Low Power Led Circuit

[andybarrett1]

Hi Everybody

Hope you can make some sense of my ramblings:-

I have a requirement to design and build a low power led circuit.... My Idea (early days) (very) is to use a PIC... Strobe the 4 - 6 outputs HPWM? or just on/off...around 60hz at least. 5% duty cycle so as no flicker...

The pic output pins driving a FET (2n7000 ?) ultamatly a string of white high lux o/p low power leds.

Has something similar been done before..... The requirement is to save power. The existing circuit we have is drawing 160mA at 24v. Just by using simple current limiting bipolar transistors. 5 rows of 25mA leds.

Any pointers advise etc accepted

Thank you

Andy

[BH_epuk]

Hi Andy

How many Led's are you running in each row? It may be a better light output / power usage comperimise to use a switch mode driver.
160ma @ 24V is 3.84W, but as an example 5 rows of 6 LED's would only draw 2.27W (94ma @24v input) so your loosing over 1W in the bipolar current limit.
The figures above are only an example using best guess for the led Vf etc and a switch mode driver would not be 100% efficiant but will waist less power.

Let me know if you want any further advice as spend a lot of time working with led based drivers.

Ben

[andybarrett1]

Hi Ben

Thanks for reply... Will tell you more about existing cct tomorrow all my notes are at work..

BR
Andy

[andybarrett1]

6489

HI All...
The circuit Above drives five rows of various LEDs at @30mA per chain... 5 chains at @30mA = 150mA Total cct.
My Idea as outlined previously is to use a pic chip with a pulsing duty cycle of around 5% at 100ish Hz
I previoulsy was thinking of sourcing into a mosfet of some description so I could use 24v DC on the high side.
Ben suggested Switch Mode LED Drivers of some description but I am totally open to sugestions....
I need to get max illumination at the lowest current.... So if we can resign this circuit to get lower than the existing
150mA the better..

Many thanks for reading and suggestions.

BR
Andy