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I built a simple inductor test jig, I use it every time I do anything smps and some other stuff, I'll send you a link if you want, it does pretty much what cruts said.
Modding it to inject dc might be doable, however I have no need for that.
For really big chokes you can use a fat cap and a scr.
About 1/3 the way down theres the test jig, you may find the info on the page a bit basic if your allready into switchers.
The thing I did diffrent with the jig was put the sense resistor between the fet source and ground, then my 'scope i/p is referenced to ground.
You also need some good low esr caps across the supply, I have 5 x 1000u caps robbed from a pc power supply and I get 50a pulses from them off a small psu.
About 1/3 the way down theres the test jig, you may find the info on the page a bit basic if your allready into switchers.
The thing I did diffrent with the jig was put the sense resistor between the fet source and ground, then my 'scope i/p is referenced to ground.
You also need some good low esr caps across the supply, I have 5 x 1000u caps robbed from a pc power supply and I get 50a pulses from them off a small psu.
Thanks for that, Ive actually come across this page before, but I might give that circuit a try, should have all the parts required.
On Tuesday I'm going to buy a bunch of low ESR electrolytics. From the approximate measurements of ESR I have made, the lower ESR ones are around 10 times lower than a regular one of a similar value. I used to think low ESR caps were a sales gimmick, but they really do make a big difference.
I have had ordinary caps blow up through too high esr!
Your equation sounds right, however working out series resistance at high freq isnt allways that easy, at 50 kc the impedance of a cap will be its xc plus the esr plus the esl, there are other parasitics , these are the main ones. esl is equiv series inductance, if you application is critical your probably better building a jig to measure it.
Yes esr will probably be higher at a lower freq then published, I'd assume esl in included in the published values.
Manufacts dont allways publish the info you need, product manufacturers must work with component manufacturers to find out what they need to know.
My test jig is very usefull, it can be used to measure esr too, as the sense resistor provides the lower 1/2 of a v divider, with 2 chans of a 'scope you can work out esr, if you do this use non inductive non wirewound r's.
My reckoning was that for capacitors of 100uF upwards the contribution of Xc would be minimal. ESL on the other hand I'm not sure. I have measured ESR at 50Khz and 326Khz and the values were different, I'm guessing that might be due to ESL. Another thing to be mindful of with esr measurements is the impedance of the test leads and clips ( mostly resistive ) Ive found that using crocodile clips to connect to the capacitor is a bit of a hit or a mis, small variations in the grip of the croc on the capacitors leads introduce marked variations in the measured value of ESR. Something I've noticed too with cheap capacitors is that the leads are very thin, probably thin enough that they probably impact on ESR, hard to determine how much as there will be other factors that could lead to higher ESR. But one thing is for sure all of the cheaper capacitors I've measured have all had higher ESR. Best results I've found were from Siemens and Panasonic capacitors. Yageo and Hitano ones have been reasonably good too.
There are some pretty good MOSFETs for smps now too. Have seen 0.006 ohm RDS(on) and probably better too, I thought my trusty IRL2910s were good at RDS(on)= 0.077 ohms!
Yes, I think you have the idea.
I'm not up on the internals of caps so I cant say more about parasitics, only a change in impedance with freq is most likely inductance.
To get a good low r measure you can use kelvin leads, 2 leads carry the current, and another 2 leads measure the voltage, so long as you put the high current leads further away from the part than the sense leads you'll get a reasonable measurement.
I've had hundreds of millohms variation on banana sockets.
The other thing about comps is cheapo ones use steel alloy leads not copper, they will be higher resistance too.
IRFZ 44's are good for low voltage fets, as well as low rds you also for efficiency want low gate charge Qg.
Ordered a bunch of low ESR electrolytic caps today from Bitsbox, they have some of the Panasonic ones, the rest are Nover RX series, I think, the data sheet for them shows good results, my own ESR measurements suggests that their actual ESR might be even lower than the data sheet. I expect the data sheet values are worst case ( it didn't specify )
I've still to try out the TI and ST variants of the mc34063 to see if there's any differences to that of the On Semi type that I've been using.
I also bought an LM386N-4 as I came across a design for a dcdc converter using an lm386 and schottky diodes and capacitor. Want to have a go and see how this compares with inductor based converters, I expect it won't be as efficient, we'll see!
Interesting article on the audio amp converter, I've never used one for that, I used a couple of lm386's a while back to drive a aero guage, sine and cosine, I cheated and drove one flat out and the other had amplitude control, worked well.
I've been working with a mc34063 on the bench, a led light for the bench itself, 5v in from a pc supply and 36v out for 3 x 12v led panels, I had to use a gdt to up the voltage for the gate drive, the circuit pulls around 10 amps and warms up the iron dust core a bit too much, so I'll make or find another.
Sometimes I think there's a little bubble surrounding my workbench in which the normal laws of physics cease to apply! I built the lm386 circuit, attached diagram with exact components that I used. The thing is not that the circuit doesn't work , it does and surprisingly well. Its that the lm386 is oscillating at nearly 150Khz! I checked my scope against a known reference just to be sure that it was measuring correctly and it was. The circuit in the article was supposed to operate around 25Khz, which sounds about right for a 10k timing resistor and 2.2n, I tried 1n and 1n8, it did slow down marginally going from 1n to 1n8, this is a bit of a mystery to me, though I managed to get ~83% efficiency with 10 volts in and a 240 ohm load yielding just over 17 volts at the output.
I forgot to include another 1u ceramic in parallel with the electrolytic output capacitor in the attached diagram, I did use one in the actual circuit.
Sometimes I think there's a little bubble surrounding my workbench in which the normal laws of physics cease to apply! I built the lm386 circuit, attached diagram with exact components that I used. The thing is not that the circuit doesn't work , it does and surprisingly well. Its that the lm386 is oscillating at nearly 150Khz! I checked my scope against a known reference just to be sure that it was measuring correctly and it was. The circuit in the article was supposed to operate around 25Khz, which sounds about right for a 10k timing resistor and 2.2n, I tried 1n and 1n8, it did slow down marginally going from 1n to 1n8, this is a bit of a mystery to me, though I managed to get ~83% efficiency with 10 volts in and a 240 ohm load yielding just over 17 volts at the output.
I forgot to include another 1u ceramic in parallel with the electrolytic output capacitor in the attached diagram, I did use one in the actual circuit.
Ok, it seems that the laws of physics are still safely intact !
Having examined the lm386 data sheet today it is clear that there was an error in the original article, however when operated at the intended frequency of 25khz it didn't perform as well as when operated at 144Khz!
I was surprised that this IC was able to work well at this frequency, though looking at the data sheet it maintains 26db of gain up to around 80-90Khz, and gain at 144Khz was only a little down. It surprised me that this circuit worked well as a square wave oscillator with such little gain, in fact with pins 1 & 8 tied with a 10u capacitor to set the gain at 46db the circuit worked less efficiency! It is beyond my ken of circuit theory to explain this, but if anyone else wants to have a go, you are welcome!
I've used tda2030's and 2050's at 50kc without any problems, and I prototyped a xy crt monitor and used audio amp ic's to drive the deflection coils which were rewound, tda2030's were much better than any other chip.
I've used tda2030's and 2050's at 50kc without any problems, and I prototyped a xy crt monitor and used audio amp ic's to drive the deflection coils which were rewound, tda2030's were much better than any other chip.
I'm going to try the same idea with an lm380, I have 2 or 3 of the old ceramic cased ones, and see how well it works, would imagine I could draw at least 2~3 times as much current as that from the lm386 circuit.
Yes, I dont know if its still in use however I maintain various pieces of industrial junk, new and old, one piece of kit had a merc arc rec in it, another had a tungar rec in it.
Tungar rectifiers. That is ancient electronics. COOL!!
Now to your comments on SMPS on breadboards: Yes it can be done, if one really knows how they operate and thus what needs to be done with the high current/high frequency paths.
Unfortunately......Not everyone does.
The lm380 didn't fair as well as the lm386 in terms of bandwidth, -3db point around 100Khz. Might still try it as a dcdc converter around 30~40Khz. It occured to me that it ( the lm380 ) could end up permanently bonded to my cheap breadboard ( they only cost about $2USD from China! ) as the six middle pinsof the chip are supposed to be soldered to a large area of copper for heat dissipation. The chip shuts down over 150°C, but I reckon the breadboard could have started melting by that point! I have several more of these breadboards and another two lm380s, so won't be the end of the world if it does happen!
That idea actually occurred to me too. We only have one AM radio left in the house, its part of a radio-alarm clock, might try an experiment with am broadcasting at some point in the future.
The lm380 worked quite well in more or less the same configuration as in post #30 It operated most efficiently with a switching speed of 40Khz, I think beyond this the slew rate of the amplifier results in increased power loss during the transitions between on and off. This circuit clearly had a lower output impedance than the same circuit with an lm386. I will compile the results and create a table of results for any interested parties. I might try a few other audio amplifier IC's in this role to see how they compare. ( I have tba820, tda2030 )
I dont spose if your generating a high freq sine wave that it is a switcher, more a high freq inverter, one thing there will be very little harmonics or rfi generated.
You can get heatsinks to glue onto dip packages, though for a one off you could probably hack a standard 'sink to fit, and you could use some metal loaded epoxy to glue it to the chip, obviouslt making sure its away from the pins.
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