Help identifier component 3 pins TO-92 chip

On Fri, 20 Apr 2012 14:26:57 +0200, "Quim" put finger to keyboard and composed:

Can you supply a direct link to the images, without the popups, banners, ads, etc?

- Franc Zabkar

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Regards

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On Mon, 23 Apr 2012 12:13:49 +0200, "Quim" put finger to keyboard and composed:

The only switchmode device in a TO-92 package that I managed to find was this one:

However, it doesn't look anything like yours. Its sense resistor is internal to the package. Moreover, I would have expected a coil somewhere in the circuit.

It may help us if you could draw a circuit diagram.

- Franc Zabkar

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Many thanks Franc I seee that works directly at mains voltage this supertex driver, it is interesting

The circuit :

Not have any coil, I think that surely the cables themselves serve as inductance at this frequence 500khz.

Regards

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On Tue, 24 Apr 2012 01:21:57 +0200, "Quim" put finger to keyboard and composed:

inductance

If your circuit is correctly drawn, then I suspect that the component that you have identified as a 1 ohm resistor may in fact be an inductor.

According to the IC's output waveform, if the component were indeed a

1 ohm resistor, then it would be passing 3A current pulses. If the duty cycle were 50%, then the power dissipation in the resistor would be 4.5W. I don't believe any designer would be silly enough to waste this much energy in a battery powered torch. Moreover, I doubt that a TO-92 package would be robust enough for that kind of continuous current rating.

Otherwise, if the component were indeed an inductor, then your circuit would look like a boost converter, with the IC incorporating a PWM controller and an N-channel MOSFET, possibly with current sensing as well. In this case I suspect that your torch may be just as bright using two 1.2V NiMH or NiCd cells, or maybe even a single cell.

- Franc Zabkar

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Yes, yo're right, I have disambled other time the head lamp, unsoldered this resistor, and Ok, it is one inductor, the tipical as one resistor 1/4W with the body a litle green. I measured it and indicate 0,012mH, really are brown, brown, black, 11uH.

Yes, the current and voltage is estabilized within certain limits. I see the limit down are in the input 1,33v for to work well, and the output are 2,7vpp in the waveform, and the led ligths. Input Volts dc - output to the led, waveform voltage zero to peak

3 - 3,2 2,5 - 3,1 2 - 2,9 1,5 - 2,8 1,33 - 2,7 1 - waveform not square and I can't syncronize.

Regards

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On Wed, 25 Apr 2012 17:35:27 +0200, "Quim" put finger to keyboard and composed:

and

in

In retrospect we could have estimated the value of the inductor from your first measurements.

Your 1W LED would have a rating of about 300mA at 3.2V.

The voltage across the inductor would be given by ...

V = L . dI/dt

So dI = V . dt / L

Assuming a 50% duty cycle at 500kHz, then dt = 1 usec.

So dI = 3 . 1E-6 / 11E-6 = 270mA

AISI, your "004" device probably has an internal current setting of around 350mA. I still haven't managed to identify it, though. :-(

- Franc Zabkar

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Very well the formulas and the calculatios.

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