# convert circuit to 6 volt

Discussion in 'The Projects Forum' started by mpatterson557, Sep 10, 2011.

Jul 3, 2010
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2. ### t_n_k AAC Fanatic!

Mar 6, 2009
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One first needs to know the range of the input signal at 'IN'. You'll possibly note the 10k pot wiper range (to comparator (?) pin 6) is from +6V to -6V indicating the input 'IN' may lie somewhere in this range.

3. ### SgtWookie Expert

Jul 17, 2007
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The triangular symbol is used for both comparators and opamps, so without part numbers, it can be difficult to determine what was used in the original schematic. However, many common comparators have open-collector outputs, which means that they can sink current, but cannot source current; so a pull-up resistor on the output is required. With that in mind, your circuit most likely used an opamp instead of a comparator - even though the function is that of a comparator.

Reducing the supply voltage means that you'll need to be more selective of the opamp used; it will most likely need to be a rail-to-rail type. D1 should be replaced with a Schottky diode like a 1N5817, as the Vf (forward voltage) will be ~1/2 that of a standard silicon diode. The 20k resistor on the base should be reduced to 10k Ohms; but the actual base resistor will need to be calculated according to what the collector current is, which is the relay coil current.

There is no "flywheel" diode shown for the relay coil. Although C2 will slow the turn-off time of the transistor, a flywheel diode should still be used; if C2 fails, the transistor turn-off will be rapid, and the resulting spike will destroy the transistor.

4. ### mpatterson557 Thread Starter New Member

Jul 3, 2010
21
0
In is signal from a audio device that usually outputs to a headphones,
IE MP3 or the like

After reducing the voltage I would like to replace the relay with an electronic component.
The end result is that when the circuit activates I would like to electronically disconnect the IN2 from the OUT and connect IN to the OUT.
So with this in mind is it still recommended to replace the c2 with a flywheel diode?

5. ### mpatterson557 Thread Starter New Member

Jul 3, 2010
21
0
Thanks all for yopur advice. Will continue to work more on this project.