# generating 50KHz sinusoidal current (test)

Discussion in 'General Electronics Discussion' started by eem2am, Jan 17, 2013.

1. ### eem2am

429
0
Aug 3, 2009
Hello,

I need to generate a ~50KHz sine current of peak = 350mA (actually 350mA to 1A is fine)
Is this an OK way of doing it?
http://i46.tinypic.com/vgrc5z.jpg

.....the resistor on the RHS is the resistor in the test circuit, into which the 100KHz will be injected.

Last edited by a moderator: Jan 18, 2013
2. ### Harald KappModeratorModerator

12,455
2,984
Nov 17, 2011
This will give you a square waveform, filtered by the output L and C to look not so quare anymore. Bit it is way off a sine wave. Use a true sine generator (Google) using some OpAmps and RC components.

3. ### eem2am

429
0
Aug 3, 2009
Thanks, though the book i have by babani on oscillators says that sine wave sources with opamps are a bit hit and miss.

(And sorry it was 50Khz not 100Khz)

Here is the circuit so far any way..................is there a simpler way to generate an approximately 50Khz sine of peak value approx = 600mA?

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429
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Aug 3, 2009
5. ### eem2am

429
0
Aug 3, 2009
Also, you say its way off being a sine..............but here it is.........

http://i50.tinypic.com/1r3mza.jpg

.............that's easily sinusoidal enough for my purposes......so whats wrong with my circuit, and is there a simpler way of doing it?

************************************************************
As an alternative way of getting a sine.............I am considering this £100 sig gen...(i can fiddle things to use this sig gen).....................

GFG-8015G sig gen
http://www.gwinstek.com/en/product/p...&mid=73&id=106

...but it doesnt say if its output is isolated?, or if it can produce sine wave voltages of peak just 15mV and do this accurately?

Do you know the answer to these?

Last edited: Jan 17, 2013
6. ### Harald KappModeratorModerator

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Nov 17, 2011
If you are satisfied with the output signal, then there's nothing wrong with your circuit. There are other solutions, but your circuit is already rather simple.
OpAmp circuits are a bit tricky to stabilize, but modern OpAmps can handle 50kHz without problem. Again, however, no need to change your circuit.

As to your current requirements: I can't decide on this issue from my place. Just test the circuit drawing as much current as you need and check the waveform. just make sure that the inductor at the output is rated for at least that current so it will not saturate. If the inductor saturates due to overcurrent (with respect to the ratings), it will loose inductance and will no longer filter as expected.

7. ### eem2am

429
0
Aug 3, 2009
Thanks, what about the problem i am having here with a DC level appearing in the sine wave output of a filtered square wave circuit?.........................

I have produced a 50KHz sine wave by filtering a 5V, -5V square wave in LTspice.

Despite the output being capacitively coupled, the output sine wave has managed to acquire a DC level of 70mV…….the input square wave has an input DC level of 0mV.

How has the sine wave got this DC level?…here is the schematic….(its also attached )

Schematic
http://i49.tinypic.com/2953lom.jpg

Here is the output sine waveform, showing its been “Lifted”….

Output waveform
http://i45.tinypic.com/wi4ag.jpg

Here is the LT1006 op amp datasheet:
http://cds.linear.com/docs/Datasheet/1006fa.pdf

the ltspice file is also attached.

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8. ### Harald KappModeratorModerator

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Nov 17, 2011
Don`t trust the simulation too much. The OpAmp has a max. offset voltage of 50µV.

Also let the simulation run for some more time. As you can see already in the short interval that you posted, the DC level is declining with time. This is due to the coupling capacitor. 10µF take some time to be charged. The charge current produces the DC offset at the output. At 50kHz you don`t need 10µF. Use a 100nF ceramic capacitor instead.