Author Topic: DIY Power Supply  (Read 34710 times)

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Offline nessatse

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Re: DIY Power Supply
« Reply #25 on: February 24, 2012, 08:20:02 am »
why people like to complaint on "built and proven to be working" stuff? instead of providing better idea?


Because putting a slow (yes it is slow in this scenario) microcontroller followed by a piss poor DAC implementation inside a control loop is simply stupid, when even the cheapest op amp will do a better job.  You can get exactly the same features by using your microcontroller to play a management role, instead of screwing around in your feedback loop.


No need to provide a better idea.  All regulated power supplies are exactly the same at the core (even this one), a negative feedback control loop.  I don't think anyone has come up with a better concept, but many manage to fuck it with designs like this.
 

Offline electrode

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Re: DIY Power Supply
« Reply #26 on: February 24, 2012, 11:41:14 am »
Now we just need to see someone combine the tuxgraphics design with an ATX power supply to win an award. :D
 
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Offline baljemmett

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Re: DIY Power Supply
« Reply #27 on: February 24, 2012, 12:07:43 pm »
iirc, the very adc chips are used in Dave's psu design? for feedback loop? i maybe mistaken :-\

I think you are -- isn't the feedback loop in Dave's design built into the LT3080 regulator itself?  He feeds it with the desired voltage, synthesised by the DAC and amplified to 0-10.24V by the voltage set op-amp, and the LT3080 uses that as the reference on one side of its control loop with the output being the other.
 

Offline davec

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Re: DIY Power Supply
« Reply #28 on: February 24, 2012, 05:00:53 pm »
Here's one I made earlier:

http://tynemouthsoftware.blogspot.com/2012/01/universal-laptop-power-supply-update.html
http://tynemouthsoftware.blogspot.com/2012/02/universal-laptop-power-supply-further.html

This was a switchable voltage laptop charger which was rehoused with a slightly improved voltage selection and an ammeter, here is the original unit teardown which lead to the rehousing.

http://tynemouthsoftware.blogspot.com/2012/01/universal-laptop-power-supply-teardown.html

It's a fairly simple smpsu (does that necessarily equal bad?) and so the output regulation isn't fantastic under large load. One day if I get around to it, I'm going to replace the guts of this with a better switch mode (a meanwell perhaps?).

I never intended this to be a proper bench supply, I've several of those anyway, both professionally and home made, and I intend to add a uSupply to that collection once the kit is available. It's just meant to be a slightly better version of what it used to be, and I think it achieves that. It's also a handy high(ish) current supply for applications where I'm not too bothered about noise or regulation within a couple of 100 mV.

Thanks,

Dave
 
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alm

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Re: DIY Power Supply
« Reply #29 on: February 24, 2012, 10:29:31 pm »
why people like to complaint on "built and proven to be working" stuff? instead of providing better idea?
I have never seen tests of noise rejection or transient response. Even a rheostat will make a working variable power supply if you don't care about transient response. It appears that it was only built by people without any analog design experience, since anyone skilled in analog design would immediately dismiss this implementation. As for a better idea, Dave's design is much better, or any of the Agilent designs like the E36xx series, or the German ELV design I linked to several times.

have they actually build themself one similar or have experience with the part used in the link?
You have skills in mechanical design, right? Do you have to build a car with wheels with a 10 cm diameter to figure out that this car will have trouble with speed bumps or bad roads?

iirc, avr adc can do KHz level of adc sampling (even faster using dedicated adc chip),
I think the ADC sampling rate was is the order of 10 kHz or so. It adjusts the DAC by 1 count every time the voltage/current is too low or too high, I don't remember if it implemented any hysteresis. There is an additional hack to fix a dead short (if current > somevalue output = 0). But the response from no output (shorted) to the full output voltage would take 1024 ADC samples (10-bit DAC), or 0.1 second. That's a slew rate of 0.3 V/ms. Even jellybean op-amps slew orders of magnitude faster than this, even the ancient LM741 slews about a thousand times faster. Tracking ripple will be slightly better, assume 10% ripple, then the response would be about 10ms. 60 Hz ripple has a period of 8.3 ms, or 4.15 ms from minimum to maximum. Hence my comment that it would have trouble tracking mains ripple. Never mind faster transients. I guess it would be a nice example for a control systems theory course to see how bad things can get.

human eye can notice slower than 30fps moving pictures, some front panel have to slow that down even further to avoid annoying jumping up and down figure on 7 segment display. and iirc, the very adc chips are used in Dave's psu design? for feedback loop? i maybe mistaken :-\
Fortunately Dave is not an idiot and he put the control loop in analog electronics. It's not about the update rate of the LCD, it's about the response of the control loop.
 

Offline jaycee

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Re: DIY Power Supply
« Reply #30 on: February 26, 2012, 12:10:35 am »
If you want to do a discrete linear supply, the method used by Mastech in their linear supplies works very well. I have been playing around with this myself.

I use a regular 2x9V transformer to make 0-9-18V AC, with a relay to switch between the taps to reduce power dissipation in the output. A small 9-0-9V transformer provides 12V unsmoothed for the relay and +/-5V for the opamps.

The clever trick is that the control circuitry uses a supply that floats around the output voltage. This is similar to the way the good old MC1466L works as well.
« Last Edit: February 26, 2012, 12:27:48 am by jaycee »
 

rabakomaba

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Re: DIY Power Supply
« Reply #31 on: March 12, 2015, 12:18:02 am »
NOTE: This message has been deleted by the forum moderator Simon for being against the forum rules and/or at the discretion of the moderator as being in the best interests of the forum community and the nature of the thread.
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« Last Edit: March 12, 2015, 06:50:20 am by Simon »
 

Offline Martini

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Re: DIY Power Supply
« Reply #32 on: April 30, 2016, 08:27:51 pm »
why people like to complaint on "built and proven to be working" stuff? instead of providing better idea?
I have never seen tests of noise rejection or transient response. Even a rheostat will make a working variable power supply if you don't care about transient response. It appears that it was only built by people without any analog design experience, since anyone skilled in analog design would immediately dismiss this implementation. As for a better idea, Dave's design is much better, or any of the Agilent designs like the E36xx series, or the German ELV design I linked to several times.
So, you would use the DAC to...control an op amp, which will drive the power transistor?
 

Offline imidis

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Re: DIY Power Supply
« Reply #33 on: May 03, 2016, 01:19:11 pm »
Here's one I made earlier:

http://tynemouthsoftware.blogspot.com/2012/01/universal-laptop-power-supply-update.html
http://tynemouthsoftware.blogspot.com/2012/02/universal-laptop-power-supply-further.html

This was a switchable voltage laptop charger which was rehoused with a slightly improved voltage selection and an ammeter, here is the original unit teardown which lead to the rehousing.

http://tynemouthsoftware.blogspot.com/2012/01/universal-laptop-power-supply-teardown.html

It's a fairly simple smpsu (does that necessarily equal bad?) and so the output regulation isn't fantastic under large load. One day if I get around to it, I'm going to replace the guts of this with a better switch mode (a meanwell perhaps?).

I never intended this to be a proper bench supply, I've several of those anyway, both professionally and home made, and I intend to add a uSupply to that collection once the kit is available. It's just meant to be a slightly better version of what it used to be, and I think it achieves that. It's also a handy high(ish) current supply for applications where I'm not too bothered about noise or regulation within a couple of 100 mV.

Thanks,

Dave

Thanks for the idea dave, I'll have to find a decent one and get a similar setup, loads of useful for what I do.  :)
Gone for good
 


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