Classic Circuits You Should Know: Transformerless Power Supply
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- เผยแพร่เมื่อ 4 ม.ค. 2021
- Classic Circuits You Should Know: Transformerless Power Supply
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in this video we take a look at the transformerless power supply also known as the capacative dropper. This PS is a simple way to get low current DC power from AC mains. But, be careful. Playing around with AC can be deadly. If you don't know what you are doing you should not attempt this circuit.
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May I suggest that if anyone wants to play with these circuits use an isolation transformer. Which a Variac is NOT. But you can use them together to isolate first, then control the voltage.
You can still get hurt touching both AC leads at the same time, but a much much smaller chance of injury from touching either side while being grounded.
if you touch the neutral nothing happens
if you touch the hot wire (black) and you are grounded, electricity flows from the wire into you into the ground and you die
Thanks for the video, but I wish you’d explain some of the operation. Maybe looking at the waveform at each stage and showing how it changes
I promise to just watch and keep both hands behind my back.
I like the Bana Jack modification you did on the variac, I have the exact model.
I liked your design. I was just trying to make a half wave rectifier with no input transformer yesterday.
Nice one. Happy New Year Paul.
Yesterday I disassembled a rechargeable LED bulb 💡. The circuit was made with 335j 400V drop cap, 244 SMD bleeder resistor, MB06S Bridge rectifier, 100uf 50V E-cap, 2x SS14 SMD schottky diode as anti back-flow, D965 transistor to drive LED panel and 621 SMD resistor to supply the base current to the transistor.
LED bulb was claimed to be 125W, it can be used as a normal AC LED bulb or DC emergency LED bulb (there's a switch DC-OFF-AC). The brightness was same with AC or DC. I measured the current consumption of the LED, it was 1A @ 3V. But as soon as I removed the battery (4V SLA), the LED lights went dim, now it only consumes 180mA @ 2.6V when runs on AC. Now even if I connect the battery it doesn't have the same brightness as before, but when it runs on battery it works normally.
I have no idea what went wrong, could you please help me?
Very cool and handy circuit. Thank you
HAPPY NEW YEAR PAUL... BTW THIS LOOKS VERY MUCH LIKE AN IMPEDENCE CIRCUIT LOL...THANKS FOR THE WORK ... KEEP IT UP
Heard of the circuit, never seen it laid out on breadboard...very informative!
would you explain calculations for this circuit? Thanks
It's good to see you and your work again. How is the old ticker doing now days (I hope well)? Me, I've been to Pluto and back working on antique radio restorations and reading up on Tesla & "Practical Guide to free energy" pdf of late. Admittedly sometimes we forgot over the years those tidbits in electronic basics we all need, and yet here you are. I like your approach (take) on a transformer less design, Hobart used something similar on their intended for 'commercial use' 'restaurant type built coffee makers' to power their displays some few years ago. Again, enjoy the video and design. Best wishes and Happy New Year
love these episodes. thanks, Paul
Very interesting, thanks for sharing.
How durable is a setup like this compared to the older style heavy power bricks power supplies (wall warts) ?
Thanks for your clear explaining of how this all works!
I bought a pzem-004 current sensor that uses this circuit to power its self, wasteful it is. I need 30 of them so i what to figure out how to power them more efficiently.
You rightfully warn that this is a dangerous circuit so i want to know precisely how it works before i start pickup the soldering iron on this.
Nice video! How much current should we expect from this circuit?
Good Content. Thank you.
You find these kinds of thins inside motor speed controllers for vacuum cleaners etc to drop the voltage down to what the pwm IC can handle . You will also find that the speed control potentiometer is made of plastic so you don’t get electrocuted !
Far safer for the home hobby guy to use a switch mode supply or a transformer based supply but it is good that you have shown this type of circuit so they can identify it and know to leave it well alone !
Good stuff as always
thank you for the video! very interesting circuit
Hi , is there any simple coil designs to construct a step down transformer??/to utilise single digit - Ac voltages
thank you!!!
What was the value of the first filter cap after the bridge?
Tip for beginners, isolation transformer and/or GFCI. Use them, might just save you from cooking.
does the size of the dropper capicator govern the output voltage?
What is the voltage before the Zener diode ?
Great videos love them
sir , can you make a video on voltage multipliers . thank you in advance
The first capacitor input no transformer power supply I encountered was in a Heathkit photo cell annunciator system from the 1970s.
So can the voltage be changed by selecting an appropriate Zener? Anything else needed?
it has become popular recently in my city, but I couldn't find more information about those capacitors, dropping value and etc. ....is there anything you have got...? any manual or something else about it...?
Really Classic i like it Sir. 👍
Hi learnelectronics! A few weeks ago, I got myself a PS-3010F Powersupply from Kaiweets and I saw that you also have one. Now, I have a question about this power supply. Is there a current limit featue? Everytime I try to set the current, its jumps into CC mode and setting the current knobs for CV mode doesn't work for me at all. Please help!
I now feel like this power supply is Cr@p and I should get a new one where I can limit the current.
I can imagine it is useful if you want to make a timer for light, in a switch. Its cheap and you don't need a bulky transformer behind the light switch in the wall.
Awesome!
Yeah I’m glad to know how to build this circuit, but man I will not use it. I know that theoretically it’s fine and safe but all I can think of is what happens if something fails open. Great video Paul, thanks for stressing the danger behind this one.
I am looking to make a 1.5v battery eliminator for a wall clock which happens to have a 120v socket right behind it. I am getting tired replacing the battery every few weeks (or swapping out a rechargeable). The circuit needs to be small and low profile to fit behind the clock. I like the clock (smooth second hand no ticking) otherwise I would get one designed for direct AC power. I was even thinking using a mini USB charger and dropping the 5v to 1.5 with a resistor divider - current should be low less than 50ma I would imagine but I will have to check that. Any ideas? I could use your example but any solution would have to be reasonably safe (insulated mains side). Update - looks like it draws less than 1 ma as my PS show 0.000A - measuring with my DMM - less than 1ma at about 0.8 ma peak (varies between 0.6 and 0.85 ma @ 1.5v
Is it possible to use the output from a display driver to drive a thermal inkjet printhead? Using the gate driving and source driving outputs in a multiplexing array seems to be pretty much the same circuit as the one in a printhead. The voltage seems to be correct with many going all the way to 30v p-p and the mA per source pin seems about right as well with up to 5-8mA. I am just not sure if the combined current output would be enough with so many firing at the same time.
A piezo printhead would not be possible most likely because the voltage is too low except on the LED driving pins but then there are better options because there are so few backlight LEDs.
I also considered Plasma TV drivers but they are harder to find datasheets for and the chips themselves are hard to buy new since no one makes plasma TVs anymore.
😎. Cool cheers and happy new year to all..
just a query, at 4.41min where is the output of the first diode connected? I want to make a 20led string of rgb leds and was thinking this is a better way to power it than going out to get a ph charger and muck around with extra leads and sockets, but I can't see where the diode is connected
How is this different from the earliest form of dc voltage production I studied, and handled, many times; with a 35W4 (vacuum tube; of the All-
American Five Radio) rectifier. Admittedly, it would only supply about 600 mA at 140 V; more than enough to kill any person.
I handled that circuit many times with my bare hands; there were an awful lot of All-American-Five radio receivers built at that time. This period was between World War II (1945) and the proliferation of transistors about 1970 - 1980. I know transistors were developed in 1948, but they had to figure out how to build battery operated receivers with components designed for 150 Volts and 500 mA.
The first AM receiver that was transistorized that my family owned was built in 1961, long before they became popular, the problem was that you had to be prepared for the batteries to go dead about the 6th inning. And batteries were expensive, nearly $1 (in 1960 dollars, probably nearly $9 today.
This is certainly above my level of comfort and I have lots of respect of mains current
Great channel, just thoughts... short circuit current 100mA at 100V, power dissipation in the Zener 300mW, in the resistors 4.7W.
TKS SO MUCH DEAR
I don't think I quite have the confidence to start "playing" around with mains voltages just yet, so I'll give this one a miss for now. Just curious, though - in the U.K. the mains voltage is 240V, pretty much twice what it is in the U.S. - is it still possible to use this circuit here? What about the wattage ratings for the resistors, diodes and capacitors for the increased voltage?
I wasn’t sure it was the same guy until I recognized the sausage fingers. I wonder about how dangerous 120 v is compared to the actual power lines. I always thought 120 is no big deal as long as you don’t touch a live wire
So im new to this (actually getting back into it) I was wondering how you calculated the resistor value, are you calculating it based on the load at the output? Using ohms law it seems that the load you are shooting for would be 3.3 volts .200mA, am I correct or am I missing something?
Hi wanted to know if one could use this circuit to run a strip of back light 9 led's for a lcd tv? I have 6 rows of 9 led chips. The problem is when the led strips are connected to the main TV board it causes a overload. When I disconnect the led's from the main TV board the board works fine. So I'm running the led's off of 2 batteries. But the current draw is 3 amps and it kills the batteries out in 1 hour. So I'm trying to fined a circuit that will let me run the led's from AC but at 1 amp draw. So is there any way I can do this? Thank you.
Does a bread board have enough protection for line voltages? I thought the maximum voltage rating for a bread board was about 40 volts.
If I put a coil in series to the dropper capacitor, will I be able to get rid of the negative effects to the power factor, so the shift of voltage against current?
Should I do so?
Sure, the coil would have its own resistance due to self induction, so I'd have to make the capacitor drop less, so use a smaller one.
Right?
How's the ticker?
You should know how to make a circuit that kills. Yes, yes I should. What is an "X2" capacitor?
Nice video
Perfect natural selection diagram lol. Sry bad joke lol. Well done. I was actually hunting for something like this. I ran outa step down transformers lol.
Cool circuit. I would like to probe every stage and see what happens if I remove one. For example to see the difference between having a regulating stage vs not having it.
Definitely something more safely done in an online circuit simulator!!
Why is there a resistor in parallel to the capacitor?
It is to discharge it, when the power is cutoff :)
Another idea I had was the possibility of two diacs in the circuit vs 4 diodes.
I do not understand the use of both a 3.3 uF capacitor and a 470 Ohm resister in the beginning of the circuit. Is it the capacitor that "lets a little through" or the resistor? The resistor is too low value to be used just as a bleeder resistor. Does a resistor and a capacitor in parallel form some kind of tank circuit? 120V across a 470 Ohm resistor = .25A. 120V X .25A = 40 watt. You call for a 1 watt resistor. Obviously, I am missing something or making a gross mistake. Thank you in advance for your help. I am ready to build this circuit to drop 240V to 12VDC to a 555 timer circuit to engage and disengage a starting capacitor for starting a 3 phase motor on single phase. The timer part is working perfect. I would like to make my own power supply.
Instead of using the Zener Diode could you use an LM317 and regulate your voltage output?
yes
I know what the bridge rectifier does, and how electrolytic capacitors work, as well as resistors. However I am curious how these film type large capacitors actually reduce the voltage, I am curious about how it actually works to achieve this, so it somehow drops the voltage, this is incredible. I have tried to quickly research how it does this, but I cannot find a precise breakdown of how it actually is dropping the voltage, most websites just say that it's used to drop the voltage and don't explain how it does this. Inside the film capacitor are rolls and rolls of shiny film, I want to know what the high voltage source is actually doing when it enters the film capacitor.
I have learned that zener diode needs a resistor before zener. Why you have not used any resistor?
Always exciting to see dangerous projects. Hopefully their is a GFCI in the experimentation lab.
this may seem stupid but could you show an example of what one would touch to get shocked? of course with out the power on. dont worry im not going to attempt this as i understand nothing about this stuff but its interesting.
I think the 470 ohm resistors have to be about 4 to 5 watts. If input is 100 volts and each resistor is 500 ohms and we toss out the little Zener for a second, then we have to drop 100v over 1000 ohms in series. Current is 100ma. I squared * R means that quiescent power at each resistor is about 5w... Plus or minus 20 % :-). Or do I miss something?
This is a pretty interesting design. I never thought you could make a transformerless power supply. :D
Check out BigCliveDotCom's channel. He examines all manner of electronic devices, and many of them use this kind of power supply. Quite a lot to be learned from his videos.
It's a simple filter - using capacitive reactance. The math is pretty simple if you've ever done filters - most of us think of filters as working at least at audio frequencies. I've done a lot of those but this (classic) one still gives me the willies even though I know how it works. It just "feels" wrong when you've always worked with transformer-based droppers.
I'll add another vote for @bigclivedotcom because he's not just beautifully spoken with an awesome goatee and a wicked sense of humour, he's also a great guy. He also flambe's stuff. ;)
One of the most entertaining electronics channels on YT but I love this one too - both are different and both great.
@@marcdraco2189 i think i once made a voltage regulator that dropped it down to around 2 volts using a npn and a capacitor and the output capacitor being attached through a resistor to the gate and the output of the npn through a resistor to the positive lead of the capacitor which is also tied to positive with another resistor and it ended up getting around 2 volts out of 5 volts
@@marcdraco2189 also thanks for the nice comment that explains stuff well
Actually many circuits that are common in the industry have no transformers and work on mains voltages. Look up a common ldr circuit that turns on and off at night and day. Many use mains voltage with scr and triac and diac. Many related circuits use some similar methods of using mains to low power without without a transformer. But its a good little circuit.
Like standing on stepladder 3.4 high at the edge of a ravine 125 deep. The stepladder won’t kill you.
I guess if you would wanna try this in a safer way you could use an old bicycle dynamo (alternator) as the AC source.
As always, straight to the point. Many thanks. If you stand on a thick rubber mat, and/or wear a pair of rubber boots the electric will have a hard job going to earth.
Also using the one hand only rule helps too when working around HV circuits.
Cool, You could make more this kind of videos "Classic Circuits You Should Know:" :-)
If you don’t know what you are doing don’t do I t ! Excellent video
It should also be noted that some of the USB wall chargers can be very dangerous - people have gotten electrocuted while bathing and picking up their phone - one side of the DC out was connected to the hot side of the AC. Usually this happens with the el cheapo no name chargers but I would not use any device connected to these chargers while bathing or grounded. Some other u tubers did teardowns of many of these chargers and some have downright dangerous designs.
Looks like the 470 ohm & 47 k ohm have got interchanged locations.....the 47k ohm IMHO should be the " bleeder " res. across the series cap.. & the 470 ohm does the inrush current limiting..
I usually like your watch you videos but as a professional EE engineer this scares me. Especially when there might be less experienced people actually trying this. This goes against all safety design practices there are. When showing main voltage circuits I do believe that as a engineers we have a specific responsibility. Some comments I have on this design
1. Never connect mains to an open breadboard (yes I saw you were using an alternator which have some additional protection but you mean the circuit to be used connected to mains.) The maximum breaking current might go up to several 100A some ms before the circuit breaker kicks in which could be enough to have the BB explode in you face if you short circuit.
2. The circuit needs to be protected by a sand-enclosed fuse (not glass - again they could explode)
3. Good practice is to use a couple of MOVs as protection
4. Never connect a normal capacitor to mains directly, use safety-caps (e.g. X2 caps)
5. Use inrush current limitation (e.g. NTC SD15 or similar)
6. Also, the voltage drop mainly takes place in the resistors so depending on the load they need to be properly sized especially since there are no over-current protection (and ideally several resistors in parallel which is good safety design practice)
I could go on but this is not the place for a build-your-power-supply-tutorial .This is a "toy design" which should never be implemented for real since it lacks even the most basic protections. Usually I wouldn't bother commenting but the idea that someone less experienced would actually build something like this on a BB and plug it in to mains scares the crap out of me.
Shoulda scoped it to look for any ripple/noise.
Great video. Interesting circuit. Would love to see it on the scope/meter at each stage. Going from 125vAC to 3.34vDC and no heat? Where does all that voltage go? Thanks for sharing.
It goes to the amps. I doubt you could use it with load for long periods of time. You definitely need at least some passive cooling.
The capacitor only lets some through. It's a high impedance input, so little current. But plenty to run LEDS, many LED lamps use this circuit internally.
Can you turn off autofocus?
Noob question .. with no transformer the circuit is not isolated and therefore earth grounded? as in zero whoopsie protection as compared to a floating ground?
Correct. Every part of the circuit should be considered "hot".
Normally this would be fully enclosed where nobody can touch it.
@@pileofstuff makes sense .. BigClive is always mentioning capacitive droppers and lots of them are "potted"
@@pileofstuff the distinction between earth ground and negative .. the reasoning for tying earth ground and negative together (or not) .. and the historical reasoning for doing so .. is all slowly starting to make sense .. you'd think this information would all be gathered in one spot for noobs like myself.
@@stevenspmd Gathering it all in one place would be a several years long video!
Ouch. I'll stick with a transformer.
Thanks Paul.
I preffer to use a transformer so that the circuit is isolated from the mains.
i died tryin this
pop quiz question: what happens when 3.3uF "dropper cap" shorts?
Boom
Good AC Warning there...!!!...A fuse..!!
To all the people who say this design is dangerous and the video should be deleted, I say to you: How else can you learn? New ideas and examples are great tools. There are literally thousands of similar mains projects on the internet already, one more doesn't mean more people will die, it means, one more lesson to learn from. I do agree an isolation transformer would be best and so many other safety options can be used also but looking at a video doesn't mean death.
This circuit is used in so many consumer electronics things that we buy -- so I can't understand why everyone gets up in arms when the circuit is described and demonstrated, w/ appropriate safety warnings.
That's the whole point of education, after all..
HOWEVER - the 470ohm resistor across the 3.3uF dropper capacitor is a MAJOR BLUNDER - it should be 470k to 1M Ω !!! Please PIN this correction as a PINNED COMMENT !! The circuit as described will BURN UP 🔥!
Grate video Paul l sent you a private message on your email about Arduino long and short could you do a video on programming for the IDE and basic coding. Thanks Donald G Hiscock
again, what does it do and where and how can it be used...
It can be used to charge your phone. CHANGE ZENER TO YOUR NEED
@@poochie1480 cool, how many amps could it charge with? my wireless charger needs 18-20 watt.
oh and I have 230 volts in my outlets
@@christiannielsen3863 since charger draws 20W use P=VI to get current
@@poochie1480 at 5 volt 20watt the circuit should draw 4A right?
120VAC to 3.4vdc without using a transformer, what are the advantages and disadvantages of not using a transformer to convert 120VAC to 3.4vdc?
Biggest disadvantage is no isolation from the power input. Don't use this circuit anywhere near people. :-) seriously, if you have to ask it's too dangerous to mess with.
@@mschwage having no isolation will cause what types of issues and problems?
@@waynegram8907 possible scenario: you're on your work bench, you have a grounded power supply, you are adjusting voltage, you leave your hand on the power supply and fiddle with the hot side of your circuit with your other hand. Zap! Or: you decide to build a gadget with this as the power source, your wife is holding the gadget, there's a path to hot through the case of the gadget, she turns on the kitchen tap- Zap! You come home from work and find her on the floor, electrocuted. Maybe you're really careful and you think your gadget wiring is ok, that's fine but I won't touch it unless you get it ul listed first :-).
First lesson should be, how to build a gfci test plug, he he
It’s a one handed rule circuit.
This is not correct . I don't mean to embarrass you or anything but with the components you are using the voltage is being dropped by the resistors , not the capacitor . The electrons will take the easiest path , so with the resistance of the resistors being lower than the resistance of the cap , the electrons will go the resistor route . if you want the electrons to go the route of the capacitor , you need to have higher rated resistors . Thats my understanding anyway . I could be wrong but , I dont think so .
Everything is better with cheesy. I like that, electronics designer must aim for cheesy.
@learnelectronics
The most people here are not professionales. It is too dangerous to show such a circuit.
Think about that some people will connect an ESP32 to this circuit and will connect it to a PC!
It will destroy the PC.
Better to delete this video...
Some serious mistakes in your circuit and therefore very dangerous!! Might be useful to remove this video for the safety of others?