Current amplifier for 0-30MHz signal generator?

[neazoi]

Current/Voltage amplifier for 0-30MHz signal generator?

Hello,
I have built a 20KHz-30MHz signal generator project **broken link removed** and I need a suitable circuit to boost the output current, so I can drive more power hungry loads such as transformers, to test their saturation. Or do I better need a voltage amplifier?

Could you suggest such a circuit?

 

[chuckey]

First of all, I think the output level is about .7 V. Are you using the power amplifier?, if you are then its is being fed from the low output, feed it from the high output - you should get ten times more !! - not actually because you have not got a high enough Vcc, so the power amp will limit. What sort of level do you want?
Frank

 

[neazoi]

I consider the technique "Measuring arrangement with a digital oscilloscope" described in this page https://meettechniek.info/passive/magnetic-hysteresis.html
I think my oscillator is not powerful enough to drive toroids into saturation. I do not know if I need a voltage or a current amplifier after the oscillator?

 

[FvM]

You probably noticed that the link is referring to a low kHZ frequency range where active current sources (e.g. using a L165 power OP) can be implemented easily. For MHz frequencies or wide band function generators, 50 ohm matched outputs are the regular way. It's a matter of calculation which voltage levels at a 50 ohm output can drive your cores into saturation.

 

[chuckey]

From your link the power is " own powers the made transformer. E.g.: 15 Vtt / 50 Ω (with a 50 Omega; load). The open terminal voltage is therefore also 15 Vt, and the maximum current is 15 V / 50 Ω =300 mAt. A normal drive amplitude should be feasible at 10 % ". So I guess you need 15 ^2/50 ~ 5W. So either look for a super beefy Opamp, or get one that operates from at least+-12V and follow it with a power FET output stage.
Frank

 

[neazoi]

From your link the power is " own powers the made transformer. E.g.: 15 Vtt / 50 Ω (with a 50 Omega; load). The open terminal voltage is therefore also 15 Vt, and the maximum current is 15 V / 50 Ω =300 mAt. A normal drive amplitude should be feasible at 10 % ". So I guess you need 15 ^2/50 ~ 5W. So either look for a super beefy Opamp, or get one that operates from at least+-12V and follow it with a power FET output stage.
Frank

All right that was the sort of value I needed. About 5W then would be a fine value for testing purposes.
My generator outputs a lot less, so I will try to find a suitable amplifier.
For audio frequencies, shall I try a class-D audio amplifier, to get more efficiency? It would be easy to get something like 5W

 

[chuckey]

You started of by saying you have a 20KHZ- 30 MHZ generator which you want to use to test transformers with. We have determined that you need about 5W. Now you are saying that you want to use a class-D audio amplifier, this will have a upper cutoff frequency of the order of 25 KHZ. So what frequencies are you actually going to use?
Frank

 

[neazoi]

You started of by saying you have a 20KHZ- 30 MHZ generator which you want to use to test transformers with. We have determined that you need about 5W. Now you are saying that you want to use a class-D audio amplifier, this will have a upper cutoff frequency of the order of 25 KHZ. So what frequencies are you actually going to use?
Frank

It depends. For implementing magnetic audio amplifiers something like 20-35KHz is needed, which should be easily inplemented using a class-D amplifier like TDA7480.
For lower frequencies the same amplifier will do.
For higher frequencies another way may be needed, usially a power amplifier.