Filament LED bulbs, Jack connector arrays, ceramic cap linearity - Page 1
Forum section: electronics / general

author: Yansi
author_rank: Super Contributor
timestamp: March 08, 2015, 01:50:12 am
content: Hi,I have a three completely unrelated questions:http://www.talaled.com/uploads/3/1/0/9/31090387/s825693237280359478_p18_i1_w640.jpegDo these type of bulb have an inverter? or are they powered directly from mains? How's than managed the current to be constant with the varying voltage? (considering the VA characteristic of LED) Cause I don't see any place in the bulb on the picture, where the costant source driver circuitry should fitHave you seen this type of jack array connectors at any component supplier? (See picture in attachement please) They have somewhat standard imperial-grid (0,1 inch) fotprints, tied together and colored inlets? Where can I buy them? (Yes it is a sound card type conector array - exactly that I need)Would you consider a ceramic capacitor with same capacity (eg 1uF) and dielectric (eg X7R) but higher voltage rating to be more linear considering the same bias voltage and voltage swing accross the cap? I simply needed a coupling cap for audio signal level stuff for a simple project, and my mind has gone:"Oh well, using a ceramic in a signal path... crap! But I don't have any aluminium electrolyte caps of 1uF... nor have I 1uF tantalum in my drawer. What will I do? Wait a minute, will the change of voltage rating of the ceramic change something, if I overrate the voltage?"So how does really "the linearity" of X7R ceramic cap (at the same operating conditions) change when changing the voltage rating of the cap? Will there be any difference, between distortion produced by 6.3V rated cap and 50V cap?Thank you for your help,Y.

author: sleemanj
author_rank: Super Contributor
timestamp: March 08, 2015, 02:14:06 am
content: Quote from: Yansi on March 08, 2015, 01:50:12 amYou really don't need much of anything.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 08, 2015, 04:05:16 am
content: Quote from: Yansi on March 08, 2015, 01:50:12 amI'd be far more worried about microphony than distortion on a coupling capacitor!Yes, the C(V) curve is more-or-less proportional to the voltage rating, so it is substantially linear for voltages under 20% of ratings.More importantly, the linearity is considerably better for small voltages swings, due to calculus. There's no way you'll see > 0.1% distortion, at the cutoff frequency, for a 1V RMS signal.Tim

author: Yansi
author_rank: Super Contributor
timestamp: March 08, 2015, 10:10:37 am
content: sleemanj: Thanks, taht explains why they suggest using trailing edge dimmers with these bulbs. (That fact was originally the starting point of my investigation).T3sl4co1l: Microphony, linearity and all sorts of that things were in the cr*p word in my description. I needed to build and test an SMD circuit very fast... but I changed my mind and tommorow I'm going to buy tantalum cap. Size A (EIA3216) fits exacly the 1206 pads I left on the board yesterday, for the 1 mike 50 volt ceramic.And yea, the smaller the swing accross the cap, the smaller the capacity change. Cap was calculated for the cuttof to be round about 8 Hz, so the voltage acrross cap in the passband should be small enough.I admit I have never got caught by ceramic cap microphony phenomenon. For THT, I use foil/ellytic automaticaly as needed, but I haven't done much audio stuff in surface mount. Maybe I will make an experiment. What do you suggest to use as a cercap and PCB configuration, to magnify the the phenomenon? Would be interesting and educative, to make and SMD cap microphone...I think mechanical stress make the capacity change, so I should use some thin PCB substrate for that.. (and apply some DC bias to get the result)Thx for repliesY