# 0-3.3v amplification required

Discussion in 'The Projects Forum' started by stefan6582, Mar 10, 2016.

1. ### stefan6582 Thread Starter New Member

Mar 10, 2016
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I'm looking for an op-amp circuit to amplify a TTL signal from 0-3.3v ( Micro-controller operating voltage ) up to 0-10v range. Some explanation on how a circuit like this works would be useful as well

2. ### GopherT AAC Fanatic!

Nov 23, 2012
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I assume to drive a Mosfet transistor? Please clarify what the 10V will be used for and current requirements. Switching speed info is also helpful. What is supply voltage to bring up to 10V

3. ### stefan6582 Thread Starter New Member

Mar 10, 2016
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Not really a mosfet transistor, but that would be an application i would look into in the nearest future. It is used to control the amount of mains power coming in to a busbar. The idea is that eventually the system will control how much current is drawn from the (simulated) mains power supply,

Feb 24, 2006
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5. ### stefan6582 Thread Starter New Member

Mar 10, 2016
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I'm currently interested in something that's not an actual IC, more like a solution that involves transistors or op-amps if that's a possibility. I've came across that and it's something we've looked into recently and we're still looking for other solutions

6. ### shteii01 AAC Fanatic!

Feb 19, 2010
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In my senior design project we used automotive fan, like the one under the hood of your car. It used 0 to 10 VDC signal to control fan speed. Our micro (Arduino Due) had (on paper) DAC that was 0 to 3.3 VDC (in reality it was 0.5 to 2.7 VDC). My guess is that OP has similar situation.

7. ### stefan6582 Thread Starter New Member

Mar 10, 2016
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It is the same sort of situation, i've found several designs on internet and they don't conclude a clear way to solve issues like this, unfortunately

8. ### shteii01 AAC Fanatic!

Feb 19, 2010
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Just pick any op amp that is single source (that way you use one power supply to power the op amp) and rail to rail. You will have 4 parts: one op amp, two resistors, one power supply.

Here is simple one: http://www.electronics-tutorials.ws/opamp/opamp_3.html
You want $A_{(V)}=1+\frac{R_F}{R_2}=3$ or a little more than 3.
If you pick R2=1 kOhm and RF=2.2 kOhm, then AV=3.2. But. Resistors are not perfect, they likely be a little less than their "official" values. So you will get AV of 3 or 3.1 or so. When you need maximum speed and your micro puts out 3.3 VDC, this 3.3 VDC will be multiplied by AV and you will have 9.9 to 10.3 volts, which will tell your fan (or whatever you are controlling) to go full speed. When your micro puts out 0 VDC, this zero is multiplied by AV is still a zero, so your fan will get a signal of zero volts which tells it to stop.

The really interesting thing happens between those extremes. When your micro sends 0.1 volts, this will by multiplied by AV and come out something like 0.3 volts so the fan will see the speed control signal of 0.3 VDC. Notice that 0.1 volt step on the micro resulted in 0.3 volt step in the fan control. If you need really very fine control of the fan speed, this might not work for you. If you go from 0 to 1 volt on the micro, the fan control signal goes from 0 to 3 volts. So. Like I said, be careful, this very simple approach has its negative points in that you loose ability to do very fine adjustments to speed control.

Last edited: Mar 10, 2016
9. ### GopherT AAC Fanatic!

Nov 23, 2012
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If you are only turning on/off a signal requiring low current, this will work.

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Feb 19, 2010
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12. ### AnalogKid AAC Fanatic!

Aug 1, 2013
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The description of the circuit requirement still is very poor. It sounds like you want to take a 0-3.3V digital signal and turn it into a 0-10V digital signal.
Of unknown minimum frequency.
Of unknown minimum pulse width.
Of unknown maximum pulse width.
Of unknown output impedance.
Of unknown output current.
Of unknown output risetime and falltime.
With unknown circuit power supply voltage.

As mentioned above, one way is with two transistors, acting as inverting saturated switches, in series.
This can be reduced to a single transistor circuit if you can invert the logical polarity of the driving signal in the microcontroller.
Do you need a totem pole output, or is a pull up/down resistor ok?

ak

13. ### Harshil Shah New Member

Dec 14, 2017
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I am exactly having the same problem and i was finding solution for this on Internet & came across this thread. Can you please tell me, Have you been able to find a correct solution. I have also tried implementing the 2-stage CE amplifier solution, but, there seems quite a heat dissipation across the collector resistor. Can someone help & throw more light on the same?

Last edited: Dec 14, 2017