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Registered Member #10052
Joined: Thu Feb 07 2013, 11:31PM
Location: Overland Park, Kansas
Posts: 78
teravolt wrote ...
I am not trying to read you a sermon I just think they should be more robust for less experienced builders outside the laboratory.
Short of replacing the regs with DC-DC converters, like these 78xx drop-in replacements, or integrating a SMPS (the added complexity of which may be inconvenient to "builders outside the lab"), there may be no simple solution.
I do know that in several cases (mine included), coilers have had much more luck with the ON Semiconductor MC78xx series regs, which can deal with up to 35 volts max input, even down to the 7805's.
Eric's new layout also makes it very easy to stick on some RAM heatsinks. Just drill some holes in the enclosure behind the regs, and set up a small draw-through fan.
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
teravolt wrote ...
What you say about Fairchild may be correct but the dissipation of those regs are about 1 or 2 watts with out a heat sync so when a stranger connects them to there transformer they may think it is ok to connect them to the 20vac transformer. First of all 20vac is 20/.707=28.28vdc at the capacitor with no load and with about 26 with a load. second of all as jmorlockny states all transformers were not born alike. I have had some of those 20vac transformers up to 25vac and if you do the math it probably will exceeded most specs.
I had the same problem generating the 20vdc for my drivers and I fixed it with a simple peace of bent aluminum. I am not trying to read you a sermon I just think they should be more robust for less experienced builders outside the laboratory.
In regards to input voltage, granted it's a limited range and it should be checked. However there is not much that can be done to widen this range without making the board a lot more costly or complex; nether of which are my goals.
Your point about heating is taken however the regs are rotated 90 degrees for easy heat sinking, that was part of the changes for the UD2.5 to make it easier for heat sinking. The photo linked above was of an older UD2.0
Registered Member #18516
Joined: Sat May 18 2013, 09:09AM
Location: Lancashire, UK
Posts: 38
Goodchild wrote ...
In regards to input voltage, granted it's a limited range and it should be checked. However there is not much that can be done to widen this range without making the board a lot more costly or complex; nether of which are my goals.
Would running the 9/12v reg in series with the 24v reg not sort this issue?
The 24v reg will typically handle the higher voltages, and will then ensure the 9/12v part never sees any more than 24v on its input?
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Aragorn,
Linear regulators a simple pass elements. They can be stacked in whichever way you would like. However, because they are linear, the total load current will pass through each of them.
To do this properly, you would simply need to determine what the maximum load currents are for each of the 24V, 9V, and 5V regulators. Then determine what your range of input voltages are. From there, you can calculate the the amount of heat dissipation that would exist in each regulator depending on stacking them.
Remember, the total heat dissipation of the the three linear regulators will ALWAYS be constant. But how you stack them or connect them will just determine the overall distribution of the heat dissipation.
Another approach you can use is to use a series pass resistor on the input of the regulators and use this resistor to drop the voltage before it gets to the regulator. This will also help spread out the heat dissipation between regulator and resistor.
However, you will need to know exactly what the range of loads (minimum to maximum) and range of input voltages to properly select a resistor to ensure that the regulator always has the appropriate amount of headroom for operation.
Aragorn wrote ...
Goodchild wrote ...
In regards to input voltage, granted it's a limited range and it should be checked. However there is not much that can be done to widen this range without making the board a lot more costly or complex; nether of which are my goals.
Would running the 9/12v reg in series with the 24v reg not sort this issue?
The 24v reg will typically handle the higher voltages, and will then ensure the 9/12v part never sees any more than 24v on its input?
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
the power dissipation is the same for linear regulators as resistors, the voltage drop over the regulator times the current through the regulator. most of those to-220 packages are around 25W dissipation thoroughly heat sunk. V2.5 will do fine mounted to a metal box or decent heat sync. one of the ways i fixed it is to add a 6.8v transorb in series with the raw dc and the regulator or a resistor will work to. I have been burned to many times making boards to not allow for heat syncing.
Registered Member #8435
Joined: Sun Dec 02 2012, 04:29AM
Location:
Posts: 5
Seeing the renewed interest in this board, I wanted to post to say I just got ten more of these boards made and ready to mail out if people are still looking for them. Still $12 each shipped to the USA - shoot me a PM if you want one.
Registered Member #22717
Joined: Thu Jun 06 2013, 11:37AM
Location: Upstate NY
Posts: 3
If the board were to include 1 additional bridge rectifier and an additional input from the center tap of 10/20VAC transformer then the 9/12V and 5V regulators could be powered from the 10VAC input and the 24V regulator from the 20VAC. This solution would also keep the part count and price almost the same. One additional cap and the bridge rectifier should be all that's needed.
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Universal DRSSTC Driver V2.5 (Sold Out)
