Driving capacitor with class-D
 User Name Stay logged in? Password
 Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read Search

 Class D Switching Power Amplifiers and Power D/A conversion

 Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
 8th August 2011, 09:17 PM #1 highfieldrebel   diyAudio Member   Join Date: May 2009 Driving capacitor with class-D I've asked this already in Pass Labs, but then thought this might be a more natural home... I need to drive a piezo actuator (part of an optical filter) with a 30V pk-pk sine wave at between 20 kHz and 50 kHz. The spec sheet says the piezo will show as a capacitance of 0.4 uF. I can envisage one issue with the low-pass filter class-D amps have to filter away the PWM frequencies. Other than that, would a class-D be able to drive a load like this? I calculate a reactance of 8 ohms for 50 kHz. Thanks for your help
 8th August 2011, 09:21 PM #2 Bone   diyAudio Member   Join Date: Jun 2004 Location: Dorset, UK You'd have a job to find a Class D kit amp to amplify up to 50kHz. The sampling frequency would be too low.
 8th August 2011, 09:47 PM #3 Saturnus   diyAudio Member     Join Date: Jun 2005 Location: Copenhagen, Denmark A piezo is actually electrically identical to a variable resistor in series with a fixed capacitor. There are also some parasitic parallel capacitances and resistances but they are very minor. The variable resistor part is the loss over the piezo which depends on the output.
highfieldrebel
diyAudio Member

Join Date: May 2009
Quote:
 Originally Posted by Saturnus A piezo is actually electrically identical to a variable resistor in series with a fixed capacitor. There are also some parasitic parallel capacitances and resistances but they are very minor. The variable resistor part is the loss over the piezo which depends on the output.
interesting, so when you say the variable resistor part depends on the output, you mean it depends on the output frequency or the output amplitude? Or both?

Is is possible to roughly estimate the size of the variable resistance? It might help the amplifier

Thanks
Steve

 8th August 2011, 10:21 PM #5 Saturnus   diyAudio Member     Join Date: Jun 2005 Location: Copenhagen, Denmark It varies with output amplitude but that will also vary with frequency as a fixed voltage will generate different output amplitude at different frequencies but it's pretty linear and the impedance from the capacitance will be the main effect except at the frequencies you're looking into above the audible range. For example, a piezo like an old Motorola KSN1001 is electrically identical to a 33ohm resistor in series with a 0.3uF capacitor, so at the frequncies you're looking into the resistance part will be the main part of the impedance.
highfieldrebel
diyAudio Member

Join Date: May 2009
Quote:
 Originally Posted by Saturnus It varies with output amplitude but that will also vary with frequency as a fixed voltage will generate different output amplitude at different frequencies but it's pretty linear and the impedance from the capacitance will be the main effect except at the frequencies you're looking into above the audible range. For example, a piezo like an old Motorola KSN1001 is electrically identical to a 33ohm resistor in series with a 0.3uF capacitor, so at the frequncies you're looking into the resistance part will be the main part of the impedance.
excellent, thanks Saturnus, that should help my search for an amp, but maybe I'll need to go higher in voltage also

 9th August 2011, 06:43 AM #7 trevmar   diyAudio Member   Join Date: Jan 2011 I used to design Class E amplifiers to drive capacitive and inductive loads (RF, mainly). It is possible to use Class D to drive a reactive load, but difficult. Maybe this page can help you. Scale the frequencies and inductor to match your capacitance: http://www.tonnesoftware.com/classe.html

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is Off Forum Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Site     Site Announcements     Forum Problems Amplifiers     Solid State     Pass Labs     Tubes / Valves     Chip Amps     Class D     Power Supplies     Headphone Systems Source & Line     Analogue Source     Analog Line Level     Digital Source     Digital Line Level     PC Based Loudspeakers     Multi-Way     Full Range     Subwoofers     Planars & Exotics Live Sound     PA Systems     Instruments and Amps Design & Build     Parts     Equipment & Tools     Construction Tips     Software Tools General Interest     Car Audio     diyAudio.com Articles     Music     Everything Else Member Areas     Introductions     The Lounge     Clubs & Events     In Memoriam The Moving Image Commercial Sector     Swap Meet     Group Buys     The diyAudio Store     Vendor Forums         Vendor's Bazaar         Sonic Craft         Apex Jr         Audio Sector         Acoustic Fun         Chipamp         DIY HiFi Supply         Elekit         Elektor         Mains Cables R Us         Parts Connexion         Planet 10 hifi         Quanghao Audio Design         Siliconray Online Electronics Store         Tubelab     Manufacturers         AKSA         Audio Poutine         Musicaltech         Aussie Amplifiers         CSS         exaDevices         Feastrex         GedLee         Head 'n' HiFi - Walter         Heatsink USA         miniDSP         SITO Audio         Twin Audio         Twisted Pear         Wild Burro Audio

 Similar Threads Thread Thread Starter Forum Replies Last Post terminator12 Class D 6 17th December 2010 03:22 AM Nuuk Class D 9 19th September 2008 04:22 AM ka ming Class D 1 21st March 2007 04:27 PM montreal Class D 0 19th January 2007 04:45 PM snivit Class D 4 4th August 2005 04:20 AM

 New To Site? Need Help?

All times are GMT. The time now is 07:25 AM.

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.