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1
Projects Q/A / Re: 0-30V Stabilized Power Supply
« Last post by audioguru on Today at 08:30:11 PM »
People keep talking about inversion and that if a TL081 were there and Q1 were hooked to pin 3 it would induce that.
Certainly, But we are not using the low max supply voltage TL081 opamp that has the inversion problem.

Quote
I know that an inductor produces a voltage spike and that inrush current is also an issue with any type of inductor.  Inductance is still kind of a foreign issue to me though.
The opposite.
An inductor does not producer an inrush current. Charging the main filter capacitors quickly produces the inrush. The inductance of a transformer slows the rise in current for each half cycle.
I don't know how many half cycles it takes to fully charge the huge main filter capacitor.

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As I said, my version isn't suffering this problem on power off.  With Q1, this is limited in scope to a couple of volts depending on P1.  Without Q1, at least on redwire's version, the spike rises to 36V regardless of where the voltage pot is set and then slowly drains.  I'll try and get one of my boards modified with a Q1 within a day or two and post the results from that vs. the other board I have where I'll leave it off for now.
I do not know what produces a 36V spike or high frequency oscillation at power off. Maybe you will kill the spike or oscillation with Q1 without knowing why it happened.
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General / Re: What are these?
« Last post by robson on Today at 03:13:05 PM »
have you ever to measure  with multimiter?
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Projects Q/A / Re: 0-30V Stabilized Power Supply
« Last post by liquibyte on Today at 03:00:21 PM »
Doesn't the linear regulator eliminate the voltage spikes caused by U1? Redwire said it did.
Not that I've seen, maybe reduced it a bit.

His version without Q1 suffers from a ramp in voltage at the output once power is cut until the filter caps drain, a runaway spike if you will.  I removed the the paralleled 4K resistors on his board across C1 and put a resistor across each cap (3 4700's in parallel with a 15k each) and it reduced the bleed time but the spike remained higher than 30V no matter where the voltage pot was set.

With Q1, the spike is limited to the ranges I posted.  My version without Q1 behaves in the same way as his version with Q1 with a subtle difference, my version holds the voltage at P1 until the caps drain, no runaway.  With Q1, the caps drain quicker on his version.  My version holds voltage for ~10 seconds or so.  I haven't removed my boards to put a Q1 in yet but will soon.  The way I've got mine hooked up makes it a pain to remove the boards once everything is hooked up, live and learn.  I get no voltage spikes on power off, just a slow bleed.  Power on gives me the same results I posted, identical in fact.

Does the linear regulator produce less noise than the zener diode/U1 circuit?
I never put the scope accross the output of U1 or the regulator, just the output of the supply.  His version is much cleaner on the output than mine, even at very, very low V/div so I think it's probably an avenue worthy of exploration though I'll say it's having an odd effect on the results so far.  People keep talking about inversion and that if a TL081 were there and Q1 were hooked to pin 3 it would induce that.  I don't know, I get lost at that point.

When the mains power is turned off then the 47uF filter capacitor C3 for the negative supply takes time to discharge. The speed of any little NPN transistor is much faster.
Then the slow discharge time of C3 delays activation of Q1. Then the voltage spikes are not completely squashed.

When a powered inductor is suddenly unpowered then it produces a voltage spike.
Then does a powered transformer that is suddenly unpowered when its mains current is at a peak also produce a voltage spike? 
I know that an inductor produces a voltage spike and that inrush current is also an issue with any type of inductor.  Inductance is still kind of a foreign issue to me though.  Bear with me, I'm learning.  How long can an inductor hold the charge that it releases though?  My thinking on this is that while an inductors spike can be an issue, what I'm seeing with voltage over time is related to the filter caps stored energy and U2 doing something I don't understand.  As I said, my version isn't suffering this problem on power off.  With Q1, this is limited in scope to a couple of volts depending on P1.  Without Q1, at least on redwire's version, the spike rises to 36V regardless of where the voltage pot is set and then slowly drains.  I'll try and get one of my boards modified with a Q1 within a day or two and post the results from that vs. the other board I have where I'll leave it off for now.
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Inventive/New Ideas / Re: DC Timer
« Last post by Hero999 on Today at 02:56:06 PM »
More information is needed.

The ICM7555 can probably do this but a potentiometer will be needed to adjust the delay.

A microcontroller can be used to build a more flexible timing device but will need a voltage regulator (5V or 3.3V) and an output buffer to interface with the 18V devices.
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Electronics chit chat / Re: IC doesn't fit in pcb
« Last post by Hero999 on Today at 01:39:57 PM »
The potentiometer shouldn't be connected to the main power input.

The volume control is nearly always connected to the signal input. A potentiometer varies the amplitude of the signal going in by acting as a variable potential divider. Since your circuit has two inputs, you need to have a dual ganged potentiometer.

Another thing to look out for is that the potentiometer needs to have a logarithmic track to match the response of the human ear. Here's an example:
http://uk.rs-online.com/web/p/potentiometers/7293451/
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Projects Q/A / Re: 0-30V Stabilized Power Supply
« Last post by audioguru on Today at 01:11:48 PM »
Doesn't the linear regulator eliminate the voltage spikes caused by U1? Redwire said it did.
Does the linear regulator produce less noise than the zener diode/U1 circuit?

When the mains power is turned off then the 47uF filter capacitor C3 for the negative supply takes time to discharge. The speed of any little NPN transistor is much faster.
Then the slow discharge time of C3 delays activation of Q1. Then the voltage spikes are not completely squashed.

When a powered inductor is suddenly unpowered then it produces a voltage spike.
Then does a powered transformer that is suddenly unpowered when its mains current is at a peak also produce a voltage spike? 
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Projects Q/A / Re: 0-30V Stabilized Power Supply
« Last post by liquibyte on Today at 11:14:19 AM »
Here's the fun part.  The board he sent me and the one I'm doing this testing on is the one with the linear regulator on it in place of U1.  I've added Q1 into this board but perhaps I'm not using a fast enough transistor.  The one I'm using is from Radio Shack which is marked on the package as a 2N2222A but is more than likely a MPS2222A made by either Motorola or ON Semi.  I found the datasheet here, sorry they zipped this one for some reason.  The package came with 3 types, 2N4401, 2N3904 which is actually a MPS3904, and the above 2222.  I have a few others laying around that I got in a grab bag from Jameco to play around with but would have to look up datasheets to see if I can find something faster.

From oldest reference of the added regulator to the newest that I could find quickly.
http://www.electronics-lab.com/forum/index.php?topic=19066.msg1016994#msg1016994
http://www.electronics-lab.com/forum/index.php?topic=19066.msg1017015#msg1017015
http://www.electronics-lab.com/forum/index.php?topic=19066.msg1017302#msg1017302
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Inventive/New Ideas / DC Timer
« Last post by Inventor1 on Today at 10:51:47 AM »
I am looking for a miniature DC 18 volt timer with an on/off push button that will also turn to adjust a timer from 5 to 30 minutes. The push button needs to be wired to a bread board with a 4 inch wire lead.
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Projects Q/A / Re: 0-30V Stabilized Power Supply
« Last post by audioguru on Today at 10:35:48 AM »
Hi Liquibyte,
On your measurements it looks like Q1 turns on a little too late to completely squash the voltage spike but it reduces it a little.

Are we barking up the wrong tree?? (I haven't said that for about 50 years)
Without Q1 the 'scope photo from Redwire shows 24MHz ringing when the power is turned on and when it is turned off. But in post #? (this site does not have post numbers) he shows no ringing when he replaced U1 with a voltage regulator. I don't think he uses Q1.

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Electronics chit chat / Re: IC doesn't fit in pcb
« Last post by abador on Today at 10:24:21 AM »
I attached a schematic. I have looked at other schematics for amplifiers and it has shown the volume being ether on the input or on the main power input. Since the chip has two input pins I don't know how well it would work. I could put the pot in the main power input but my pot is only rated for about half a watt. I didn't see the volume in the schematic. Also I am in the process of trying to print my own circuit board but the pins are a little weird so who knows if I will get that to work out or not. I'm using a program called freepcb.
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