Simple, no-math transformer snubber using Quasimodo test-jig - Page 2 - diyAudio
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Old 27th September 2013, 03:01 PM   #11
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Thanks - great stuff!
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Old 28th September 2013, 12:46 AM   #12
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Thanks, guys.

I have just used snubbers on a SMPS and got excellent results: Is this real? - simulation of parasitics

(In post #123)

Quote:
Originally Posted by Johno View Post
Final point is that the snubber components need to be located as close to the transformer as possible for the best results.
Dan,

Practically, there must be some wire length between the transformer and the rectifier diodes that will be about 50nH to 200nH.

I did a bit of LTSpice simulation on this model and I remember I made the assumption that the CRC snubber need to be cloose to the diodes instead of the transformer. So your point now makes me to re-examine my previous assumption.

Could you please elaborate a bit more?

Regards,
Bill
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Old 28th September 2013, 01:38 AM   #13
Johno is offline Johno  Australia
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Close to the transformer is wise because this is where the tank circuit that is storing energy is located, in the leakage inductance and the inter-winding capacitance. We dissipate that energy at the source. The diodes do not radiate the ringing as RF, it is large structures like transformers and wiring that do the radiating. And in any case, the voltages and currents across the diodes when snubbed become nice and softly rounded no matter where the snubber is, and this is because the power factor at the ringing frequencies is now resistive.
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Old 28th September 2013, 04:24 PM   #14
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Congratulations for the excellent work.
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Old 28th September 2013, 04:50 PM   #15
Bonsai is online now Bonsai  Taiwan
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Very nice Mark! Great write up on something that is important and very useful!
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Old 29th September 2013, 01:18 PM   #16
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Looking at the finite impulse response in the time domain is a cool way to work out the damping resistance. This gave me a grin, as my experience looking at problems from this angle comes from working on PSTN line echo cancellation DSP software with adaptive filters to work out the finite impulse response of any echo coming back to you so you can produce a replica and remove it.

Definitely adding it to my bag of tricks!
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Old 6th October 2013, 03:26 PM   #17
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Mark,

considering the test circuit that you use, is there anything special about its layout considerations? I would like to make (etch or point to point) a board with it, so I am curious.
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Old 6th October 2013, 04:49 PM   #18
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Quote:
Originally Posted by audiostrat View Post
... is there anything special about its layout considerations? I would like to make (etch or point to point) a board with it, so I am curious.
If you use a gate driver IC that pumps out a LOT of current, you'll want to make short, wide, low-inductance traces for its power and ground connections. I built a 49mm x 49mm PCB (for seeed's lowest price) and used 40 mil (1.02 mm) wide traces & numerous bypass capacitors. The attachment "Quasimodo_V3_SMD_sch.png" connected to post#1 on this thread, shows its the schematic.

I also built a prototype of Quasimodo on solderless breadboard, and it worked quite acceptably: see photo here. The "gate driver" was six 74AC04 logic inverters connected in parallel, giving 6 x 24mA output current.
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File Type: jpg Quasimodo_on_perfboard.jpg (203.2 KB, 1157 views)
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Old 6th October 2013, 05:48 PM   #19
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The bypass caps are 100nF ceramic? I mean, how high quality should the actually be?
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Old 6th October 2013, 06:15 PM   #20
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Quasimodo V.3 SMD uses 0.15uF 100V ceramic capacitors, X7R dielectric, 1206 package. I happened to purchase them from DigiKey, I picked Samsung CL31B154KCHNNNE (link). As the design note says on page 22,
Quote:
For ease of pick-and-place with SMD capacitors (which are unmarked!) I chose a single capacitance value to be used in every capacitor position: 0.15 microfarads. The oscillator timing capacitor is 0.15uF, the 555 control voltage bypass capacitor on pin 5 is 0.15uF, and all seven of the supply bypass capacitors are 0.15uF. With only one value capacitor for the entire board, it's impossible to solder a wrong value cap in the wrong position.
For Quasimodo V.4 Thru Hole, I gave myself permission to use different capacitor values in different positions, since leaded capacitors have markings that tell you their value. The supply bypass capacitors I chose were Kemet X7R ceramics, 0.1uF, 100V, 0.1 inch lead spacing. I bought these at DigiKey (link).
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