Hi forum!
Last week my sister give me a 12v @1A switching power supply (wi-fi router).
My idea is to build a functional power supply, since my old DC-Brick is fully feed pedals almost all the time.
- 4 regulated 9v outputs, from 4x LM7809 regulators.
- 1590A enclosure that I've already purchased.
(http://i.imgur.com/DrMCtpll.png)
- D1/D2: 1N4007
- C1: 220/470uF
- C2/C5: 100nf
- C3: 100uf
My principal priority is the safety.
Any suggestion, advice, experience, etc, will be greatly welcome :)
I can't see your picture from work, but by the list of components you wrote down, I would imagine it will be fine. You might want to consider dealing with switching noise, though. Wifi routers don't care too much about audible noise.
Quote from: Plexi on June 11, 2017, 08:50:40 PM
My principal priority is the safety.
Unless you rip your chest open and attach those 12V to your pericardium, you have no worries. (And if you *do* rip your chest open, frankly a little 12V tingle is the least of your worries! :icon_twisted:)
Don't need to use C2 or C4. C3 need only be 10uF for stability - making it larger serves no purpose.
You might also want a CLC filter on the input, as the 78xx series is intended for linear supply work - good rejection at 100-120Hz, but very little at the high operating frequencies of switch mode power supplies. Another good idea would be a reverse-biased doide on the output to protect against reverse voltage being applied to the output (center positive pedal with cap charged by battery or something is a possibility).
Quote from: Phoenix on June 12, 2017, 04:00:38 AM
Don't need to use C2 or C4.
Standard electro caps usually have a bit of ESR at higher frequencies, so it's common to see a parallel monolithic or film cap anywhere from 10n to 1u used in certain applications.
In particular with this application, some of these regulators can oscillate, especially with weird loads (long pieces of wire, anyone?). As per the datasheets it is good practice to include a film or monolithic ceramic right up nice and snug to the regulator on both input and output. 100n is as good a value as any. The TI datasheet recommends 0.33u and 0.1u respectively.
I have soldered the monos directly to the pins a couple of times :)
david
Plexi, maybe you're the only person I've seen drawing red line for negative supply... :icon_lol:
IMHO, D2 makes no sense..
(it comes right after full wave rectification and is simply added on previous possitive pair of diodes..)
I'm not sure if any OUT-IN over voltage could be be settled through LED/Current limiting resistor on time....
D2, R1, LED and C1 can be common to 4 regulators.
Keep 100nF at regulator pins - it will reject hf noise from the supply. Those router PSU's ARE noisy.
D1 doesn't need to dump current anywhere, only clamp any backward volts across the regulator at a safe value.
Agree C3 should not need to be too big - the circuits it's feeding ought to have RC filtering on power inputs - but we know many don't. Maybe compromise at 47uF?
Quote- 4 regulated 9v outputs, from 4x LM7809 regulators.
Now then, it's a 1A supply and 7809 are self limiting at 1A each. You only need 1 regulator. 4 separate reg's won't reduce ground loop hum when they all have common ground. Might as well have only one 7809.
78L09 will limit at (what is it, 300mA?) which is better protection for the power supply and leaves 3 outputs working if one shorts out. I think the little L version would be better if you must use x4 regs. The 12v SMPS brick ought to have it's own current limit protection too, but can you be certain?
Just going to throw this reckless thought out there:
Many (most?) of the circuits we build for 9V will happily work at 12V....
Quote from: EBK on June 12, 2017, 06:50:09 AM
Just going to throw this reckless thought out there:
Many (most?) of the circuits we build for 9V will happily work at 12V....
Better watch out for those pedals with charge pumps who's IC uses 10V max before melting. But, yes, most others should be ok.
Quote from: bloxstompboxes on June 12, 2017, 09:11:34 AM
Better watch out for those pedals with charge pumps who's IC uses 10V max before melting. But, yes, most others should be ok.
That's one of many reasons I couldn't bring myself hit "Post" without adding "reckless". :icon_wink:
Thanks everyone for your suggestions!
Quote from: bluebunny on June 12, 2017, 03:21:00 AM
I can't see your picture from work, but by the list of components you wrote down, I would imagine it will be fine. You might want to consider dealing with switching noise, though. Wifi routers don't care too much about audible noise.
Quote from: Plexi on June 11, 2017, 08:50:40 PM
My principal priority is the safety.
Unless you rip your chest open and attach those 12V to your pericardium, you have no worries. (And if you *do* rip your chest open, frankly a little 12V tingle is the least of your worries! :icon_twisted:)
Sure..!
That's what I think too: I have in unused one 9v switching power supply because of noise. There's no cap or filter to save it: maybe it's dying.
No problem, the safety is for my pedals :-) (says the man that received 220v from christmas lights...)
Quote from: Phoenix on June 12, 2017, 04:00:38 AM
Don't need to use C2 or C4. C3 need only be 10uF for stability - making it larger serves no purpose.
You might also want a CLC filter on the input, as the 78xx series is intended for linear supply work - good rejection at 100-120Hz, but very little at the high operating frequencies of switch mode power supplies. Another good idea would be a reverse-biased doide on the output to protect against reverse voltage being applied to the output (center positive pedal with cap charged by battery or something is a possibility).
Great!
Usually I use the reverse voltage diode protection on 9v input on pedals, but will be good here.
I'll search for any CLC Filter; I think I have one of those in my
Miscellaneous disassembly drawer (pc monitors, tv's, pc power supply's, etc).
Quote from: greaser_au on June 12, 2017, 04:56:46 AM
Quote from: Phoenix on June 12, 2017, 04:00:38 AM
Don't need to use C2 or C4.
Standard electro caps usually have a bit of ESR at higher frequencies, so it's common to see a parallel monolithic or film cap anywhere from 10n to 1u used in certain applications.
In particular with this application, some of these regulators can oscillate, especially with weird loads (long pieces of wire, anyone?). As per the datasheets it is good practice to include a film or monolithic ceramic right up nice and snug to the regulator on both input and output. 100n is as good a value as any. The TI datasheet recommends 0.33u and 0.1u respectively.
I have soldered the monos directly to the pins a couple of times :)
david
I'll keep c2 and c3, and reduce c4.
Quote from: antonis on June 12, 2017, 05:42:55 AM
Plexi, maybe you're the only person I've seen drawing red line for negative supply... :icon_lol:
IMHO, D2 makes no sense..
(it comes right after full wave rectification and is simply added on previous possitive pair of diodes..)
I'm not sure if any OUT-IN over voltage could be be settled through LED/Current limiting resistor on time....
I want to keep it "original" ;D
Should I move the LED after the regulator?
Quote from: anotherjim on June 12, 2017, 06:08:16 AM
D2, R1, LED and C1 can be common to 4 regulators.
Keep 100nF at regulator pins - it will reject hf noise from the supply. Those router PSU's ARE noisy.
D1 doesn't need to dump current anywhere, only clamp any backward volts across the regulator at a safe value.
Agree C3 should not need to be too big - the circuits it's feeding ought to have RC filtering on power inputs - but we know many don't. Maybe compromise at 47uF?
Quote- 4 regulated 9v outputs, from 4x LM7809 regulators.
Now then, it's a 1A supply and 7809 are self limiting at 1A each. You only need 1 regulator. 4 separate reg's won't reduce ground loop hum when they all have common ground. Might as well have only one 7809.
78L09 will limit at (what is it, 300mA?) which is better protection for the power supply and leaves 3 outputs working if one shorts out. I think the little L version would be better if you must use x4 regs. The 12v SMPS brick ought to have it's own current limit protection too, but can you be certain?
Sure! C3 reduced to 47uf
You're right, but
better prevent than lament ;D
Sorry my ignorance: only to limit and distribute? In which way they will for better protection?
I've already bought 4 LM7809's... my bad! I'll go for the smaller version, they aren't too expensive.
Quote from: anotherjim on June 12, 2017, 06:08:16 AM
78L09 will limit at (what is it, 300mA?) which is better protection for the power supply and leaves 3 outputs working if one shorts out. I think the little L version would be better if you must use x4 regs. The 12v SMPS brick ought to have it's own current limit protection too, but can you be certain?
Not good, 78Lxx regulators have only 100mA output.
Quote from: rankot on June 12, 2017, 11:10:43 AM
Quote from: anotherjim on June 12, 2017, 06:08:16 AM
78L09 will limit at (what is it, 300mA?) which is better protection for the power supply and leaves 3 outputs working if one shorts out. I think the little L version would be better if you must use x4 regs. The 12v SMPS brick ought to have it's own current limit protection too, but can you be certain?
Not good, 78Lxx regulators have only 100mA output.
Should I use 10 of them, to not "overheat" the 4 ones?
See if you can make use of 78M09 version (note the "M" designator; "medium current" ... 0.5A).
Sadly, where I live, I can only get the regular LM78.
With luck, and too expensive, some LM78L (mostly 78L05, for PT2399 delays)
Should I use the LM78 anyway?
Which filter can I use?
(http://i.imgur.com/RI0JzRsl.jpg)
It's irrelevant if you don't have 78L's, but 4x100mA outputs can run a lot of pedals.
So use only one 7809 and have some spare? ...or carry on with x4 if you think you might be able to get a more powerful brick in future. It's just that x4 7809's can happily take a total of 4A which you will hope your 1A brick can handle without bursting into flames. It should protect itself properly - if it was supplied with a name brand router. Just that cheap OEM Chinese SMPS have been known to catch fire - read about dodgy i-phone chargers!
You don't really need any inductors. Without knowing what they are you might build in instability/oscillation. I would keep it simple.
Sure.. I get it.
The power supply looks robust, and I didn't test it (I'll try with a reg in the breadboard to see if they produce noise).
Ironically the brand is "Ruidir", sounds similar to "ruido"/"ruidoso" in spanish, that means "noise"/"noisy"
I assume the 1A at the input will divide into the amount of regulators, feeding 0.25 to each one... am I right?
Will this increase/decrease, or the regulators will mantain it constant on each out?
After your comment, I made the improved version, follow the advise of @Phoenix.
Should I use there a fuse (1A/250v) instead inductor?
I saw that some people use a 33R in line with the input, before each regulator: this act as fuse?
(http://i.imgur.com/uqfZaFOl.png)
A fuse would probably be the way a lot of commercial designs would protect. 1A slow blow might be best - a fast blow might act in haste.
The brick current will divide according to load on each output.
Say...
A takes 50mA
B takes 950mA
C takes 100mA
D takes 0A (not used)
Then total from the supply is 1.1A
The supply's 1A rating is exceeded while none of the 7809's are reaching their own 1A limit.
Something like 33R to each regulator will improve noise filtering of the capacitors. If they are low wattage, they "might" act as fuses. You will need to calculate the power dissipation at the current you want that to happen. Watts=I2R
*Strictly, the resistors should then be "flame proof" (ceramic coated) types*
Ok...an update here.
Tested power supply with the noisiest pedal in the history of noise pedals: EHX Pitchfork with one LM7809 breadboarded, no filter or caps.
Zero noise, nothing, cero: leave it connected a few hours, no heat.
Quote from: anotherjim on June 12, 2017, 04:47:54 PM
A fuse would probably be the way a lot of commercial designs would protect. 1A slow blow might be best - a fast blow might act in haste.
The brick current will divide according to load on each output.
Say...
A takes 50mA
B takes 950mA
C takes 100mA
D takes 0A (not used)
Then total from the supply is 1.1A
The supply's 1A rating is exceeded while none of the 7809's are reaching their own 1A limit.
Something like 33R to each regulator will improve noise filtering of the capacitors. If they are low wattage, they "might" act as fuses. You will need to calculate the power dissipation at the current you want that to happen. Watts=I2R
*Strictly, the resistors should then be "flame proof" (ceramic coated) types*
Great... thanks for the explanation!
Just when I was considering the 1/6 watt small ones :icon_rolleyes:
(sorry my ignorance)
I have a question which may prove unhelpful. if we have a transistor like the BC548, it is rated ~500mA maxx collector current and can be series-pass [?] wired to boost the current capacity of a regulator. can we wire say 3 transistors series-pass w/ one reg, and provide 3 outputs w/ higher current rating than the nude reg, or will we lose control of the regulation?
Quote from: duck_arse on June 13, 2017, 11:38:37 AM
I have a question which may prove unhelpful. if we have a transistor like the BC548, it is rated ~500mA maxx collector current and can be series-pass [?] wired to boost the current capacity of a regulator. can we wire say 3 transistors series-pass w/ one reg, and provide 3 outputs w/ higher current rating than the nude reg, or will we lose control of the regulation?
Give me a few hours to translate what you said ;D
So... I wait for the expert people to answer that.
Do I smell some guy trying to take something for nothing..?? :icon_cool:
You can always by-pass the regulator with current passing transistor(s) but you'll need Emitter ballast resistors (to equally share the current for common load - not necessary for split outputs..)
If you use p-n-p pass BJT, Emitter is tied to unregulated IN, Base is also tied there AFTER a resistor (it's value is set to create a 600mV voltage drop across it for the current you want to start by-passing - take in mind the minimum necessary current for regulator operation) and Collector to OUT (load)..
In case of n-p-n pass BJT, Collector to unregulated IN, Base to regulator's OUT (via current setting/limiting resistor) and Emitter to load..
(take in mind the VBE voltage drop - e.g. for 9V regulator, final OUT should stand on 8.4 Volts..)
Quote from: duck_arse on June 13, 2017, 11:38:37 AM
I have a question which may prove unhelpful. if we have a transistor like the BC548, it is rated ~500mA maxx collector current and can be series-pass [?] wired to boost the current capacity of a regulator. can we wire say 3 transistors series-pass w/ one reg, and provide 3 outputs w/ higher current rating than the nude reg, or will we lose control of the regulation?
It depends the on the configuration. using Antonis's two positive regulator examples (thank you!):
With a PNP series pass transistor, the base bias is derived across a resistor that feeds the regulator, so the regulator current drain is what controls the transistor. We are effectively paralleling the regulator's internal series pass transistor (is the external resistor the internal transistor's ballast resistor? :) )... That is: the operating conditions of the transistor are intimately tied into the operating conditions of the regulator- I'd say you could not split the outputs. As the output monitors the collector, and the regulator is a closed feedback loop, the output voltage should be just about as stable as it would be from the regulator alone across the range of sensible current output.
WIth an NPN series pass transistor, all it needs is a stable base reference voltage, and it will try to hold the emitter at (about) 0.6V below that. Just a standard resistor and zener diode regulator on the base would suffice... so yes, a bunch of transistors with separate emitters could be used. in this case the transistor's rE will cause the emitter voltage to droop as the current rises.
However, either way, watch out for the dissi.........................pation! 3V at 500mA is 1.5W. a TO-92 has a junction-to-air thermal resistance of something like 200C/W, so by the time you're pulling 500mA, the device is on fire!
david
Quote from: greaser_au on June 13, 2017, 09:54:27 PM
We are effectively paralleling the regulator's internal series pass transistor (is the external resistor the internal transistor's ballast resistor? :) )...
(with the risk of pouring oil on the troubled waters..) :icon_redface:
Academically speaking, only if internal series pass element is also a p-n-p transistor and a resistor of equal value of the one between Emitter & Base of the external p-n-p series pass transistor is placed in front of outer pass transistor Emitter..
But yes, as long as by-pass current "triger" resistor actually works as an internal current pass limiter, we can undoubtedly consider it as a ballast resistor..!! :icon_biggrin:
Quote from: antonis on June 14, 2017, 05:35:06 AM
(with the risk of pouring oil on the troubled waters..) :icon_redface:
Academically speaking, only if internal series pass element is also a p-n-p transistor and a resistor of equal value of the one between Emitter & Base of the external p-n-p series pass transistor is placed in front of outer pass transistor Emitter..
Note the emoji (sorry, I do have a perverse sense of humour) The internal series pass device is an NPN in the usual 'reference' circuit diagram, and the 'sense' resistor function here is completely opposite to a ballast resistor... :)
david
So, to shake hands we have to compromise the term "ballast" for "not_necessarily_equal_current_sharing".. :icon_wink:
Quote from: antonis on June 14, 2017, 06:53:17 AM
So, to shake hands we have to compromise the term "ballast" for "not_necessarily_equal_current_sharing".. :icon_wink:
There's no need to compromise, I was messing around... (EDIT for clarity: we can shake hands here without any need for compromise. your usage was essentially correct).
I first used the PNP 'boost' circuit that you outlined in a high school electronics project back in 1980, right out of the data section in the back of the Dick Smith Electronics catalogue (no doubt Duckpops will now tease me again about no longer being able to find my Dick, even though I'm sure it's in a box I left at my parents' house :) ).
david
I did say may prove unhelpful, and greaser, you've only yourself to blame for the following:
I do know where my dick is, and looked at it last night just before bed. that's when I realised I had a few legs in the air (emitters, in my proposed/dreamed configuration) that were doing nothing.
antonis: not so much something for nothing, but more for less.
Quote from: duck_arse on June 14, 2017, 10:39:11 AM
antonis: not so much something for nothing, but more for less.
Sorry Duckie, I perstistently forget that your sink drains CCW... :icon_redface:
Update
(http://i.imgur.com/nOsIuPxl.png)
The caps will preferably be ceramic, and other stages will be added aside (copy / paste only).
About 78Lxx and 78xx, I was thinking: what about A's if I use, for example:
- 2 78xx
- 2 78Lxx
If I use only the 78Lxx, and not the 78xx stages, both are supporting 1A ...?
Or have a "relief" from other stages?
To avoid overheating.
78LXXs can handle a maximum current of 100mA (don't even think about 1A..) :icon_mrgreen:
Most important is their power dissipation capability which is about 200oC/W (as for all TO-92 devices and as above well said by greaser_au)
e.g. a 78L09 powered from 12V unregulated PS (which is the minimum working voltage difference) may handle 100mA continuous current but, for sure, can't do the same powered from 18V PS.. :icon_wink:
(at least, not without sufficient cooling - a junction temperature of 160oC is marginally OK for a relatively little working time..)
To put it another way, 300mW should be considered maximun power dissipation for an "open air" non-smoker 78LXX regulator..!! :icon_wink:
As long as you'll not avoid possible groud loop issues (by feeding them from a common rectifier..) I can't see the reason for copy/paste and not a larger PCB with a common ground plane..
(it will save space, cooper & wiring lengh..)
The regs have thermal shut down too.
Maybe it would be helpful to know what your amperage needs are?
A while ago I noticed I had a large stock of 10R 1% 1/8 watt resistors, so on a narrow offcut of strip board, I soldered 10 of them in parallel, fitted some scrap test probe cable and crocodile clips - made a 1ohm resistor. You can do better and give it 2.1mm output plug and a 2.1mm socket. The 1ohm goes in series with the + wire and just wire the 0v straight through.. Include a test clip hook at each end of the 1ohm.
Power each pedal with this thing in line. Measure the voltage across the 1ohm with the pedal working. The volts reading is directly also a current reading, so 10mV means you have 10mA.
Good morning people!
Going back to this :-)
Antonis:
So, my idea of add some 78L to have one/two 100mA regulated will make no sense with the idea of use a power supply "whatever I found from 12 to 24v, with 1A or more".
Even if I use without one LM78xx..
BUT! it can be IF I place them after one LM78xx stage... that would be correct, but very redundant...avoiding again the 1A.
>As long as you'll not avoid possible groud loop issues (by feeding them from a common rectifier..) I can't see the reason for copy/paste and not a larger PCB with a common ground plane..
(it will save space, cooper & wiring lengh..)
Sure, you're right.
But now I ask: at least two or three regulators feeding, in any way... can stabilize more the signal? Helping each others?
Maybe betters if one day I upgrade the power supply to 18v/>1A to add one 18v slot.
Jim:
My amperage needs are low... at least if I'm planning to feed two delays and some OD with it.
Maybe I'll use the space left to give bipolar power, using a LM7908 and re-drawing the schematic (last minute idea).
About the 1ohm resistor in series before the pedal, direct to +: it's like a fuse?
QuoteAbout the 1ohm resistor in series before the pedal, direct to +: it's like a fuse?
Yes, in-line in the + feed. With it in series with the feed to a single pedal, all the current that pedal takes must pass through the 1R. That current will cause some voltage to be dropped across the 1R. If you measure that voltage with your DMM and use Ohms law, you can calculate the current. The magic thing about 1R is it makes the voltage reading the same numbers as the current - no need to calculate. I=V/R. If R=1 then I=V. So 100mV reading means 100mA is flowing.
If you put the 1R in the feed to a daisy chain lead, you get the total current of all of the pedals on the chain.
Reading current is one area where I especially wouldn't trust a cheap/average quality DMM. Even a good pro quality DMM needs really good clean connections/test probes to be trustworthy reading milliamperes. Also switching the DMM to current can be bad for it (or whatever you connect it to) if you forget to change it back to voltage. On current ranges, the DMM is a very low resistance between the test probes - pretty much a dead short.
I like to use 10R (I=V/10) or 100R (I=V/100) value in the RC power input filters in my pedal builds - makes it easy to know the pedals current draw. Nothing to stop you doing it if the R is 47ohm or any other value. 1R happens to be a no math no-brainer, but 1R is unfortunately too small value to act as a filter with the input capacitor.
Apply all the advices... thanks!
I added a bi-polar segment too.
Ok.. I need a second eye around here.
I think it's done:
(http://i.imgur.com/3wtCTkcl.png)
Don't even dare to power it up...!!! :icon_biggrin:
(polarity-mind items are ready to declare you their official public enemy..) :icon_redface:
Second eye sees the 220μF electro placed with wrong polarity...!!
Second mouth says you have to take a look - from time to time - at components datasheets (79XX pin-out is ADJ - IN - OUT)
Despite the above, this isn't the way for getting negative output..!! :icon_wink:
(or else, we would use 79XXs as voltage inverters..)
You can get it from a center-tap secondary with GND on middle lug and full wave rectifier's (-) connected to 7909 IN (pin 2) or from an "ordinary" secondary of twice the voltage you want for (+) & (-).
In any case, you have to "split" positive & negative voltages (with reference to GND) before any regulation..
P.S.
To hate me even more, I should point you that, despite any current circuit arrangement, you can't get -9V from a -8V regulator - like DC-DC converter.. :icon_wink:
You got it, Antonis!
As I assumed, a total disaster :icon_redface:
I followed this layout:
(https://s-media-cache-ak0.pinimg.com/736x/e6/be/46/e6be46741b8f68e2dcf1efbb271eae74.jpg)
You're right, I didn't check the LM7909 pinout, just used as reference in the layout...a HUGE mistake, my bad.
Sorry, at least, my typo: must be 7909 ;D
I'm in the right path?
Ignoring the voltage, huge mistake in pinout, and my last layout :icon_rolleyes:
(http://musicfromouterspace.com/analogsynth_new/WALLWARTSUPPLY/wall%20wart%20supply%20with%20load%20resistors.gif)
(http://mysite.du.edu/~etuttle/electron/circ274.gif)
As for the center-tapped, it's OK..
As for wall-wart supply, it has to be AC..
(don't get tangled up in the usual DC wall-warts supplies for pedals or similar..)
I can't see any reason for R1 & R2, other than for "adding" their 5mA current draw to regulators quiescent current (?) (and maybe for C10 & C5 bleeding resistors when power off) so I don't take a stand.. :icon_redface:
(maybe a more experienced person in PS design could enlighten us..)
C1,2,3 & C6,7,8 power bank of 10mF each is - maybe - an overkill..
(of course, in your scheme, it comes to smooth the great voltage ripple due to half-way rectification in combination with output current..)
If you want a current of 1A, CR1 & CR2 should be rated at 3A/50V or greater..
(I don't like designs where diode's maximun continous current rating is marginally the same with circuit's normal need..)
P.S.
Considering price of center-tapped & "ordinaly" transformers the same, the cost of 2 additional diodes is much less than the cost of elevated filter capacitance need - double diode voltage rating cost difference (if any) for half-wave rectification is negligible.. :icon_wink:
Antonis...thanks a lot!
Update, sad update: :icon_rolleyes:
I built it, everything was fine... until every sound got muted; check and the LED was on, without light almost off.
When I check for voltage coming out: 2,4v.
Nothing was burned and not even hot.
Changed the LM7809, and it start to run again at 9v.
What happened!?!?
YOU'VE JUST PROCEEDED TO YOUR MYSTERIOUSLY BURNED REGULATOR COLLECTION ENRICHMENT.. !! :icon_biggrin: :icon_biggrin: :icon_biggrin:
@Plexi: With nothing burned - nor even hot -, no reverse polarity, no short-circuit, no continious overcurrent e.t.c the only explanation is your mains power supply over 70% low fluctuation.. :icon_wink:
Yep... :icon_rolleyes:
I'll use sockets where the regulators are ;D
Quote from: antonis on June 29, 2017, 07:51:44 AM
no reverse polarity, no short-circuit, no continious overcurrent e.t.c the only explanation is your mains power supply over 70% low fluctuation.. :icon_wink:
Sorry my ignorance: what does it means?
What would prevent it?
12v zener at the input, instead the 33R resistor?
9.1v where the 100nf cap is (or parallel to it), after regulator, would help if regulator fails and start to over feed?
That's what I meant with 'safety' :icon_rolleyes:
:icon_biggrin: :icon_biggrin: :icon_biggrin:
I mean that, according to your description, everything seem to be OK..
But your regulator failed so, for sure, something caused it..
Regulators are prone to damage either from overvoltage or reverse polarity..
(assuming they have internal current limitation in the form of thermal shut-down..)
Some days ago, I destroyed a 7815 regulator WITH reverse polarity protection (diode from OUT to IN) by just momentarily feeding it with reverse supply..
(with no visible results but with a very audible "tsaf"..) :icon_wink:
Quote from: antonis on July 03, 2017, 05:54:54 AM
:icon_biggrin: :icon_biggrin: :icon_biggrin:
I mean that, according to your description, everything seem to be OK..
But your regulator failed so, for sure, something caused it..
Regulators are prone to damage either from overvoltage or reverse polarity..
(assuming they have internal current limitation in the form of thermal shut-down..)
Some days ago, I destroyed a 7815 regulator WITH reverse polarity protection (diode from OUT to IN) by just momentarily feeding it with reverse supply..
(with no visible results but with a very audible "tsaf"..) :icon_wink:
Again, you're right!
Now I remember.
I'm 90% sure the short did it when I was dealing with a non-functional MKII Tone Bender (PNP, + ground... a lot of wires from transistors bias).
Is there any protection type to avoid that shortcuts/fails?
It's my main power supply in my workshop to test all the specimens on progress (you know...guts all around, test caps and mods, etc) :icon_lol:
Quote from: Plexi on July 03, 2017, 12:25:09 PM
Is there any protection type to avoid that shortcuts/fails?
It's my main power supply in my workshop to test all the specimens on progress
There is, of course, but you'll have to deal with current limiting circuits..
A simple power diode on PS out should be acceptable in most cases, also.. :icon_wink:
You're right.
The design didn't have "power diode" (would be 1N4007 with anode to ground and cathode to +?)
No, because in such a case you would short-circuit your power supply.. :icon_wink:
To avoid reverse voltage applying to some circuit INPUT you have to place a diode just after possitive IN with anode to IN..
(something like uni-directional jumper..)
To obtain the same for circuit OUTPUT (i.e. on a battery charger..) you have to place that diode just before possitive OUT with cathode to IN..
Do you have an schematic?
Quote from: antonis on June 21, 2017, 05:46:28 AM
I can't see any reason for R1 & R2, other than for "adding" their 5mA current draw to regulators quiescent current (?) (and maybe for C10 & C5 bleeding resistors when power off) so I don't take a stand.. :icon_redface:
(maybe a more experienced person in PS design could enlighten us..)
I don't claim to be that "more experienced person", but some regulators have a minimum current draw requirement to meet the claimed specification. E.g. under very light loads, you might well see out-of-spec voltage or ripple. You sometimes see resistors in the regulator circuit to guarantee this minimum load. Again, check the datasheet or nuke the site from orbit. It's the only way to be sure.
HTH,
Tom
Every info are welcome :)
I spent a lot of time searching, and found a lot of power supplys.
As I said: my principal worry is not to burn any more pedal :icon_rolleyes:
I left the board with 3 slots free, soon I'll add one stage for 18v, another for 12 just in case.
I'm waiting my 4 years old haircut machine die, and feed this little boy with 24v and 2A power supply.
Quote from: Plexi on July 05, 2017, 05:55:04 PM
As I said: my principal worry is not to burn any more pedal :icon_rolleyes:
As we said: Use power diodes in series with correct polarity.. :icon_rolleyes:
(if you REALLY mind of their forward voltage drop, use LM317/337 instead of 78/79 XX series..)
Quote from: antonis on July 06, 2017, 06:16:17 AM
Quote from: Plexi on July 05, 2017, 05:55:04 PM
As I said: my principal worry is not to burn any more pedal :icon_rolleyes:
As we said: Use power diodes in series with correct polarity.. :icon_rolleyes:
(if you REALLY mind of their forward voltage drop, use LM317/337 instead of 78/79 XX series..)
Quote from: Plexi on July 05, 2017, 09:15:38 AM
Do you have an schematic?
:)
Bump with a dumb-question!
If I have 4 stages, and I'm only running one: the other unused ones will affect the overall functioning?
Here's an update, my dear folks:
(http://i.imgur.com/Ec1bI02l.jpg)
(http://i.imgur.com/NeOLfOWl.jpg)
(http://i.imgur.com/tI5w8CMl.jpg)
Questions:
- Is normal that when it's unplugged, the voltage out 'oscillates'?
Between 8.84v to 8.87v.
- If I have 4 stages, and I'm only running one: the other unused ones will affect the overall functioning?
0.3% shouldn't be considered as "oscillation" - especially under floating output (no load)..
(it should be a good idea to firstly refer to technical specifications and then worry about any deviation...) :icon_wink:
No unused stage will affect the overall functioning - as long as their individual outputs are seperated..
(do your home unused mains outlets affect the overall functioning..??) :icon_wink:
Quote from: antonis on July 24, 2017, 05:40:01 AM
0.3% shouldn't be considered as "oscillation" - especially under floating output (no load)..
(it should be a good idea to firstly refer to technical specifications and then worry about any deviation...) :icon_wink:
No unused stage will affect the overall functioning - as long as their individual outputs are seperated..
(do your home unused mains outlets affect the overall functioning..??) :icon_wink:
You're right.
Thanks, as always.
With 'stage', I mean another caps/resistors/regulator: are we talking about the same?
Quote from: Plexi on July 24, 2017, 11:20:22 AM
are we talking about the same?
We are, aren't we..??
Quote from: antonis on July 24, 2017, 12:35:37 PM
Quote from: Plexi on July 24, 2017, 11:20:22 AM
are we talking about the same?
We are, aren't we..??
...don't get me wrong.
>No unused stage will affect the overall functioning - as long as their individual outputs are seperated..
(do your home unused mains outlets affect the overall functioning..??)I get confused about the meaning of "stage" to you: 'multiple outs from one regulator' or 'multiple regulators'.
I don't know about that, but maybe if one regulator stage is unused: isn't the caps 'sucking' the overal + feed?
<...don't get me wrong.>
If I got you wrong I would gave up many pages ago... :icon_biggrin:
To make things clear:
Your layout indicates many individual regulators outputs, isn't it..??
You call them "stages" (and I also agree) and your query consists in possible reacting between them, isn't it..??
All those stages are fed from a common unregulated power supply, aren't they..??
That common supply "sees" many stages inputs INDIVIDUALLY, isn't it..??
As long as the total current need (with every stage loaded) doesn't overcome unregulated supply's capability it shouldn't have any problem, should it..??
In case of some "open" outpus, total current should be less than maximum one, shouldn't it..??
Given that, all things should work more than fine, shouldn't they..??
P.S.
Caps are great suckers only when they're uncharged - the major cause of blown fuses.. :icon_wink:
An off load series regulator like 78xx isn't usually a problem. If it worries you, at least an "output good" LED can be fitted on the output so there is always a little current drawn and adds a pretty light!
From stuff I've read, it took a few goes to get the design of those regulators to a stage where they were mostly situation/idiot proof. That includes being able to tolerate the local capacitors.
They are a servo feedback controller. It compares a reference voltage to the output voltage and changes the conduction of a series output transistor to make the output voltage match the reference. This sounds like a flawless approach, but what if there is a time lag between it commanding a change in output voltage and it getting there? What if, changing to meet increased or reduced current demand causes a change in the input voltage which means another adjustment - and with some time delay in that?
The effect of time delayed reaction is to make the regulator "hunt" around without ever giving a completely stable DC output voltage. At best slight ripple is present, at worst it can be full on oscillation. Frequency of ripple can be AC supply or cyclic load related or, if unstable, according to values of the reactive elements in the circuit such as inductors and capacitors.
It's the same with op-amps. Many are prone to oscillating if there is too much capacitance on the output. Cure is some resistance between output and that capacitance, but it's not an ideal thing to do with a power supply as we don't want the voltage to drop a resistor would surely cause.