General 3 Legged Reg PCB (Possible Group Buy?)
- Mike H
- Amstrad Tower of Power
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#121 Re: General 3 Legged Reg PCB (Possible Group Buy?)
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."
#122 Re: General 3 Legged Reg PCB (Possible Group Buy?)
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
I can post the model if folk want to have a play?
cheers,
Andrew
Analogue, the lost world that lies between 0 and 1.
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#123 Re: General 3 Legged Reg PCB (Possible Group Buy?)
Ah!!! I see. That makes much more sense, thanks Andrew.
#124 Re: General 3 Legged Reg PCB (Possible Group Buy?)
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
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
#125 Re: General 3 Legged Reg PCB (Possible Group Buy?)
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
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.
#126 Re: General 3 Legged Reg PCB (Possible Group Buy?)
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.
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