Need Circuit Verification: Signal Amplification

Discussion in 'The Projects Forum' started by anjancontractor, Jul 29, 2015.

  1. anjancontractor

    Thread Starter New Member

    Jul 29, 2015
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    Hello,

    I'm new to analog circuit design. I need to obtain 120VAC,500mA output at 40KHz frequency to run piezo actuator. I used full wave rectifier and transistor to obtain desired output. I have attached circuit diagram with this thread. Can somebody verify this? I will truly appreciate your help.

    Link of Diagram: https://app.box.com/s/89rdo0znuqmkdri0a0mc44zotlsj8p6m

    Thanks!
    Anjan

    Amp_anjancontractor.gif
    Circuit Source.
     
  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    If it works, that is a very inefficient amplifier. R3 would have to be at least a 100 W resistor. Also, you have an asymmetrical output impedance. Does you piezo transducer require a low impedance driver or high impedance?

    60 W at 40 kHz is a lot to ask from a single transistor, especially a power transistor. What you have is a class A amplifier. Have you looked into audio power amp designs? Many of them can make the power and frequency you need, although they would have to be adjusted for the relatively high voltage / low current load requirement.

    ak
     
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  3. anjancontractor

    Thread Starter New Member

    Jul 29, 2015
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    Thanks for your reply. I'm trying to drive this piezo actuator: http://www.bjultrasonic.com/40khz-60w-ultrasonic-cleaning-transducer-pzt4/

    I looked into audio power amps. They reach frequency and power I need but they're usually low voltage high amp devices (i.e. 6V- 10Amps). How can I make such signal to 120V 0.5Amps? Any simple solution?

    I have noticed several fixed frequency drivers for it: http://www.bjultrasonic.com/60w-110v-ultrasonic-pcb-generator/ and several on ebay but I'm looking to change/fine tune frequency and power. I have also noticed several variable frequency and power piezo actuator drivers but they're out of my budget (http://www.piezodrive.com/products.html)

    I'm a Mechanical Engineer and have never done a difficult circuit design (such as this) in the past.

    Best,
    Anjan
     
  4. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Is sinewave drive a requirement, or can you get away with squarewave? OR, a squarewave driver (very efficient, relatively simple) driving the transducer through a resonant filter?

    ak
     
  5. anjancontractor

    Thread Starter New Member

    Jul 29, 2015
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    Square wave should work fine.
     
  6. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Good answer. Opens another question, do you need a sine wave at the transducer, or can it be driven with just a simple squarewave (no resonant filter)?

    ak
     
  7. anjancontractor

    Thread Starter New Member

    Jul 29, 2015
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    It can be driven with square wave.
     
  8. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Then this is an easier problem to solve than the one in post #1. Rather than use a linear amplifier, you can use two power transistors, either bipolar or MOSFET, acting as saturated switches. You still will need heatsinks for the power parts, but efficiency will be very high.

    1. Is this a school assignment, product design, personal hobby...?

    2. What kinds of electronic components do you have access to?

    3. What is you experience level in building electronic circuits?

    ak
     
  9. anjancontractor

    Thread Starter New Member

    Jul 29, 2015
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    Thanks for your reply. It's for hobby. I'm a beginner in electronics. I have done quite a few projects with Arduino and prototype circuit boards but with high power I'm new.

    Thanks!
    AC
     
  10. ScottWang

    Moderator

    Aug 23, 2012
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    The voltage of C1(470uf/250V) will be as :
    Vc1 = Vin_ac*T_rate*1.414-(0.7V*4)
    = 120Vac*1.66*1.414-(0.7V*4)
    = 199.2Vac*1.414-(0.7V*4)
    = 281.7Vdc-(0.7V*4)
    = 278.9Vdc

    Why you want to used the turns ratio of coil as 1:1.66, why not 1:1?
    Why you need the voltage so high?

    You just doing the simulation on computer or did it in the real world as breadboard or soldering the components on PCB?

    If the piezo actuator can be works with squarewave then maybe this is the way to do:

    The power supply:
    AC120V → 120Vac(1:1 transformer) → Full wave rectifier + Cap Filter → 170 Vdc → LM317HV → 120 Vdc

    The signal control :
    NE555 PWM → N type Mosfet → piezo actuator
     
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  11. anjancontractor

    Thread Starter New Member

    Jul 29, 2015
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    Thank you for your reply. I can follow the logic but do you think LM317HV can handle 170 Vdc (http://www.digikey.com/product-search/en?KeyWords= LM317HV&WT.z_header=search_go)? I had hard time finding a voltage regulator in that range so I didn't use it in my design.

    I used 1:1.66 because I have that transformer handy.

    I started with Multisim simulation. As this is my first high power project I wanted to be very careful. I don't want any injuries or accidents happening because of my half baked knowledge.

    Thanks again!
     
  12. ScottWang

    Moderator

    Aug 23, 2012
    4,853
    767
    LM317 can't handle 170V, but it can handle up to 57V, if you insist to use 1:1.66 transformer then it could be change as this:

    AC120V → (1:1.66 transformer)199.2 Vac → Full wave rectifier + Cap Filter → 278.9 Vdc → TL783x2(80V) in parallel → (198.9Vdc) → TL783x2(80V) in parallel → 118.9V Vdc
    TL783 only has 700mA, So I used two in parallel.

    Or
    AC120V → (1:1.66 transformer)199.2 Vac → Full wave rectifier + Cap Filter → 278.9 Vdc → LM317HV(40V) → (238.9Vdc) → LM317HV(40V) → 198.9 Vdc → LM317HV(40V) → 158.9 Vdc → LM317HV(40V) → 118.9V Vdc

    If use three LM317HV then 53V will be close to the rating voltage 57V, so I used 40V for four LM317HV in series.
     
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  13. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    The LM317 voltage rating is from input to output, not input to ground. You can use a single 317 to regulate 1033 volts down to 1005 volts with no problems. If the worst case input to output voltage differential is less than 43 V or 57 V, ok.

    ak
     
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