#837

Episode 837
I make a voltage regulated boost converter using an NE555 timer IC. Not a great circuit but gets the idea across
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[@davidsmith9063]

This is extremely clever. I really like this topology. We can all do fancy/fast up/down timer PWM but this is just clever, and a great use of a simple circuit. I always listen to you when I'm at my bench building, but this one made me stop and build it, which I did. 🤓 Excellent!

[@zaprodk]

I built a 180V boost converter with a 7555, for powering nixie tubes. It's been running for years now, still very stable and functional :)

[@Enigma758]

Is it open loop, or did you find a way to have feedback regulation as per the video?

[@zaprodk]

@@Enigma758 Feedback ofc. Open-loop wouldn't do with varying load. Instead of the 1N7000 i'm using a NPN BJT in that place.

[@alexstone691]

Do you have a schematic, im quite interested

[@zaprodk]

@@alexstone691 Google it :)

[@PhattyMo]

I rigged up a very similar circuit for about 200V output,with a TL431+pot in place of the 2N7000. It worked quite well.

[@gkdresden]

It works with a mix of pulse width modulation (at higher voltages) and pulse frequency modulation (at lower voltages).

[@ChrisSmith-tc4df]

Low-sophistication offline switchers use an optocoupler with a zener diode in series with the LED to set a stable regulation point, but they are essentially "digital" feedback as well.

[@d614gakadoug9]

It depends on what circuit you are considering, but you can get good, stable linear feedback with an optocoupler and a zener. It is crude in comparison with using something like a TL431 instead of the zener, but it does work.

[@lmamakos]

The 555 device in the analog world seems like a NAND gate in the digitial world - with enough of them, you can build anything.

[@bayareapianist]

I have never been a fan of 555. Ever. Whatever you want to do with a 555 you can do it with a couple of cmos gates or Schmitt triggers. I did a lot of PWMs and VCOs using logic gates. I was happier not to learn the internal of it, but now how it works seems to be very trivial for me. On the other hand, LM723 was designed just for PS which has similar stuff and has a kind of accurate voltage reference.

[@robinbrowne5419]

Another cool use for the 555.

[@ruhnet]

Cool stuff and very clever! You'll turn the 555 into the DC-DC converter "standard" before it's over with hehe 😄

[@lonniehutchinson4310]

Hit and miss boost converter. Good enough for farm work!

[@IMSAIGuy]

You got that right!

[@gkdresden]

You can damp the oscillation by use of a snubber network and / or a recovery diode.

[@d614gakadoug9]

That magnitude of ringing is horrendous. My guess is that the circuit is very crudely built, has no local capacitance on the input supply and is using an ordinary diode instead of a fast one - note huge spike at turn-off of the FET.

[@youtuuba]

Pretty much the same idea as the old gasoline "hit-and-miss" 1-cylinder engines. An occasional 'pop' puts enough energy into a large flywheel (from which the load is taken), and when the flywheel speed drops below a certain threshold, a centrifugal switch allows the spark plug to fire, resulting in another 'pop', more energy back into the flywheel, whose speed increases, so the centrifugal switch cuts off the spark again. On light loading, you only get occasional pops, on medium loading you get slow, regular pops, and on heavy loading you get frequent, regular pops, approaching a normal gas engine operation. There are seemingly limitless variations of 555 circuits. I saw one clever example in an early Heathkit budget DMM, where pins 2 and 3 were swapped in what would otherwise be a normal monostable oscillator circuit. The push-pull output on pin 3 was used to operate the RC ramp-generating sub-circuit (instead of pin 2), and the open-collector output on pin 2 was used, with a pull-up resistor, to generate the output waveform. The advantage was that with pin 3 adding current into the RC network while 'on', the duty cycle could be modified in a specific way that would require another one or two parts to achieve by other circuits, hence a small cost savings.

[@gkdresden]

In the regulating mode you can also use 50 per cent duty cycle and connect pin 2 and 6 across a resistor to pin 3. You don't need pin 7 anymore. Instead of the MOSFET you can also use a BJT (BC547 or 2N2222) to control pin 5. In this way you get a reference voltage of 0.65 V instead of 1.2 V.

[@imadnehme4773]

I did the same but also used pin 5 of the NE555 for feedback.

[@jdmccorful]

Cool, what could we use it with? Interesting! Enjoyed watching.

[@dwinurrizkia61]

This great and real schematic,...to control output use pin 5 of ne555

[@TheRetiredtech]

Help a lot to know what loads you are talking about. Cool demo

[@TechwithHari]

I have a doubt Can we put in that feedback to the reset pin instead of control voltage 😅? Will it still work the same?!

[@pir869]

Do you know what frequency the 55 was running at,most of the dc-dc converters using a 55 as pwm controller have 100uH inductors,but from what i see the pwm of around 100Khz boost controller uses 100uH but these are usually quite large,higher Fhz use smaller value and smaller physical size inductors. This circuit you made then has a Fbv of around 1.2v,so if the fhz is raised a more compact smd version could or should be viable,even making the frequency variable would set a good teaching platform. The cutting off is called pulse skipping,which would be best done with higher frequency time base ,for audio use in case the skipping of pulses lowers the pulse rate into the audio spectrum.

[@alexstone691]

As i can't really get switching regulators easily, how bad is it? if i place a linear regulator after it would the output still suck?

[@rjordans]

My first guess it's that the 1.2 volt reference is not very stable. It will change from component to component and with temperature. You can indeed compensate for this by aiming high and dropping with a more well defined regulator after it. Besides that, the current version looks quite noisy but that could be sure to the way it's constructed. Make sure to add some more capacitance on the input side too though, that is currently unbuffered.

[@alexstone691]

@@rjordans As im pretty sure this could be used as a buck converter as well, i was thinking of dropping most voltage with it and then actual regulation probably done using discrete linear regulator to get a pretty efficient power supply

[@rjordans]

@@alexstone691 that would work fine probably. You won't get any fancy protection for thermal of story circuit but it should give you a nice working circuit indeed

[@peterkis4798]

@@rjordans In theory you can use a TL431 instead of the the FET.

[@rjordans]

@@peterkis4798 That would help indeed, it will give you a higher reference voltage as well (2.5V) but that shouldn't give much problems

[@threeMetreJim]

Pulse skipping, pretty much like a 34063, which isn't too far off from the 555 in sophistication or vintage.

[@plugplagiate1564]

from me there you get a half thumb up. pulse is a timeless instance, switching off the whole 555 is disturbing, and finaly, the coil produces a kilovolt signal. there is no cheap diode that can withstand it.

[@IMSAIGuy]

I don't understand your comment on switching off the whole 555. it is on all the time. I don't think 1000v is generated but if it was a simple 1N4007 is very cheap. this was a teaching aid circuit. the real circuits will use a nice Schottky diode for fast switching times

[@bayareapianist]

Don't you also need a high voltage FET for switching?

[@nickcaruso]

Could you talk about why it’s a bad circuit?

[@glasslinger]

There are numerous low cost 3 terminal switching regulators that work much better.

[@alexstone691]

@@glasslinger I have no local retailer that sells switching regulators (i think they have few ancient ones that are 10x the price), so i am really interested why this is bad

[@glasslinger]

@@alexstone691 Are you in the USA? Google Mouser Electronics, or Digikey. You can get virtually any component from them in the mail. I use Mouser all the time. They are the "Amazon" of electronic components!

[@alexstone691]

@@glasslinger No i am not, shipping is really expensive for all distributers (>20e if they want to ship at all)

[@odissey2]

@@alexstone691 buy on eBay or AliExpress any $1 DC-DC converter and de-solder controller

[@mattmiller220]

Don’t even know the values of your various parts. 🤦‍♂️