Test Board for Amplifying Bipolar Pulse from Arbitrary Function Generator?

Question

Hi,

My electronics knowledge is limited, so I am framing my question with the information I have. I am not sure if I am in the right forum to post this question, so if I am very off, please guide me in the right direction.

I want to find a test board /chip combination to amplify a bipolar waveform. The reason I want to try a board is because if I find the right one, and it works for my application, at the end of the day, I will be a step ahead with the amplifer electronics I need. I've also looked at amplifying test equipment that could cost as much as US$2,500. I could probably test 100 different boards with that much money, which I don't have eitherway.

Here is the description of my project, what I already have, including some of the equipment and information:

Equipment I already have:

- USB powered Osciloscope/wave generator combo product, which has an arbitrary wave generator. The specs for the wave generator are here:

Syscomp CRG-101 Datasheet

It works pretty well, but I realized I need more power for my application.

Application:

- Electrokinetics to move fluid though a wet porous material (the Resistance of my electrode system is below)

What my function generator puts out (from the datasheet above):

- Square pulse

- Max. pulse amplitude 6 Vpp

Description from the pulse I need:

- Square pulse, bipolar

- Frequency between 1Hz&100kHz (I might need something close to DC, and then some at AC)

- Amplitude: 100 Vp-p

- the resistance of my system is below

- I don't need the pulse to have very high resolution / precission

Description of the characteristics of my system:

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

1. Wet = 10kOhm

2. Semiwet = 100kOhm

Some information I have already looked at but have not fully understood:

- The waveform generator vendor's recommendations for amplification:

Increasing output current from Signal Generator (Syscomp)

- The two sets of product descriptions I have been browsing (not all have test boards) :

1. Analog Devices High Voltage Amplifiers

2. Analog Devices High Supply Voltage Amplifiers

So Finally the question is:

- If you had to pick a testboard/chip combination that met my requirements, which one should it be?

Thank you very much in advance,

J.

michaelkellett · Accepted Answer

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.

RWM · Answer

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.

JRR · Answer

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

JRR · Answer

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/NOPB LME49810TB/NOPB . Here is their relevant list of modules: http://connexelectronic.com/index.php/cPath/39_40 Thanks very much in advance, J.

JRR · Answer

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.

Test Board for Amplifying Bipolar Pulse from Arbitrary Function Generator?

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