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Old 24th December 2012, 05:52 PM   #171
Jenyok is offline Jenyok  Russian Federation
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wintermute
.
Try to simulate our Russian circuit of power reg, see results of simulation and compare results with LM317 as a power reg.
Output voltage ~= + - 15 Volts .
Output load current ~= 0 ... 1 A .
ASC file of circuit for LTSpice IV is in ZIP file.
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File Type: jpg power_draft2.jpg (834.7 KB, 665 views)
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File Type: zip Draft2.zip (3.1 KB, 41 views)
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Old 25th December 2012, 05:21 AM   #172
Jenyok is offline Jenyok  Russian Federation
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Pay your attention to Texas Instruments products
.
TPS7A3001 Vin = -3 ... -36 V , Iout = 200 mA
TPS7A4901 Vin = 3 ... 36 V , Iout = 150 mA
.
TPS7A3301 Vin = -3 ... -36 V , Iout = 1 A
TPS7A4700 Vin = 3 ... 36 V , Iout = 1 A
.
as improvment and changeover to LM317, LM337 .
.
http://www.ti.com/product/tps7a4700?...ps7a4700-pr-in
http://www.ti.com/product/tps7a4901

Last edited by Jenyok; 25th December 2012 at 05:29 AM.
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Old 5th January 2013, 10:03 PM   #173
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Default Zobel network at LM317 output

I have noticed that Morgan Jones uses a 2R7 resistor in series with a 1uf capacitor at the output of the LM317 circuit. Is it there to prevent possible ringing or oscillations? Are LM317's notorious for such incidents?

By the way, I have built a simple guitar preamp using 30V regulated with the aid of a LM317 circuit. But when turning on the amp, there is a high frequency audible noise (close to 20kHz - maybe 15kHz? - I don't know) for 1 or 2 seconds, and then normal conditions - just like charging noise of electric weapons . I have noticed that it happens when the electrolytics have been completely discharged. When turning off and on again quickly, no such sound can be heard.

Is it possible that this is a momentary oscillation? The sound is like a pure sine wave. I am using two 100k resistors at the output to cut the 30V in half, putting a 220uf cap in the 15V joint. And of course this cap charges slowly, could it be the cuplrit of the transient?

Thank you for any input!
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Old 5th January 2013, 10:12 PM   #174
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Yes the resistor in series with the cap on the output is to suppress a resonance that occurs due to the output inductance of the regulator forming a tuned circuit with the output capacitor (normally only an issue if you use low esr capacitors of fairly large value).

2.7 ohms seems a little on the high side (I used 0.33 ohms on mine, which was right on the edge in the simulation).

Jenyok, I didn't see your subsequent posts. My levels of knowlege are relatively low it would take me a while to analyse these new circuits (and I still might not understand what they are doing )

Tony.
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Old 5th January 2013, 10:17 PM   #175
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Quote:
Originally Posted by wintermute View Post
Yes the resistor in series with the cap on the output is to suppress a resonance that occurs due to the output inductance of the regulator forming a tuned circuit with the output capacitor (normally only an issue if you use low esr capacitors of fairly large value).

2.7 ohms seems a little on the high side (I used 0.33 ohms on mine, which was right on the edge in the simulation).
I am using Nippon 22uf (63V, KMG series) - I don't know if these have such low ESR, but I don't know if this is the problem. I can experiment using an additional resistor and tantalum cap. Thanks for the answer!
Any tips on the weird charging noise? Could it be the resonance you mention?

Last edited by audiostrat; 5th January 2013 at 10:28 PM.
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Old 5th January 2013, 10:45 PM   #176
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The resonance frequency is dependent on the size of the cap, I can't remember but I think from simulations that the cap had to be pretty big for the resonance to be in the audible range.

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Old 5th January 2013, 11:16 PM   #177
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Not really, here's a handy graph:

Using 3-pin regulators off-piste: part 3

NB the effective synthetic inductance of the output does depend slightly with the current drawn from the 317, dropping a lot from 5 to 50mA output - with pretty negligible change much beyond that point.
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Old 5th January 2013, 11:33 PM   #178
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Thanks Martin! I suspect that the inductance in the model I have for the LM317 doesn't reflect reality I just simmed with 22uF cap (with no esr to get a really obvious peak) and the resonant peak was at 29Khz..

Attached pic to give an idea, red curve is with 0.5ohms in series with the 22uF cap
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Old 6th January 2013, 05:31 PM   #179
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Tony

Have you taken into account the fact that the o/p inductance of the LM317 reduces significantly as Iout increases? I think Erol Dietz's measurements of resonant frequencies were for a datasheet implementation of the LM317 circuit with 5mA or 10mA Iout, but doesn't your circuit have a larger Iout and therefore a lower o/p inductance?

Last edited by Gopher; 6th January 2013 at 05:36 PM.
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Old 7th January 2013, 06:12 AM   #180
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Hi Gopher, I tried the sim with low current, as you are correct the sim I posted above was using a 1A current source. I ran it at 10ma and there was virtually no difference.

However, I then realised that I was using my YARPS config (which is an implementation of Fred's 1 transistor upgrade earlier in this thread) and when I ran with a standard implementation the resonance peak indeed comes down

Blue is with 10ma load and yellow is with 1A load.

The version with the transistor shifts the resonant frequency up by quite a margin and also has very little difference between minimal and higher current.

Tony.
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