I was using the function generator in the lab to generate a 50kHz 5V square wave to power a mosfet of a boost converter.
On the generator I have both the "50 ohm impedance" output and the "TTL/CMOS" output ... I tried both and the circuit worked.
But what is the difference between these two?
When to use one and when to use the other?

 

The 50 ohm likely has an adjustable voltage output and wave shape.
The TTL/CMOS output likely has a fixed 5V pulse output.

Check the function generator specs to be sure.

 

Make and model number of the FG?

Photos of the front panel?

ak

 

Marca e numero di modello della FG?

Foto del pannello frontale?

Ak

Instek SFG-2110 10 Mhz DDS Generatore di funzioni w / contatore, sweep e AM / FM | TEquipment

 

Also of note is that the 50 Ohm output should be used when driving 50 ohm transmission lines (coaxial cables) the fact that it is 50 Ohms means that it will minimize ringing as a result of reflections, while the TTL output might not be able to drive the cable the cable without much mainly because of the capacitance of the cable.

 

Another difference is the offset adjustment on the front panel. This usually applies only to the non-TTL output (50 ohm, 600 ohm, whatever). As the name says, it adds a DC offset to the output waveform. In this way, you can cause a square wave output to go from 0 V to +7 V, or -3 V to 0 V, +4 V to -4 V, etc.

The 50 ohm output will be able to source more current than the TTL output. Enough to power a DC/DC converter? Only at a very low power level.

ak

 

AK raises an important point: you would probably do well to insert a gate driver circuit between the TTL output and the MOSFET gate.

Example of an integrated gate driver:
http://www.es.co.th/detail.asp?Prod=017611211

Made of discreet parts:
https://electronics.stackexchange.c...-base-current-to-bjts-in-gate-driver-circuits

 

Another difference is the offset adjustment on the front panel. This usually applies only to the non-TTL output (50 ohm, 600 ohm, whatever). As the name says, it adds a DC offset to the output waveform. In this way, you can cause a square wave output to go from 0 V to +7 V, or -3 V to 0 V, +4 V to -4 V, etc.

The 50 ohm output will be able to source more current than the TTL output. Enough to power a DC/DC converter? Only at a very low power level.

ak

Moderator's note: Quote translated from Italian. Please only post in English on this site.

Thank you for the answers.

I don't have the instrument with me at the moment and I don't remember if I could adjust the offset either using the TTL output or the 50 ohm output ... anyway I need a square wave not centered in zero, that is, an offset that brings it to 0-6V (not -3 3V).
So, in your opinion, I should use the non-TTL output (50 ohm, 600 ohm, whatever) to create it.

Am I wrong?

 

The 50 ohm output will be able to source more current than the TTL output. Enough to power a DC/DC converter? Only at a very low power level.

Can you explain again why this happens? It is not very clear to me

Thanks!

 

Because that's what the Manufacturer Specs say on the link you posted.

The TTL output can drive 20 standard TTL loads. That is, it can sink 32 mA and source only about 1.6 mA. Also, the high-state output might be as low as 3 V.

With the offset and output adjusted for a peak output voltage of +10 V, the 50 ohm output can produce a peak output current of 200 mA. This is common in function generators.

ak