Test Board for Amplifying Bipolar Pulse from Arbitrary Function Generator?

If you could live with a reduced frequency range I would suggest that an audio amplifier might be a cheap way round your problem. Farnell owned CPC sell a DA500 power amplifer for £99 which should be able to output at least 100V pp into 8 ohms so no problem with your 10k load. It's pretty  basic so the frequency range will be 20Hz to 20kHz or so (not quoted on CPC website).

If you want to meet your spec you will pay a lot for a ready made amplifier but it wouldn't be that hard to make your own - are you prepared to solder ?

Michael,

Thank you for your kind response.  I like the fact that you provided (a) a poor man's solution (the amplifier), and (b) a path to the solution, solder my own.

Last night, before I could see your answer, I bought a 15w per channel audio power amplifier (Pyle PTA1 mini); now that I look at the spects of the DA500 (500W), I see that I might bought something a bit short on the side of power.  This is kind of close to your solution (a).

On the other hand, regarding solution (b), I am preparing myself to soldering, and would like to hear a bit more about solution (b).  But, my question before I dive into a project is if there is any test board with amplifying circuit that would minimize the soldering?.  I found two sets of options within Analog Devices where to pick from, but I don't know enough to select a best option.  In the past, I bought a network analyzer test board from them, and it actually worked pretty well for what I needed at the time (I got lucky that time, me thinks).  These are the two sets of amplifier options, some of them have test boards, which is what I am looking for.  However, I might be completely off in trying to select something from those lists because it might not be adequate, in which case, I will be ready to start the project.

   1. Analog Devices High Voltage Amplifiers

   2. Analog Devices High Supply Voltage Amplifiers

Thank you very much

Hello -  look up all you can on National Semiconductor's LME49830. None of the AD parts in your references will do but the LME49830 can meet your spec. NS give  a pcb layout in the data sheet - you can buy ready made from Digikey bit it is a bit pricey. This link takes you to a web site where they sell modules http://www.audiomodule.com/store/Power_Amplifier_1.html. I've never done business with them and I can't vouch fro them at all.

You might need to tweak the design to get the frequency range you want.

I will give it a try.  The website owner has another page with more information on the specifics of the modules.  ( http://www.audiomodule.com/amp37.html ).  The specifications look like they match what I need.  In comparison to the digikey demo board, the price looks very reasonable.  They even have the power supply for the module in there.  I think this is an application by probably the same author: http://www.diyaudio.com/forums/chip-amps/172100-two-pole-compensation-lme49830.html.

Thank you very much

In fact, LME49830 without output MOSFET stage would be sufficient (as it has 47mA minimum output current, page 5 in http://www.national.com/ds/LM/LME49830.pdf), but amp module will be easier to use.

Alternatively, you can look for ultrasonic pulsers like Supertex HV738

http://www.supertex.com/feature_HV738_HV748_HV758.html

http://www.supertex.com/pdf/datasheets/HV738.pdf

However, demo board HV738DB1 costs a lot more than LMC solution - $188.

Hi J,

Not  the cheapest solution but great value for money,

http://uk.farnell.com/agilent-technologies/dsox2002a/oscilloscope-2-channel-70mhz/dp/1859768

The 70MHz 2 channel DSOX2002A from Agilent is £830 for a high specification oscilloscope and you can unlock the waveform generator option

Order Code: 1904004 for an additional £337.

http://www.element14.com/community/message/37679#37679/l/infiniivision-x-series-from-agilent-dso-and-mso-msox3000-dsox3000-msox2000

Please see the above blog and watch the video for more information. this way you can get 2 new toys in one!

I hope this helps

Peter

Sorry Peter - is it my brain failure or yours -  how can the OP use a scope as an amplifier ?

Michael Kellett

Michael, all,

I received the Pyle 15W per channel amplifier.  I conneted it up to the function generator and oscilloscope combo, and started testing it.  I found out the following:

1. If I went below 10Hz, it would not amplify as well, and it would only reproduce square waves correctly above 20Hz.  Makes sense since the amplifier's frequency response is 20Hz-20kHz I believe.  The LME89430 in the module's specification for frequency response starts at 1Hz.

2. The Voltage is limited to 10V for the 15W amplifier.  This seems to be because of a constrain with the speaker resistance of 8ohm.  Based on this the next point. (I could post the scopes screenshots if anybody is interested).

3. I made a graph to see what sort of pre-made audio amplifier I would have to buy to reach my wanted Voltage based on the 8ohm impedance/resistance, and it didn't make me very positive about buying a high W amplifier, because it seems they mostly have this 8ohm restriction.  See graph below:

According to this graph I made, it seems I would need a 1300W amplifier.  Maybe this safety limiting factor can be removed from the module (which seems to have it as well).  Or I might be totally wrong here as well?

4. I contacted the person with the LME89430 module and asked a few questions til I bored him.  He said his module should work, although now that I went to the specs again, it seems to also have the limiting voltage because of the 8ohm speaker protection.  If this is the case for the modules as well, can they be modified to change this restriction?

5. I found another site that has other modules based on similar chips as well.  They have a 500W module based on the LME49810TB/NOPBLME49810TB/NOPB.  Here is their relevant list of modules:

http://connexelectronic.com/index.php/cPath/39_40

Thanks very much in advance,

J.

As you have stated in first post:

- Resistance has ranges between (given by my material and my electrode geometry)

  1. Wet = 10kOhm

  2. Semiwet = 100kOhm

So you don't need 1300W amplifier because you will have load resistance 10kOhm minimum, but you need Vpp 100V. As your load resistance is over 1000 times higher than 8 ohm, you need not such high output current which is needed for 8ohm. You need power amplifier with LME and output transistos which can withstand over 100V of source-drain voltage. Amplifier stated in fourth post http://www.audiomodule.com/amp37.html is good as it has 200V IRFP240/9240 transistors.

Power limitations and protections are valid for 8 ohm load, in your case (10 kohm) output current and power  should be over 1000 times lower than for 8 ohm.

As to low frequency limitations, you should change input and loop capacitors to 20 times bigger or remove them. If I would have schematic, I could point them.

RWM,

Yes, that is why my 15W amplifier should work, but it doesn't.  It will not go over 10V.  I am running the amplified signal over a 1000ohm load, and the maximum voltage I can get is 10Vpp.  Here is the graph of my signals (original in red, amplified in blue) at 12Hz, and then the same signal when I crank the volume up on the amplifier.  Look at how it finds a ceiling and floor at +/- 10V.  My input is about a Vpp = 5.4V, and the output of the 15W amplifier can reach 10Vpp without distrotion, but, if I try to get more out of it, I get the image on the right, where the voltage never exceeds 10Vpp.  if you continue, you just get sort of a square wave that does not exceed that 10Vpp limit.  If it wasn't for this, my 15W, US$20 would be more than enough.  At 10kOhm, 1W would be enough to drive 100Vpp.