# Amplify Triangular Wave

Discussion in 'General Electronics Chat' started by stesmall, Apr 18, 2013.

1. ### stesmall Thread Starter New Member

Apr 18, 2013
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Hi,

I have a voltage source which is ramping from 0 to 10V and then back down to 0V (repeating).

The load I want to drive is a 180 Ohm coil. I want the current through the load to ramp as does the voltage. The voltage is ramping from 0V to 10V and I want the current to ramp from 0A to 0.15A concurrently (at a similar rate).

Can anyone please recommend the simplest circuit to achieve this? Something really basic and quick which will get the job done? My electronics background/knowledge is limited so please bare with me.

Thanks alot!

2. ### Ron H AAC Fanatic!

Apr 14, 2005
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We need to know the frequency of your triangle wave, and the inductance of your coil.

3. ### studiot AAC Fanatic!

Nov 9, 2007
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First and foremost you can't define both current and voltage simultaneously like that.

You either force the voltage to ramp and accept that the load will define the current waveform or you force the current to ramp and accept that the load will define the voltage waveform.

Do you understand this?

DerStrom8 likes this.
4. ### #12 Expert

Nov 30, 2010
16,685
7,323
To get 10 volts to deliver .15A, the load has to be 66.666666 ohms.
The resistor in parallel with the 180 ohm coil will be 105.882 ohms.

Stupid answer? Best I can do with what we were given to work with.

5. ### Ron H AAC Fanatic!

Apr 14, 2005
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I don't think he wants the voltage across the coil to be a triangle. I think the current needs to be a triangle which is controlled by a triangle voltage waveform.
He can use a voltage-controlled current source. I have one designed, but, as I said, we need the frequency and the inductance. We need these to determine the maximum voltage across the inductor, so we can select the supply voltage.

6. ### Ron H AAC Fanatic!

Apr 14, 2005
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Delete works well.

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7. ### DerStrom8 Well-Known Member

Feb 20, 2011
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Oops, I'm used to ETO, where they don't let you actually delete the post

Thanks Ron. It should be gone now

8. ### stesmall Thread Starter New Member

Apr 18, 2013
6
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Thanks for replies.

Yes, I understand.
I want to force the current to ramp up to 0.15A linearly and then back down (triangular wave)

The voltage source giving the triangular wave up to 10V only has a small output current. It gives 0 to 10V on open circuit. When I short circuit the current is approx. 30mA and also the current is not stable but tends to reduce.

Not sure of coil inductance. Is that necessary?
I can alter the rate of increase/decrease of the repeating triangular wave

9. ### Ron H AAC Fanatic!

Apr 14, 2005
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What is the maximum frequency?
Do you mean that the duty cycle is variable?

10. ### stesmall Thread Starter New Member

Apr 18, 2013
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I mean the gradient of the slope. Msx is 2v per second. So 5s to go from 0 to 10.
But have option to choose lower ramp rate.
The triangular repeating waveform is always positive. It goes 0 to 10 to 0 to 10 etc at the rate that is set.

11. ### Ron H AAC Fanatic!

Apr 14, 2005
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Is the maximum falling slope also 2V/sec?

12. ### stesmall Thread Starter New Member

Apr 18, 2013
6
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Hi,

Yes. Falling slope is the same as the rising slope.

13. ### stesmall Thread Starter New Member

Apr 18, 2013
6
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Thanks Ron and others for your help.

Measured the inductance of coil at 1030mH.

cheers

14. ### Ron H AAC Fanatic!

Apr 14, 2005
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This works in simulation. I can't guarantee that it will work in hardware.
R3, R5, and C1 prevent oscillations that are dependent on the capacitance of the inductor. I tried it with inductor stray capacitance values from 0 to 10nF, and it was stable when those 3 components were included. Without them, it oscillated with some values of stray capacitance.

• ###### triangle current source.png
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stesmall likes this.
15. ### stesmall Thread Starter New Member

Apr 18, 2013
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Hi Ron that is great. Thanks very much.

I know this request may seem a bit compulsive but I would really like to know how you came to design the circuit the way you did and what each component is doing.

My electronics knowledge is OK but when it comes to designing circuits and systems I struggle.

If it is not too much to ask I would really appreciate if you could shed some light.

thanks once again.

16. ### Ron H AAC Fanatic!

Apr 14, 2005
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I don't want to address every component. Attached is a basic explanation of how the circuit works. I explained R3, R5, and C1 in the post with the working schematic. The other parts are a voltage regulator and some power supply decoupling capacitors.

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17. ### atferrari AAC Fanatic!

Jan 6, 2004
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Be aware:

Criminals with double identity tend to mislead investigators.

Multi-forum members tend to mislead themselves.