-5V converter Bandido II uMax

[Nepumuk]

Hi !
I'm trying to build the Tesoro Bandido II µMAx, but now a question has occured. I hope someone of you can help me. The -5V converter I have build has only an output of -3V . I have checked the circuit several times, there is no wrong connection in it. On the other hand I've used BC546 and BC557 as Transistors, but i think that doesn't matter.
I think the problem is that one of the switching Transistors is connected to +5V , when the transistor is connected to + 9V I'm getting an output of -6,3V. When the transistor is connencted to a supply of +5V I think it is not possible to get an output of -5V because of the losses at the transistors and diodes. What do you think, am I wrong?

Best regards

Nepumuk

[Nepumuk]

Sorry I've forgotten to mention that I've used Carl Morelands Schematic.

Best regards

Nepumuk

[kt315]

> when the transistor is connected to + 9V I'm getting an output of -6,3V.

good decision. with this connection you can try to use 79L05 instead T7 and get really -5 V.

[Nepumuk]

Thanks for your reply, but does this mean that I'm right and the supply only delivers -3V? Doesn't this effect the correct working of the operation amplifieres, because they need a symetric power Supply ( +5V/-5V) ?

Best regards

Nepumuk

[kt315]

you are right, certainly. they need the symetric power Supply ( +5V/-5V), but they can function on slightly unsymetric voltage. in this case if you need in maximum amplitude from preamp, you may get off one-side amplitude clipping.

[kt315]

you can try to use a voltage tripler as you see here. in this schematic you must invert all capacitors' and diodes' polarity for negative output voltage. use 7905 or 79L05.

[Nepumuk]

Thank you for your idea, I'll try it out.

Best regards

Nepumuk

[Carl-NC]

Thanks for your reply, but does this mean that I'm right and the supply only delivers -3V? Doesn't this effect the correct working of the operation amplifieres, because they need a symetric power Supply ( +5V/-5V) ?

Yes, the Bandido inverter only supplies about -3v. No, the opamps don't really need symmetric supply voltages... depends on the design of the circuitry. The opamps will run quite happily on +5V/-3V; the lower negative voltage might limit signal swing or something else, though.

- Carl

[Ulf]

> when the transistor is connected to + 9V I'm getting an output of -6,3V.

good decision. with this connection you can try to use 79L05 instead T7 and get really -5 V.

Hello

This will only work if the voltage at R5 and R6 will also swing from 0 to 9 V. For that you have to increase the voltage at the output of the 4024 by an additional transistor with a pullup to 9V.

Ulf

[Siliquae_Sid]

Gash Tesoro design again.. OMG these guys need to get some REAL Engineers in who know what they are doing!!

Carl is right, the op-amps don't need a symmetrical supply, but it helps on large signals (and small signals too). Stops saturation in the negative region on large, and helps with the overall noise figures.

In my design, I ran the supplies off the Tx oscillator which gives out >20V pk-pk. a simple full wave rectifier then gives a + / - 10V for the supplies, and the battery life MUCH impoved. The whole things draws 2mA at full tilt from a stack of 8 AA size 2200mAh Ni-Mh's and gives a phenomenal 70 hours of batterylife. The whole things works down to "almost flat" batteries too as I have used a bootstrap system in the Tx power supply. The Tx generates it's OWN supply, and by clever (?!?) design brings itself and all the other supplies up in under 2mS. It's also a regenerative system hence the massive increase in battery life.

I'd love to post the design, but it's in the patent office as we speak.

[Bojidar]

Hi Nepumuk I use that shematic and don't have problems with supply You can use a single supply op.amp (like TLCxxx) and wih small changes in shematic will work,but noise performance are better when use split supplay.
Only for generator you need high-voltage(around 12V),because you need from high amplitude in TX coil.Use high performance rail-to-rail,low noise op. amp in recive section and will not a problems. All the best

[khuben]

Hello friends! do not bother with the bull**** negative voltage use 7660 or 7662
These kovvertori have almost 100% beneficial actions and