Abysmally Poor L7805CV Performance.. Counterfeit or "CV" variant limitation?

[Mechatrommer]

came to my attention after my whole mcu/digital circuit misbehavior during servo transient (changing servo's angle location)... i bought a bunch of L7805CV earlier from ebay china... then the 7805CV is now in the circuit providing supply to Radio Receiver, mcu (pic10f206) and a Servo Motor as shown in 1st setup picture, dont mind the H-Bridge + DC motor, that is supplied direct from 12V (solid lipo battery), only controlled by mcu through IO pin... now with this newly bought L7805CV, when the servo changes location, there is load spike (as usual), the 7805CV cant keep up, from DSO probing, it dipped down to nearly 2V for a few ms, i believe this situation may renders the mcu browned out, and probing also proved the Radio Receiver output signal got distorted due to this failed regulation resulting mcu translation going wacko...

i was wondering what happened? luckily i got other old 7805s stock that i salvaged from old circuit, i have 2 variant for testing and performance comparison, they both don't have "CV" label, i replaced them in place of the newly bought from china "CV" variant. surprisingly, the old stocks perform a lot better with no intermittent circuit/mcu problem. the three variant of the 7805 are shown in 2nd picture. and voltage regulation performance during servo transient is in the 3rd picture. A (old stock) is the best performing foolwed by old stock B and lastly the poorest is the newly bought 7805CV variant. i'm wondering...

1) is this new 7805CV (C in the 2nd picture) counterfeit? but i cant find the report in the net, only one, but he mistakenly identified "an original but old die design from ST" as counterfeit..
2) is this something got to do with the "CV" variant? but i dont see any difference in the datasheet...

if you have better opinion please draw in, for now i'm not sure between 1 or 2, but i prefer (1), its a counterfeit chip. since in this modern era, this poor performance should never happens. ps: this regulator is ok though for low load, such as supplying the Radio Receiver and mcu alone.. when transient spike high load such as the servo, then problem reveals...

[Kostas]

It doesn't look like any of the genuine ST regulators I have seen. The markings look quite poor.

[ivan747]

It doesn't look like any of the genuine ST regulators I have seen. The markings look quite poor.

The logo does indeed look quite malformed.

[Mechatrommer]

yup i also noticed the weirdness of the logo, so i take photo to compare with my other ST's LM317 chip logo (see attached photo). someone may slam if my LM317 is also a counterfeit?

[SL4P]

Probably worth mentioning that the To220 7805 can supply nominally 1A when mounted on a substantial heat sink (over extended periods), and the RC servos can draw a lot more than that under load... perhaps sag on the Vcc is causing problems?

[wraper]

yup i also noticed the weirdness of the logo, so i take photo to compare with my other ST's LM317 chip logo (see attached photo). someone may slam if my LM317 is also a counterfeit?

IMO both of them are fake. On both parts logos are wrong. Right part is 100% obvious fake. Both parts have wrong font for newer laser marked ST parts.

[Mechatrommer]

Probably worth mentioning that the To220 7805 can supply nominally 1A when mounted on a substantial heat sink (over extended periods), and the RC servos can draw a lot more than that under load... perhaps sag on the Vcc is causing problems?

Vcc is solid 11-12V i probed it. the datasheet specifies 0.75A typical short circuit current, i also agree during transient, the servo requires more than that, perharps triggering short circuit protection inside the regulator... lets rule out external circuitry imperfection in my setup, because i did the very same (imperfect) circuit on the 3 different 7805 variant, the older one performs best under the load... i just tested the smaller 78M05 chip that i also bought from the same seller on the circuit. also showing abysmality, same mutilated logo on it, but that is 0.5A rated chip. need to test more on AMS1117 and even the big LM317 adjustable regulator, that for later...

[retrolefty]

Put me down for suggesting that your servo is drawing transient current amount above the fold-back/therm protection inside those 1 amp regulators. Your servo looks like a standard/larger servo size and could easily draw more then 1 amp briefly when asked to move some distance.

[Kostas]

yup i also noticed the weirdness of the logo, so i take photo to compare with my other ST's LM317 chip logo (see attached photo). someone may slam if my LM317 is also a counterfeit?

IMO both of them are fake. On both parts logos are wrong. Right part is 100% obvious fake. Both parts have wrong font for newer laser marked ST parts.

Aggreed. The logo isn't quite correct and the font is wrong. It should look something like this:

[Siwastaja]

Don't buy any semiconductors or capacitors from Ebay. At least 90% are fake, especially from MOSFETs, regulators, LEDs and electrolytic capacitors.

I didn't look at your case very closely, so take this as a general advice that will probably at least partially apply to you:

Larger electrolytic in parallel with a small ceramic or film capacitor as near as possible to the servo motor power rails solves worst transient problems, by reducing propagated spikes and RF emissions and all kind of EMI problems. You don't want large spike currents go through wire loops that have inductance in them, especially if the wire loops are shared between the MCU side, i.e., the capacitance that actually supplies the spike current is far away. The regulator cannot respond quickly enough, no matter how good it is. So add a large cap near to every point of load. Add reverse protection diode directly from the 7805 output to its input to prevent it from blowing up because of the output capacitance (see datasheet).

Quick load changes in power lines shared with the MCU can even cause overvoltage spikes large enough to kill the MCU.

[Mechatrommer]

Don't buy any semiconductors or capacitors from Ebay. At least 90% are fake, especially from MOSFETs, regulators, LEDs and electrolytic capacitors.

this can go on.... dont buy products from china because china designers may use parts from china. a rigol ds1054z may contains lots of fake semiconductors inside?

So add a large cap near to every point of load.

done that. the closest i can put the big cap is on the radio receiver power rail, problem not solved (you can see the detached cap in the setup picture laying around). i cannot put the big cap any nearer or inside the servo, thats not standard procedure, or simply like blaming the servo designer for not doing their job. we assume the servo is ok with its built in circuitry.

Add reverse protection diode directly from the 7805 output to its input to prevent it from blowing up because of the output capacitance (see datasheet).

already in place..

Quick load changes in power lines shared with the MCU can even cause overvoltage spikes large enough to kill the MCU.

this is the OP problem...

[BravoV]

Just curious, file the the metal tab a bit, is it copper inside ?

[Ian.M]

Make up a splitter cable to take the servo supply and ground directly from the power board, *NOT* via the radio.   Use a genuine L78S05CV from a reputable supplier.

You may also need to separate the servo and radio supplies or at least, feed the radio via a diode so that -ve going transients on the 5V rail don't immediately reset it. 

Here's how I stopped a PIC MCU resetting whenever a fast servo movement occurred:

[Len]

Don't buy any semiconductors or capacitors from Ebay. At least 90% are fake, especially from MOSFETs, regulators, LEDs and electrolytic capacitors.

this can go on.... dont buy products from china because china designers may use parts from china. a rigol ds1054z may contains lots of fake semiconductors inside?

I'm pretty sure Rigol doesn't buy their parts on ebay. 

[free_electron]

font and logo are wrong.
also note the 'rounding' on the edges of the epoxy.

[Mechatrommer]

Just curious, file the the metal tab a bit, is it copper inside ?

i i. ok its copper since its yellowish-orangeish-copperish. see attached picture (red arrowed). so is it a fake? so far from the outside everybody voted yes..

Don't buy any semiconductors or capacitors from Ebay. At least 90% are fake, especially from MOSFETs, regulators, LEDs and electrolytic capacitors.

this can go on.... dont buy products from china because china designers may use parts from china. a rigol ds1054z may contains lots of fake semiconductors inside?

I'm pretty sure Rigol doesn't buy their parts on ebay. 

i mean, fake parts in ebay must be from somewhere right? so i believe its from well... china right? i dont think chinese bother to import fake from thailand dont they? so perharp rigol got their parts from the same source as where the ebay sellers got...

[Siwastaja]

Don't buy any semiconductors or capacitors from Ebay. At least 90% are fake, especially from MOSFETs, regulators, LEDs and electrolytic capacitors.

this can go on.... dont buy products from china because china designers may use parts from china. a rigol ds1054z may contains lots of fake semiconductors inside?

You don't seem to have a clue what you are talking about.

No, this can't "go on".

There are a lot of good China designs. Rigol is a known, good brand.

China has many legit component sources. Sometimes Alibaba/Aliexpress is just fine.

But China Ebay is full of counterfeit components, especially the types I listed: mosfets, simple ICs such as regulators, LEDs, and electrolytic capacitors. It's purely stupid to buy those, but you are free to do so if you want to.

Chinese designers DO NOT buy components from Chinese Ebay, because most of the time, Chinese designers want their products to work! They also want their products to be cheap, and Ebay counterfeits are ridiculously expensive. They have proper component sources, and also sources for proper low-cost parts that may be of lower quality, but knowingly so.

How do I know? I have bought a lot of those Ebay counterfeits before I came to my senses. My personal rate of underperforming counterfeits was about 80-90%, as has been the case with anyone else I have asked. You can find a lot more experience on this forum. For example, MOSFETs may have four times the RDSon, as happened to me. Or 1117 regulators may have wrong printing on top, they are different voltage what they are sold as (and what is printed on them), as happened to me. Or LEDs fail after a few minutes and become randomly blinking leds, as have happened to me several times. Or electrolytic capacitors are wrapped on fake wrappers, as happens to everyone - I haven't done this myself.

If you want to be stubborn, go and bang your head on the wall - it will be more productive than buying KNOWINGLY bad components with similar prices you can get KNOWINGLY good components with.

Hope this helps. Sometimes I really wonder why the heck I'm writing on this forum! Asking for help and then ignoring solid, knowledgeable answers from people who know their stuff is the stupidest thing I can imagine here.

[Mechatrommer]

i think i need to treat these parts with respect from their cloneliness, inductive load seems not to be their league. congratulation to me while testing AMS1117-ADJ i successfully reproduce the magic smoke, the mcu is killed along with all the h-bridgade i believe apart of the problem i guess is lack of sleep, i've made very little progress here, very well.... ps: AMS1117-ADJ is way way abysmal than the fake L7805CV

Ian.M thanks for the suggestion, the diode to mcu supply is neat, i also implemented that in my earlier circuit. i'll think the other ways or your ways tomorrow, maybe i'll need to supply the servo from separate buck convertor. these clones are simply cannot cut it...

[georges80]

A 'real' company will purchase from a reputable distributor that sources their parts from manufacturers and thus can provide a traceable pedigree of the components. Static/humidity/storage requirements followed.

Purchasing on ebay or from various grey markets means you have no idea what the source of the parts is. They could be seconds or worse other components that have been relabeled. There is a thriving business in counterfeit components.

I can't imagine why anyone would purchase components from such sources and be surprised that the part may not actually be authentic and then chase their tail trying to figure out whether their circuit is at fault or the component.

cheers,
george.

[JoeB83]

Don't buy any semiconductors or capacitors from Ebay. At least 90% are fake, especially from MOSFETs, regulators, LEDs and electrolytic capacitors.

+1

This. I don't mean to sound rude but I'd almost expect semiconductors and the like to be trash when purchased on eBay.

[Mechatrommer]

Chinese designers DO NOT buy components from Chinese Ebay, because most of the time, Chinese designers want their products to work! They also want their products to be cheap, and Ebay counterfeits are ridiculously expensive.

so where the "chinese ebay" get their supply from?

If you want to be stubborn, go and bang your head on the wall - it will be more productive than buying KNOWINGLY bad components with similar prices you can get KNOWINGLY good components with.
Hope this helps. Sometimes I really wonder why the heck I'm writing on this forum! Asking for help and then ignoring solid, knowledgeable answers from people who know their stuff is the stupidest thing I can imagine here.

so please do suggest where to get legitimate parts to malaysia without having to pay $40 shipping with track number cost for few $5 ICs supply. that $40 SH i got from digikey, please advice somewhere else...
element14 can be one of them? i need to check them back, last time i try to order they have a system error...

[Siwastaja]

Chinese designers DO NOT buy components from Chinese Ebay, because most of the time, Chinese designers want their products to work! They also want their products to be cheap, and Ebay counterfeits are ridiculously expensive.

so where the "chinese ebay" get their supply from?

From con artists specialized in making fake parts? You know, the thing called 'crime' exists in this world, and shouldn't be surprising that it works professionally. There are factories doing fake parts, just as there are factories doing fake clothing.

Sometimes these can be originally genuine parts, but different parts (for example, a cheaper FET with lower specs), or parts that have failed production testing (binned to trash can), and the conning is just a relabeling operation.

Sometimes they are deliberate products designed from scratch, only to be a slightly different kind - a type that can be manufactured with much lower cost, and then sold at premium prices.

You know, Ebay is not a store itself, it's just a market place. You can sell stuff there, I have sold stuff there. So anyone can do it, and so can any scammer.

A lot of Chinese design is actually just fine, and designed properly, using proper component sources. Components are cheap! In many designs, the human work is the most expensive part, even when done in countries with lowest wages.

Even the Chinese designers designing low-quality products must have their own sources of low-quality components - even they want to know something about the component. They may accept a counterfeit, but it must work at some level. And they want it much cheaper than the genuine part (which already is rather cheap). Ebay counterfeits are bloody expensive! That's also part of the scam; people have their doubts about cheap components, so they sell at high enough prices so that they could be real.

I don't know about Malesian distributors. Is there, by any chance, any redistributor who takes orders from small players and then orders from Farnell/Element14/Digikey/etc. daily or weekly or so? We have one company locally here specialized in just that, and I'm doing similar service to my friends every since and then here at a local club.

[Mechatrommer]

I don't know about Malesian distributors. Is there, by any chance, any redistributor who takes orders from small players and then orders from Farnell/Element14/Digikey/etc. daily or weekly or so?

none that i know. even if they are (i know some small sellers in our local online store), it will be multiple fold more expensive. i'd rather buy direct from element14.com.my thanks all guys for suggestions. so i guess this part is guilty as charged. i will take this matter more seriously in the future time. i need togoto bed now thanks all again.

[krish2487]

@mechatrommer


I suspect that the ebay 7805 what you tried might be a "reject" from the factory production and not an outright clone.
The fact that it "sort of works" is proof.


I also suspect that the lettering at the end like A,C, CV, CT, ACT etc might have to do with their performance in a circuit.
I have gone through 4 different datasheets (two from TI - LM and uA , one from ST and one from Fairchild) and while the functional block diagram remains the same, there are several variations in the finer details. Most notably what jump out are the "multiple fan out collectors in two of them, compensation capacitor (polarised vs non polarised).


I suspect that these elements might be the culprit. Maybe an A/B comparision of same versions between different manufacturers and A/B comparisions between different suffix models might yield more information.

[wraper]

Don't buy any semiconductors or capacitors from Ebay. At least 90% are fake, especially from MOSFETs, regulators, LEDs and electrolytic capacitors.

this can go on.... dont buy products from china because china designers may use parts from china. a rigol ds1054z may contains lots of fake semiconductors inside?

Rigol don't buy parts on ebay or Alibaba but from manufacturers directly or through some big distributors. As of parts which can be easily counterfeited, they will be. Many parts are almost impossible to buy genuine on ebay or other shady places. Your ICs on the photos are certainly counterfeits, that tells a lot about sources you buy from. I buy parts on ebay/ali too, but only what is hard to counterfeit or very hard to get by other means.