It is worth noting that the same principle of cascading stages of a CW doubler/multiplier applies here. I just put together a 2-stage voltage inverter that provides about -6.2V from USB's +5V, and -5.9V at around 15mA of load with negligable ripple (circa 10-12mV); plenty for driving an opamp. Caps are 330uF/16V electrolytic, diodes are BAT46 schottkys, ~6.8kHz square wave drives a 2N3904/2N3906 pair. Could be more efficient without the transistors, but I wanted to isolate from the PIC12's 50mA pin. Altogether less than $1US worth of parts. Great video, very helpful.
I love your tutorials Dave. I learn something while haveing my lunch. And come back to work with the knowledge that i at least learned something today.
50 cents can be a big part of your BOM cost if you are watching the cents. Also the cheapest 100mA one Digikey have is is the MAX660 at $0.61 in 2500 volume. If you don't care about cost, sure use a switched cap chip.
Dave, when going through the voltage doubler, next you should do it going through the tripler. This is a clever design where multiple circuits can be connected in cascade and voltage can be multiplied millions of times. Used in old TV's to generate high voltage for CRT
try to build circuits from time to time just for fun, I find that doing stuff alone helps you learn a lot about the components and you also learn what working techniques works for you. don't be afraid to look at datasheets, they can really help you out some times.
Hey!! Question for you.. I know you say that this only permits a few tens of amps. What if we instead drove an NPN transistor rated for, say, 2 amps from the input square wave and upped the diodes to 1/2 watt diodes. Additionally, imagine that the collector on the transistor has an input of +15 volts. It seems that this should allow us to drive a 555 square wave from a 5 volt source and invert a +15 volt supply and get at least 1/2 amp out of it. Thoughts? I'm not much of an electronics engineer but I have a need to build just such a circuit!! Thanks!
Sure, that's all part of the typical design trade-off for any design, and I alluded to that in the video. Every design is different, that is why this diode technique is not uncommon.
In huge quantities, cheap diodes and caps end up costing a couple of cents each. Since you're already ordering them, adding a couple more per product lets you pocket that extra 45 cents on each unit, or buy better knobs that aren't crap or something.
The TPS60151 is $0.50 direct from TI in 1k quantities. I don't disagree that a discrete solution can be cheaper, it's just that at higher current ranges the single chip solution really closes that cost gap. Plus it's a simpler, more reliable design and you get extra features like soft start, shutdown and power good outputs. Not to mention the fact that they can switch in the hundreds of kHz to help prevent ripple.
say you have a cap, charge it at 5V, then hook the positive lead to ground, on the negative lead you should measure -5V from ground, now put a diode and another cap which is referenced to ground (and discharged) conected to that -5V, the second cap should (dis)charge to -5V, now just repeat. That's what happened, but instead of doing it manually, the second diode which has connected directly to ground did it. Imagine the current flow, and you should see how the diodes do the job.
kinda a noob and just decided to use a depletion mode mosfet instead of a nc relay to drain a cap bank on a cd welder(either when user requests lower voltage or when machine is turned off and or unplugged)... id assume this is going to be enough to open the path to the bleed/drain power resistor? next up ive gota figure out your damn adc/pwm pot replacement. damn it dave why do you put these ideas in my head!? lol thanks for the awesome videos!
Hi EEVblog great video, I Was wondering if theirs anyway to have an voltage inverter for more high power applications, or am I better of using an transformer with 3 terminals and just using one of those as an negative source.
I just fixed a fried inverting converter that uses an inductor rather than a capacitor. I'm curious what difference inductor-vs-capacitor makes in one of these.
Very true, keep in mind I'm mainly talking about higher current need situations. If you just need a few mA to throw +-10V at an opamp or something like that, going discrete is a fine solution! Needing a uC for a PWM output is the only issue I have with this method. Could you perhaps show a cheap and simple way to generate a 50 to 100kHz pulse for this (without using a micro)?
If it is for a product, I can agree, go find some of the shelf component and done. But this is my situation: I'm using a protoboard with a 16x2 LCD + 3.3V micro battery powered. Not making the product yet, just trying stuff. And the LCD is the only one requiring 5V. Then at this moment I can't think a better solution than using a Dickson doubler or the inverter. See Ramtron an502. In the end, the situation "choose" the solution.
There is a practical limit; you aren't going to pull half an amp using crap parts and this simple design. Plus the higher you go in frequency, the more inductance on your traces/leads matters. You're also going to have problems with using standard 1N001 diodes because of switching losses. If you need a negative source with lots of current capability, you're probably better off grabbing a shelf part than dickering around with discretes.
If you only need 5 or 10mA, sure, but once you start factoring in bigger caps (to smooth out the ripple), higher quality diodes (to reduce dropout) and more components (to increase current capacity), I imagine you're looking at 20 to 40 cents. Plus board space for all those components and don't forget you've got to feed it from a uC. Or I could get 150mA with a 2x2mm QFN from TI for 50 cents, and it doesn't even tie up a uC pin!
Is there a practical limit on switching frequency? If you get into the MHZ range, can you support an even higher load with the same crappy parts? What would it take to drive say .5A?
Consider this, you are the engineer who developed a product, and that $0.50 part costs $1,000,000 because you ship 2mil units a year, then Dave and I come in, and tell the company let us do a quick rework of the design, pay us each $100k and you will save $800k first year, and $1mil each additional year.
Hi Dave, Can you please next time, explain the Op Amp configuration in order to perform any kind of linear conversion ? I mean, for example, with an Op Amp, convert 2-8 into 0-5V and those kind of conversions... those are cool circuits that are pretty useful..
Inductors don't change their current instantly. If the capacitors are replaced with inductors, would the circuit operate on the current rather than the voltage? What characteristics would it have, ie would it double the current?
Yeah, see that's a totally useful situation for this sort of thing. Though, keep in mind that you can get free sample chips from all the major players, which is normally what I end up doing. :)
It seems to be a very nice, simple circuit to use with op amps in some cases, doesn't it? Since opamps draw small current that should do the job, I have to try it. Cheers :)
Hello. Can you plz help me and tell me how can I get -5V DC output from +5V DC input. I have made an astable multivibrator to generate the square wave pulse. Now we can't it to get -5V. Can you please help me? Thanks in advance
Softec's Spyder form QGx (HCS08 based) microcontrollers plus CodeWarrior works like a champ and even come with a little micro (socketed) in the programer to parctice. But I took the micro out and use the programer. Works so fine that even took it to the factory and people programed 5000 board with this cheap stick. Winner. It cost me, three years ago, only 25 bucks. Arrow gave us a second one for free. Come with the CW, drivers, schematics, examples and manuals on a CD. Best value IMHO
Why go through all the trouble of a discrete design like this when you can buy a monolithic IC that will do it better (100-300mA) for +-$0.50? (Don't get me wrong, it's awesome to see it all broken down and understand the magic behind it, but for practical use?)
ditto, if you read the wikipedia articles about electromagnetics, pretty nice theory and stuff but it's useless, you'll still need the books and practical material along with the tools to get an idea of how it works.... And no, youtube didnt help either, there's not a single video about how to calculate the windings for switching tranformers nor stuff about the air gap or how it all works, just basic theory about standard 60hz mains transformers, not even in depth....
It is worth noting that the same principle of cascading stages of a CW doubler/multiplier applies here. I just put together a 2-stage voltage inverter that provides about -6.2V from USB's +5V, and -5.9V at around 15mA of load with negligable ripple (circa 10-12mV); plenty for driving an opamp. Caps are 330uF/16V electrolytic, diodes are BAT46 schottkys, ~6.8kHz square wave drives a 2N3904/2N3906 pair. Could be more efficient without the transistors, but I wanted to isolate from the PIC12's 50mA pin. Altogether less than $1US worth of parts. Great video, very helpful.
Haha. I love how you tell about the concept so clearly, then basically say, "but don't worry about it!" Many levels of awesome. Thanks.
I love your tutorials Dave. I learn something while haveing my lunch. And come back to work with the knowledge that i at least learned something today.
50 cents can be a big part of your BOM cost if you are watching the cents. Also the cheapest 100mA one Digikey have is is the MAX660 at $0.61 in 2500 volume. If you don't care about cost, sure use a switched cap chip.
Dave, when going through the voltage doubler, next you should do it going through the tripler. This is a clever design where multiple circuits can be connected in cascade and voltage can be multiplied millions of times.
Used in old TV's to generate high voltage for CRT
try to build circuits from time to time just for fun, I find that doing stuff alone helps you learn a lot about the components and you also learn what working techniques works for you.
don't be afraid to look at datasheets, they can really help you out some times.
When Point 1 is high the diode is forward biased and conducting, so it "steers" or "pulls" point 2 to ground (or one diode drop above ground).
Hey!! Question for you.. I know you say that this only permits a few tens of amps. What if we instead drove an NPN transistor rated for, say, 2 amps from the input square wave and upped the diodes to 1/2 watt diodes. Additionally, imagine that the collector on the transistor has an input of +15 volts.
It seems that this should allow us to drive a 555 square wave from a 5 volt source and invert a +15 volt supply and get at least 1/2 amp out of it. Thoughts? I'm not much of an electronics engineer but I have a need to build just such a circuit!!
Thanks!
Sure, that's all part of the typical design trade-off for any design, and I alluded to that in the video. Every design is different, that is why this diode technique is not uncommon.
I see you've renewed your DaveCad licence. Must've cost a fortune ;-)
Nice,fundamentals Friday...can't wait to next Friday ..
In huge quantities, cheap diodes and caps end up costing a couple of cents each. Since you're already ordering them, adding a couple more per product lets you pocket that extra 45 cents on each unit, or buy better knobs that aren't crap or something.
If we use this power supply for power an opamp, it surely will reflect the fluctuation on output of opamp (negative side)?
The TPS60151 is $0.50 direct from TI in 1k quantities. I don't disagree that a discrete solution can be cheaper, it's just that at higher current ranges the single chip solution really closes that cost gap. Plus it's a simpler, more reliable design and you get extra features like soft start, shutdown and power good outputs. Not to mention the fact that they can switch in the hundreds of kHz to help prevent ripple.
say you have a cap, charge it at 5V, then hook the positive lead to ground, on the negative lead you should measure -5V from ground, now put a diode and another cap which is referenced to ground (and discharged) conected to that -5V, the second cap should (dis)charge to -5V, now just repeat.
That's what happened, but instead of doing it manually, the second diode which has connected directly to ground did it. Imagine the current flow, and you should see how the diodes do the job.
Great explanation!
kinda a noob and just decided to use a depletion mode mosfet instead of a nc relay to drain a cap bank on a cd welder(either when user requests lower voltage or when machine is turned off and or unplugged)... id assume this is going to be enough to open the path to the bleed/drain power resistor? next up ive gota figure out your damn adc/pwm pot replacement. damn it dave why do you put these ideas in my head!? lol thanks for the awesome videos!
Hi EEVblog great video, I Was wondering if theirs anyway to have an voltage inverter for more high power applications, or am I better of using an transformer with 3 terminals and just using one of those as an negative source.
I just fixed a fried inverting converter that uses an inductor rather than a capacitor. I'm curious what difference inductor-vs-capacitor makes in one of these.
Very true, keep in mind I'm mainly talking about higher current need situations. If you just need a few mA to throw +-10V at an opamp or something like that, going discrete is a fine solution!
Needing a uC for a PWM output is the only issue I have with this method. Could you perhaps show a cheap and simple way to generate a 50 to 100kHz pulse for this (without using a micro)?
Love the t-shirt!!
the screwdriver over the oscilloscope screen makes me cringe :D
If it is for a product, I can agree, go find some of the shelf component and done.
But this is my situation: I'm using a protoboard with a 16x2 LCD + 3.3V micro battery powered. Not making the product yet, just trying stuff. And the LCD is the only one requiring 5V. Then at this moment I can't think a better solution than using a Dickson doubler or the inverter.
See Ramtron an502.
In the end, the situation "choose" the solution.
My mind confuses words like that all the time, no pun intended!
There is a practical limit; you aren't going to pull half an amp using crap parts and this simple design. Plus the higher you go in frequency, the more inductance on your traces/leads matters. You're also going to have problems with using standard 1N001 diodes because of switching losses.
If you need a negative source with lots of current capability, you're probably better off grabbing a shelf part than dickering around with discretes.
if you use J-fet as current limiter you can get -9.6v out of 5v suply :P
If you only need 5 or 10mA, sure, but once you start factoring in bigger caps (to smooth out the ripple), higher quality diodes (to reduce dropout) and more components (to increase current capacity), I imagine you're looking at 20 to 40 cents. Plus board space for all those components and don't forget you've got to feed it from a uC.
Or I could get 150mA with a 2x2mm QFN from TI for 50 cents, and it doesn't even tie up a uC pin!
Cool, thanks for sharing, that was great
have you ever done a video or teardown on consumer power inverters? I couldn't find one
+slaznum1 I supposed a UPS would have most if not all of the elements so I'll check out that video
Is there a practical limit on switching frequency? If you get into the MHZ range, can you support an even higher load with the same crappy parts? What would it take to drive say .5A?
Consider this, you are the engineer who developed a product, and that $0.50 part costs $1,000,000 because you ship 2mil units a year, then Dave and I come in, and tell the company let us do a quick rework of the design, pay us each $100k and you will save $800k first year, and $1mil each additional year.
Hi Dave, Can you please next time, explain the Op Amp configuration in order to perform any kind of linear conversion ? I mean, for example, with an Op Amp, convert 2-8 into 0-5V and those kind of conversions... those are cool circuits that are pretty useful..
I don't know why I thought this video was called MINDcontroller Voltage Inverter Tutorial... lol
when was the voltage inverted in the video? I just see a voltage double type of circuit, the type that we saw before in a previous video.
good
I gave it thumbs up!
Inductors don't change their current instantly. If the capacitors are replaced with inductors, would the circuit operate on the current rather than the voltage? What characteristics would it have, ie would it double the current?
Yeah, see that's a totally useful situation for this sort of thing. Though, keep in mind that you can get free sample chips from all the major players, which is normally what I end up doing. :)
Pretty awesome video, I gotta say...
Could you make one about measurement circuits, too?
It seems to be a very nice, simple circuit to use with op amps in some cases, doesn't it? Since opamps draw small current that should do the job, I have to try it. Cheers :)
board space too, which can become really expensive if you need to fit everything in a tight casing.
Hello. Can you plz help me and tell me how can I get -5V DC output from +5V DC input. I have made an astable multivibrator to generate the square wave pulse. Now we can't it to get -5V. Can you please help me?
Thanks in advance
Very cool 😎
I may be a bit late but is this possible on sbus?
I really like DaveCad, but its getting a little long in the tooth, when do you expect DaveCad 2.0 to be out? (blue sticky notes?)
Do you have any good circuits for generating -10v and +200v with a microcontroller for driving a 6e5?
I mena, differential amp, with a fixed voltage reference
Depends on the MCU family you intend to use.
Perfect :).
Is it possible to combine inverter and multiplier to achieve, let's say -2*Vcc ?
if you manage to make a +2*vcc square wave then yes
is there a high power solution keeping it simple
Anyone got the serial for DaveCAD? I can't find it online anywhere and my shareware expired :(
Can you recommend me a cheap microcontroller programmer/burner? I'm a student and don't have alot.
Softec's Spyder form QGx (HCS08 based) microcontrollers plus CodeWarrior works like a champ and even come with a little micro (socketed) in the programer to parctice. But I took the micro out and use the programer. Works so fine that even took it to the factory and people programed 5000 board with this cheap stick. Winner. It cost me, three years ago, only 25 bucks. Arrow gave us a second one for free. Come with the CW, drivers, schematics, examples and manuals on a CD. Best value IMHO
Why go through all the trouble of a discrete design like this when you can buy a monolithic IC that will do it better (100-300mA) for +-$0.50?
(Don't get me wrong, it's awesome to see it all broken down and understand the magic behind it, but for practical use?)
Check out his video review and teardown. It is an OK quality scope, but is severely lacking when compared to others in the same price range.
ditto, if you read the wikipedia articles about electromagnetics, pretty nice theory and stuff but it's useless, you'll still need the books and practical material along with the tools to get an idea of how it works....
And no, youtube didnt help either, there's not a single video about how to calculate the windings for switching tranformers nor stuff about the air gap or how it all works, just basic theory about standard 60hz mains transformers, not even in depth....
Stress me out seeing the screwdriver almost scratching the screen each time. The screwdriver is unscrewing this videoblog .
Awyeeeah!
cause we got bugger'all current so aussie
Too easy.