I've recently sold two different TS type pedals to two different people and let them know what power supply to use. Both plugged ac adaptors into them which fried a resistor in each pedal. So my question is, is their a protection circuit that I could incorporate that would prevent parts from frying, take up little pcb real estate and be reasonably inexpensive?
Thanks in advance.
You're still lucky that just a resistor fried, had that happen and all the JFet, OpAmp and Electro died.
From what i know there's no protection against AC.
Seems there is an expensive chip that might do the job, LTC4365. Bit of discussion (started by chromesphere) and links over at diystompboxes a year ago but can't tell whether anything came of it.
Polarity Protection schemes from that diystomp thread. http://digital-diy.com/general-electronics/419-power-protection-circuits.html
The thread. http://www.diystompboxes.com/smfforum/index.php?topic=101708.0
dave
On geofex.com there is a good solution,2 transistors and 4 resistors,works with anything.☺
Inviato dal mio Nexus 7 utilizzando Tapatalk
Never ended up testing this out. Could make a good 'add-on' board a bit like the roadrage but sort of a comprehensive input voltage protection board.
Wow! All good things to know.
I just put a 1N5818 schottky diode in series from the power input. It drops about 250mV when the power supply is connected regularly. If the power supply is reversed is will provide protection as long as less than 30 volts is applied.
If AC power is applied, it will block the negative wave, making a half wave rectifier. This should protect pedal from damage. The pedal might even still work depending on the size of the filter caps used, though the ripple could cause more hum.
It costs $0.08 from Tayda.
Am I missing something here?
I use schottky diodes on everything too. You get a small voltage drop, but you also get decent (enough) protection.
Guitarists seem to stand alone in thinking you can plug any supply into any pedal and it will just work.
I think the quicker the demise of the PP3 and battery connections in pedals, the more aware people will become about PSU's and what they can, and can't, use.
First of all, thanks to all who replied. Lots of good info here!
Quote from: GrindCustoms on April 24, 2014, 02:39:31 AM
You're still lucky that just a resistor fried, had that happen and all the JFet, OpAmp and Electro died.
From what i know there's no protection against AC.
Yeah, very lucky. Both of these boards were the same and were based off of a paisley drive schematic. It seems that the 10ohm series resistor took all the punishment.
Quote from: electrosonic on April 24, 2014, 06:45:18 AM
I just put a 1N5818 schottky diode in series from the power input. It drops about 250mV when the power supply is connected regularly. If the power supply is reversed is will provide protection as long as less than 30 volts is applied.
If AC power is applied, it will block the negative wave, making a half wave rectifier. This should protect pedal from damage. The pedal might even still work depending on the size of the filter caps used, though the ripple could cause more hum.
It costs $0.08 from Tayda.
Am I missing something here?
If this will do the trick, it definitely seems like the way to go. I've seen this method more and more lately in schematics.
I have plenty of schotky and couple AC and DC adapters, I'll make some tests this weekend. That's pretty cool.
Quote from: GrindCustoms on April 25, 2014, 04:37:00 AM
I have plenty of schotky and couple AC and DC adapters, I'll make some tests this weekend. That's pretty cool.
Did you get a a chance to test this out?
Quote from: Dc10 on April 28, 2014, 03:52:28 AM
Quote from: GrindCustoms on April 25, 2014, 04:37:00 AM
I have plenty of schotky and couple AC and DC adapters, I'll make some tests this weekend. That's pretty cool.
Did you get a a chance to test this out?
Forgot about it.... ::)
Doing it now, give me a few minutes.
Using a 1N5819 1Watt
9VDC Supply at input, output of diodes gives 8.92VDC
-9VDC at input, output -0.92VDC
No matter how much AC i send through the diodes, tried up to 24VAC, it will pass through and you also get about half DC voltage of the AC supply, wich makes sense since AC is the total of a negative and positive wave and DC being just one side of the 0V.
Both type can flow through... so i'd say that it does'nt protects against AC.
There's some current leakage with Schottky diodes. In some cases, the amount of current that gets through won't be an issue. In others, it could be. One thing I've done is to use a 1N4001 in a crowbar after the 1N5817. I still don't think that this is a perfect solution, but it could help in some situations and it's pretty cheap in cost and complexity.
Quote-9VDC at input, output -0.92VDC
Are you measure the open circuit voltage? This seems to me to be the leakage current times your mulimeter impedance (usually 10M) implying 92 microamps of leakage current.
The data sheet for the Fairchild version shows a maximum of 500 microamps (0.5 mA) at 25 degrees C.
The main question is - will this small amount of current damage anything? I think not, but don't have data to back it up.
QuoteNo matter how much AC i send through the diodes, tried up to 24VAC, it will pass through and you also get about half DC voltage of the AC supply, wich makes sense since AC is the total of a negative and positive wave and DC being just one side of the 0V.
Both type can flow through... so i'd say that it does'nt protects against AC.
Not sure what you mean by this - can you explain your test setup - I will spend time at the bench to see what I find.
Andrew.
Edit: Just went to the bench found a 12VAC wall wart. I connected it to a 1N5818 diode then to a typical RC power line filter you see in pedals. (a 47 ohm series resistor and a 100uF cap to ground).
At the filter cap I saw the DC rectified voltage (about 20 volts as expected 12VAC (rms) * 1.41.
The over voltage may cause a problem to a circuit which was designed for 9VDC, but I see no issue with reverse voltage in this case.
Quote from: RobA on April 29, 2014, 05:08:35 AM
There's some current leakage with Schottky diodes. In some cases, the amount of current that gets through won't be an issue. In others, it could be. One thing I've done is to use a 1N4001 in a crowbar after the 1N5817. I still don't think that this is a perfect solution, but it could help in some situations and it's pretty cheap in cost and complexity.
What about PTC's for high current protection?
You see these a lot now in other equipment, but not often in guitar stuff (including amps).
They are relatively cheap, and can withstand fairly high maximum currents before breakdown.
You can get 50ma/100ma variants that could be in the right ballpark to trip before you damage any of the expensive stuff in a circuit.
I think PTC would work fine as long as you left enough space for the heat dissipation and people knew to wait for it to come back online after it blew. I haven't tried it in the case of an AC input, so might the repeated trip cycles for the thing blow it if someone left the AC plugged in too long?
How about a bridge rectifier made from 1N5817's? If you did it right and had enough capacitance after, you could plug anything into it of the right voltage level and it should work. Hmm, I think I'll give this a try.
I tried the PTC in series preceding the 1N5817 using only the Schottky for reverse polarity protection. If the circuit tries to draw any current, the voltage at the output of the diode drops to essentially zero and the current across the PTC is unmeasurably low. I don't think the PTC is really going to get you much except in the case of a failure of the Schottky. If you wanted to get extra safe, you could go PTC into 1N5817 with a 1N4001 crowbar following. This will give decent protection against AC as well, since it is really a half-wave rectifier. But, at the cost of just 2 more diodes...
I built a bridge rectifier using 1N5817's. For either polarity of 9V DC input, you get the correct polarity out with a minimal voltage drop. The voltage drop across the rectifier is from 9.42V to 9.19V. Put an AC voltage on it and you still get (a noisy) correct polarity voltage out. If you pop on about 470µF of capacitance (~1200µF is actually better) you get a pretty clean output voltage. The warning here is that an input of 9VAC is going to end up with about 12VDC. So, you would need to know that the following circuit could take that voltage. But, this would give perfect polarity protection (noting that you would still need isolated supplies to mix polarities in different pedals) and very good AC protection (as long as the circuit can take the output DC).
If you can live with a bit more of a voltage drop, using a W06G or DB102 bridge rectifier would simplify the circuit a bit more.
Well, of course there has to be another downside. Thinking about this a bit more, I think you would have to use the bridge rectifier idea with every pedal or you would end up with different potentials tied to ground. Is there a way around that issue?
Yeah whenever I have seen PTC's used they are 'first in line'. Like a fuse; you want it to be the thing to pop first!
Could a combination of a schottky and a zener be a good combo. You could then get over-voltage protection from any high dc voltages, or those caused by the rectification of AC?
I guess the simple solution is; plug the right bloody PSU in!
It's amazing how guitarist think they can plug any old PSU in and have a pedal work!
Quote from: electrosonic on April 29, 2014, 06:34:33 AM
Quote-9VDC at input, output -0.92VDC
Are you measure the open circuit voltage? This seems to me to be the leakage current times your mulimeter impedance (usually 10M) implying 92 microamps of leakage current.
The data sheet for the Fairchild version shows a maximum of 500 microamps (0.5 mA) at 25 degrees C.
The main question is - will this small amount of current damage anything? I think not, but don't have data to back it up.
QuoteNo matter how much AC i send through the diodes, tried up to 24VAC, it will pass through and you also get about half DC voltage of the AC supply, wich makes sense since AC is the total of a negative and positive wave and DC being just one side of the 0V.
Both type can flow through... so i'd say that it does'nt protects against AC.
Not sure what you mean by this - can you explain your test setup - I will spend time at the bench to see what I find.
Andrew.
Edit: Just went to the bench found a 12VAC wall wart. I connected it to a 1N5818 diode then to a typical RC power line filter you see in pedals. (a 47 ohm series resistor and a 100uF cap to ground).
At the filter cap I saw the DC rectified voltage (about 20 volts as expected 12VAC (rms) * 1.41.
The over voltage may cause a problem to a circuit which was designed for 9VDC, but I see no issue with reverse voltage in this case.
I simply put the diode on my Test rig that has a variable -24VDC/24VDC and variable 0-24VAC and bringing the different source of power to the diode and taking the measure at is other end.
Testing the diode in «stand alone».
From what I can tell I will stick with the series 1N5818 schottky diode.
Lastly, there is the p-channel mosfet method as shown on the geofex site.
http://www.geofex.com/article_folders/mosswitch/mosswitch.htm (http://www.geofex.com/article_folders/mosswitch/mosswitch.htm)
It uses BS250P mosfets which are reasonably cheap on ebay (~$0.50 each or less). I just noticed that the Sunking 2 uses this method.
http://www.madbeanpedals.com/projects/Sunking2/Sunking2.pdf (http://www.madbeanpedals.com/projects/Sunking2/Sunking2.pdf)
Andrew.
Quote from: raulduke on April 29, 2014, 04:13:53 PM
Yeah whenever I have seen PTC's used they are 'first in line'. Like a fuse; you want it to be the thing to pop first!
Could a combination of a schottky and a zener be a good combo. You could then get over-voltage protection from any high dc voltages, or those caused by the rectification of AC?
I guess the simple solution is; plug the right bloody PSU in!
It's amazing how guitarist think they can plug any old PSU in and have a pedal work!
I think PTC into 1N5817 followed by a 10V (for a 9V pedal) zener would be pretty good. If the zener started to draw to much current from over voltage, the PTC would trip and that should solve the problems with the zener overheating. Could be a good solution.
Quote from: GrindCustoms on April 29, 2014, 04:25:15 PM
[...]
I simply put the diode on my Test rig that has a variable -24VDC/24VDC and variable 0-24VAC and bringing the different source of power to the diode and taking the measure at is other end.
Testing the diode in «stand alone».
Can you try it with a bit of a load after the diode? I tried it with using an LED with a 4.7k resistor and this seemed to be enough drop the output current (and voltage) to an unmeasurable level. But, my meter is the greatest in the world.
Quote from: RobA on April 29, 2014, 04:50:36 PM
Quote from: raulduke on April 29, 2014, 04:13:53 PM
Yeah whenever I have seen PTC's used they are 'first in line'. Like a fuse; you want it to be the thing to pop first!
Could a combination of a schottky and a zener be a good combo. You could then get over-voltage protection from any high dc voltages, or those caused by the rectification of AC?
I guess the simple solution is; plug the right bloody PSU in!
It's amazing how guitarist think they can plug any old PSU in and have a pedal work!
I think PTC into 1N5817 followed by a 10V (for a 9V pedal) zener would be pretty good. If the zener started to draw to much current from over voltage, the PTC would trip and that should solve the problems with the zener overheating. Could be a good solution.
I agree, that could a nice simple protection scheme. I had a look and ptc's come too around 50p for the 100ma trip varieties
Quote from: RobA on April 29, 2014, 04:53:40 PM
Quote from: GrindCustoms on April 29, 2014, 04:25:15 PM
[...]
I simply put the diode on my Test rig that has a variable -24VDC/24VDC and variable 0-24VAC and bringing the different source of power to the diode and taking the measure at is other end.
Testing the diode in «stand alone».
Can you try it with a bit of a load after the diode? I tried it with using an LED with a 4.7k resistor and this seemed to be enough drop the output current (and voltage) to an unmeasurable level. But, my meter is the greatest in the world.
Sure can!
So you have the greatest meter in the world? ??? ;)
Quote from: GrindCustoms on April 29, 2014, 08:23:01 PM
[...]
Sure can!
So you have the greatest meter in the world? ??? ;)
:-[ I don't know how come, but I do that way too often. I seem to have problems typing "n't".
So i added a load after the diode, 4K7 resistor and super bright 5mm blue LED.
I get the same voltage reading on my DMM when supplying negative voltage and AC.
And i've tried 5 different 1N5819, Fairchild, so no knockoff or whatever.
Quote from: GrindCustoms on April 30, 2014, 10:04:42 AM
So i added a load after the diode, 4K7 resistor and super bright 5mm blue LED.
I get the same voltage reading on my DMM when supplying negative voltage and AC.
And i've tried 5 different 1N5819, Fairchild, so no knockoff or whatever.
Thanks for trying this. Seems I do need to get a better DMM. I should try this on an O-scope too.
So, in some cases at least, a crowbar 1N4001 post the 1N5817 would be needed to block the leakage current from the reverse voltage applied to the Schottky. If a zener were being used to block over-voltage, it might be enough to reduce the -V too.
Quote from: RobA on April 30, 2014, 01:04:31 PM
Quote from: GrindCustoms on April 30, 2014, 10:04:42 AM
So i added a load after the diode, 4K7 resistor and super bright 5mm blue LED.
I get the same voltage reading on my DMM when supplying negative voltage and AC.
And i've tried 5 different 1N5819, Fairchild, so no knockoff or whatever.
Thanks for trying this. Seems I do need to get a better DMM. I should try this on an O-scope too.
So, in some cases at least, a crowbar 1N4001 post the 1N5817 would be needed to block the leakage current from the reverse voltage applied to the Schottky. If a zener were being used to block over-voltage, it might be enough to reduce the -V too.
IIRC, Zener when supplied negative voltage if not re-oriented, do nothing.
Curious, about the voltage drop with a 1N4001 going to ground after a Schottky in serie... give me a sec will try it out..
Dinner hour for Science! ;D
The Zener should behave like a normal diode for forward voltages below the breakdown voltage, so it should work for reducing the voltage of the leakage current from the 1N5817. I tried it with a +/- 15V supply on a 12V Zener (using a CLR in front of the Zener). When I put the +15V on the CLR, I get about +12V at the Zener. When I stick the -15V on there, I get around -0.7V. So, I think that part is a working OK.
When I do the proposed setup of PTC (about 10Ω resistance) into 1N5817 followed by a crowbar Zener or 1N4001, with the -15V I get -0.55V with the Zener and -0.41V with the 1N4001 at the power output.
Caveats:
This was all done with my now suspect DMM.
The power supply I used can only source 30mA, so this didn't test the PTC part at all, but I really wanted to see what the voltage would be before the fuse could blow.
I haven't considered using PTCs before. Looking at the data sheet on the Tayda site, I see a max trip time of 2.5 seconds. I think that is too long to be considered reasonable protection - a lot of components can be fried in less than that time.
Andrew.
Quote from: electrosonic on May 01, 2014, 04:38:49 PM
I haven't considered using PTCs before. Looking at the data sheet on the Tayda site, I see a max trip time of 2.5 seconds. I think that is too long to be considered reasonable protection - a lot of components can be fried in less than that time.
Andrew.
There are others available with different characteristics. But even if you could get one that is really fast, I don't think I'd use it as the primary protection. In the proposed setting, it's really only protecting the diodes on the input. There have been bunches of reports of Zeners blowing from overheating. The PTC could be a good way to protect them without having to put a big CLR in front of them in the cases where you can't take that much voltage drop if the correct voltage is being used. Even with that, there are going to be lots of cases where you wouldn't want to use the PTC because the 10Ω or so resistance is too high. It's all going to depend on what the circuit is that you're trying to protect.
This thread reminded me of the Plimsoul schematic that is floating around.
Like this for example:
http://1.bp.blogspot.com/-nKJVWJcLM_k/T1X4UruQ5_I/AAAAAAAABDM/vhqoDtuIUHI/s1600/plimsoul.PNG (http://1.bp.blogspot.com/-nKJVWJcLM_k/T1X4UruQ5_I/AAAAAAAABDM/vhqoDtuIUHI/s1600/plimsoul.PNG)
I couldn't figure out what D3 was for. Now I think it's purpose is to shunt the leakage current that will pass through D4 if the wrong polarity power is applied.
Andrew.
Quote from: RobA on May 01, 2014, 02:38:52 PM
The Zener should behave like a normal diode for forward voltages below the breakdown voltage, so it should work for reducing the voltage of the leakage current from the 1N5817. I tried it with a +/- 15V supply on a 12V Zener (using a CLR in front of the Zener). When I put the +15V on the CLR, I get about +12V at the Zener. When I stick the -15V on there, I get around -0.7V. So, I think that part is a working OK.
When I do the proposed setup of PTC (about 10Ω resistance) into 1N5817 followed by a crowbar Zener or 1N4001, with the -15V I get -0.55V with the Zener and -0.41V with the 1N4001 at the power output.
Caveats:
This was all done with my now suspect DMM.
The power supply I used can only source 30mA, so this didn't test the PTC part at all, but I really wanted to see what the voltage would be before the fuse could blow.
That makes lots of V and mA drop in the end, where you able to take the mA reading at source and after the whole array?
I've got some UF4004 diodes handy, might worth to see what the differences could be using them... but those will let the AC pass thru with no restriction at all.