auto buck booste curcuits

[hoffmyster86]

hi all,

has any one got practable knowladge using these type of boards?

http://www.ebay.co.uk/itm/DC-DC-Aut...902?pt=LH_DefaultDomain_0&hash=item5d36ece366

http://www.ebay.co.uk/itm/DC-DC-Adj..._Measurement_Equipment_ET&hash=item3366d3e7b7

i've tried the red board, very accurate at various inputs from single 3.7 cells to 14v..the output was the same @12.31v.

on an osillioscope theyre noisey and have a pulse signature there at 200us 10millisecs..but its a similar scope reading to all my 12vdc mains adaptors.

so what noise levals are acceptable etc? do the auto buck boostes have any draw backs? do they shorten life spand etc etc..

help?

thank you.

 

[hoffmyster86]

anyone?

 

[AnAppleSnail]

I can't tell you what noise levels are acceptable without knowing what your application is.

 

[hoffmyster86]

cctv cameras, a reversing screen @ 12v and olson black LED @3v

eather running from 12v and stepping down to the 3v or seperatly with a auto B/B board supplying each seperatly.

 

[SemiMan]

cctv cameras, a reversing screen @ 12v and olson black LED @3v

eather running from 12v and stepping down to the 3v or seperatly with a auto B/B board supplying each seperatly.

I expect that pulse signature is at 20usec, not 200usec, i.e. 50KHz switching frequency.

They claim Sanyo caps ... but those markings do not look like Sanyo to me (or Panasonic) as they typically have a voltage code and series code, not cap/volt/series. If they were Sanyo great, but if not .... well. They do have a secondary LC filter which will keep the noise down.

That said, unless you really know what you are doing, measuring noise on a switch mode supply is not easy.

No issues at all driving the LED.

With the camera it will all depend on the camera and what is inside it. It may have no issues, then again you may see regular bands across the display at the beat frequency between the line rate of the camera and the switching rate of the power supply. Sorry if those terms do not mean anything, but it is hard to express it any other way.

If you have issues, then put an inductor, say 10 uh, designed for 2-3 amps in series with a good 1000uf, low ESR capacitor that is parallel with a 10uF tantalum or ceramic cap. Make sure they are of sufficient voltage. .... if your camera load is low, you could even do a 1-2 ohm resistor in series with a capacitor.

 

[hoffmyster86]

semiman, thank you for that.

yes theres white bands floating up the screen, like the old valved tv's used to get when they needed setting.

where do i put the inductor set up? before or after the board? or where to put the resistor and capaciter? is it literaly on the posative wire so to speek.
1 camera is 130mah, the other states 250 mah, the screen draws abut 130mah also.

(my thoughts were to rectify it...eather with the old 4 diodes way or using a bridge rectifier).

 

[SemiMan]

semiman, thank you for that.

yes theres white bands floating up the screen, like the old valved tv's used to get when they needed setting.

where do i put the inductor set up? before or after the board? or where to put the resistor and capaciter? is it literaly on the posative wire so to speek.
1 camera is 130mah, the other states 250 mah, the screen draws abut 130mah also.

(my thoughts were to rectify it...eather with the old 4 diodes way or using a bridge rectifier).

It's already rectified. There is nothing to be done there. The RC or LC filter would be after your converter. It will help some, but you also need to be careful of ground loops. Switching noise can be a pain to deal with.

+ output of converter to one lead of inductor, other lead of inductor to + lead of cap, - lead of cap to - output of converter. Your cameras and screen connect now across the capacitor.

You must use a high frequency low ESR capacitor (one designed for switch mode power supplies) and you should have in parallel a ceramic or tantalum cap for the highest frequencies.

As the board already has a secondary filter inductor (in theory), you may just be able to solder across the existing capacitor with a bigger/better one.


Semiman

 

[hoffmyster86]

hey, thank you for that, some light at the end of the tunnel..