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SDS800X HD Actual Use Cases
mawyatt:
--- Quote from: Performa01 on May 14, 2024, 07:36:10 pm ---
--- Quote from: mawyatt on May 14, 2024, 06:01:37 pm ---Since Bode is in dB, and Y axis is 20Log(V1/V2)
--- End quote ---
It is worth mentioning that Bode Plot doesn't have to be in dB. It can also use Vpp and Vrms.
--- End quote ---
Yes, but because of the expected range of the measurement (~1000X) better displayed in dB than in linear.
Best,
mawyatt:
Setups for PSRR and Output Z measurements & plots.
Best,
mawyatt:
Here's a KIA7810AP +10V regulator in TO-220 case (#10), we isolated the AWG (see setup above) with 2000uF and used 100 ohms for the sense resistor R in the output impedance setup. Load was established with Electronic Load (SDL1020X-E) at 100 ohms for a load current of 100ma.
So output impedance starts at 100Hz as Z ~ 100*(10^(-100.6/20)) or 933 micro-ohms and at 1MHz is Z ~ 100*(10^(-62.8/20)) or 72.4 milli-ohms.
In the next plot (#11) is the PSRR with a load current of 100ma. The range between 100 and 1KHz shows the PSRR improving, this isn't likely and caused by the setup coupling capacitance.
Edit: Added PSRR #13 which extends to 10MHz and shows some fixture setup resonates at ~3.5MHz.
Best,
mawyatt:
Another interesting use of the SDS800X HD features, the Multi-Channel Bode Plot capability.
Here we have a 3rd Order Butterworth Active Low Pass Filter implemented with Equal Valued Components, see note #23 below.
https://www.eevblog.com/forum/beginners/calculation-of-the-3rd-order-rc-filter/msg5343509/#msg5343509
This circuit was implemented with 3 equal resistors and 3 equal capacitors and a single dual op-amp (LM358).
The Bode function allows one to "see" the voltage waveforms as they progress down the 3rd Order Filter Chain, from the 1st section C2 (note amplitude peaking which allows this overall transfer function to implement the 3rd Order Butterworth Response), followed by the 2nd section (C3) and the final result (C4) with the steeper roll-off response.
Edit: Added a High Pass by simply swapping the Rs and Cs in the Equal Valued 3rd Order Butterworth Active Filter.
Also, note how the op-amp artifacts (LM358) begin to effect the stop band LP performance and the HP upper frequency response. A better (faster) op-amp would yield better LP stop band and HP upper frequency responses.
The Rs were 1K 1% and the Cs were all 0.1uF 5%, which should yield a Low Pass and High Pass 3dB corner of 1.59KHz.
Best,
mawyatt:
Here we've changed the R to 10K with same C (0.1uF), this should move the 3rd Order Corner down to ~159Hz. Here you easily see the 60dB/decade stop band response of the classic Butterworth Low and High Pass responses!
Edit: For those with some Complex Variable/Circuit Analysis interest, the Low Pass has a normalized transfer function of :
Vo/Vi = 1/[S^3 + 2S^2 + 2S + 1] and thus = root(2)/2 or -3dBV at S=j {w=1} at -135 degrees phase shift and at {w=0} Vo/Vi = 1 (0dBV)
For the High Pass:
Vo/Vi = S^3/[S^3 + 2S^2 + 2S + 1] and at S=j, root(2)/2 or -3dBV at +135 degrees and at {w=0} Vo/Vi = 0
Check the posts below for R = 10K and C = 0.1uF, tau of 1ms {w = 1000, f = 159Hz} and -3dBV points, note phase shifts :-+
Best,
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