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Old 22nd April 2002, 03:55 PM   #1
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Default CCS reposting

Ok, sorry, I try again !. This time I'm trying to send a jpg image file.

Hello All,
This 2 terminal constant current source circuit is shown in a recent EW magazine - Circuit Ideas.

Quote:
"Constant current diode look-alike" ....... .........The 2 terminal circuit shown here is composed of a pair of complimentary constant current sources, where each provides a constant current for the voltage reference of the other, thereby improving performance.
Compliance is excellent and the current can be set to almost any value.
Power dissipation and voltage withstand are limited only by the transistors chosen.
The circuit can be made up on a tiny piece of stripboard, and makes an excellent replacement for current setting resistors in many audio power amplifiers.

David N J White
Bearsden
Glasgow
G3
[IMG]c:\ccs 317.jpg[/IMG]

The formula given is - Iconst = 2 * [(Vf - Vbe)/ R], where

Vf = Led voltage drop,
Vbe = vbe for Tr1 & Tr2,
R = R1 = R2.

Simulation with red leds shows
10v - 8.810 mA
20v - 8.833 mA
30v - 8.854 mA
40v - 8.873 mA
50v - 8.891 ma

Maybe this is old hat to some of us, maybe useful to others of us.
Modifications/improvements ?.
Is this good performance ?.
Is there more to be known regarding application of ccs's.
HH thoughts on green leds ?.

Regards, Eric.
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Old 22nd April 2002, 05:37 PM   #2
tiroth is offline tiroth  United States
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mrfeedback, please use the "attach file" box on your .jpg image. This will upload it to the diyaudio server. It is smart enough to know that a .jpg is an image it can display. If you send a .bmp this way it will be attached, but not displayed.
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Old 22nd April 2002, 06:30 PM   #3
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Next try......
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Old 22nd April 2002, 06:35 PM   #4
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Default next ......

[IMG]C:\ccs 317.jpg[/IMG]
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File Type: jpg ccs 317.jpg (21.0 KB, 878 views)
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Old 22nd April 2002, 06:37 PM   #5
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can anybody see the image ?
Harry ?.
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Old 22nd April 2002, 06:51 PM   #6
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I can see it.
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Old 22nd April 2002, 06:52 PM   #7
mlloyd1 is offline mlloyd1  United States
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I can see it! I actually deleted an attempt to put my guess of a picture in for discussion since you were not yet successful.
mlloyd1
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Old 22nd April 2002, 07:14 PM   #8
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Ahhh, success at last. Thanks for the replies telling me so !.

Can you read the previous text too ?.
Comments etc ?.

Regards, Eric.
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Old 22nd April 2002, 07:53 PM   #9
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If you want an even more extreme current source use cascodes and if you want even more use darlington connection for the "upper" transistors.

Instead of LED (temperature sensitive and not very predictable) use a LM431! Now the current source starts to look my kind of style (overkill and monster design)!
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Old 23rd April 2002, 01:34 PM   #10
Geoff is offline Geoff  United Kingdom
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Eric

Thanks for posting the schematic (eventually :-). Apart from the advantage of it being a two terminal arrangement, I don't see too much benefit in the circuit. In simulation, the current variations with ambient temperature and load are slightly greater than those for a standard LED/transistor ccs. The current change with supply rail voltage variations is however significantly better, but this is only of relevance if unregulated supplies are used.

The standard two-transistor ccs has better temperature characteristics and far better load tolerance than either of the LED circuits and is mid-way between the two LED circuits so far as current v supply rail voltage is concerned.

The two-transistor ccs can be made into a two terminal arrangement, as shown below, using a similar philosophy to the circuit you posted. With this ccs, the temperature and load characteristics are similar to those of a standard two-transistor ccs and the current change with supply rail variations betters David White's circuit by a factor of 10.

Geoff
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File Type: gif 4trccs.gif (1.3 KB, 773 views)
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