DESIGNING A SUPERCAPACITOR CIRCUIT

[magicasd]

hi, i'm given a project assignment of building a supercapacitor which can store roughly 700V to 1000V.
Now i'm designing a circuit (discharging) which can help me light up a few LEDs  using Voltage  charge stored in the
supercapacitor. The purpose of the circuit is to show that the supercapacitor can Light up the LEDS for a certain period of
time..    I would like to know  how to design a circuit which can  control the rate of discharge of the supercapacitor.
what are the components required to step down and control the high voltage in order not to destroy the LEDs...

[pyrohaz]

Well, remember that you will need to consider the self discharge of the capacitor (The capacitor 'looses' charge through leakage over time) you will obviously need some form of step down converter to a voltage useable by the LEDs, it might be quite hard to design a step down converter using discreet components and i'm personally not sure of any commercial step down converters (im quite sure they exist though :)

To control the rate of discharge, you can vary the current flow from the capacitor.

If you have a set discharge, you can just use a simple resistor and LED series configuration. While you probably won't be able to control the current through the LEDs too well, you could probably work out the rate of discharge from the current being drained from the capacitor. This wouldn't be a very efficient way of stepping down the voltage as the excess voltage will be given off as heat through the resistor. Also, since you stated a 300v difference in charge, teh resistor would either have to be configured for the highest voltage (1000v) or variable with the voltage.

At 1000v with 1 LED, the value would need to be 56k at around 22w! Thats a lot of power dissipated as heat.

[saanvi]

hi ,good project to work on,but i think instead of voltage you must concentrate on charge stored,you can use 1 farad /5.5 v capacitors in parallel and you have to use 2 led in series (and now make parallel combinations of such 2 leds)in india  i could get this cap at http://www.onlinetps.com/shop/index.php?main_page=product_info&cPath=95_96&products_id=667 ,.u could also get it at your place ,just search though its hard to find value ,u can go for higher capacitance like 10 f but low voltage so that u dont need to apply resistance.

[Hero999]

Hee needa a 1000V capacitor which would mean putting 200 5.5V capacitors in series.

The most efficient way is to use a switching regulator which I'd say is the only choice if you want it to last for as long as possible. Usign a lower is much more sensible as it's safer and can be more easily stepped down to a lower voltage. You don't want the voltage to be too low though as it will mean less energy can be taken from the capacitor. I'd recommend going for 60V because it will make finding an SMPS IC easier.