[SOLVED] Doubling Voltage Output

[Aztec]

Hello all, I hope this is the right place to post this since this is my first post.

I have a USB data acquisition device that is connected to my computer and has a pin for analog output. The analog output only has a voltage output of 5V. I am trying to use this analog output as a remote to control a high voltage power supply that requires 0-10V for 0-100% power control. Now, with 5V, that will only enable me to power the high voltage power supply to 50% of its potential, whereas I want to have full control to 100%.

So I am trying to increase the output voltage from the data acquisition device from 5V to 10V. I am not very good at circuit design and physics and do not know the best way to go about doing this. Will I need a transformer, or some kind of voltage multiplier design?

Any help is much appreciated, and thank you for providing this great website:wink:

Let me know if you require any other resources such as the power supply manual, etc.

 

[Sink0]

If you dont need much current to perform that control a very simple solution would be to use a wide supply range OPAMP and double your voltage. The circuit itself is very simple, you can take a look at the web for non-inverting amplifier ciruit. You jus need to take care with the OPAMP output. If you want to use the whole control range i would recomend you to use a rail-t-rail opamp. I can give you any sugestion right now. Just go to TI or analog devices and take a look at opamps that meet that specifications. Maybe other user got a better solutions.

Cya

 

[Aztec]

Thanks for the suggestion.

It turns out I will need to control current going into the high voltage power supply in order to control the voltage too. I had it set up as just voltage but no current control, so it was basically the same thing as putting in 0V. What would be the best way to be able to have a current control so I can freely control the voltage output 0-10V from my USB device to have the high voltage power supply have an output of 0-100%.

I've attached links to two pictures from the manual that describes how to set up the remote programming, so you can get a better idea of what I'm talking about.

I'm a circuit noob so any help is much appreciated, thank you!

Imageshack - manual1o.png
Imageshack - manual2.png

 

[FvM]

a very simple solution would be to use a wide supply range OPAMP

Funny suggestion! Have you ever seen an OP sourcing 10V without a supply voltage of at least 10V? I didn't.

So in any case, a DC/DC converter is required. Voltage doubling can be performed by a simple switched capacitor circuit, but unfortunately, VUSB isn't guaranteed to give more than 4.3V worst case. If you want have 10V for sure, you need a boost converter with some voltage margin.

 

[Aztec]

So I decided to use a simple non-inverting op amp to multiply my 5V source to 10V. I used another power supply as a current control for the high voltage power supply, and I used the high voltage power supply, which has a +15V output pin, to power to op amp. I am using the LT1001 op amp, Linear Technology - LT1001 - Precision Operational Amplifier for this design. I am using two 215ohm resistors and have the correct setup, according to **broken link removed**. When I first tested this design, I was reading a 10V output from the op amp Vout. Now I am getting random readings, ones that seem to divide the Vin by 2 or by 10, leaving me with Vout of 2.5V or .2V. I have tried rewiring my non inverting op amp circuit every possible way and can't seem to get 10V output again, do you know what the problem is?

 

[FvM]

LT1001 requires a bipolar supply (e.g. +/- 15V), because the minimum common mode input voltage is about 1V above the negative supply. Furthermore two 215 ohm resistors are sinking a unsuitable high output current from the OP, you should change ist to e.g. two 1K or 10 K.

Using a rail-to-rail OP would allow single supply operation, if you can accept a few 10 mV minimum output voltage.

 

[heri.aza]

I'm still a little confused with the output of electric current from the circuit, because as i know, the electrical current from the USB it is very small. I think that by doubling the voltage will create an electric current to be reduced.

 

[FvM]

I think that by doubling the voltage will create an electric current to be reduced.

Unfortunately the point has been rather unclear, but the orignal poster finally stated, that he's using an external power supply for the amplifier. So it's apparently not a problem of pulling power from the USB. The 5V comes into play, because he uses an USB interfaced DAC with 5V output range. To achieve 5V DAC output, the "USB data acquisition device" would have to use alreadys ome kind of internal DC/DC converter, because USB isn't guaranteed to have 5V VUSB, and the output amplifier causes a voltage drop anyway. There are, by the way, also USB analog interfaces, that step-up there internal supply to achieve +/- 10V analog range. The delivered current is of course limited according to the available USB power, but it shouldn't be a problem for a moderately loaded analog control voltage.

 

[Aztec]

Thank you very much FvM, that really helps. I don't get how I was initially able to successfully double my voltage?

Anyways, is there any specific rail-to-rail op amp you would recommend for my purpose? I am looking at Newark's website, Your Search Results | Newark.com

 

[Aztec]

would this rail-to-rail work, or would another one on the page I linked in my previous post be better?
NATIONAL SEMICONDUCTOR|LF356N/NOPB|IC, OP-AMP, 5MHZ, 12V/µS, DIP | Newark.com

 

[FvM]

LF356 is a good old OP, but not rail-to-rail. For up to 15V supply, I'm often using Texas Instruments TLV2371.

 

[Aztec]

So, I've tried to solve this simple circuit and still can't seem to get it working. I ordered TEXAS INSTRUMENTS|TLV2371IP|IC, OP-AMP, 2.4MHZ, 2V/µS, DIP | Newark.com which is a rail-to-rail op amp, and I've replaced my two resistors with two 10K resistors. I'm powering my op amp with a +15V pin from the high voltage power supply and the other side is GNDed. I can only seem to get about 4.2V with an input of 5V, and even when I turn off the +15V supply, I still read 4.2V, I'm assuming my op amp is not working right. Here's a picture of my setup, can you tell me any mistakes I'm making? Thank you
**broken link removed**

 

[FvM]

No problem can be seen in the photo. How did you connect the different grounds?

Generally, the problem should reveal when measuring each circuit node.

 

[Aztec]

I've finally figured it out! I'm able to control my high voltage power supply via DAQ to 100% Thanks a ton FvM, I really appreciate you helping me out through this process, I couldn't have done it without you.