Why don't we use 555 for voltage doubling/negative voltages?

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frequencycentral
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Post by frequencycentral »

FACT: The go-to devices for +/-9 volts from a 9 volt supply and +18 volts from a 9 volt supply in stompboxes are MAX1044, TC1044, LT1054 etc...........

The humble 555 appears capable of performing both these roles.

Here's the voltage doubler link: http://www.circuitsonline.net/schakelin ... ne555.html

.....and here's the negative voltage link: http://www.circuitsonline.net/schakelin ... ne555.html

The text is in Dutch, so you'll need to use Goggle's translation feature, but the schematics are in the international language of electronics.

Both the linked circuits run at around 20kHz, if whining occurs (like in an unboosted MAX, or an ICL7660) it should be possible to lower the value of the timing cap to get the 555 oscillating at a frequency higher than human hearing.

Compared to a dedicated charge pump chip, the additional parts count is negligable, and the 555 is very cheap and possibly to most plentiful chip on the planet - and unlikely to go out of production any time soon.

I was actually re-reading that post to see if there is a way to get a negative voltage from a 555 already set up as an SMPS, I'll have to do some experimenting there.....

Maybe it's also possible to use additional voltage doubling stages to get higher voltages too?

So.........why are we using MAX1044, TC1044, LT1054 etc to do this job, and not NE555? I know there are issues with 555's crowbarring the supply - but this can be worked around pretty simply. Additionally, 555's are used in a few stompboxes already, eg, Crash Sync, Uglyface.

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Post by cpm »

i have tried a charge pump with the 555.
it worked fine but it was short of current output for my project, neither was a max1044, so i guess both implementations are at the same level (i finally used lt1054)

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Post by frequencycentral »

AG's schematic is interesting.

I just successfully added a -12 volt output stage to the 555 based SMPS I'm using for my submini tube amp experiments. Actually, just a touch under -12 volts, more like -11.7 volts. Just two 10uF caps and two 1n4148. That's cool! Now I need to add some more stages to it to get to around -33 volts to negative grid bias my 5902.

Also, if I can work out a 555 charge pump that delivers around 80 volts at the same current as a MAX1044 I'd be a happy man.

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Post by frequencycentral »

frequencycentral wrote: Now I need to add some more stages to it to get to around -33 volts to negative grid bias my 5902.
Target achieved: viewtopic.php?f=2&t=7747

frequencycentral wrote: Also, if I can work out a 555 charge pump that delivers around 80 volts at the same current as a MAX1044 I'd be a happy man.
Not having success with this target though, just fried a 555. :(

Any suggestions on how to add multiple doubling stages?

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Post by DeanM »

ibodog2 wrote:http://analogguru.an.ohost.de/193/schem ... iplier.gif

Analogguru covered this here somewhere at one point. I actually just did a vero layout for the circuit above but haven't tried to build it yet to see how well it would work for projects I'd like to try.
Has anyone built this circuit? Or used the 555 in this kind of application before?

I built it and its behaving oddly. I measured the outputs and they were perfect. +17V & -16V (or there abouts anyway). the next time i measure it tho the outputs changed. the positive rail is stil up around 17V. but the negative rail has halved and is only around just under 8V. Has anyone seen this happen before?

I put the circuit together in LTspice (file attached) and the output at pin 3 it says should be a 9V squarewave which it is.the junction between D3 and D4 in the simulation shows -9V squarewave which there is also. at the junction between D4 and D5 the simulation shows there should be -9V DC but there isnt! between D5 and D6 there should be a 9V squarewave sitting on top of the 9VDC so swinging from 9V to around 16V. but because there is no 9VDC it swings from 0V to 9V. so basically something is not right around D5 and C7. Its not holding its charge for some reason but i cant see or think why. I actually removed them from the circuit and the output didn't change. so its like they are not even in the circuit. Its really wierd.

Any ideas?
Cheers,
Dean

PS: caps are all oriented properly as are diodes.
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Post by DrNomis »

DeanM wrote:
ibodog2 wrote:http://analogguru.an.ohost.de/193/schem ... iplier.gif

Analogguru covered this here somewhere at one point. I actually just did a vero layout for the circuit above but haven't tried to build it yet to see how well it would work for projects I'd like to try.
Has anyone built this circuit? Or used the 555 in this kind of application before?

I built it and its behaving oddly. I measured the outputs and they were perfect. +17V & -16V (or there abouts anyway). the next time i measure it tho the outputs changed. the positive rail is stil up around 17V. but the negative rail has halved and is only around just under 8V. Has anyone seen this happen before?

I put the circuit together in LTspice (file attached) and the output at pin 3 it says should be a 9V squarewave which it is.the junction between D3 and D4 in the simulation shows -9V squarewave which there is also. at the junction between D4 and D5 the simulation shows there should be -9V DC but there isnt! between D5 and D6 there should be a 9V squarewave sitting on top of the 9VDC so swinging from 9V to around 16V. but because there is no 9VDC it swings from 0V to 9V. so basically something is not right around D5 and C7. Its not holding its charge for some reason but i cant see or think why. I actually removed them from the circuit and the output didn't change. so its like they are not even in the circuit. Its really wierd.

Any ideas?
Cheers,
Dean

PS: caps are all oriented properly as are diodes.

It may be that D5 and D6 might have gone open-circuit, have you tried replacing them with new diodes?, also check to see if the diode polarities are correct too.... :hmmm:
Genius is not all about 99% perspiration, and 1% inspiration - sometimes the solution is staring you right in the face.-Frequencycentral.

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Post by DeanM »

DrNomis wrote:It may be that D5 and D6 might have gone open-circuit, have you tried replacing them with new diodes?, also check to see if the diode polarities are correct too.... :hmmm:
Nope they still measure normally. all caps are correctly oriented as are the diodes. it WORKED! voltages were correct and then i checked again before adding any new circuitry and the negative rail had halved! It could be the bread board! its an old one and is a bit dodgey lookin! and i think underneath the holes there is nothing separating the leads from shorting if pushed in too far. I just did a test....shoved a capacitor leg in and it went in up to an inch!

thanks for the suggestions tho.

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Post by DrNomis »

DeanM wrote:
DrNomis wrote:It may be that D5 and D6 might have gone open-circuit, have you tried replacing them with new diodes?, also check to see if the diode polarities are correct too.... :hmmm:
Nope they still measure normally. all caps are correctly oriented as are the diodes. it WORKED! voltages were correct and then i checked again before adding any new circuitry and the negative rail had halved! It could be the bread board! its an old one and is a bit dodgey lookin! and i think underneath the holes there is nothing separating the leads from shorting if pushed in too far. I just did a test....shoved a capacitor leg in and it went in up to an inch!

thanks for the suggestions tho.

No worries, if the cap lead went into the breadboard an inch, that does suggest that the breadboard itself is the cause of your problem, if you wire a 555 IC as a 60kHz square wave oscillator, then use 3 gates from a CD4049, wired in parallel with each other, as an output buffer, you should be able to use it to easily drive a voltage-multiplier circuit made up from diodes and capacitors, go to PAIA.com, and download a copy of the Stack-In-A-Box Tube Preamp, if you have a printer, make a hard-copy printout of the schematic, now have a look at the schematic and note how the +42V supply for the tube is derived, paying particular attention to the diode-capacitor network, that's called a Voltage-Multiplier, by adding more diodes and capacitors, you can increase the output voltage, just make sure that the voltage-rating of the caps is greater than the wanted output voltage though.... :thumbsup
Genius is not all about 99% perspiration, and 1% inspiration - sometimes the solution is staring you right in the face.-Frequencycentral.

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