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5v and -5v from 9v? Answered

How can I get +5v and -5v from a single 9v PP3? Not 4.5v, I could do that easily with a voltage divider. Preferably using only passives and discretes (Inc. voltage regulators)?


For a 7106/7 ?


Hey, do you think you could check my circuit for me? You seem to know a lot about the 7107. I think I have it sorted now, with the power supply, the input, and the outputs, and common anode LED displays. The 74HC02 I used is the same as the 4009 suggested in the datasheet, but it is the same (hex inverter). The input is going to be from 0v-400mv, and the datasheet said the schematic is for a 0v-200mv input, but it looks looks I can just adjust the potentiometer. Here is a larger image.

Digital Thermometer.jpg

You'd be better using an LCD rather than LED if you're going for battery power - LEDs are a killer for it, even if you use HE ones.

You're right, you should get the adjustment range you need without too much difficulty. Of course, you might be able to adjust Vin to be in the range of the output of the LM35 directly....


Yea. also, after looking at the datasheet again, it looks like it is supposed to work with common anode LED displays, is it possible to use CC?

No, if its CA you need, making it CC is a LOT of trouble.

From the datasheet

ICL7107 Power Supplies
The ICL7107 is designed to work from ±5V supplies.
However, if a negative supply is not available, it can be
generated from the clock output with 2 diodes, 2 capacitors,
and an inexpensive lC. Figure 10 shows this application. See
ICL7660 data sheet for an alternative.
In fact, in selected applications no negative supply is
required. The conditions to use a single +5V supply are:
1. The input signal can be referenced to the center of the
common mode range of the converter.
2. The signal is less than ±1.5V.
3. An external reference is used.

Thanks, I didn't see that part. I guess I'll have to get some common anode 7-segments then


7 years ago

There are different (I think it was called) rail splitters for one or two 9V batteries for CMoy headphone amps.
I'm not that much into electronics but was looking for a headphone amp before I got to know that european iPods have an 83dB restriction built in.
Since I took that off, the volume level is high enough for sufficient in car use with my poor stock car audio.

But they discuss the different power supply options for the amp here:
and it seems to be what you're looking for.

An ICL7106/7 can be run with 9V, according to the PDF here: http://kitsrus.com/pdf/7106.pdf

But anyway, running a device with an LED display from a PP3 will not result in a long battery life. Can you use a LCD instead?

Getting +/-5V (and thus 10V from + to minus rail) from a single 9V is not possible without some switching circuit and some inductors (coils).

And, remember that the 9V printed on a 9V battery is only a nominal value. It will have a higher voltage when full (new) and degenerate while discharging.