| Fuling |
Not that I´m not busy working on my Xsoz, I felt that I needed a little side project too:rolleyes:
I have a pair of bookshelf speakers with TB 3" and Peerless 5-1/4" drivers that sounds quite good, actually so good that they deserve biamping with class A amps.
Nothing too serious though, just a handful of components assembled on veroboards an then mounted on a big heatsink that I have leftover from the Xsoz project.
After searcing this forum I sort of fell for the Baby Zen, a small "inofficial" Zen amp with low power mosfets and lower rail voltage/bias current.
A version with dynamic current source is also floating around somewhere.
On top of all this I´m curious about cascoded gain stages, I´ve read alot about it but never tried it myself.
After some cut n´paste engineering I came up with these two circuits, A) for the TB fullrange drivers and B) for the Peerless woofers. |
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| Fuling |
| And B, which didn´t make it in the first post: |
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| carpenter |
Of the two, I find "A" more intriguing. I'll bet that with a bit more research, you can convert the CCS into an aleph version complete with sensing resistors. Then the amp can drive harder transients without clipping.
John:) |
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| woody |
In circuite A the drain of irf510 is only connected to the gate of
irf530. I don`t think you have any current path with this connection.
Woody |
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| Fuling |
Circuit A) is cascoded and has a static CCS, B) is not cascoded but has a dynamic, Aleph-type CCS. I guess any combination of cascodes and CCS`s is possible, this is only my attempt to optimize for the different frequency ranges in my biamped system.
| quote: | | In circuite A the drain of irf510 is only connected to the gate of irf530. I don`t think you have any current path with this connection. |
I don´t quite understand, I look at the schematic and I see a straight line between the drain of the IRF510 and the source of the IRF530. The gate of the `530 is connected to a voltage divider for about 6,5V bias and has, as far as I can see, nothing to do with the drain of the `510.
Just for clarity: IRF510 is the input mosfet and the IRF530 is the cascode transistor which keeps the input transistors drain at a constant 2,5V or so. |
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| bobsinclar |
Hello ,
I think that what means Woody, is that the cascoded IRF 530 , althought is biased,does not see any AC modulated signal to it's gate... just thought , but I'm not sure I really understood cascoded stages anyway...I'm still studying it;)
Vince |
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| carpenter |
| quote: | | B) is not cascoded but has a dynamic, Aleph-type CCS. |
Ah, yes... there's the little Aleph ******. Why not run B with the addition of a cascoded topology--sort of like blending the two layouts. BTW, I really like the simple way you executed your design.
John:)
edit: how come the word bug-ger is censored?
Also, Fuling, can draw your prints a bit larger? I can't make out all the values. I'm saving your drawings anyway.
Thanks. |
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| Variac |
| quote: | | how come the word ++++ is censored? |
Ask someone from the Commonwealth:o |
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| Fuling |
| quote: | | althought is biased,does not see any AC modulated signal to it's gate... |
A modulated cascode would of course be even better, but since I don´t have a source resistor there is no place to get that modulation signal from. At least not as far as I can see.
A "static" cascode should be a significant improvement over the basic circuit anyway, at least I hope so.
| quote: | | Why not run B with the addition of a cascoded topology--sort of like blending the two layouts. |
Might be a great idea, but somehow I have this prejudice that the active CCS is inferior to a regular one when it comes to microdynamics and stuff. I might be totally wrong here though!
The reason I´ll use it in the bass amps is that I want to have better current capability to drive the woofers.
This whole reasoning might sound silly considering that we´re talking 5W amps that will drive 3" and 5" speakers, but for me this hobby is all about experimenting and having fun.
When finished I will of course try both topologies with different speakers (including my main speakers, not the tangbands) to find out if one of them is significantly better than the other.
I can draw better schematics tomorrow, I did these ones in a hurry at work.
By the way, I´ve spent a couple of hours doing some metalwork tonight and now the PSU is almost finished and attached to the heatsink. The heatsink has about a million M3 tapped holes so it´s kind of building Lego or something:D
The Fets and everything else should arrive on Tuesday or Wednesday so this shouldn´t take too long to finish. |
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| lineup |
I see you have 23 VDC supply.
Is this from a 18VAC trafo?
What type of transformer and VA rating?
Maybe you use a 2x18VAC,
with each channel using only one of windings?
Tell a bit more of your idea for the power supply.
This is an important part of any power amplifier,
as you know.
How much is the bias idle current for each baby-zen?
In case you haven't already mentioned.
lineup |
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| Spasticteapot |
| Can you post some pictures? (Totally unrelated, I know.) |
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| Fuling |
Lineup: 2x20V 200VA toroid transformer, each winding feeds a bridge rectifier, a 15000uF 40V cap and a simple capacitance multiplier. If I had just a couple of volts more available I´d use CLC-filters before the C-multiplier to get extra quiet PSU´s, I use that configuration in another amp and the background is pitch black!
Spasticteapot: Yes, but not today. I´m on my way to work now and will be stuck there the next 29 hours or so...:bawling: |
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| lineup |
| quote: | Originally posted by Fuling
The PSU:
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Very Solid and Good supply!
Some time maybe, I will get myself to buy such good stuff
to my amplifiers.
Sure is what any power amplifier should have - for best results.
Very Nice, Fuling |
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| Fuling |
Thank you!
It´mostly buy used and surplus parts, that´s the only way for me to afford building class A amps all the time!
Since I´m mostly into trying out new circuits and having fun I rather build five different amps with cheap components (not everywhere though, I tend to use good caps for example) than one super amp for the same money.
Sometimes when I´ve made some prototype that sounds really good I build an improved version with better components later, but most of my projects are quite temporary.
Anyway, I noticed that the caps are assembled in opposite directions, please remind me to turn one of them 180 degrees before I start connecting things:D
I got the missing parts for my Xsoz today so this project will be put aside for a (short) while, I also forgot to order output connectors so I´ll have to wait for them to arrive.
I can probably populate the veroboards within a couple of days but the remaining mechanical work might take longer. |
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| carpenter |
:snowman: :santa2: :cheers: I can't wait to hear your impressions on its sound qualities.
John:) |
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| Fuling |
| quote: | | I can't wait to hear your impressions on its sound qualities. |
I had a first listening session with this amp today.
Since my active crossover needs some modifications before it can drive the Baby Zens and my Tangband speakers, I listened to each pair och amps with my FE167E speakers and an input buffer.
Impressions: Both sets of amps sounded quite good, but the HF amps definitely had better highs than the LF amps (big surprise, huh?:D )
I believe I can thank the cascoded gainstage for this, the treble sounded very clear compared to what came out of the more aggressive bass amps.
This was only a first impression based on one hour (or so) of listening to each pair.
I´ll give the amps some time to break in and then report further, meanwhile I will also mod the active XO so I can try the amp out with the speakers it´s intended to drive.
Conclusion so far: Cascoding is the way to go!!
This is definitely not my last amp with a single cascoded gainstage! |
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| carpenter |
An amp for different applications in the audio spectrum...
I totally missed that point. Now, you're going to have to give me many more details.:D For instance, does the bass amp not deliver the highs intentionally (i.e. designed for bass applications only); with the aleph current source connection, it should have more power, correct? How does the cascode treble amp sound doing full spectrum? I want all the juicy detail--all in due time, of course.
My hat's off to you fuling, excellent job in audio exploration!
John:)
btw: can you rewrite those component values in larger print? |
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| Fuling |
Yup, both amps works fullrange but they are optimized for different frequency ranges. The cascodes are there to clean up the highs in the HF amps and the Aleph CCS´s are meant to deliver extra current to the woofers.
If I had to choose one of the amps for fullrange use it would definitely be the cascoded one with static CCS.
I can post better schematics tomorrow night. |
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| carpenter |
| Thanks for offering to rewrite the schematics.:) |
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| Fuling |
Don´t get too excited, I have no software for drawing schematics so the new ones will also be drawn by hand but I´ll try to make them readable (ist that a word?).
Right now, I´m trying to decide what Mosfets to use in a bigger version of the cascoded Zen, I have a few types to choose between but none of them are optimal. OTOH I´d prefer to use parts that I already have at home... |
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| carpenter |
You can download a free copy of schematic drafting software from Express PCB. I use it to draft electronic circuits as well as an aid to designing my pcbs.
btw, speaking of pcbs, I'm firing up my newest version of the ZV7-T today. My circuit boards are working perfectly, so far. The only glitch is my power resistors (Q1 and Q2 drain to ground) are getting hot. I can't even begin to touch them. I'm thinking about using the "light bulb" technique to replace the power resistors. I just have to find which wattage gives me 47 ohms.
Here's to hoping you have a wonderful week-end.
John:) |
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| Fuling |
Ok, I´ll have a look at the free software whenever I get the time to do it.
Drain to ground, I assume that would be output to ground (I don´t have the schematic in front of me right now)?
If so, I´d use bigger power resistors instead of lightbulbs.
In my world lightbulbs belongs in lamps, not between output and GND in power amps:) |
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| carpenter |
I built a heatsink array around the power resistors and now they are quite happy--or maybe, I'm quite happy.
John:) |
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| Fuling |
| Good! Don´t bother too much about power resistors running hot, they are designed to do that!:hot: :D |
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| carpenter |
They were hot! The paint on the plywood box they rested against melted...:redhot: Now, the heatsink keeps them around 50 degrees C.
John:) |
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| lineup |
| quote: | Originally posted by Fuling
I have no software for drawing schematics
so the new ones will also be
drawn by hand .....
. |
| quote: | Originally posted by carpenter
You can download
a free copy of schematic drafting software
from Express PCB.
I use it to draft electronic circuits
as well as an aid to designing my PCB.
. |
thanks, carpenter
www.ExpressPCB.com Download.htm
I decided to try.
I downloaded latest version, May 2006.
It is a good and very easy to use Schematic program.
Two parts:
1. ExpressSCH ... for adding components symbols and wires into a schematic
The Circuit can be exported, Saved, directly to a .BMP image, with different selectable resolutions
or
The Circuit can be Copied to Clipboard and so imported into your Image program.
And from there saved in what format you like: PNG, GIF ....
2. ExpressPCB ... for creating PCB Layout from your circuit
This one I did not test,
because I don't make PCB
.. there are so many members at this forum
that can do this much better .. if we ask them nicely ;)
==========================================
Carpenter,
thanks for the hint about ExpressPCB www.expresspcb.com
Easy and good tool for diyaudio members. (I guess only for Windows users, I have XP Home)
Carpenter,
as a reward you can freely use my circuit I created quickly using this ExpressSCH software.
While I was learning how it works.
( I even did not have to consult the 'Quick Guide' or 'Help documents'! )
:att'n: All you others :att'n:
Please note and respect that this Attachment below
is for carpenter only!!!!!
lineup :) |
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| carpenter |
What a sweet layout.
I'm still studying it's properties, but I see I can have a bunch of fun with this.
Balanced front end
Fet for bias voltage
Push/pull output
All transistors have their own ccs
very cool, and I'm glad you enjoyed the software,
John:) |
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| lineup |
:)
- not to mention balanced in and/or output
- input for driving two power amplifiers in bridge ( one from +out and one from the -out
Most Non-Lineup operational amplifiers
have only one non-inverting output.
:cool:
1. Resistor in JFET CCS source, should first be adjusted,
to get like 0.6V in that current source feeding two input transistors.
The current in those 1N4148 diodes
determines this voltage across R1 ~ 0.60 Volt.
2. Those other two trimmers (one for CCS in +output, the other for -output stage)
should then be used to achieve balance at the output stages.
We can say this is the Output DC-offset adjustment.
3. Can of course like most Op-Amps be used with single or dual supply.
For single supply, we need input and output caps, of course.
4. Each output stage has got idle Class A!! ~6mA ( 0.6V/100 )
Can for example drive +-4-5mA into 5 kohm= +-20-25 peak ~15 Volt RMS
5. BF245A .. the JFET is only for 30 VDS. So max dual +-15V if using that one.
Use some other JFET, for higher voltage operation.
There are some 40-50 Volt JFET that are easy to find.
For example 2SK170 takes 40 Volt = +-20Volt operation
6. BC550C, BC560C takes 45V, so max +-23 Volt supply for them.
7. By using other types of JFET and BJT small signals
you may tailor your Op-Amp for much higher voltages,
higher currents output
or whatever.
lineup
PS. I hope Fuling decide to download ExpressPCB.
It is a tool what many would need.
Instead of trying to describe circuits with words ... DS. |
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| carpenter |
lineup, I cut, pasted and saved your last discourse. Thanks; I'll build this amp at a later date when I'm done with my ZV7-T series.
Hey choky, that's a neat set of drafting symbols and will work great with "paint".
Life is great,
John:) |
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| Fuling |
If everything goes as planned I´ll post some better schematics a couple of hours from now.
Handdrawn, since I haven´t had time to check that software out (I´m at work). |
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| Fuling |
| If you guys can´t read this, get thicker glasses!:D |
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| Fuling |
Although the circuit works if built as shown above, I have some suggestions for modifications that probably would improve the performance:
Higher rail voltage. I lost a few volts more than I had expected so I´m running mine on 21,6V, it works but a few more volts would probably be great. 28V would probably be ideal, 3V across the gain transistor and 25V to be shared between the cascode and the CCS.
Higher current. Of course!! I´m limited to 25-30W dissipation per channel by my quite small heatsink, if I could I´d definitely change the 0.56R resistor to 0.47 or even 0.33R
In that case I´d also change the CCS mosfet to something that can take a little more power, like IRF9530 (or -9540 or 9640 or whatever, you get my point).
A trimpot in the voltage divider for the cascode would be nice, I ended up with about 2,8V across the gain Mosfet but perhaps it would be interesting to play around with that voltage a bit?
As far as I can understand the internal capacitances in the Mosfet changes with the voltage, so one or two extra volts to play with could be fun.
I needed quite high input impedance to match the output of my active crossovers, people with good preamps could lower the values of the feedback resistors and probably get improvements here.
Putting the feedback loop outside the coupling caps might also be a good idea, but now we´re getting of the track.
While we´re of the track, why not add an input buffer and an active CCS? ;)
The possibilites are endless, but the amp sounds really good as drawn in the schematic and would probably sound even better with just a little more voltage and current.
As promised, I´ll build a bigger version someday with IRF540/9540 for the cascode/CCS and IRF530 as gain transistor, 28V rails and plenty of current. I got a pair of really huge heatsinks earlier this week and I already have a nice 2x24V 750VA toroid...
Not that I need more amps, but after my first listening I got the impression that the cascoding is a winning concept that deserves proper implementation. |
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| carpenter |
Excellent job, fuling! -- and thanks for the enlarged drawing.
John:) |
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| lineup |
| quote: | Originally posted by Fuling
If you guys can´t read this, get thicker glasses!
:D |
No problem, dear Fuling.
You make nice schematics with your method.
Your digital camera is not bad.
lineup :cool: AC-län lappland |
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| lineup |
| quote: | Originally posted by carpenter
lineup, I cut, pasted and saved your last discourse. Thanks; I'll build this amp at a later date when I'm done with my ZV7-T series.
Hey choky, that's a neat set of drafting symbols and will work great with "paint".
Life is great,
John:) |
I tested and tweaked my special op-amp, with both non-inverting and inverting output.
In my MultiSim.
At unity gain +1, buffer, and +15 -15 volt supply.
With input impedance resistor 10k and 10k feedback resistor.
Into 5kohm load.
I got 0.000% THD for input voltage <= +-6.12 V peak input.
At 6.13 V peak input got 0.001% ( -100dB ).
So almost 50% (7.5V) input before my analyzer can see any distortion!
At 1 V RMS input/output,
I get of course no distortion in +OUTPUT, using 10kohm feedback resistor.
But the -OUTPUT (inverted, which has got no direct feedback)
I get
0.102% THD at 1 V RMS input.
And for 2 V RMS this is twice (0.204%) and so on .....
It shows an perfect linear function, where dist is in proportion to output voltage
Besides, this is almost only 2nd harmonics, for the inverting output.
I do not know how to add feedback from both output.
Is there any way, to use for example
two 20k feedback resistors, one from each output?
There has got to be a solution for this,
so both outputs shows 0.000% THD.
:confused:
Enlighten me, somebody please.
Thank you!
My op-amp circuit is a couple posts up here.
lineup |
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| Fuling |
Thanks guys!
I gave the schematic/PCB software a quick try but I soon realized that it would take a while (for me) to get it going, will investigate it further when I get the time to do it. |
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| Zen Mod |
| quote: | Originally posted by Fuling
Thanks guys!
I gave the schematic/PCB software a quick try but I soon realized that it would take a while (for me) to get it going, will investigate it further when I get the time to do it. |
I still prefer hand-drawing and scanner...........at least for smaller schmtics..........everything bigger I draw in blocks , and that makes them same ;) |
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| Fuling |
| I just posted a new thread with some questions and design considerations regarding a higher power version of the cascoded Baby, FYI. |
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| Zen Mod |
| quote: | Originally posted by carpenter
lineup, I cut, pasted and saved your last discourse. Thanks; I'll build this amp at a later date when I'm done with my ZV7-T series.
Hey choky, that's a neat set of drafting symbols and will work great with "paint".
Life is great,
John:) |
I'm lost in all this threads....... |
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| carpenter |
| Now, that's what I call pretty!:D |
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| lineup |
I have had a look at your latest schematic
in this topic, Fuling ( man you are really UGLY, Fuling )
Here it is:
http://www.diyaudio.com/forums/atta...tamp=1165697731
I think it looks good.
And you say it works, too:att'n:
If you want to use higher voltage and/or currents = more power,
you can do some math, on the heat and temperature.
Ths way we can figure out what MOSFET to use.
TO220 are good and often fast and fairly low capacitance
But they have a limit how much power can be used.
At least before they start operation so bad, it will be distortion = bad sound.
TO247 and TO3 can take more powers.
But at the cost of less speed and more capacitance.
And will be a bigger load for input stage and so maybe
have a higher distortion level and be a bit slower.
-----------------------
Advice, if your math & calculations show, that TO220 can be used
within good margin of max temperature of transistor,
then use TO220.
But if the temperature of operation (junction temperature)
gets >=100 degrees, then I would step up to a bigger power transistor.
Because it is very probably this bigger device, would give less distortion, anyway.
------------------------
It is not too difficult to calculate what the junction temperature will be like.
Tyimo has learned this, by my instructions!
You have formulas here, and some examples:
http://www.diyaudio.com/forums/show...904#post1069904
See this post, and the following posts!
Once you have the data of your heatsink
it is no advanced math. Only multiply and addition.
If you have not exact data of a big heasink, like a big piece of aluminium or Your amp Chassi,
then you can make a good guess,
by comparing WEIGHT, in KG, to other BIG heatsinks in ELFA catalog.
The value we want is like:
0.7 C/W.
( each watt will increase temperature 0.7 degrees C )
------------------------------------------------------------------------------
Link to ELFA heatsinks, with DATA:
http://www.elfa.se/elfa-bin/lt.pl?l...1474382&1474384
lineup
I am an astronaut, I am an astronaut
Daddy's away and mom's asleep
I am an astronaut |
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| flg |
I'm sorry guy's. I'm reading all this and I just have to ask the obvious:D With everything involved in a baby ZEN, with cascoding and all, why not build a ZV9 variant??? A Baby ZV9???
Less parts:smash: Probably less THD:smash:
I'm trying to build a slightly bigger ZV9 variant :scratch: :scratch: :scratch: with my L Loaded thread:confused: |
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| Fuling |
flg: ZV9 would be great, but I don´t have any power Jfets...:bawling:
lineup: My new heatsinks are bigger than anything in the Elfa catalog, probably 0,25 degrees C/W so they are probably big enough, but as you say I´ll have a look at the "internal" thermal resistance of each mosfet.
Edit: 75645P has a junction-to-case thermal resistance of 0,48 C/W, while IRF540 has 1,1 C/W.
Seems like 75645P would be a good choice for everything except the gain transistor in the bigger version.
The pre-drilled holes in my heatsinks is another limiting factor, there´s a row of M3 tapped holes at 20 mm C-C, so if I use T0-220 devices I can use alu-oxide insulators but if I choose T0-247 I must use modified silicon tabs.
So, T0-220 it will be! |
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| lineup |
| quote: | Originally posted by Fuling
lineup: My new heatsinks are bigger than anything in the Elfa catalog, probably 0,25 degrees C/W so they are probably big enough, but as you say I´ll have a look at the "internal" thermal resistance of each mosfet.
....
The pre-drilled holes in my heatsinks is another limiting factor,
....
So, T0-220 it will be! |
Such big heatsink is good for TO220 cooling.
Another good rule of the thumb, for the heatsink size itself:
At the total watt to cool from all devices placed on the heatsink
the heatsink should not be hotter than air around
with more than +40,+50 degrees
The formula using this rule would be (for 50 degrees C increase):
50 / Total Watt = heatsink required C/W
Say we want to cool total 100 watt running through transistors fitted on heatsink.
50/ 100Watt = 0.50 C/W
The temp of heatsink will be, at room temp = 25 C
25 + 50 = 75
-------------------------------
Of course if using the more strict value 40 C increase, 10 degrees more safety margin,
we would use formula:
40/100 Watt = 0.40 C/W heatsink (would give 25+40=65 C temp of a 0.40 C/W heatsink)
Other ways to use this rule of thumb:
Say we have an heatsink like 0.25 C/W.
How many watt for an increase of 40 degrees?
Yes,
40/0.25 = 160 Watt.
By this rule your heatsink should be good for cooling total 160 Watt, something.
----------------------------------
Now things aren't quite that easy.
Even if heatsink is only 65 C,
if we use transistors with too high C/W, the temp inside transistor
can be very high, even if heatsink is not more than 65 degrees.
But think is not problem in this case.
1.1 C/W is a good low value for TO220.
But some other TO220 has got 1.4 and 2.0 C/W .......
Like IRF610 and IRF9610 have higher values.
In fact is very easy to find out what value a TO220 has got.
Without datasheet!
You only need to know max effect, power for the transistor.
125/max power ~ C/W value.
for TO247:
150/max power ~ C/W value.
for TO3:
175/Transistor Max power Rating ~ C/W value.
The exact formula:
[Max junction temp of the package -25 (for room temp=25)] / Max Power Rating = C/W value.
TO220 - Max Junction temp 150.
150-25 = 125
As IRF540 probably is a 125 Watt transistor,
we get 125/125 ~1.0 C/W .... or as you say 1.1, more correct.
lineup
hope you got it ;) |
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