Boosting Output of Function Generators

Chip amp would be my choice.

Don't bother with amplifiers, as the load is unknown for many applications. just tell your students to measure the input voltage as well as measuring the resonance voltage.

Especially if they will be making Q measurements, but if its only for observing the voltage peaking at resonance then ignore the generator's output voltage drop....

John.

An even better method is to use a free software program such as ARTA to make the impedance measurement using your PC's sound card.

You can program the sweep start and end points and the program will produce a graph of the results and you can see the slope of the network.

If you are trying to teach someone how to use a signal generator, that is another thing, but if you just want to do this manually, then you can also find free signal generator programs for the PC that use the sound card and take voltage measurements at the network to do this manually.

It depends on the goals of the course.

I like that sound card business. I only have a couple of crappy old laptops available, and they may not have real sound IO connectors, but I should be able to get something useful out. I'm an engineer; I can jury-rig anything. On the plus side, once I pop the plastic off to get at the sound, I can schlep a voltage divider in there and make a cheap oscilloscope. Thanks. I'll let you know.

chip amps or matching transformer are the choices. The common 'line to voicecoil' type would serve here. The line is the so called 70 volt line, also called a 600 ohm line.

In a pinch you can use a 6.3 volt to 120 volt 1 amp or smaller filament transformer, with the 120 volt side to the 600 ohm side. This is not perfect but might be an improvement over what you have. A larger transformer may waste too much power for your 600 source.

Yeah, I tried the filament transformer (one I found in my junk box) and the losses were too great. I don't have access to much in the way of transformers. Do you have a source for the matching transformers?

Have the more advanced students wind their own matching transformers for the noobs! it'll be a potential learning opportunity about maximum power transfer and impedance matching...

Oy! You are an optimist. I can't even get the electronics instructor interested in winding coils. I've got to be careful not to be too much of an old fart or they'll cart me off to the home where I can babble about "home-made Yagis".

well, you could always cobble together a little 741 op-amp circuit to impedance match it.... should be dead simple.

Duh! Thanks! I hadn't even thought of that. That's why I always like to ask folks who are smarter than me.

NOOOOOOOOOOOOOOOOO

A 741 op amp can't deliver into less than 10 ohms.... especially when we are talking about a load which is varying in reactive and impedance....

Forget all the talk of amplifiers - they will never be stable under all the conditions you might require.

Matching transformers are useless as the load is once again of varying impedance....

It all depends on what you want to do.... if its measuring Q factors then you will need a suitably designed generator.... if its just to see the peak / dip of the circuit at resonance then use them as they are....

do you really want to add a power supply and amplifier to each and every one of these function generators????

There is always a TDA2002 or similar.

That link took me to a 'news' site describing a fire in texas or something....

A little off topic eh????

oops, must have clicked on the wrong link. mea culpa.

http://www.datasheetcatalog.org/datasheets/400/378176_DS.pdf

Radio Shack has 70v line matching transformers. The secondary has 4 & 8 ohm taps.

model #NX-70VTR catalog # 55013095 $15.99 each.

Thanks. I'll check those out.

I have a similar problem. Looking to boost up the output power of a function generator in the range 10 to 100 kHz. Output power +/- 100 Watt. The load is acting capacitive.

Can someone suggest me a solution ?

What are the values of the RLC? And is it parallel or series resonance.. or both?

This doesn't seem to be a quantitative experiment; more concept demonstration. Why not add resistance in series with the whole network, measuring only the voltage that either peaks or dips at resonance. It would also allow for extra discussion of circuit analysis - phase shift, etc. I assume the students are using oscilloscopes, so peak resonant voltage, won't have to be very large across the network.

An update. I may have the solution.

My supervisor sent me an e-mail saying she had found these old sensor interfaces in a drawer. She thought they were maybe outdated. They were used with ultrasound position sensors that were no longer used.

Well. A little digging revealed that the boxes should also contain a Voltage-Driven-Oscillator with a DAC input, a linear power amp with a 4Ω output, and a power supply. If so, I'm like a hog in mud! Oh, the position sensor probably had a voltage-divider ADC in the box as well.

I'll keep you guys posted after I get my hands on one of these. This is like dumpster-diving without all the messy garbage.