How much current can the AWG output on the Rigol MSO5074? - Page 1
Forum section: electronics / testgear

author: spiff72
author_rank: Regular Contributor
timestamp: October 15, 2021, 04:41:43 pm
content: Hello all,I haven't been able to find this info through google searches (or I am not skilled enough with my google-fu to find the right search terminology)...Simple question - if one wanted to output a sine wave of a certain amplitude, and drive current through a resistive load, what is the upper limit of current that it can source? I think the output voltage is limited to 5v (not sure offhand if this is 5Vpp or RMS), so I am curious how large of a resistor should be used to keep the current under the max allowable given my selected (not necessarily 5v) amplitude.Thanks!

author: RoGeorge
author_rank: Super Contributor
timestamp: October 15, 2021, 05:12:53 pm
content: The output of a 50 ohms AWG is in fact an ideal voltage source series with a 50 ohm resistor.That means if your AWG is set for 1Vrms/50ohms it will deliver 1Vrms on a 50 ohms external resistor. Therefore the AWG internal source with no load is generating 2Vrms.When you short circuit the output to measure the max I out (don't worry about shorting the output, any AWG is designed to withstand a permanent short circuit) you'll find I = 2Vrms / 50ohms, so you'll measure 40mArms with an external DMM (set the DMM to measure AC current).

author: egonotto
author_rank: Super Contributor
timestamp: October 15, 2021, 05:19:30 pm
content: Hello,the Arbitrary Waveform Generator has max 5 Vpp and 50 Ohm.If your resistor has R Ohms than the max current I isI = 5/(R+50) If R = 50 than I = 0.05 AppIf R = 0 than I = 0.1 AppIf your output voltage is 20mVpp <= U Vpp <= 5 Vpp thanI = U/(R+50) Best regardsegonotto

author: spiff72
author_rank: Regular Contributor
timestamp: October 15, 2021, 06:04:44 pm
content: Thanks to both of you for the responses!I noticed that the AWG has a setting to switch between 50 ohm and High Z. Should this be set to 50 ohms for the above statements to be true?What I would like to try is to replicate the process shown this video - evaluating a cheap current probe (which hasn't arrived yet) using the bode plot function of the Rigol:I was just trying to understand the setup...Thanks again!

author: RoGeorge
author_rank: Super Contributor
timestamp: October 15, 2021, 06:39:49 pm
content: Quote from: spiff72 on October 15, 2021, 06:04:44 pmUsually high Z only changes the numbers displayed on the AWG, it does not change the internal resistance of the generator. For example if you set 1V/50ohms and measure the output voltage with no load, you'll find the output has in fact 2V, not 1 as you set it. Only if you add a 50 ohms external load you'll see 1V as expected.That is why the high Z setting. When you set 1V/High Z you'll measure 1V output with no load (and only 0.5V output if you attach a 50 ohms load).I didn't watch the video you linked.The circuitinsidea generator has a series 50 ohmsat all times, HighZ or not, like explained in this video:

author: spiff72
author_rank: Regular Contributor
timestamp: October 15, 2021, 09:59:50 pm
content: Thank you! That video helped immensely (showing me the voltage divider circuit). It has now clicked for me!