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Old 22nd February 2011, 12:06 PM   #1
zei is offline zei  Sweden
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Default Sanity check on this multi cap supply

Could someone take a peek at this at see if there are any crazy flaws that i,m missing..
Would be soooo great.. !

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Thanx a cassilliiion biilliion

/JZ
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Old 22nd February 2011, 01:20 PM   #2
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Are you hoping for regulated output? R4 acts as a voltage reference, a zener or string of zeners adding up to .6V above your desired output voltage would MUCH work better.

At 1K for R3 you should have enough base drive current available, but you should consider darlington connecting a general purpose highish gain transistor to the bases of the the TIP3055s to reduce the output impedance. An MPSA42 would work. If you have enough voltage to drop, you could use IRFP240(s) to pass the current using the existing reference. Then you'd set the reference voltage to ~4V above the target.

How much current are you hoping to deliver? There seems to be a mismatch between the pass devices and the bridge chosen. If your bridge is rated at 3A or so you can probably get away with a single pass device unless you are dropping a lot of voltage.

Look closely at heat sinking. How much power will be dissipated by the pass devices? Does the heat sink adequately cool it? There are profiles that work better than your choice. Consider adding holes in the board around the pass devices to allow better airflow to the heat sinks.

C5 doesn't need to be so big. It just provides filtering for the voltage reference. Move it in parallel with C4 and use 10-100 uf possibly paralleled by a 1 uf film cap in its position.
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Old 22nd February 2011, 01:30 PM   #3
zei is offline zei  Sweden
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Hi

Thanx very much for the reply. This is based from something found on Rod Elliots site.
I,m going to use 2 TIP141 in parallell (But these where not in the library) so i took something similar for layout purpouse.

Regarding the bridge, i found this in the library however i have,nt checked what kind of ratings this PCD mounted devices an handle. I might need to go with an "off" PCB version. Like a standard 10A rectifer

Again thanx for the suggestions! i,ll take a closer look and see if i understand full what you mean.

Best regards
/JZ
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Old 22nd February 2011, 01:35 PM   #4
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Take a look at the power supply here: http://www.passdiy.com/pdf/balzenpre.pdf Nelson Pass does a good job explaining how it works. Shoot for around 5 mA through your zener reference.

A "full" sanity check requires knowing your goals for the supply - What are your intended output voltage and current. What are you intending to power with it?
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Old 22nd February 2011, 02:35 PM   #5
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And to see what I meant by darlington connected, refer back to Rod's project 15 that inspired your design. See the way the the BD and TIP devices are connected? That's it.

Capacitance multipliers are fine, but it takes very little to stabilize the output further.
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Old 23rd February 2011, 11:07 AM   #6
AndrewT is offline AndrewT  Scotland
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The nice thing about capacitance multipliers is that they actively reduce output ripple, both mains frequency and interference frequencies.
The other nice attribute is that they minimise the heat generated in the transistors, making more available to power the amplifier.
Finally they work over a very wide range of mains voltages, far beyond the ~ +-10% that would normally be allowed for in the design of a regulated power supply.
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