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4hv.org :: Forums :: General Science and Electronics
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Circuit with unknown function

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ShawnLG
Thu Mar 23 2006, 03:22AM Print
ShawnLG Registered Member #286 Joined: Mon Mar 06 2006, 04:52AM
Location:
Posts: 399
I have pulled this from something(maybe a VCR) a long time ago and I did not know what it did. It is a module that was soldered by its two pins on to the main circuit board. Why would engineers put this circuit on its own board? What did it do? The number that is partially hidden on the board is 21015.
1143084158 286 FT0 Uboard
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cjk2
Thu Mar 23 2006, 04:22AM
cjk2 Registered Member #51 Joined: Thu Feb 09 2006, 04:17AM
Location:
Posts: 263
Three ideas that may be completely wrong: a voltage regulator? a current regulator? an IR reciever?
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...
Thu Mar 23 2006, 04:39AM
... Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
looks to me like a constant current source (ie current regulator). Try hooking it up to a variable supply and measure the current it draws...
The spacing of the pins looks about right for a resistor. So my guess it that there was originally supposed to be a resistor there, but they decided they needed better regulation, so they made up those little boards to replace it instead of scrapping all of the others.
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Hazmatt_(The Underdog)
Thu Mar 23 2006, 04:42AM
Hazmatt_(The Underdog) Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
ya .....current source
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Sulaiman
Thu Mar 23 2006, 09:14AM
Sulaiman Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141
My guess is;
A temperature-compensated bias-voltage generator for a class AB amplifier,
Should give about 2V - 5mV/degree at 1 mA.
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Steve Conner
Thu Mar 23 2006, 10:30AM
Steve Conner Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I'd guess it's on a little board of its own because it's a fix for a bug in the original design, and it turned out more cost-effective than redesigning the main board. It's more of an adjustable-temperature-dependent-voltage source than a current source.
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ShawnLG
Sat Mar 25 2006, 04:58AM
ShawnLG Registered Member #286 Joined: Mon Mar 06 2006, 04:52AM
Location:
Posts: 399
I have calculated its resistance with each voltage setting applied to it. The circuit give an interesting nonlinear function of its resistance with respect to volts. Warming up the transistor gave a very little change in current. I don't know how it would be a constant current source. The more volts it sees, a lot more current it draws. cheesey

1v, 0.31ma, 3225ohms
2v, 1.15ma, 1739ohms
3v, 2. 48ma, 1210ohms
4v, 3.70ma, 1081ohms
5v, 4.97ma, 1006ohms
6v, 6.35ma, 945ohms
7v, 7.6ma, 921ohms
8v, 8.9ma, 899ohms
9v, 10.2ma, 882ohms
10v, 11.5ma, 870ohms
11v, 12.7ma, 866ohms
12v, 14.07ma, 853ohms
13v, 15.39ma, 845ohms
14v, 16.69ma, 839ohms
15v, 17.85ma, 840ohms
16v, 19.18ma, 834ohms
17v, 20.48ma, 830ohms
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HV Enthusiast
Sat Mar 25 2006, 03:34PM
HV Enthusiast Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Without knowing the rest of the circuit, its almost impossible to tell what its function is. You might as well try to guess the funtion of a single resistor hanging by itself on a similar board.
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Marko
Sat Mar 25 2006, 04:22PM
Marko Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
If that 1K resistor is replaced with diode/zener diode then we would have a current source.
This circuit looks very similar but its obivously not that, and measurements prove that (current is not constant).

See Link2 for basics, I hope everyone knows that...
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Thingmaker3
Sat Mar 25 2006, 05:14PM
Thingmaker3 Registered Member #124 Joined: Fri Feb 10 2006, 01:30PM
Location: Portland Oregon
Posts: 35
Crude graph based on Shawn's numbers:

1143306827 124 FT5259 Mysterygraph
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