Help on designing a LED circuit

[Morcego]

Hi all,
I need your opinion on a circuit:

I have 12 panels of 55 Leds each. Each panel is powered by 24 VDC (as internal limiting resistors. the total current is about 300mA). The 12 panels must be able to shwitch in sequence or all at the same time.

This is not a problem of course. The problem is that I must also control the brigtness of ALL panels at the same time using PWM.

So if I have the negative side of the panels connected to the ground via a MOSFET transistor that does the PWM, wath is the best way to switch on and off each individual panel while mantaining the PWM ?

Use anothe transistor at the 24V side?

(I cannot use relays because the switching frequency can be about 200ms)


Thanks in advance

M

 

[LionelHutz]

You have 12 on-off outputs or bits to control the panels to make your arrow pattern "moving".

You want to vary the brightness of all panels the same amount.

So, set-up one PWM output in the software. Then just software AND the new PWM output and the on-off output you already have. Make the AND output signals the new outputs to the panels.

You already have the required hardware....

 

[SteveMeisel]

Thanks macgyvers2000
Not trying to hijack the thread.
The pwm is ONE (there are two) of my two newest and biggest problems. I am going to try to set up it in an interrupt. My specs call for a much slower clock than the 1kHz, that should not be a problem, but I have a pwm signal accuracy of +/- 50ns that has to be maintained, this is my worry.

 

[itsmoked]

Steve start a new thread and we can all look at it. Sounds interesting.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[MacGyverS2000]

I hope you have a fast processor... 50ns accuracy is 20MHz. If you plan on running something like a PIC, don't forget the clock signal is divide-by-4... even at 80MHz you won't have any slack if interrupts lag for one reason or another.

As Keith suggested, start a new thread and we'll help where we can.


Dan - Owner

http://www.Hi-TecDesigns.com