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redwire
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I tried at 3V with the current at max and I got a flat line with no load. I tried with 12V and got a ringing. I am using a darlington power transistor so tomorrow I want to swap to a non darlington transistor.
I moved the emitter ground to the transformer side of R7 but it did not solve the problem. I'm using R7 of 0.27ohms. The ringing seemed to be around 10-12 mhz. I need to check the inverting and non inverting inputs of U2. -
I populated a new board and set up the clamp down transistor as shown on the original project but using the new resistor values. I tested and when I remove the negative voltage to the base it will turn off. I then setup the scope on the output set at 12V connected to a tail light bulb and pulled the plug on the transformer and the first picture is the result. I added a second channel to the scope and connected it to the emitter of the clamp down transistor. That result is shown in blue on the second photo. Note that the second photo is at a greater scale but it is nearly identical to the first.
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For those who are interested in this type of project this will be a good series of videos.
https://www.youtube.com/watch?v=qrCdINP0BTg
Pretty interesting, can't wait for Part 3. It doesn't use negative rail or a clamp down transistor so it is much simpler. Lets see how well it works -
How about a soft start such as:
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Hey liquibyte, if you need more boards, I've got one or two populated through hole variants without the linear regulator and film cap if you run out of space to place jumpers on the smd variant. ;D -
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?
I proclaimed victory too early. I found the spike on the posted board with certain settings on the scope. I replaced U1 with a linear regulator and with the scope on the same settins I did not see a spike ,probably because it was happening at a significantly lower frequency. I failed do anymore testing thinking the issue was resolved until I sent a populated board to Liquibyte. He noticed the spike. Unfortunately, I had already packed up my other board, scope, and test equipment while I'm remodeling a room at my house to work in. Right now I don't have an adequate workspace to do any testing.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 suspect that the transformer is the source of the spike but I don't know how to test or eliminate.
As for the output transistor, I am using a darlington MJ11016 driven by a STN 851 transistor. I have plenty of headroom so there is no problem reaching 30V and no heatsink is required for the STN851.
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I'll second the comment about RV1 having no measureable effect on the circuit.
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I don't have a DSO so I can't really see much more than what I have is capable of but I do see spikes on power on and off when I have an old analog hooked up across the output. I haven't had much time to implement some of the suggestions offered for mitigating this due to other things taking up my time. I was hoping that you'd found out the cause and figured out a way to fix it, or at least minimize it. The boards I did do work extremely well except for that one issue.
Thanks for the feedback. -
audioguru, redwire in an old post talk about some issue with the power supply. It generate some output ripple at both startup and shutdown. He resolved this issue by changing U1 and associated components by an integrated 12V linrear regulator.
Do you think that U1 was the problem ?
Is there any other solution to this issue?
Is there any new schematics using this new regulator?
Hi EmbeddedCom, I built a smd version of this PS and it seemed to work fine, except I finally bought an oscillosope and started testing things and noticed a ripple at start up and shut down. I always wanted to try a linear regulator instead of U1 so i built another smd board. I didn't not observe the ripple on the board with the linear regulator. Well ,this leaves a lot of reasons why the previous board had ringing. 1) Bad solder joint; 2) bad component 3) interference on board 4) bad layout, and this list goes on. I requested others who have built the board and have a oscilloscope to test their boards and report the findings. No one has yet. If just one person reports back that they have no ringing then it is likely a individual problem. I am not convinced that the linear regulator was the fix or that there is anything wrong with the current design. The good news is that the only smd part that gets fairly hot is the resistor for "power on" led. No problem with the smd op amps. -
Ops, sorry, I was thinking in another piece at the time. :P
Not even farnell have this one in DIP socket here.
I will have to find something similar to this.
Then build it with the SOIC 8 package. You will have a choice between the TLE2141 or the MC34071. -
Hi Twentysix,
By the way the only change I have made to the design is I added an NPN (BC546) transistor between the neg rail and pin 6 of U2 to eliminate any voltage at output after the PS is switched off and a 24v Zener at pin 7 of U1
what design did you use and what values did you use for R13 and R14? The reason I ask is because if you use the latest design that has a negative rail of -1.2 V instead of -5.6V and you use the original values for R13 and R14 then the voltage to the base of Q1 may be positive all the time instead of being slightly negative until shutdown. -
Redwire, here is the link:
http://diyfan.blogspot.com/2013/03/adjustable-lab-power-supply-take-two.html
Thanks I wish I could read Czech to see the designers write-up from the original article. -
Have you guys seen this variation?
Something similar was discussed several pages back. IC1A seems to be missing the connections on pins 4 and 7. It lists older OpAmps Tl082 which has a maximum voltage rating of 36 which is where it must operate. I think the components used for the 9.5 V reference voltage is overkill, but I support the concept. This design uses a voltage regulator for the negative rail. I prefer the simplicity of the dual diodes to create the negative reference voltage and the 10V zener to tame down the rail voltage for the op amps that Audioguru has suggested. It may be a matter of preference.
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A few weeks ago I changed the board by deleting U1 and associated components and replaced it with a 12V linear voltage regulator (PN L78L12ACUTR). I added two cap to keep the voltage regulator smooth. Today the new PCB boards came in. The only other board change was C7. I switched to a film instead of electrolytic. I ran the same tests on the scope and there was no ringing. Based on that, I assume the ringing was U1 trying to stabilize when the power supply was removed but C1 still had a charge.
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Audioguru, The power supply generates this kind of output at both startup and shutdown. Here is a shot of the startup with voltage set at approx. 0V. The frequency is approx 24Mhz.
As a side note if you end up leaving the load connected to the PS and start the unit or if you accidently have the output shorted when you start up, the current control does not take over. For some reason I have done both at least once and it will usually let the blue smoke out of some part. Now it works well once the unit has stabilized.
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Oh. Do you have a very inductive shunt on a current meter in series with the output of this power supply?
Or maybe R7 is inductive?
I have a IC and LCD display attached and powered from a separate small transformer. I tested it with the display on and off. Perhaps I need to disconnect it then retest.
Edit I disconnected everything from the PS and still get the spike. -
The first photo is when it is set at 12V and the transformer is unplugged.
The second photo is at when output is at max (approx. 30v) and the transformer is unplugged. It looks like it is swinging approx. 30 volts negative then 30V positive resulting in approx. 64 Vpp. -
I was checking the output of the power supply when the power is quickly disconnected and discovered some large spikes. I set the PS at about 12V hooked up the scope to the output with a trigger at 13V and got the following picture. I did the same thing with the output at max with the same result. I also checked the output with a load and had similar spikes. I'm wondering the Q1 protection needs to be added back. Has anyone else check the output at shutdown?
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what are you powering? What are the output requirements?
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When turning the voltage down (like from say 25 volts to 5 volts) the voltage descends rather SLOWLY. Raising the the voltage is just about instantaneous, but lowering it makes me wonder.
Any ideas??
Are you using a single turn or multi turn pot to adjust the voltage? Is the slow descent only when there is no load? C7 does need some time to discharge. -
tcjeep, I agree that a 1uF is a bit large, I had the same concern. I have a single turn pot and really didn't have issue with the responsiveness. How often is there a need to instantly change the current control setting on pin 3? Usually it is set ahead of time for a particular use. When I get time I'll try a .1 uf .
Hey the 1074Z is niccccccccccce! -
I just received my Rigol 1074z scope. I'm probing around the circuit and learning how to use this thing at the same time. Here is a screen shot of the output with the voltage set at zero- there is about 35mV output. I am using a 10uF electrolytic cap, when I get a film cap i'll post the results. The only unusual thing I noticed was that Pin 3 of U3 had substantial noise, this could be my set up and perhaps having 12" of wire from the pot to the board had an effect. I had a 1uF cap handy so I hooked it between ground and pin3 and it tamed things down substantially. I didn't notice any substantial change with the output whether or not this extra cap is utilized.
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Wow! I'm out of breath just reading this.
The case of the 2n3055's is the collector which means if you have all 4 on the same heatsink and not insulated, then all will be live when either transformer is live. Separate each side first. when you trouble shoot. -
why don't you connect a resistor and led to the output (pin 3) of the 555 first. You can visually see what's going on. Then work in the relay.
0-30V Stabilized Power Supply
in Projects Q/A
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I was using a darlington MJ11016 power transistor with long leads (18") so I hooked up a 2n5886 with shorter leads and didn't notice any elimination of spikes.
I ordered a 0.22ohm current sense resistor but in the mean time I used a jumper across the wirewound sense resistor. While it kills the overcurrent feature, it did not seem to make a difference in terms of spikes.
I cut off the negative charge pump but didn't notice much difference besides I could not go any lower than 1.8V.
I will insert D10 and R15 and test later.