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Pulsar circuit for Ultrasonic transducer

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rafakath_aimil

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Sir,
I am working on Pulsar circuit which will drive ultrasonic transducer. I need to exit transducer at 600v to 800v, but pulsar circuit provide 400v max. even if VDD is 600v. What could be the resion for voltage drop kindly suggest.

Attach circuit diagram.
I have experiment by changing R and C value.
Excitation Pulse duration is 10uSec at a frequency of 50mSec is applied to MOSFET gate.

pulser_circuit.png
 
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We need to know more about the transducer to be sure but it is quite likely that at that frequency the diode is unable to switch fully, you should consider using a fast diode or Schottky type.

I assume the transducer is resonant at 10us rate, otherwise it will present a low impedance load and the 31K drain resistor will not be able to supply enough current to maintain the voltage.

Brian.
 

Hi,

and additionally the transducer waveform (and it´s peak) depends on gate drive voltage (waveform) and gate drive current.
...and transducer capacitance ....

--> there are a lot of informations missing.

Klaus
 

Hello Sir,

MOSFET specification:
gate pulse voltage applied is : 12v
Rds(on) : 1.95 ohm and max is 2.4 ohm
Total gate charge : 39nC

Transducer Specification
Type: Single-Crystal
Frequency: 54 kHz ± 5 kHz
Bandwidth: < 10 kHz
Driving voltage: -1000 V to +1000 V
Matching inductance: absent
Piezo electrical cell capacity: 2 nF
Connector type: BNC
Operating temperature: -20º C…+60º C
Contact surface diameter: 4 mm
Dimensions: Diameter: 49.7 mm
Length (without BNC connector): 99.43 mm
Length (including BNC connector): 111.43 mm
Weight: 244 g
 

Which waveform do you actually see at the transducer, where is the said "400 V"?

What means "frequency of 50mSec"? 20 Hz repetition rate?

The circuit only drives one negative edge with slow exponential decay to the transducer. Why?

The purpose of the 1N4007 diode isn't clear at all.
 

Hello Sir,
1. 400v is at output where transducer is connected.
2. frequency of 50mSec is repetition rate at which 10uSec pulse is provided to excite transducer.

Image attach.

pulser_circuit.png
 

I would expect a negative swing equal to Vdd. But there are possible reasons why it's not achieved, exact oscilloscope measurements can tell.
 

Sir,
Kindly suggest me what I have to look into oscilloscope while measuring signal at o/p (transducer side.)
 

Look at the first 50 us after pulse start. I see this principle transducer waveform in a simulation

piezo.PNG
 

To Fvm,
Thanks for your response, I am getting same output waveform at transducer. But output is limited to 400v even if I am applying 600v at MOSFET VDD. The problem is that I want max. o/p volt( around 600v or volt equal to VDD) at transducer. I got hangup here, not able find solution.
 

The result is only feasible if MOSFET Vds is already limited. You can check by operating the pulser with disconnected coupling C.
 

To Fvm,
Hello Sir,
I have checked removing coupling C, got Voltage = 490v and when capacitor is connected then Voltage is : 400v. So it means that 90v is drop across MOSFET Vds.
 

Looks like the coupling C doesn't fully charge during repetition period. According to given parameters (31k, 440 nF, 50 ms), it should charge to 97 % of Vdd. May be something is different from the schematic.
 

Hi,

What is your gate voltage waveform?
is your capacitor rated for 600V? What exact type is it?

It shouldn´t be too much effort to upload
* a scope picture of the transducer voltage
* a scope picture of the gate voltage
* and a photo of your circuit with part types / values

Klaus
 

My exact concerns
The 1N4007 should be replaced by an UF4007

The Mosfet could be going into avalanche

The capacitor’s rated voltage may be too low or have an excessive ESR.

And of course, a DUAL trace scope showing Vgs and Vds
 

rafakath_aimil said:
Transducer Specification
...
Frequency: 54 kHz ± 5 kHz
...
Driving voltage: -1000 V to +1000 V
...
Piezo electrical cell capacity: 2 nF
Click to expand...

Here is an oscillator made from a full H-bridge. It's a concept which you may be able to adapt for your transducer, to result in the above parameters.

transis H-bri astable auto-resonant LC series 800V 54kHz.png

The series RLC is strung across the H-bridge. It is an approximate model of a resonant component. It shows how to tap at each end of the resistor, to detect zero crossings. The zero crossings cause the H-bridge to send alternating current through the transducer.

Bias resistors need to be adjusted so the right amount of current goes through the transducer. Your current draw is probably less than my simulator portrays.
 

Hello Sir,
Thanks for quick response, I have got expected output... it was oscilloscope connection that could not show correct value.

I need solution for, how to remove ringing on output waveform.
Vout@transducer.JPG
 

Attachments

  • Vout@transducer.JPG
    Vout@transducer.JPG
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I need solution for, how to remove ringing on output waveform.
Click to expand...
That's basically not possible. It's the transducer oscillating at it's resonance frequency. Even an ideal transducer termination can only reduce the oscillation decay time.

You didn't yet tell what you try to achieve and why you want to defeat the transducer oscillation.
 

rafakath_aimil said:
Sir,
I am working on Pulsar circuit which will drive ultrasonic transducer. I need to exit transducer at 600v to 800v, but pulsar circuit provide 400v max. even if VDD is 600v. What could be the resion for voltage drop kindly suggest.

Attach circuit diagram.
I have experiment by changing R and C value.
Excitation Pulse duration is 10uSec at a frequency of 50mSec is applied to MOSFET gate.

View attachment 146395
Click to expand...

to understand better driving ultrasonic cleaning transducer a comprehensive guide and project was publish in EPE and Siliconchip based on PIC12F675 as frequency generator and driver you can check it, you also required an Inductor to match resonance frequency of the transducer
 

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