TSP  

Yes Shariar, you clearly state that the circuit is just for educational purposes and I'm absolutely convinced that you'd come up with all its shortcomings easily. However, some of your followers might want to start by just copying your circuit as-is, since you're showing it in the video, playing with input voltages that seem reasonable and seeing that it doesn't work and instead maybe even blowing up their $ 20 power opamp, even with enough heat sinking and limiting current. The real educational value starts there... I *am* one of your followers, enjoying your videos of high quality in several respects.

The Signal Path would love an ep on frequency synths. I believe eval boards up to 6 or 7 GHz are within budget

Stability can be tricky. You can certainly learn a lot by figuring out ways to fix it, but knowing where the dragons lie (and how to avoid them) before you get there is probably a better way. There are plenty of cases where you can design and prototype something and it works fine, but is marginally stable. Sometimes this results in a circuit that only goes haywire under very specific conditions. Trying to track that down can be very educational, but I think knowing the tricks beforehand makes it a better experience (and certainly a less frustrating one). A good resource I've found for this is a set of presentations from Texas Instruments: e2e.ti.com/support/amplifiers/precision_amplifiers/w/design_notes/2645.solving-op-amp-stability-issues. Which goes into a number of simulation tricks to diagnose stability issues before blowing up $20 amplifiers. FWIW, I'm also a follower. The amount of technical depth Shariar brings to all his videos is fantastic, and I've definitely learned a lot by watching. [edit: this didn't seem to get tagged as a reply to Raymond above, but it was meant to be]

@@guyvanburen ujjfjjtj

@@guyvanburen jjjfijijgs

This.

That actually seems like the reason that's there.

I wonder how long the trial is good for lol

@@beenn15 It is probably only a few minutes, but since Dave has to tell you, it will take at least 45 minutes.

RIP BB.

Came to say that. I have just tested a capacitance multiplier today and it works wonders! Sure, the line regulation is lost, but I have just built a circuit which uses the 7809 regulator as a reference and as long as the transistor base current is high enough, the output is fairly stable... and I suppose one could always toss in an opamp and stabilize it more... :D

you can actually get op amps up to 100A like the PA50 by apex, problem is they are very pricey, $20 or so for the one used, $500 for the 100A PA50, if your after a power supply replacement in old equipment that need 2 amps best use a switcher module and manually set a couple of LM317s would be cheaper

I'm not sure, it costs a fortune. Also not granted it can drive capacitive load. I'd go with a discrete pass element, it should be much cheaper, although it would require a separate over-current and over-temperature protection.

I'm afraid it's a hardware issue.

wtf is scanlime.

oh the cat women... I prefer signal path's cat.

ru-vid.comvideos

At around 900MHz I'm thinking about home automation gadgets on an ISM band.

900kHz not Mhz, so i would also assume it comes from AM Radio stations

Depending on the switching power supply controller, 900kHz is in the range of switching frequencies. That noise wasn't very heavily attenuated by the addition of the opamp, but the PSRR of the opamp has likely fallen off a cliff by that frequency. Could also be anything else in the room...maybe the cat; does the cat have a pirate radio station? Definitely looks like a modulated signal.

it does not look like AM to me, looks more like FM

It's unlikely that any local rf source would couple this strongly into a 25 ohm load. However, it most probably comes from a spread-spectrum oscillator driving a dc/dc converter.

This model is a DPH buck/boost unit, so I'm not sure if OpenDPS will work here, though it has been tested on other DPS buck units. See, for example, this thread: github.com/kanflo/opendps/issues/197

Yes, of course. As I mentioned this is just for exploring the noise.

Sorry, on a re-read of my original comment I realized I should have worded it differently. I'm sure you're aware of the array of issues in a design like this - I should have worded it more as a general comment or addition to the conversation in the comments. It is very cool seeing the noise benefits of even a simple op-amp LDO in this sort of demonstration.

Not exactly, because then the voltage would be a function of the load as the junction voltage changes with both current and temperature.

I agree that a simple emitter follower with filtering on the base would filter out much of the noise. Could you break out the feed back loop within the power module to the transistor's emitter to remove the voltage drop error? I have one of these units and was going to give that a go. BTW, that's a broadcast station, right? If it is, then some those spikes you are seeing may be direct induction from the inductors in the power supply...ie if you getting radio stations, you will get other stuff. Cheers doug

Pro version has layers, I've seen Dave using it.

You don't want more capacitance at the output of any bench power supply because it allows overshoot in current-limiting mode and can thus fry the very load that you are trying to protect. Current-limiting modes are supposed to protect against dead shorts, yet capacitors inherently dump current into such a short. Capacitive filtering at the output is a crutch used to fix a poorly designed power supply. I like the DPS/DPH models as they were initially a great value, but they are quite noisy. That noise is not harmful for most hobbyist applications and there are circuits like this one that can reduce this noise. It's still hard to beat the DPS prices and features and I'm unaware of competitors to the DPH buck/boost models, but the manufacturer has understandably leveraged customer demand into higher prices across the line.

Pure linear regulators don't make noise. They may pick some up from elsewhere, but so would any regulator.

It's pretty wide though - each sideband is 100 kHz.

Kyle McInnes ya but really what could be else?

The article is interesting for low current applications. I have noise reduction needs in the 20 to 50 Amp range.

I agree that scaling up to 20 to 50 amps would be more challenging, but with respect to Shahriar’s use case in his video, the power op amp that he’s chosen would be able to inject sufficient inverse noise current into a correspondingly low resistance shunt on the order of 100 milli-ohms - perhaps much less. In a pure AC configuration, one benefit for the power op amp is that it is only burdened with carrying the noise power, so it should run quite cool - even at full load. Unfortunately, that configuration would require higher rail voltage on the op amp to effect a bipolar output about the target output voltage. By purposely introducing an offset into the op amp circuit to cause it to draw DC current statically through the shunt, a new virtual mid-point could be established within the anticipated noise amplitude and reduce or eliminate the higher op amp power supply requirement. Even better, use the power op amp as a driver for a large bipolar or FET transistor to scale up even higher. I propose this only as an interesting way to use a power op amp in this use case. Otherwise, L-C filtering or a downstream high-current adjustable LDO would serve the same purpose as the op amp series regulator, but at a much lower cost, better rejection, and available survivable current limiting.

Totally agree, long wires compromise performance. In my measurements every centimeter from output cap makes transient response worse. Also, wires work as antennas.

It is more difficult than you think. An LC network will have its own impact on rise/fall behavior of the power supply not to mention on the CC/CV switch over. But is is worth trying it to see what is the best you can achieve.

Old post but just saying this in case some stumbles upon this comment. The "float voltage" youre talking about is the peak to peak voltage. Unless you load the transformer, this is the voltage it will output. So you connected a 35V supply to a module with 32V max input and it went up in smoke. No surprises there.

Check the AM Radio Stations in the area, also possibly a fluorescent lamp.

900kHz, not 900MHz, vidas v

eye sight plus old timers lol yes, after looking at it again i can plainly see it much better once i bumped up the video resolution to 720 !

It is at 900 kHz

oooh. my mistake. now that i think about it he said it measures up to 1 MHz... soooooo my bad

Uwe Zimmermann nope, no switching is done in the battery pack, it's just 3x LiPo in series. They'd never be able to get enough current to start a car otherwise