General 3 Legged Reg PCB (Possible Group Buy?)

What people are working on at the moment
User avatar
Mike H
Amstrad Tower of Power
Posts: 20157
Joined: Sat Oct 04, 2008 5:38 pm
Location: The Fens
Contact:

#121 Re: General 3 Legged Reg PCB (Possible Group Buy?)

Post by Mike H »

Yep, or using a stock value, 750R, or even down to 470R. What I'm not sure about is further Voltage drop by the rectifier and regulator circuit, as that's the only path for the LED current to flow through.
 
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
Andrew
Eternally single
Posts: 4206
Joined: Thu May 24, 2007 2:18 pm

#122 Re: General 3 Legged Reg PCB (Possible Group Buy?)

Post by Andrew »

The idea is that if the polyfuse trips the LED will light, it was suggested as a possible enhancement so I thought I would include it. Basically, if the fuse goes high impedance the reg will be running off the parallel circuit that contains Rled and the LED, so you're look at several diode drops to ground plus Rled for whatever you input voltage is, my spice model say between 470R and 560R should be fine for 9v input.

I can post the model if folk want to have a play?

cheers,

Andrew
Analogue, the lost world that lies between 0 and 1.
simon
Thermionic Monk Status
Posts: 5600
Joined: Thu May 24, 2007 11:22 am
Location: People's Republic of South Yorkshire

#123 Re: General 3 Legged Reg PCB (Possible Group Buy?)

Post by simon »

Ah!!! I see. That makes much more sense, thanks Andrew.
SimonC
Old Hand
Posts: 545
Joined: Mon Sep 24, 2007 11:34 am
Location: West Yorkshire

#124 Re: General 3 Legged Reg PCB (Possible Group Buy?)

Post by SimonC »

Hi Andrew,

Just want to check that I'm reading the silk screening correctly:

The Vout calc on the silk screen looks to be different to what I'd expect. The last portion is usually (1+R2/R1) but this is showing (1+R1/R2) once I transpose the x,y & z. I usually just use a voltage reg calc app so I'd not noticed this before...

I'm building a high current one at the moment with an LM1084. Its proving to be a slightly quirky device; I should have read the datasheet properly, I got as far as it being pin-compatible with LM317 and dropped it in to a board I'd already built, but its not playing nicely. Looks like it needs more current on the adjust pin than a 317 to get it to regulate and I'd not picked up on that until just now. Thats this evenings job sorted then :)

Cheers
Simon C
Andrew
Eternally single
Posts: 4206
Joined: Thu May 24, 2007 2:18 pm

#125 Re: General 3 Legged Reg PCB (Possible Group Buy?)

Post by Andrew »

Could be my mistake, I'll check; the calcs are on the data sheets

Could it be oscillating?

Don't forget the silkscreen printing on one of the caps is upside down, the PCB mostly follows convention in that the negative of the electrolytics are pointing down as you read the writing one of them the silkscreen marks negative as positive.

Andrew
Analogue, the lost world that lies between 0 and 1.
SimonC
Old Hand
Posts: 545
Joined: Mon Sep 24, 2007 11:34 am
Location: West Yorkshire

#126 Re: General 3 Legged Reg PCB (Possible Group Buy?)

Post by SimonC »

Andrew wrote: Mon Mar 20, 2017 9:21 am Could it be oscillating?
Andrew
Probably, it looks like it needs 10uF on the input and a touch more current on the adj pin to get it stable and regulating. Easy mods to try now I've got my head into the differences.
Andrew wrote: Mon Mar 20, 2017 9:21 am Don't forget the silkscreen printing on one of the caps is upside down, the PCB mostly follows convention in that the negative of the electrolytics are pointing down as you read the writing one of them the silkscreen marks negative as positive.
Yep, I'd marked up all my PCB's with the changes when t'other Simon spotted they were inverted. I'm using tantalum bypass caps so its a non-issue on this build in any case.

Cheers
Simon C
Post Reply