accurate so that it lies within the tolerance of your Piezo transducers that is 42khz to 47khz
There is nothing to stop you using for example a 555 timer IC Or a Cmos oscillator with nand gate attached to the output to give you inverted and non inverted drives to the fets although you do need to observe your drive voltage to the gates of the Fets typically this shouldnt exceed 5 volts for given fets
thx ur helps is usefull but in the web links that u put,( http://www.picproje.org/index.php?topic=45268.0 )(turkish) i thing one thing is wrong, because in that circuit, he use transfirmer in last step an after amplifying,and in this situation if we want to have 120 watt power ,in output we have to have 50 volts voltage and 2.5 amps current and actually in primary stage of transformer by turns (12/50) then we have to have 2.5*4=10 amps current,isnt it???or i think wrong???
Cant see how you calculated your current though dont forget the primary acts as open circuit at 42 khz so current I would have thought would be about 0.75 amp or so for 50 watts in secondary at 67.5 volts
so if i wanna have 120 watt in secondary(output) and input of transducer,how much voltage need current i need in secondary??????? why primary act as open circuit????? can i use IRFZ840 istead of two transistors(MOSFETs)??? ty again
I calculate 1.75 amp which means halve the gauge on the secondary winding looking at the data sheet cant see why not IRF 840 should be ok Id = 8 amps and max vgs = +- 20 volts you are only using 5 volts gate drive which gives 3 amps max Ids acc the graph
Someone else might have a far better answer to this but thats what i would do
Only one way to find out I suppose Try it and see I'd be interested to see how close my answers are last time round i did this It worked out A ok
Im sure there are many other points that you would have to take into account like the type of core etc but for these purposes I think It may just work You may have to take one or two turns off or on thats to get resonant frequency correct but to all intensive purposes It will work ( thats what matters at the end of the day Does it work or not )
dear Mark i have a question i saw that in some made circuits , some producer use PWM controlling for controlling frequency because of chnaging frequency during running, do you know do i have to use frequency controlling for driving algae removal circuits or this technique is optional and is not necessary??? do you have any information about Lp-Bs(Low Power Bright Signal) Technolgy??does it electronical technique or Mechanical type?? how can i use this technique for my circuits? can i use this circuits as my driver?(attached file) thanks mi mejor amigo
✨ The discussion addresses driving a 120W piezoelectric transducer, focusing on the required high voltage (~400V) and the apparent discrepancy with the radiation resistance (~20 ohms). It clarifies that achieving 120W output involves high voltage and current levels, typically requiring a transformer after the power amplifier stage for voltage step-up and isolation. Calculations suggest secondary voltages around 65-68V with currents near 1.75-2.5A to deliver the desired power, while the primary side current depends on transformer turns ratio and wire gauge. The primary winding behaves almost like an open circuit at ultrasonic frequencies (~42kHz), reducing current draw. Driving the transducer commonly uses a PWM or square wave oscillator at the transducer's resonant frequency (42-47kHz), with frequency accuracy important to maintain resonance and efficiency. Frequency control circuits or timer interrupts can be used to generate the drive signal, but strict frequency control is not always mandatory. MOSFETs such as the IRFZ840 are suitable for switching, provided gate drive voltages are within specifications. Wire gauge selection for transformer windings is critical to handle the required currents. Additional questions concern the necessity of frequency control for applications like algae removal and the nature of Low Power Bright Signal (Lp-Bs) technology, with no definitive answers provided. Reference materials and example circuits were shared to assist in transformer winding and drive signal generation. Generated by the language model.
TL;DR: To deliver ~120 W into a piezo, target 42–47 kHz and ~65–68 V RMS at the transducer; “frequency needs to be reasonably accurate.” [Elektroda, Mark Harrington, post #21669325]
Why it matters: Correct frequency, transformer ratio, and MOSFET drive prevent weak cavitation, overheating, and device failure for DIY ultrasonic cleaners and algae-removal builds.
Why do people mention “400 V” when my transducer looks like ~20 Ω?
This thread’s working solution used a transformer to step up to only about 65–68 V at the transducer, not 400 V. The key is matching frequency near resonance and selecting turns ratio for the needed secondary voltage and power, instead of forcing very high primary voltage. That approach delivered roughly 100–120 W without extreme voltages. [Elektroda, Mark Harrington, post #21669327]
Do I need frequency control or can I run it open-loop?
Hold frequency within the transducer’s tolerance band. The guidance here is 42–47 kHz, and the output “needs to be reasonably accurate.” Open-loop can work if stable, but include a means to trim or tune so drift does not move off target. [Elektroda, Mark Harrington, post #21669325]
How do I generate a 42 kHz drive with an AVR/Arduino?
Use a hardware timer interrupt to toggle two pins in antiphase every ~11.9 µs. 1) Configure the timer compare to overflow at 11.9 µs. 2) In ISR, invert both output pins. 3) Feed each pin to a MOSFET gate driver leg. This produces a ~50% duty, two-phase square wave at ~42 kHz. [Elektroda, Mark Harrington, post #21669323]
Is PWM strictly required, or is a square-wave oscillator fine?
A square-wave oscillator with accurate frequency works. You can also use a 555 or CMOS oscillator with an inverting path for complementary MOSFET drive. PWM with ADC feedback can stabilize voltage, but it is not required for basic operation. Watch the gate-drive limits. [Elektroda, Mark Harrington, post #21669325]
Why use a transformer, and how do I size the ratio?
You use the transformer to step up the low-voltage drive to the tens of volts the transducer needs and to provide isolation. Apply ES = EP × (NS/NP). In the example, the math yielded about 67.5 V on the secondary from a low-voltage primary. [Elektroda, Mark Harrington, post #21669327]
How much voltage and current do I need for ~120 W output?
One working point here is about 65 V and 1.79 A at the transducer, giving roughly 116 W. This shows that tens of volts at resonance can deliver power effectively, provided the drive frequency and transformer ratio are chosen well. [Elektroda, Mark Harrington, post #21669329]
What wire gauges should I use for the transformer?
In the example, primary current capacity drove the choice toward about 23 AWG for several amps and secondary around 26 AWG for roughly 1.8–2.2 A. Keep the same turns, change gauge to meet current. Verify temperature rise under load. [Elektroda, Mark Harrington, post #21669329]
Can I use an IRF840/IRFZ840 as the power MOSFET?
Yes, IRF840 class parts were suggested. With ~5 V gate drive, expect around 3 A per device from the transfer curve. Respect ±20 V VGS max and ensure proper gate drive and heat sinking. “Cant see why not IRF 840 should be ok.” [Elektroda, Mark Harrington, post #21669329]
Why does the primary seem like an open circuit at 42 kHz?
At the operating frequency and with proper tuning, the transformer’s primary presents high impedance except for the magnetizing and reflected load components. The contributor noted the primary “acts as open circuit at 42 khz,” which limits primary current. [Elektroda, Mark Harrington, post #21669327]
How do I set up complementary gate signals safely?
Drive one MOSFET with the timer output and the other with an inverted copy. Keep gate drive near 5 V for the devices referenced. Confirm dead-time if your topology needs it, and verify with a scope before connecting the transformer. [Elektroda, Mark Harrington, post #21669325]
How can I fine-tune resonance without complex control?
Trim the transformer turns by one or two to nudge the effective frequency point if your mechanical load shifts slightly. This simple tweak helps you land in the transducer’s tolerance band without closed-loop frequency tracking. [Elektroda, Mark Harrington, post #21669331]
What’s a simple, practical frequency math check?
Use period = 1/f. For 42 kHz, the period is ~23.81 µs, so toggle each half-cycle at ~11.9 µs. Implement this with a timer compare ISR and verify on a scope before power testing. [Elektroda, Mark Harrington, post #21669323]
Is frequency tracking mandatory for algae-removal applications?
Not mandatory here. Maintain accuracy within the 42–47 kHz band and include an adjustable element (timer preload or turns). That keeps performance acceptable without a closed-loop frequency controller. [Elektroda, Mark Harrington, post #21669325]
Any edge cases or failure risks I should watch for?
Excessive gate drive or inaccurate frequency can stress MOSFETs and reduce output. Keep logic-level drive near 5 V for the cited devices, and stay within the transducer’s tolerance band to avoid poor cavitation or extra heating. [Elektroda, Mark Harrington, post #21669325]
Does this thread cover LP-BS (Low Power Bright Signal) technology?
No. The discussion focuses on practical transformer ratios, MOSFET drive, and timer-based generation. LP-BS is mentioned as a question only, with no documented method or data here. [Elektroda, Milad Rad, post #21669334]
