My spec sheet for HC595 very clearly states the output current as much 
higher than 6-8Ma. You'll get at LEAST 25ma per output.

--Bob

brusque@HotPOP.com wrote:

> Hello,
>
>     I'm working on a project that is basically a high intensity LED 
> sign. My actual design is using some 74HC595 to power the LEDs the LEDs:
>
>     Controller        long data                LEDs
>        unit              cable                 unit
>     ,---------,                            ,---------,
>     |         |                            |         |-------LED1
>     |     DATA|----------------------------|         |-------LED2
>     | PIC     |                            | 74HC595 |-------LED3
>     |       CK|----------------------------|         |-------LED4
>     |         |                            |         |-------LED5
>     |    LATCH|----------------------------|         |-------LED6
>     |         |                            |         |-------LED7
>     |         |                            |         |-------LED8
>     '---------'                            '---------'
>
>     However, the maximum currente at the '595 outputs are 6-8mA and I 
> need to power the LEDs with 20mA, to have more luminosity.
>
>     I've been thinking about the MAX6966, but it's expensive and not 
> easily available. Another possibility would be to use some PIC16F627A 
> on the LEDs unit just to control the LEDs.
>
>     Someone here can give me some sugestions?
>
>     Thanks,
>
>     Brusque



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