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2000 WATT SOLA REGULATOR
Sola CVS 2000 Watt Constant Voltage
Transformer provides a very well regulated sinusoidal waveform that is isolated from variations and disturbances
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2000VA. 17.8x11.4x9.6, 115 lbs sh. Unused, $300
ZM- 4 Wheatstone Bridge used
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range 1 ohm to 1,011 M ohms
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ohms. The current limit of the
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78 NUTS & VOLTS November 2005
Continued from page 31
receiver circuit board is shown. Figure 6 actually shows the transmitter circuit board. Sorry for the errors.
>> WICK IS RIGHT?
In your October 2005 Stamp Applications article on the
electronic candle, I am concerned about the Figure 2 schematic on
page 15. It shows 220 microfarad 25 volt capacitors connected
between ground and the outputs of a ULN2003 Darlington driver IC.
When the output is off, the capacitors can charge up to the 12 volt
power supply level. When the ULN2003 outputs turn on, the main
things limiting the discharge current through it are: the capacitor
ESR, the wiring inductance, and the on resistance of the ULN2003.
The current could easily exceed the 600 milliamp peak rating of the
device outputs. I would recommend that a 1/4 watt current limiting
resistor of 20 ohms be added in series with each of the ULN2003
outputs to limit the current to within the manufacturer’s specification. Other than that, it was a clever application of a handy Parallax
The reader is technically correct but in practice (and we've built
a lot of these candles) we have experienced no problems —
probably because the rating of the part is shown at 100% duty cycle
and the instantaneous charge/discharge (depending on circuit) is too
short to dissipate much energy through the ULN2803.
The actual error, however, that another reader pointed out is
that I show the capacitor in the wrong position in the printed
schematic. I have corrected that and posted the correction in our
forums at http://forums.parallax.com/forums/default.aspx?f=
Columnist, Stamp Applications
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