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ok    hum  transplanting parts could be problematic .... maybe a bus buffer  or your strange parts numbering ?
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Repair / Re: E4407B Tracking Generator Repair
« Last post by smgvbest on Today at 10:50:48 pm »
1-what are these numbers? what does -57 mean?
2-what did you measure them with? I mean was it scope or a spectrum analyzer?
3-the most important thing is what probe did you use?

4-for VCO this is very strange! but we dont know what that pin is so please measure the VCO
at the RF input to the mixer (pin 3) and also more importantly measure the IF output
you can measure at pin 2 of mixer but better is to measure at the output of the big filter which is the input pin of the blue "LF3" filter

#4,   Pin3 is 182.5Mhz,   782.5Mhz at input of LF3
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General Chat / Re: Your pet peeve, technical or otherwise.
« Last post by KL27x on Today at 10:48:03 pm »
People who take the exit lane as soon as it appears and then speed up to pass traffic on the left.

Some exits lanes go for half a mile or more before they split off, and not everyone else is keyed up on coke watching and waiting for the instant that exit lane appears.
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General Computing / Re: SD card won't write...
« Last post by David Hess on Today at 10:43:21 pm »
The write endurance might be exhausted.
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Here is a good example of how to do it right:
https://www.seventransistorlabs.com/Images/Flashlight2Sch.png
https://www.seventransistorlabs.com/Images/Flashlight2_Schematic.png
This is only a boost circuit, but the same control scheme applies perfectly well to buck, forward, etc.

The key is the control circuit monitors the inductor current.  Anything can happen to the circuit around it: supply and load voltages can be anything, doesn't matter, as long as the inductor current is known, the output power will be limited and the switch current will remain safe.  (Obviously for a boost, the output voltage can't be much below the input, but that is an exception beyond our control.  Everything else, we have total control.)

This happens to be a battery-powered flashlight, so the inductor current can be sensed at the low side, through the battery.  If high side sensing is needed, a current shunt resistor and current-sense amplifier can be used, or a Hall effect sensor (which is also isolated, so can sense secondary side current as well).

The control is fully discrete, so implements everything that you should expect to see in a controller's block diagram.  Top left (IC2A and such) is the ramp oscillator; IC2B is the PWM modulator (compares a PWM setpoint voltage, to the ramp, thus generating PWM output); IC1 is the gate driver (here just a logic buffer, no need for anything fancy); and IC3B is the current error amplifier.  INSP is the current setpoint, and IC3B controls PWM such that the feedback signal IBATT is balanced with INSP.  As INSP voltage goes up, IBATT voltage falls, i.e., inductor current goes up.  C11, C15 and R20 set the rate at which the error amp responds, so that it can be tuned to a stable response over all source and load conditions.

What good is current?  We want voltage!

Well, even if you wanted regulated current, you wouldn't quite have it yet, because this controls input current, not output.  In the boost converter, the output current is less, by the duty cycle (give or take).  So you'd have to multiply by that to know it, which... can be done, that's not too awful to build a circuit to solve.  But we can measure it even easier, and that's simply what ILED is doing.  Since this is powering LEDs, a constant-current output is desirable: this gives a fixed brightness regardless of battery voltage, until the battery is so low that it simply can't provide enough power at all.

For a constant-voltage output, simply wire ILED to a voltage divider on the output: then IC3A adjusts the current setpoint to compensate for changes in load voltage.  The output capacitors (C3, 4, 7, 8) deliver load current in the short term, and after some time constant (set by C10, C13, R19, values chosen again for stability) the converter takes up the load.

This is better than simply wiring IC3A to IC2B (i.e., voltage feedback to PWM), because if the voltage is very low, it will demand 100% PWM (i.e., IC3A's output saturates to +V).  But a boost converter doesn't deliver any voltage until it switches off at least once... it'll just latch on, and burn itself to pieces. :palm:  Okay fine, so just limit it so it doesn't go to 100% PWM -- divide it down so it only goes to, say, 70 or 80 or 80% PWM.  Then it keeps switching, so the output will keep rising while "full throttle" is being delivered.  Ah, but how much throttle is it really doing?  How do we know if it's drawing 1A or 10?  We have no clue.  The inductor current is a free variable, it just does whatever it does.

Instead if we have an inner loop controlling inductor current, then it simply goes to whatever we set it to.  If IC3A saturates, it demands, well, whatever 3-4V corresponds to at INSP.  (The resistor divider R16-R22 translates this to a smaller (negative) voltage at IBATT, and R1-R2 convert this voltage to a current.  So, about 7A it seems.  Hmm, that's quite a lot for a 18650, I might've been rather optimistic with these original component values...)

Note that IC3B is allowed to command fully 0% to 100% PWM.  There's nothing wrong with leaving the transistor on for an extended period of time -- it's controlled by inductor current, so the only thing that can happen is the inductor current just isn't rising, and, well, the switch can handle the current it's designed for, so it's not going to smoke or anything.  Anyway, this could only happen if the supply voltage were quite low, which can't happen, so it would only stay on for, eh, a few cycle or something like that.  Long enough to ramp up the current to the setpoint.

(This is also acceptable behavior on a boost or forward converter with current sensing in series with the transistor: while the transistor is on, inductor current is known.  This control method (average current mode control) isn't so suitable with such a connection however (the current is not known while the transistor is off!), something to keep in mind.)



Sounds like you are describing a current mode controller lol. :) I read up on those a little while back when exploring how to power an XHP70.2 LED from a couple 18650's and choosing a boost converter for the job. I'm familar with it and yes it is generally more popular than PWM control with a butt-ton of compensation to slow the loop down enough to be stable.

Obviously, for a full-wave forward converter, you'll have alternating switches, which needs a different PWM modulator; and you'll have a secondary side inductor, for which a Hall effect sensor is probably a good idea (isolated current sensing).

A TL494 can be used as a mostly-all-in-one block.  It even has two error amps, though, they're wired in parallel rather than cascade, so I suggest disabling one, and using an external error amp to regulate voltage.

Which, again due to isolation, should be located on the secondary side.  A typical solution, then, would use a TL494 on the primary side, to regulate secondary current (sensed with a Hall effect sensor).  Its setpoint is driven by an optoisolator, which is driven by a TL431 or similar voltage regulator IC.  (The TL431 is typically drawn as an adjustable zener, but it's actually a three-terminal op-amp, with a conspicuously large, yet suspiciously stable, input offset voltage.  Thus, you use it just like an error amp, with compensation RC across it, and that closes your voltage loop.)

This can all be drawn out in the simulator as well, indeed you can put in the above schematics, and use stock models, and you should be able to get it working.  Then you can replace certain parts (say the voltage reference, or current setpoint) with VPULSE sources, and observe the step response for example.



I actually ended up taking inspiration from the venerable TL494 to implement the alternate switching transistors to drive the forward converter, in the simulation. I like the clever use of a D flip flip to divide the clock by 2 and the use of logic for driving the outputs, the use of an OR gate to combine several error amps into a single PWM output of the highest duty cycle (which results in the lowest duty cycle out on the output, easier to analyze  the demorgan's AND equivalent with a NAND and AND gates following the Dflop.)   ;D and yes, just like the 494, the 431 is another one of those old but venerable voltage references which always come in handy!

Well, just don't do that... :scared:

In the full bridge, you can still use a coupling cap if you like.  It can even be rated lower voltage, since it's not expected to have full supply across it.  (Ah, which makes type 2 ceramics actually rather attractive, as they have maximum capacitance near zero voltage.  Who needs derating?!)  Not so much in push-pull, where matched pulse widths are required, and some mitigation is had by reducing the transformer inductance a bit (by increasing the air gap) and limiting the maximum duty cycle (per switch) to somewhat less than 50%.

(This allows some dead time, during which the transformer's built-up flux imbalance, manifest as unbalanced primary current flow (inductance is the ratio between flux and current, H == V.s / A), is able to speed up or slow down the voltage transition from one transistor to the other (commutation).  Thus, lower primary inductance increases the current flow for a given imbalance, forcing the waveform to be faster or slower on one side or the other.  You don't want to lower the inductance too much, as that increases reactive energy storage: energy drawn from, and returned to, the supply, without performing useful work (output power).)

Tim


Oh! Of course, I didn't consider that. Having (ideally) no DC bias on the capacitors does help a lot, class 2 and 3 MLCC's can apparently lose 90% of their capacitance with the full DC rating across them. Although it is still probably a good idea to have them rated for the supply voltage(?)
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Greetings! Wrapping up quarterly planning at work... I'll be back! ::)

Welcome back Mr. Catch-up, how's life? All well, I hope?  :D

Yes, generally going fine. Crazy busy at work, but things will calm down pretty soon. Got my flu shot, too, so I'm ready for winter.

How have you been, Mounty? Looks like the TEA house hasn't gone up in flames. ;D

....with 100 more pages of TEA to read.  >:D  >:D  >:D >:D

Fortunately, only 82. :P I'll process them in parallel. That seemed to be more manageable last time.
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General Chat / Re: USB-C mechanical design is flimsy and pathetic.
« Last post by ajb on Today at 10:38:51 pm »
I don't know about you, but every. single. time. I plug in a rectangular connector I have to look at the connector, look at the socket and see if it's the right way round.  Whether it's a micro B, full size A, or DP, or even a ribbon cable.  Oftentimes it's in low light or sometimes in a place I can't see.  You don't have to be a woo woo visionary to see that if you can solve that problem by designing a connector with 180d symmetry the life-time cumulative ease of use improvement is HUGE.

Reversible micro usb cable
https://www.scorptec.com.au/product/Cables/USB/63777-U2MCAB-02RR
Sure, if it's possible to design a compatible reversible connector without having to remove so much material to defeat the keying that it's no longer durable enough for use, that's an okay solution.  But it would be better to design reversibility into the connector from the ground up.

Who needs a 8 mm thick phone that you can barely hold becuase ia so slippery? After all we all throw a rubberized case. I would prefer a 12-15mm thick phone with a larger battery and space for a hugged connector.

Sure, YOU would prefer a thicker phone, but that's clearly not what the overall market wants.  If it did, then we might see more and better phones similar to the Cat branded ones.  Whether or not the market is "wrong" about that is a silly thing to worry about, and calling consumers stupid for having different priorities than you do, as some in this thread are doing, is arrogant to the point of dickishness.  People like phones that fit easily in a pocket and have reversible connectors, and there's nothing wrong with that even if those aren't your top priorities in a mobile device.

Exactly. What "need" is served by a diminutive thickness? None.
Do you not carry your phone around?  Do you never put it in a pocket?  Because fitting in a pocket (or handbag or whatever) is a "need" that the vast majority of people who use smartphones have, and diminutive thickness absolutely serves that. 
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Test Equipment / Re: Siglent SDS2000X Plus
« Last post by tautech on Today at 10:37:25 pm »
The fact, that the sds2k+ will compare seriously to a true 12 bit lecroy...And doesn´t suck....Wow, just wow.
13 bit mode.  ;)
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Test Equipment / Re: Test Equipment Anonymous (TEA) group therapy thread
« Last post by 25 CPS on Today at 10:36:58 pm »
   Mmmmokayyy... I'm off to get mugged at ESI; pray for me.  :scared:   I will be taking the boi for immoral support.  >:D

mnem
 :bullshit:
So how did it go?

                        

Here's a few highlights... sorry for the crappy phone pix; I really was not prepared for the spelunking expedition this turned out to be. ;)

This place is huge, stacked floor to ceiling with just the sort of stuff we all look for and love. The guy who runs it is reasonable, and he knows what the stuff is worth. But I, unfortunately, did not have enough discretionary funds for the stuff I wanted. There were a few items; a PSU especially that still niggles at me, but I just don't have the budget to spend that much on a fixer-upper right now. :-\

In all honesty, I really shouldn't have gone today so soon after my fall; my back and knee were just killing me by the time I got halfway through the place and it was all I could do to stand while we discussed prices. However, I'm sure I'll be back after I flip a few unneeded stuffs.

mnem
 :popcorn:

Looks like you had a nice visit.  I don't know if they own the building or if they lease it but you can see why I wonder how long a business like that can last in a neighbourhood like that where the condos have been encroaching fast and hard from the east where Caledonia Rd. and Castlefield Ave. are.  It's amazing how much time I spent in that neighbourhood 18 years ago when I worked in the area.  Fond memories of walking the train tracks from St. Clair to Lawrence with a friend from work and seeing the backsides of all the industrial sites.  Walking down almost down to the Commisso Bros. & Racco Italian bakery but calling it off once it became clear that the police were raiding it.  Noticing how a bunch of the security cameras on Commisso's weren't pointed at the premises but were aimed up Kincourt Rd. or down Castlefield Ave. and a bunch of other after work mischief that's not possible with how Toronto's getting so sanitized.  Now I'm only ever there if I'm going to ESI looking for test equipment scores...
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Test Equipment / Re: Test Equipment Anonymous (TEA) group therapy thread
« Last post by 0culus on Today at 10:35:53 pm »
Greetings! Wrapping up quarterly planning at work... I'll be back! ::)

....with 100 more pages of TEA to read.  >:D  >:D  >:D >:D
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