DC-DC Voltage Doubler with Op-Amps

Thread Starter

Okaghana

Joined Jan 14, 2017
9
Hello there!

Ok: In a school project I want to controll a light dimmer. The old dimmer needs a 0-10V signal to controll the lights. I have a Arduino Uno, but as probably known, the Arduino only have a system voltage of 5V. So I need to double the PWM Output signals from the board.

For this purpose I design a small circuit with an OP-AMP. But to Output a 10V signal, I also need a 10V supply Voltage. On the attached File, you can see the basic circuit. The two lower cables needs to be supplied by the 10V and a 0V Voltage. The right cable is the Output.

So my question is: what is the best way to supply the 2 supply Voltages?
I had 2 basic ideas:
  1. The whole construct is supposed to be only powered by a USB-Port. But if I have to, I could power it by in an external powersupply with goes into a socket.
  2. I take the 5V output from the Arduino and double it once using a method without Op-amps. Something like: convert the 5V to an AC signal and then double the Signal by an AC-DC Voltage Doubler like this
Okaghana
 

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DickCappels

Joined Aug 21, 2008
6,381
Your opamp circuit is fine, but make your resistors much larger than 100 ohms so a real life opamp can drive it. I suggest 10K to 100k for the two resistors. The LF351 was a great opamp in its time and it is still useful but it needs more power supply voltage than modern rail-to-rail opamps.

Suggestions: Use a modern rail-to-rail opamp, Make sure your power supply is sufficient to get the opamp's output to +10V, and make sure the opamp you select can work witih the input equal to the negative power supply rail.

The old standby, LM358 will do for working with the inputs at the negative supply rail, but you would need a converter to take the + power supply to more than 13V.

For that you can consider the MC34063, a simple enough switching regulator.
 

MisterBill2

Joined Jan 23, 2018
6,027
Hello there!

Ok: In a school project I want to controll a light dimmer. The old dimmer needs a 0-10V signal to controll the lights. I have a Arduino Uno, but as probably known, the Arduino only have a system voltage of 5V. So I need to double the PWM Output signals from the board.

For this purpose I design a small circuit with an OP-AMP. But to Output a 10V signal, I also need a 10V supply Voltage. On the attached File, you can see the basic circuit. The two lower cables needs to be supplied by the 10V and a 0V Voltage. The right cable is the Output.

So my question is: what is the best way to supply the 2 supply Voltages?
I had 2 basic ideas:
  1. The whole construct is supposed to be only powered by a USB-Port. But if I have to, I could power it by in an external powersupply with goes into a socket.
  2. I take the 5V output from the Arduino and double it once using a method without Op-amps. Something like: convert the 5V to an AC signal and then double the Signal by an AC-DC Voltage Doubler like this
Okaghana
The simple way to get the 10 volts is a circuit called a charge pump, which rapidly charges capacitors in parallel and then puts them in series to deliver the voltage. There are lots of the circuits around, and even ICs made for that purpose. AND you can use a clock signal from the processor board to drive it. Much more efficient and effective than using an op amp or two. And probably cheaper as well.
 

Thread Starter

Okaghana

Joined Jan 14, 2017
9
The simple way to get the 10 volts is a circuit called a charge pump, which rapidly charges capacitors in parallel and then puts them in series to deliver the voltage.
Thanks! But.. could you send me the schematics, or a video for explonation, or something like this. I find lots and lots of thing, but many different versions of the circuit, some for AC, and I dont know which one is the right.


Much more efficient and effective than using an op amp or two. And probably cheaper as well.
What I didnt write (but should have) is, that I need to controll about 20 lights, so I need to double the PWM-Voltage of the Arduino about 20 (+1) times. Is this a problem?
 

Thread Starter

Okaghana

Joined Jan 14, 2017
9
Your opamp circuit is fine, but make your resistors much larger than 100 ohms so a real life opamp can drive it. I suggest 10K to 100k for the two resistors. The LF351 was a great opamp in its time and it is still useful but it needs more power supply voltage than modern rail-to-rail opamps.

Suggestions: Use a modern rail-to-rail opamp, Make sure your power supply is sufficient to get the opamp's output to +10V, and make sure the opamp you select can work witih the input equal to the negative power supply rail.

The old standby, LM358 will do for working with the inputs at the negative supply rail, but you would need a converter to take the + power supply to more than 13V.

For that you can consider the MC34063, a simple enough switching regulator.
Ok. I get the thing with the LF351. I need to double 20 signals. Are there fitting opamps that are 14-pin or more??

About the thing with the MC34063 and the converting. I have no idea what you mean and what am I supposed to do. I understand the basics, but not more. Could you please explain this a little bit more?
 

DickCappels

Joined Aug 21, 2008
6,381
If you want the output to go all the way to 10 volts you will need a power supply of more than 10 volts. If there is no significant load on the opamp and you can tolerate a maximum output of a little less than 10 volts you can use a 10 volt supply and a rail-to-rail opamp like the TLC22272 from Texas Instruments. http://www.es.co.th/Schemetic/PDF/TLC2272.PDF
upload_2018-3-3_3-9-3.png
Then you can use a simple voltage doubler that takes in 5V and outputs 10V. The MAX1682 is such a chip.

upload_2018-3-3_3-51-33.png

If you really need to get all the way to 10 volts then you are going to have to power the opamp from more than 10 volts. One such solution is to use a switching regulator to more than double the 5 volt power supply. Using on of many different switching regulators, the MC34063 from On Semiconductor is one possibility.

upload_2018-3-3_3-31-26.png

Or something like the LT1026 as a voltage quadrupler.
upload_2018-3-3_3-40-37.png
Search for voltage multiplier circuits on the internet and you will find many options.

Getting the output to go all the way to ground can be done by just placing a resistor from the output to ground for some types of opamps, others will need a negative power supply.

The ICL7660 can convert +5 to -5 with very few parts

upload_2018-3-3_3-46-39.png

Depending upon how close you need to get to +10V and ground you have some options.
 

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MrAl

Joined Jun 17, 2014
7,587
Hello,

A voltage doubler is usually good for low current applications where the power requirement isnt too great.
A boost circuit though, like the one with the inductor in the previous post, is made for higher output current.

The drawback to any of the voltage increasing circuits is that the current available to the output is always less than the input current. With ideal elements, the current available on the output is equal to the inverse voltage ratio of the input to output of the current available on the input. So if you have 5v and 500ma available on the input then the max output current you can get at 10v output is 250ma. That's why some USB hubs are called "powered" USB hubs because they use an external wall wart to power the USB devices rather than take the power from the host computer USB port directly.
5v 500ma to 10v 250ma is also an "ideal" condition, where all the parts are perfect and have no losses. Efficiency usually lowers that and it can be significant. For example, with 5v 500ma input and 10v output at 80 percent efficiency leads to 10v 200ma output max.
Also, diodes drop voltage so you loose some top end voltage unless you compensate somehow. This leads to less efficiency but that has to be done. Schottkey diodes work well for this kind of app because they drop less voltage than regular Si diodes. Regular rectifier diodes like 1N4001 should never be used for this kind of application.
 

Thread Starter

Okaghana

Joined Jan 14, 2017
9
If you want the output to go all the way to 10 volts you will need a power supply of more than 10 volts. If there is no significant load on the opamp and you can tolerate a maximum output of a little less than 10 volts you can use a 10 volt supply and a rail-to-rail opamp like the TLC22272 from Texas Instruments. http://www.es.co.th/Schemetic/PDF/TLC2272.PDF
View attachment 147415
Then you can use a simple voltage doubler that takes in 5V and outputs 10V. The MAX1682 is such a chip.

View attachment 147423

If you really need to get all the way to 10 volts then you are going to have to power the opamp from more than 10 volts. One such solution is to use a switching regulator to more than double the 5 volt power supply. Using on of many different switching regulators, the MC34063 from On Semiconductor is one possibility.

View attachment 147416

Or something like the LT1026 as a voltage quadrupler.
View attachment 147418
Search for voltage multiplier circuits on the internet and you will find many options.

Getting the output to go all the way to ground can be done by just placing a resistor from the output to ground for some types of opamps, others will need a negative power supply.

The ICL7660 can convert +5 to -5 with very few parts

View attachment 147421

Depending upon how close you need to get to +10V and ground you have some options.
Ok. That explains it much better. But now I have another question: Could I use 20 MAX1682 to amplify the 5V PWM signal in the first Place and just Ignore the rest with the Op-Amps?

If Yes: Is that practical and affordable (I have to double a Voltage 20x on an arduino shield)?

If no: Ok. I can just quadruple the 3.3V output of the Arduino. But why do some Op-Amps need negative Voltage, even if they are only supposed to output positive Voltage?
 

ebp

Joined Feb 8, 2018
2,332
My advice is don't even think about building a switch mode power supply. They can be nasty things to get working properly. You could spend more time messing with trying to get the switcher to work well than with building the rest of your circuit.

The simplest thing to do is buy a 5 volt to 12 volt (or 15 volt) regulated DC-DC converter module rated at about watt. They are switch mode converters internally, but they are easy to use. Power your op amps with12 volts or 15 volts, set them for a gain of +2, and off you go. Depending on the amplifier you use and how much current the dimmer input requires, you might need more than 1 watt. There are lots of 2 W modules available (a typical ordinary op amp will require only about 1 mA or less; 20 x 1 mA x 15 V = 300 mW) Don't forget you have to have enough power from your 5 V supply to run the converter - check the efficiency data for the converter; most are reasonably good but not great.

Here is an example of on that takes 4.5-5.5 V in and puts out 15 volts (isolated) at 1 watt. It costs less than US $3
https://www.mouser.com/ProductDetail/CUI/PCSA1-S5-S15-S?qs=sGAEpiMZZMvGsmoEFRKS8LplFs206tN2Md1oaSkus%2bBek3rKABFwXw==

There are many others available from just about any components supplier - DigiKey, Mouser, Allied, Farnell/Newark, etc
 

ebp

Joined Feb 8, 2018
2,332
an aside on terminology:

The term "voltage doubler" is normally used to refer to something where the output power is taken directly from the input power - there is no external power supply.

If you use an amplifier, the normal term used is "gain." For your requirement, you need a gain of +2 (often just said as "a gain of two" - the "plus" is omitted just as you usually would in saying any positive number. You can also have a gain of -2, said as "a gain of minus 2." Vout = -2 * Vin). You can have a gain with a magnitude of less than one, such as +0.5 or -0.2. That might be called "attenuation" depending on what it is referring to.
 
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DickCappels

Joined Aug 21, 2008
6,381
Ok. That explains it much better. But now I have another question: Could I use 20 MAX1682 to amplify the 5V PWM signal in the first Place and just Ignore the rest with the Op-Amps?

If Yes: Is that practical and affordable (I have to double a Voltage 20x on an arduino shield)?

If no: Ok. I can just quadruple the 3.3V output of the Arduino. But why do some Op-Amps need negative Voltage, even if they are only supposed to output positive Voltage?
The number "20" shows up twice in your post where I would expect to see the number "2". Are those typos or is there something that I missed about your project? Are you going to make 10 channels?

"Could I use 20 MAX1682 to amplify the 5V PWM signal in the first Place and just Ignore the rest with the Op-Amps?"
That is thinking outside the box and with an ideal voltage doubler it would work. You cannot use multiple cascaded MAX1602's in your application because the maximum input voltage is 5.5 volts. Another reason that these would not work in your application is that they need a minimum input voltage before they can operate and if you need to get close to ground then you might have troubles. The minimum input voltage for the MAX1682 is 2.5 volts.

If no: Ok. I can just quadruple the 3.3V output of the Arduino.
That sounds like that might work, just be careful about the voltage losses in each stage.
upload_2018-3-6_14-44-12.png
THE ICL7660 can apparently be cascaded for your application to drive an opamp.

But why do some Op-Amps need negative Voltage, even if they are only supposed to output positive Voltage?
Because everything that has current flowing through it has a voltage drop, except at absolute zero, and transistors don't work down there :)

A clear and more comprehensive discussion of the reason can be found that the link below.
https://electronics.stackexchange.com/questions/346478/what-exactly-is-stopping-opamps-from-reaching-vcc-gnd

What you have not told us but is important to selecting a solution is how close you need to get to +10 and ground. Also of possible importance what the input of the dimmer input looks like (how many ohms and is there a capacitor on the input), your PWM pulse repetition rate and minimum pulse width (clock rate, (prescaler setting and resolution), and how quickly the dimmer must respond to changes in pulse dutycycle.

Depending upon the answers to these last few questions there might be some much easier approach.
 

ebp

Joined Feb 8, 2018
2,332
That Wikipedia article is pretty useless, but ...
It seems likely that you actually have to "source" a small amount of current into the input:
- from Wikipedia: "Receivers have a nominal input impedance of 100±20 kΩ"
"Source" here means that you have to put "conventional current" into the input. Conventional current is considered to flow from positive to negative. "Sink" would mean the opposite - conventional current would flow from a positive voltage to a more negative point.

This is helpful when you have op amps that run from a single positive supply voltage because the amp does not have to try to sink current into its output to ground. Sinking current to ground to accomplish a very low output voltage with respect to common is almost impossible for any amplifier to do without a negative supply, even those specified as operating "rail to rail." Typically an amp specified to operate to the negative "rail" (circuit common or "ground" with a single positive supply) will get within a few millivolts to tens of millivolts of the rail but it can't get any closer.
The fact that you need a non-inverting amplifier also helps the output get to a very low voltage. The output has to source current to the resistors that set the gain.
Both the load (if the dimmer input is what it appears to be) and the gain setting resistors require the amplifier to source current into them. This means that the ability of the output circuit in the amp to sink current to its negative rail (again, circuit common when the amp is powered with a single positive supply) will never be an issue.

There are lots of amplifiers with inputs that work properly right down to the negative rail, but won't work with the inputs or output very close to the positive rail. If you need +10 volts at the output, you can use any power supply that assures the amplifier in question can get the output to the maximum voltage you require. A positive supply of about 12 volts is enough for many such amps.

Here is a bullet point from one such amp:
- Large Output Voltage Swing 0 V to V+ − 1.5 V
What that is saying is that the output can get to any voltage up to 1.5 volts less than its positive supply - perfect for you for a 10 volt output with a 12 volt supply.

That line is from the TI data sheet for the LM324 quad op amp, which is extremely popular and very inexpensive. It takes less than 1 mA of supply current per amplifier There is an "A" version (LM324A) that has better specifications, and it looks like it may actually be cheaper than the ordinary version from some suppliers (TI LM324AN is 58 cents, US, from DigiKey).

So, I recommend a 1 watt 5 V to 12 V (regulated) DC-DC converter and a handful of LM324 or 324A amps.
 

Thread Starter

Okaghana

Joined Jan 14, 2017
9
The number "20" shows up twice in your post where I would expect to see the number "2". Are those typos or is there something that I missed about your project? Are you going to make 10 channels?
Yeah. You missed something out. I said it here:

What I didnt write (but should have) is, that I need to controll about 20 lights, so I need to double the PWM-Voltage of the Arduino about 20 (+1) times
I thought you migtht have maybe seen it, but aparently not.

What you have not told us but is important to selecting a solution is how close you need to get to +10 and ground. Also of possible importance what the input of the dimmer input looks like (how many ohms and is there a capacitor on the input), your PWM pulse repetition rate and minimum pulse width (clock rate, (prescaler setting and resolution), and how quickly the dimmer must respond to changes in pulse dutycycle.

Depending upon the answers to these last few questions there might be some much easier approach.
Nah... Classic... Not enough information!
Ok: I dont know how close I have to get to 10V, but I think it isnt that precise. If I reach at maximum only 9.8V or so, that is probably sufficient. So I have a space to move in.
The dimmer input is first a rs232-25-pin-cable, but the transforms into a weird looking connection that i cant name. Basically the first 24 channels of the cable are for the light signals and the 25th is ground. But I only need th output 20 lights, because every 6th channel is a dead one (we only have 5 colors of light, and 4 different regions).
The questions to capacitors and ohms i cant answere, bc we dont know where the dimmers are from and we also have no schematics.
The repetition rate of the arduino is about 500Hz and the minimum pulse with will probably be about 0.02ms (so 1/100 of the full pulse width), if you ignore a pulsewidth of 0.
The dimmer dont need to respond quickly. The lightbulbs alone need their time to lighten.
 

Thread Starter

Okaghana

Joined Jan 14, 2017
9
My advice is don't even think about building a switch mode power supply. They can be nasty things to get working properly. You could spend more time messing with trying to get the switcher to work well than with building the rest of your circuit.

The simplest thing to do is buy a 5 volt to 12 volt (or 15 volt) regulated DC-DC converter module rated at about watt. They are switch mode converters internally, but they are easy to use. Power your op amps with12 volts or 15 volts, set them for a gain of +2, and off you go. Depending on the amplifier you use and how much current the dimmer input requires, you might need more than 1 watt. There are lots of 2 W modules available (a typical ordinary op amp will require only about 1 mA or less; 20 x 1 mA x 15 V = 300 mW) Don't forget you have to have enough power from your 5 V supply to run the converter - check the efficiency data for the converter; most are reasonably good but not great.

Here is an example of on that takes 4.5-5.5 V in and puts out 15 volts (isolated) at 1 watt. It costs less than US $3
https://www.mouser.com/ProductDetail/CUI/PCSA1-S5-S15-S?qs=sGAEpiMZZMvGsmoEFRKS8LplFs206tN2Md1oaSkus%2bBek3rKABFwXw==

There are many others available from just about any components supplier - DigiKey, Mouser, Allied, Farnell/Newark, etc
We are pretty sure that the current doesnt really matter in the dimmerinputs. But at all, im really thankfull for this response. Its an answere I had hoped for. (not that I want to blame the other answeres), and im pretty sure, that this is about the way i will go
 
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