Hartley oscillator: amplitude not stable

Thread Starter

patpin

Joined Sep 15, 2012
401
Hello, I made a Hartley oscill. at +- 513KHz;
My problem is the 300mV amplitude instability on a Vpp of 13.5.
The scope records 1 and 2 are made at the base of the Q2.
The third record is even more unstable at c(Q1).
Is there a way to make it better?
 

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danadak

Joined Mar 10, 2018
4,057
If you use a scope on infinite persistence and look at supply rail you
can see pk-pk noise, will tell you if you have ineffective bypass solution
for the power rail.

Battery does not guarantee power rail is fixed, no noise. Depends on its
internal ESR which rises as it discharges.

Regards, Dana.
 

Thread Starter

patpin

Joined Sep 15, 2012
401
If you use a scope on infinite persistence and look at supply rail you
can see pk-pk noise, will tell you if you have ineffective bypass solution
for the power rail.

Battery does not guarantee power rail is fixed, no noise. Depends on its
internal ESR which rises as it discharges.

Regards, Dana.
I ment a car battery of 70AH, so I guess this will be stable source.
In the mean time I found the cause. The coils were air coils.
I have put 1/4.5 th of the windings on a toroid an here are the results.
Greetings and thanks for interventions. By the way I baught a Psoc 4 in order to do some tests. I guess I cannot generate a 520KhZ wave with it?
 

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danadak

Joined Mar 10, 2018
4,057
The PSOC 4 does not have the Wavedac in it because of no DMA unless
you have the 4M family part.

If you had the 4M part it does not allow use of WavedaC but not too difficult
to set up DMA from a table feeding the DAC to get a user specified waveform.

ThE PSOC 5LP has Wavedac.

What freq do you need ?

Regards, Dana.
 
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Thread Starter

patpin

Joined Sep 15, 2012
401
The PSOC 4 does not have the Wavedac in it because of no DMA unless
you have the 4M family part.

If you had the 4M part it does not allow use of WavedaC but not too difficult
to set up DMA from a table feeding the DAC to get a user specified waveform.

ThE PSOC 5LP has Wavedac.

What freq do you need ?

Regards, Dana.
530KhZ
 

danadak

Joined Mar 10, 2018
4,057
Max sample rate = 6 Msps / .53 Mhz = 11 samples which is too small
a table to get reasonable sine accuracy and harmonic content.

I have used 32 samples, recall I had > 40 db harmonic suppression.
So that would equate to 187 Khz.

Its DAC settling time the primary issue.

Regards, Dana.
 

Bordodynov

Joined May 20, 2015
2,906
I took the liberty and corrected your scheme. I reconnected the resistor R4. This significantly reduces the load and increases the quality factor of the oscillatory circuit. I also improved the transistor bias, and this will increase the temperature stability of the mode of this transistor. I also added an active oscillator amplitude adjustment. In this case, the transistor is not saturated, which also increases stability. In addition, the output spectrum is much better.
2018-07-07_09-27-16.png 2018-07-07_09-28-02.png
 

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Thread Starter

patpin

Joined Sep 15, 2012
401
I took the liberty and corrected your scheme. I reconnected the resistor R4. This significantly reduces the load and increases the quality factor of the oscillatory circuit. I also improved the transistor bias, and this will increase the temperature stability of the mode of this transistor. I also added an active oscillator amplitude adjustment. In this case, the transistor is not saturated, which also increases stability. In addition, the output spectrum is much better.
View attachment 155749 View attachment 155750
Thanks for yr help! I need an amplitude as high as possible but (with this 8V supply) with as small variations as possible in amplitude, say 1 - 2 %.
 
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Thread Starter

patpin

Joined Sep 15, 2012
401
Do you think this circuit is robust enough to be functional (same amplitude at -10°C as at 85°C and with same amplitude variation of a few %) at -10°C as at 85°C ? (Is for automotive).
 
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Thread Starter

patpin

Joined Sep 15, 2012
401
As power supply I have used a LDO volt.reg. ( LM2940T-8.0/NOPB ) and as C 0.47µF and 47µF. Is this enough for this circuit in an automotive environment or should I add 1 or more TVS's.
 

Thread Starter

patpin

Joined Sep 15, 2012
401
I advise you to use an inductive choke and TVS.
OK. Which one of each would you advise . The main power supply is car batt. & charging system up to 14.4V.
And for the inductors L1 and L2: I do not have stable results with them. I have wound them on a toroid and L1 is less than one turn which is difficult to stabilise;L2 was 15 turns. Should I purchase one of the correct inductance or should there be a trimming possibility? for both? And in this case what would you make or buy to be robust and temp. resistant?
 
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