Hi
Use a ICL7660 or similar voltage inverter.
Klaus
I like to do it discrete, so please do not suggest me ICs dedicated for the purpose
Sure, please read my post, I said to replace this 555 with a discrete multivibrator. Maybe I was not clear enough though.Just curious but a 555 timer is not a discrete circuit....
Last post needs > 5V for source, USB constrained to +5V, so maybe
thats not a workable solution.
Regards, Dana.
Although interesting, this uses +12v for the input and I have +5V from the USB port. If I had 12v, I could make it easily with a potential divider and a floating ground.3-transistor SMPS negative regulator
Bo Nielsen's 3 transistor negative SMPS regulatorwww.romanblack.com
Now that you mention that, I remember I have something like this in my site **broken link removed**I would suggest a single transistor oscillator using a transformer to produce the feedback and voltage for the -5V rectifier. Some of the negative output can feed back to the transistor base to regulate the output voltage. the transformer can be a small ferrite core.
Brian.
Hm... I do not think the am7910 datasheet goes as deep as this, it just assumes the voltages. However the negative rail current is only a fraction of the positive, meaning that not all circuits inside the chip use it. Well I can test this, first feed the positive and then the negative and see how it behaves.One of the challenges you face is power sequencing and the loads connected
to +5 and -5. So make sure your downstream loads can tolerate the starup of
the multivibrator startup while +5 already presented to loads that need split
supply.
Regards, Dana.
I think you will find any single device (computer etc.) with two USB ports has a common ground between them.Another thought is to use two USB ports and connect their power pins in series (for a floating ground) although I do not like to mess with it.
I see...I think you will find any single device (computer etc.) with two USB ports has a common ground between them.
Personally, I would forget the charge pump idea. Unless you use active switching you should expect at least two diode drops lower output than input and probably even less. You could make a voltage trippler then regulate down but remember that 3 x voltage also means 3 x input current.
Brian.
A multivibrator can be made with quite low collectors resistor values in the range of 50 ohms without heating a transistor as the 2n2222 and allowing for quite high output current, definitely something more than 15mA. A multivibrator running from 5v with such low resistor values should be able to provide almost a full swing 0-5v. How about a Modified Dickson charge pump after that, (like the one attached) but for negative polarity (just invert the diodes is enough???). All we need is something like 15-20mA and something like -8V so that we can then regulate it to -5v with a 7905The current capability is a factor of several things but I doubt Roman's limit is calculated, more likely it is just the maximum he could draw before the feedback could no longer keep the voltage constant. You might find you can get a little more by letting it oscillate at its natural frequency instead of C1/R4 deciding it.
Incidentally, Q2 not only provides the feedback to make the oscillator run, it also starves the base current in Q1 to provide the regulation. If you take the feedback from a transformer winding instead and generate a negative output voltage, you can use that output voltage directly to pull bias off Q1.
Brian.
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