555 - HV output for the piezo with 400-450V @ 25-30kHz.

Discussion in 'The Projects Forum' started by Uskok, Aug 30, 2015.

  1. Uskok

    Thread Starter Member

    Aug 19, 2015
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    Hello everyone,

    Does anyone know any simple circuit to amplify output voltage of 555 timer to be close enough to 450V, current is not matter.
    I need about 450V at output at specific frequency...
    I need stable and fixed 400-450V.
     
  2. crutschow

    Expert

    Mar 14, 2008
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    I assume you want a square-wave of 0V to 400/450V?
    What is the load impedance/current?
     
  3. Uskok

    Thread Starter Member

    Aug 19, 2015
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    No, I forget to mention... It would be 12V to 400/450V...
    Current is less than 200mA what comes out from 555
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    Can you use a transformer? It would be simple enough, I suspect you would have to wind your own.

    What frequency? It is kinda important.
     
  5. Uskok

    Thread Starter Member

    Aug 19, 2015
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    Well I would need 25-30kHz @ 400-450V...
    I could use transformer but witch one, i don't really know how to wind one, I think it's not that simple.. ?
     
  6. crutschow

    Expert

    Mar 14, 2008
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    200mA at 450V is 90W or 7.5A from the 12V supply.
    You can't get that from a 555.
    You will need an amplifier with a 450V supply at the 555 output.
     
  7. ian field

    Distinguished Member

    Oct 27, 2012
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    You should be able to cas_c_ode the 555 output with a high voltage power MOSFET, that is you connect the gate to Vcc and the source to the 555 output pin. The current rating will be the same as that for the 555, the bipolar can handle about 200mA - the CMOS type is much lower.

    The MOSFET will need a Vgs of about 6 - 8V to turn it fully on and avoid excessive dissipation - the maximum Vcc rating for the bipolar 555 is safe for the Vgs of almost any power MOSFET.
     
    Last edited: Aug 30, 2015
  8. Marcus2012

    Member

    Feb 22, 2015
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    He might need to use a driver on the 555 output for that FET as at that frequency I don't think the 555 can supply the current to fully switch it that quickly.
     
  9. ian field

    Distinguished Member

    Oct 27, 2012
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    The output current rating is the output current rating - the bipolar can switch upto 200kHz, granted the pulses get a bit rounded, but its a lot more than the TS mentioned. The CMOS 555 is (allegedly) good for 2MHz - but at a lot less output current.

    The grounded gate MOSFET configuration I described is as fast as it gets, so anything the 555 can do, the MOSFET can do better.

    If it turns out the current rating is a bigger issue than the TS first thought, the 555 output can be boosted by a PNP emitter follower and then fed to the common gate driver stage.
     
  10. Marcus2012

    Member

    Feb 22, 2015
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    Ahh ok my bad. BTW OP what is the load?
     
  11. Wendy

    Moderator

    Mar 24, 2008
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    Drivers for a 555 are no problem.

    Just to verify, you want 200ma at 450V at 30Khz?

    That is a large current at that voltage, it needs verifying.

    Making a transformer from scratch is really no big deal, but you have to know your specs first.

    I see the 200ma at 450VAC P-P as an assumption by other people, so you do need to verify this.

    RMS and P-P for a square wave pretty close, RMS is 1/2 the P-P value.
     
  12. ian field

    Distinguished Member

    Oct 27, 2012
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    The bipolar 555 can only switch 200mA within the Vcc constraints and multiplying the secondary voltage on a transformer will multiply the primary current by the same factor - so getting 450V a 200mA via a transformer is very much a non-starter.

    That 450V is going to have to come from some sort of power supply - the additions I've suggested for the 555 output pin will switch that on and off, but not generate it.
     
  13. Wendy

    Moderator

    Mar 24, 2008
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    That follows the assumption (note that word) that the OP needs 200ma at 450V. If all he needs is a uA, then it is not the case. We do not have enough data to state anything with confidence.
     
  14. Marcus2012

    Member

    Feb 22, 2015
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    Yeah we need more data really. For example does this load actually need alternating polarisation or just on-off DC? Because if it's AC you want afaik you can't switch that high a frequency with discrete components.
     
  15. Wendy

    Moderator

    Mar 24, 2008
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    30Khz is nor much. I have worked on 40Gb digital, and that is old tech.

    Most transistors are much, much faster.
     
  16. Marcus2012

    Member

    Feb 22, 2015
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    I meant the output from the transformer (if he has one), if that's a sinusoidal 450V 30kHz I always thought you can't switch that on and off directly with semiconductors? ( but I am no expert lol) I know solid state relays can be used on low frequency AC but I've had trouble finding ones for higher frequencies.
     
  17. Uskok

    Thread Starter Member

    Aug 19, 2015
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    Hello, I am so glad that you decided to help me out with this.

    Well how much current is not really matter to me. It can mr from 1mA to max of 555 output 200mA. Because the load is piezo material. So only thing I need is suply my piezo with 400-450V @ 25-30kHz.

    I see you suggest me the power mosfet. Will that need transformer for specified output or?

    And could I use the backwards transformer?
    I already tryed backward with simple circuit but the voltage just jumps up and drop around 120 to 500V. If i only could stabilze that.
     
  18. Uskok

    Thread Starter Member

    Aug 19, 2015
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    So basically I need to drive my Piezo with 400-450 very stable volts @ 25-30kHZ. Curent from output of 555 is more than enough, so I only need amplify 555 Vout to 400-450V.
    Is there any possibility to do that without transformer? Can I integrate 555 chip in some simple power suply to switch it on/off? If so can anyone post or made that circuit.
    I really need your help guys.....it is very important for me to build this circuit and if needed I will even pay someone who make that circuit (ofc I need proof that it really works like I need it to do) I know that this kind of stuf is easy for you.
    Thanks for help.
     
  19. crutschow

    Expert

    Mar 14, 2008
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    What is the capacitance of the piezo element?
    That info is needed to estimate the load current required at 30kHz.
     
  20. Uskok

    Thread Starter Member

    Aug 19, 2015
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    Capacitance is 12.84 nF
     
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