NE555 voltage doubler

[gtudoran]

Ok guys,  a little insight on the 555 based voltage doubler.
So today i had some time to do some tests, which turned out quite nice.
For an input voltage of 9V i've managed to put out ~15V under 18K load and almost 16V under 100K load.
Part of the noise is from the fact that was made on a breadboard and high-frequency and breadboards ... well they do like each other.
Here are some pictures from the experiment.
Any questions and comments are welcomed.









Regards,
DeX

[duck_arse]

ok, I'll go - are those ripple pics of the Vcc? can you do a Vcc spikes comparison with a 7555, or is that right out?

and people will ask about ground layouts and tikkkking, but I won't.

[gtudoran]

duck i will try to give you the answers:

- keep in mind that the spike is recorded @ 5mV / div(and they are following the switching signal) so in reality is very small and the reason that is there is the fact that the circuit was on the breadboard and the power pins of the 555 were not decoupled (i do not have a 7555 so .. i can't test it with it)

- what ticking ?! the switching freq. is over 44KHz  in this case, but made some experiments with freq. over 60KHz so if you are not a dog everything should be fine.

Regarding the layout, yes some cations are needed but nothing fancy, already designed it and working like it should.

Regards,
   DeX

PS: the rectangular signal is a totally different signal / on the oscilloscope there are 2 different signals one is DC and the other is the switching one, explanations are written on each picture)

[armdnrdy]

I'll dare to ask:
Why reinvent the wheel when you can use a charge pump?

[R.G.]

Well, one reason would be more current and voltage capability than the existing charge pump chips; another would be sheer cussedness.
OK, I meant 'a fervent desire to experiment and see if you can'.   

However, this is much like the old joke - how many guitarists does it take to screw in a light bulb? Eleven; one to screw in the bulb, and ten to say how they could do it better and faster.

The 555 is a great chip, very flexible - and noisy. And it's quite difficult to get a 50-50 duty cycle out of it. Fortunately, a charge pump like this one can work with any source of rectangular waves. The CMOS versions of the 555 are a quick step forward, and eliminate much of the shoot-through noise on switching. This is not trivial. Some 555 circuits will shoot-through currents in the low amperes for a very short time each switching edge.

Another improvement would be to ditch the bipolars for switching devices and go to MOSFETs. An N-channel and a P-channel MOSFET in the TO-92 package would offer currents up to about 1A for the switching devices, and both switch faster and use less wasted power in the drive circuits. They would also switch up to about 30-40V reliably. This is probably not an issue with such a homebrew device for working from 9V, but might be in other applications.

Finally, there are a number of 8-pin switching control chips that will up-vert using just an external inductor, Schottky diode and capacitor. Some of them require an external MOSFET, but will produce amperes of output current or quite-high voltages, up in the vacuum tube plate voltage range.

[gtudoran]

I'll dare to ask:
Why reinvent the wheel when you can use a charge pump?

@armdnrdy as RG said for the sake of experiment, because it can be done and because it performs way ... way better then a charge pump chip especially in terms of noise because i can go with the sw. freq. up up in the sky. Also if my memory serves well is a little bit better also in therms of efficiency

@RG thank you for your intervention, indeed a pair of MOSFETs would be a better choice but, if you can believe that, didn't have a pair of complementary MOSFETs available
Regarding the use of a PWM (SMPS) controller it is indeed the obvious choice. Better, faster and easier to build we are entering in the SMPS domain

[armdnrdy]

Gotcha.

Without any of the OPs requirements mentioned...I was thinking along the lines of "normal" stompbox circuit use.

[gtudoran]

It can be used in any stomp-box design without any problems, in fact that was the main reason

Best regards,
DeX

Gotcha.

Without any of the OPs requirements mentioned...I was thinking along the lines of "normal" stompbox circuit use.

[anotherjim]

Nothing wrong with producing a circuit that uses parts many probably have already. For a one-off or experimental project -  being able to build it now is far more important to me than circuit efficiency.

I've yet to need a supply doubler, but if I did I can build this one now without having to wait for any parts

[PRR]

> Some 555 circuits will shoot-through currents in the low amperes for a very short time each switching edge

And IIRC, an original-recipe '555 can output 200mA either way.

16V in 18K is just 1mA.

That's 2mA from the 9V side.

*If* that were an original '555, it would seem the NPN+PNP buffer is not needed, and is losing 0.6V both sides, wasting-off 1.2V. Might be that a true '555 would give >17V (whoopee). And avoid 8 pins.

I know I have seen heavier loads off a CMOS hex inverter and some diodes. Like 35V at a couple mA. And CMOS tends to have less shoot-through ('555 has an unbiased hi-current totem-pole, CMOS only has small current). As RG says, a jackhammer in the box can be a pain to muffle.

[duck_arse]

I'll dare to ask:
Why reinvent the wheel when you can use a charge pump?

what's the type number of the 555 that dies with 0V5 too much supply voltage again?

[edit :] poorly worded but you get the drift.

[gtudoran]

@duck: Hhahaha that is true ... actually the 555 is quite tolerant in terms of supplied voltage.