Take the worst case voltage (the highest) for the LEDs and multiply it by the number in the chain. This gives you the minimum voltage you must have available. Add maybe 5V to 10V to give a safety margin.If I had to do all 70 in series, what voltage should it be?
Wouldn't the pcb heat up a lot at 3 watts each?
If I had to do all 70 in series, what voltage should it be?
So if I had to alter my design now, (and considering that 70 3W LEDS might be an over kill, I will do like so. If 230 is the max voltage I will get (without a power supply)...
2) voltage. the "G" pin on Q2 is only rated for 20V, and with this simplest circuit that will limit the input voltage to 20V (lets say 18V to be safe). if you use a different NFET, make sure to check the "Vgs" rating.
while on the other hand I could use 48V with easier access to a driver, safer, but that will need an expensive power supply.
I found this page that explains how to build one, they are labeled with #numbers and the one that might be suitable for me is #3
A linear constant current circuit is simple: R, R, Zener, BJT....and it's easy to get 1000V if you want.its not easy to get a constant current driver capable of taking more then 60v input
But in your case the constant current curcuit does not see the whole supply voltage.... just V_supply - V_LED.
Yes. But usually one wants the "headroom" to be low, to minimize loss.That is true. But any const current driver has to work within the headroom it has.
He will be having about 40-50V headroom in this case and I guess that should be sufficient - if the filter capacitor is doing its job.
600mA / h_FEHow much base drive will be needed? A
Yes. But usually one wants the "headroom" to be low, to minimize loss.
true.But sometimes it cannot be helped.
some designs do so. But it's not my way ... to desgn it flickering., the lamp will turn off for the rest of the 10 ms time.
How can it be? Circuit? Simulation?But with the load always present, the filter cap voltage perhaps will never reach 300V.
How can it be? Circuit? Simulation?
The aim of the constant current is not to provide a precision constant current. The aim is to limit the current to a safe value. 10% of deviation is no problem, no need for a 1% or better LM317So I set out to find a constant current circuit and a common one is with the use of an LM317 however I have an issue
Again you misunderstood the voltages. Since LEDs and constant_current_circuit are in series there never is the full supply voltage across the constant current circuit.Firstly since the max voltage is around 30v, (worse case scenario) I will need (7 leds in series x 3.6v + 1.25v as needed by the LM317 + 3v headroom also from datasheet).
Again a misunderstanding.resistor in series with the output with power rating of 29.45v x 700ma = 20.6W which considering is massive and I will need 14 of them. (NOTE: I hope I understood from the datasheet on pg 14 diagram 8.3.7 how to calculate the power rating of the resistor).
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?