Hartley oscillator doesn't start anymore.

Thread Starter

patpin

Joined Sep 15, 2012
401
... Something else to try as far as increasing Vpp ... place a 100 μF capacitor in parallel with R1. This should increase the Vpp amplitude ... but may require adjusting. ... Not sure why LTSpice gives a greater Vpp amplitude ...
Didn'd have such a C. I too an elco: this reduces out0 to 0 Vpp. Also a smaller C 2.2µF does the same. (Also on LTSpice oscillation dies after 0.1msec.) What do I have to adjust. Before, when the oscillator functioned during months, I effectively had 15Vpp.
 
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Bordodynov

Joined May 20, 2015
3,157
If you place your schema file in LTspice format, I will correct your schema to work. I also see my footprints in this schema. I helped somebody to develop the scheme and did an automatic adjustment (stabilization) of the oscillator amplitude. You can, of course, find the place where you took your prototype and use my original scheme.
 

Thread Starter

patpin

Joined Sep 15, 2012
401
If you place your schema file in LTspice format, I will correct your schema to work. I also see my footprints in this schema. I helped somebody to develop the scheme and did an automatic adjustment (stabilization) of the oscillator amplitude. You can, of course, find the place where you took your prototype and use my original scheme.
Thanks Bordodynov. I think I have the diagram you are talking about (https://forum.allaboutcircuits.com/threads/hartley-oscillator-amplitude-not-stable.150204/page-2 post #39) ... but did not realised it because the old (this one) one WAS functioning. I think I will change my mind and realise yours...
 

Thread Starter

patpin

Joined Sep 15, 2012
401
I would like to amplify this signal and send it through a 55µH coil with about 50mA current. Can you advise me on that. When I try it, it reduces my oscillations to 0.
 

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Danko

Joined Nov 22, 2017
1,822
I would like to amplify this signal and send it through a 55µH coil with about 50mA current. Can you advise me on that. When I try it, it reduces my oscillations to 0.
Change R1 to 51 Ohm and R5 to 100 kOhm. It will oscillate.
EDIT:
So, final:
R1 - 51
R2 - 200
R5 - 51k
R8 - 51k

EDIT more:
R5 should be 68k
upload_2019-7-23_1-21-52.png
 
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Thread Starter

patpin

Joined Sep 15, 2012
401
Change R1 to 51 Ohm and R5 to 100 kOhm. It will oscillate.
EDIT:
So, final:
R1 - 51
R2 - 200
R5 - 51k
R8 - 51k

EDIT more:
R5 should be 68k
View attachment 182229
Very nice and compact, Danko. Is there a formula for calculating resistances?
And there is another problem: thermostability is gone (joint image is at 10, 25 and 85°C
 

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Danko

Joined Nov 22, 2017
1,822
Indeed. Is there an easy solution fitting on a very small board and functioning itself at high temperatures and working on 9V
Well, are you interested in alternating magnetic field of 55uH coil and does not matter presence of its constant component?
 
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Thread Starter

patpin

Joined Sep 15, 2012
401
Well, are you interested in alternating magnetic field of 55uH coil and does not matter presence of its constant component?
I am trying to achieve this: The current is passed to a coil (the endcoil as in yr ampli), but this coil is partly in counterphase and wound on a E -type ferrite core. On the third leg of this coil there is a detection coil. This coil detects the presence of a rotating ferrite rod. Those changes (the modulation of the 600KHz wave) ares small (ferrite is 1mm diameter and turns at a distance of 1/2 mm from the legs of the E-core at a speed of 600Hz). When voltage levels at detecting coil is e.g. lower, due to temperature changes, the output of the detecting coil will detect a lower level sooner. This should not happen since the time at which the level descends to a certain threshold is important. That's why I need a stable output at the ampli.
 
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Danko

Joined Nov 22, 2017
1,822
See, voltages V(out2) are equal, therefore alternating currents in L2 I(L2) are equal, so alternating magnetic fields at different temperatures are equal.
Seems, not bad...
upload_2019-7-23_15-47-11.png

And, why not use square pulses with frequency you need, instead sine?
Much easier, and same result...
 
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Thread Starter

patpin

Joined Sep 15, 2012
401
See, voltages V(out2) are equal, therefore alternating currents in L2 I(L2) are equal, so alternating magnetic fields at different temperatures are equal.
Seems, not bad...
View attachment 182284

And, why not use square pulses with frequency you need, instead sine?
Much easier, and same result...
When I look at the currents I(L2) I see differences of at least 20% between green and red sine, or am I wrong? Could a PTC in series with L2 help and how to dimension?
 
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Danko

Joined Nov 22, 2017
1,822
When I look at the currents I(L2) I see differences of at least 20% between green and red sine, or am I wrong?
You should measure alternating current between top and bottom of red sine, not between top and ground.
Also between top and bottom of green sine.
Then compare.
They are equal, only shifted vertically.
Shift level (direct current) does not transform to coupled inductance (detecting coil).
 
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