Zetex SC310 Circuit Design Query & Analysis

[ViReN]

Hello All,

I have already ordered tens of Zetex SC310 & Related components from Digikey recently.

I have downloaded some Datasheets, Application & Design Notes relating to the SC310 Chip, Also viewed Datasheets for FMMT617, 618, 619 Transistors....

Since I have a very specific requirement, I have a few Queries

Pic1: Schematic for Max Brightness Solution

From All the studies that i have carried out on this chip, it is apperent that

1) Increase in Inductance (L1) will give rise in Output Voltage
2) Decrease in Resistance (R1) will give rise to Current Output

Are these things true ?

Also, By Default, this DC-DC Is not Regulating, and it would be wise to use MrAl's Circuit to get some regulation. Which can be viewed here

Is there any LT Spice File available for simulating Zetex SC310 Chip ?
I am using SwitcherCADIII that has been downloaded from the Linear Technology Site.

Thanks & Regards,
ViReN

 

[MrAl]

Hi again Viren,

Increase in inductance doesnt really increase output
voltage because you normally have an LED connected
on the output anyway which limits the output voltage,
and you dont usually run the circuit without a load
anyway :-)
A decrease in the sense resistor does increase output
current because it increases max current through the
inductor during the charge phase.

You're right, it's not normally regulating.

As far as i know, the only simulation model available
is the one i developed myself and i dont know if it
runs in Switchcad or not as i know only one person
who tried it and they said they couldnt get it to run
in Switchcad. I can find the model and post it if you're
interested. It's not a perfectly 'true' model as it
doesnt model EVERY aspect of the chip, but rather
simulates the chip and while running gives you an idea
what you'll see with a circuit like that shown on the
Zetex site (NPN transistor, etc.) [the 300 chip].

I've also got a *program* that simulates the Zetex 300
chip but it's not in .exe form. It's in another
language that needs a base interpreter installed
first in order to run. What would be interesting
i guess would be to put this into standard .exe form
and then allow users to input inductance value and
cap value and LED type, then do a simulation.
That would allow some experimentation with inductor
values and stuff like that...would be pretty cool
i think.

As soon as i get this next part of the course done,
which has been delayed because of the HP, i'll start
on these other things.

Take care,
Al

 

[ViReN]

Hello MrAl,

Thanks for your kind response.

Is there any other software where i can simulate the "spice" things ?....

I did try Protel 2004 .... .. but it was just an evaulation version.. that unfortunately had expired... 1 month back... and i could not use it to the fullest extent...

Any ways....

Here is my Setup that i will be working on... My aim is to run 6 - 8 LED's from 2AA Cells (may be all of em in series) or some series parallel combination (which ever will give me an Optimum config).

Since, The Datasheets have mentioned running up to 3 - 4 LED's in Series, I plan to use 2 parallely connected strings of 3 or 4 LED's in series.

For this i will be requiring about 11.4 to 15.2 Volts & current of 50 - 60 mA

So, various ways to get value of inductor & resistor is ... Either do it manually (risking components being blown etc etc...my low experiance & knowledge u see) or by Simulating the circuit using Spice Technology... & some kind of the software (lil smarter way to do the things /ubbthreads/images/graemlins/smile.gif ) ... or even using some kind of formula (i wonder if there is any(there must be i think)) to calculate value of Inductance & Resistance..... thereby reducing the chances of Failures.. and Risks involved ... thus saving cost & improving Efficiencies (in both aspects, cost & Circuit wise)

Thanks & Regards,
ViReN

 

[MrAl]

Hi again Viren,

Im not sure if you are aware of this or not but, when
we did the first Zetex 300 circuit we also built up
a 'Luxeon simulator' which is easily constructed
with three or four 1N4001 diodes in series also in
series with a 1 ohm resistor. You can hook up your
circuit using this simulator to check for basic
functionality and when it looks like it works ok
hook up the real LED.

The 1N4001 diodes are very cheap like 10 for a dollar (USD).

Also, when the circuit is first turned on feel the area
around the transistor (not the transistor itself as it
could get very hot very fast) to see if it heats up.
Disconnect power if it feels hot quick.

Take care,
Al

 

[ViReN]

Hello Mr Al,

Kool /ubbthreads/images/graemlins/smile.gif

I am excited... My Package has Reached India, (Mumbai) & is available for clearance.... It will take i dont know how much time... but ... lets see....

I will be constructing the Simulator.. I do have all the components for that...

Thanks & Regadrs
ViReN