No quite.
My calculations give a cut off of 14.5V.

Do you mean your calculations from a few posts back or from the figures I had in my previous post?

 

Do you mean your calculations from a few posts back or from the figures I had in my previous post?

From you resistor values in post #19.

Here's how I often do divider calculations:

• Their is 500mv across the 9.53kΩ resistor at the cut-off point so its current is 0.5/9.53k = 52.47μA.
• This current also goes through the 267kΩ resistor so its drop must be 52.47μA * 267kΩ = 14.0V.
• The input voltage at the top of the 267kΩ resistor must then be the sum of those two voltages or 14.5V.

 

From you resistor values in post #19.

Here's how I often do divider calculations:

• Their is 500mv across the 9.53kΩ resistor at the cut-off point so its current is 0.5/9.53k = 52.47μA.
• This current also goes through the 267kΩ resistor so its drop must be 52.47μA * 267kΩ = 14.0V.
• The input voltage at the top of the 267kΩ resistor must then be the sum of those two voltages or 14.5V.

Thanks.

I just had a look back at your initial post and see the cut-off st 14v.

So going with that & the fig13 on the PDF, I have come up with a list of components.

Would you mind passing over the list for me to make sure I've not made any errors before I hit the buy button? Thanks.

 

Those resistor values give a 14V cutoff.
Is that what you want?

Is that board compatible with the pinout pattern of the surface mount devices you ordered?

Why are is the 10kΩ resistor 0.1% while the 270kΩ resistor is 1%?
They should both be the 0.1% if you are trying to tighten the tolerance of the cutoff voltage.
If you want the voltage to be adjustable you could substitute a 20kΩ trimpot for the 10kΩ resistor.

Otherwise I see no obvious problems with your part's list.

 

Those resistor values give a 14V cutoff.
Is that what you want?

Is that board compatible with the pinout pattern of the surface mount devices you ordered?

Why are is the 10kΩ resistor 0.1% while the 270kΩ resistor is 1%?
They should both be the 0.1% if you are trying to tighten the tolerance of the cutoff voltage.
If you want the voltage to be adjustable you could substitute a 20kΩ trimpot for the 10kΩ resistor.

Otherwise I see no obvious problems with your part's list.

OK.

With you previous post showing me how you calculate the divider I have made a slight change and changed the 10kohm for 9.76k. This should give a 14.3v cutoff if I'm not mistaken, .5v above the input.

Having just worked this out and reread you reply, yes, perhaps an adjustable option could be a good idea.

The tolerances were a complete oversight, thanks for pointing it out.

Where you say 'is that board compatible...' do you mean my actual power supply unit that I currently have?

 

Just had a look again at resistor tolerances and a lowest I can see for the 270k is 1%.

Could I possibly juggle these two around bringing one down to maybe get the lower tolerance & raising the other to the limit of 0.1%. Something for me to look at

 

I have made a slight change and changed the 10kohm for 9.76k. This should give a 14.3v cutoff if I'm not mistaken

That is correct.

Where you say 'is that board compatible...' do you mean my actual power supply unit that I currently have?

I mean are the solder pad spacings on the SMT board compatible with the pin spacing of the parts you are ordering.

Could I possibly juggle these two around bringing one down to maybe get the lower tolerance & raising the other to the limit of 0.1%.

Not quite sure what you mean, but it makes no difference which resistor is the 1% and which is the 0.1%, the effect on the cutoff voltage tolerance is the same (1.1% total).

 

That is correct.
I mean are the solder pad spacings on the SMT board compatible with the pin spacing of the parts you are ordering.
Not quite sure what you mean, but it makes no difference which resistor is the 1% and which is the 0.1%, the effect on the cutoff voltage tolerance is the same (1.1% total).

Sorry half asleep posting.

Ditched board, found better elsewhere.

Have gone down the TrimPot route for more tunability.

 

Thanks to everyone that's has help thus far, pointing me gently in the right direction & a special big thanks to @crutschow for all the pestering he allowed me.

All parts ordered for the LTC4365 setup, I'll post back my findings.

Kindest regards..,

Kirk

 

Just to improve on the design a little, I have considered adding a LED that needs to illuminate when the OV fault occurs.

Researching this I have found a schematic of a demo board for the LTC4365 as well as manual.

Schematic: http://www.linear.com/solutions/4278

Manual: http://cds.linear.com/docs/en/demo-board-manual/dc1555bfa.pdf

to my surprise the schematic shows a red LED (D3) connected between the FAULT pin of LTC4365 & VIN, via CLD3 & D4

These components are listed in the manual as:

CLD3: Current Limiting Diode SOD-80 - CCLM2000
D3: LED Red - LN1251CTR
D4: Diode, 75V/200mW, SOD-523 - 1N4148WT

As for the CLD3, I cannot find this part for sale anywhere, so what would be the equivalent?

Again, the D3, cannot find this but think I have found similar: http://uk.rs-online.com/web/p/visible-leds/7870051/

The D4 is not an issue, here: http://uk.rs-online.com/web/p/switching-diodes/7614283/

So firstly, would the above components work as they are in my project?

What is an equivalent to CLD3?

Is my LED choice correct for the application?

Regards..,

Kirk

 

As for the CLD3, I cannot find this part for sale anywhere, so what would be the equivalent?

It's just a 2 milliamp limiter for the LED. I don't know why you can't do that with a resistor (because you know what the input voltage is). Mfg. = Central Semiconductor.
I could do this with a 2N4416 j-fet, but that would be running you on a strange errand when a resistor will do.

 

Again, the D3, cannot find this but think I have found similar: http://uk.rs-online.com/web/p/visible-leds/7870051/ma.

It's just a stupid LED with a maximum current of 15 ma. Anything that will physically fit will work.

 

The D4 is not an issue, here: http://uk.rs-online.com/web/p/switching-diodes/7614283/

Right. 1N4148 is so common my grandmother knew about them. The only thing stalling you is getting parts in surface mount packages.

 

After a little more searching I found the D3 as shown on the schematic was a surface mount 2.1v, so my choice is not correct, I have now changed this to: http://uk.rs-online.com/web/p/products/7693586/

 

Right. 1N4148 is so common my grandmother knew about them. The only thing stalling you is getting parts in surface mount packages.

As per my earlier post, this part was not an issue, I have since change from SMD to through hole version: http://uk.rs-online.com/web/p/products/7003674/

By the way, you grandmother was very clever

It's just a stupid LED with a maximum current of 15 ma. Anything that will physically fit will work.

Again, this I have already sorted, it's just this CLD3 part now.

Thanks for your helpful input #12

 

Find input voltage, max. Subtract LED voltage. Calculate resistor for 2 ma.
what? about (14V - 2.1V)/0.02?

 

Find input voltage, max. Subtract LED voltage. Calculate resistor for 2 ma.
what? about (14V - 2.1V)/0.02?

Cheers #12, I did look at going the resistor route.

I have now found the CLD3 part: https://www.rapidonline.com/atc-semitec-e-202-e-562-current-limiting-diode-crd-2-0ma-47-2602

 

I have now found the CLD3 part:

The price got a lot better since the last time I looked, but they still aren't down to 7 cents, like a resistor.

 

Just a quick schematic of the project:

 

Or you could put 560 ohms where D2 is.
Or make the pot 2K and place that in series with 8.2K 5% or 8.87K 1% for a finer range of adjustment.

These are not important changes. Just options, mostly to demonstrate the kind of fine tuning methods that come from experience in designing analog circuits.