Amplify Triangular Wave

Thread Starter

stesmall

Joined Apr 18, 2013
6
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!
 

Ron H

Joined Apr 14, 2005
7,012
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!
We need to know the frequency of your triangle wave, and the inductance of your coil.
 

studiot

Joined Nov 9, 2007
5,003
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?
 

#12

Joined Nov 30, 2010
18,076
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.
 

Ron H

Joined Apr 14, 2005
7,012
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?
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.
 

Thread Starter

stesmall

Joined Apr 18, 2013
6
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?
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
 

Ron H

Joined Apr 14, 2005
7,012
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
What is the maximum frequency?
Do you mean that the duty cycle is variable?
 

Thread Starter

stesmall

Joined Apr 18, 2013
6
What is the maximum frequency?
Do you mean that the duty cycle is variable?
Thanks for your reply.

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.
 

Ron H

Joined Apr 14, 2005
7,012
Thanks for your reply.

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.
Is the maximum falling slope also 2V/sec?
 

Ron H

Joined Apr 14, 2005
7,012
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.
 

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Thread Starter

stesmall

Joined Apr 18, 2013
6
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.
 

Ron H

Joined Apr 14, 2005
7,012
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.
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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