PWM using mosfets

I've got some TPIC6B595's that I'm going to use to drive some led strings, and I was wondering if I could use mosfets between the TPIC's and the leds to affect dimming? I know I could use ShiftPWM, but I wanted to know the feasibility of the approach. Additionally, would a single PWM pin be able to drive several mosfets?

DBW1341:
I’ve got some TPIC6B595’s that I’m going to use to drive some led strings, and I was wondering if I could use mosfets between the TPIC’s and the leds to affect dimming? I know I could use ShiftPWM, but I wanted to know the feasibility of the approach. Additionally, would a single PWM pin be able to drive several mosfets?

If you going to use a Mosfet to drive LED’s (PWM) then do you really need a high power shift register? A better idea might be to use a normal LED driver chip that does PWM and connect it’s output to the Mosfets.
You could drive several Mosfets from one PWM source but it will effect all the strips at the same time, is this what you want?

Yes, I do want all the strips to be effected at the same time. Thanks for verifying that for me. As to the other hardware suggestions, I already had some TPIC's and some 74HC595 so I wanted to avoid buying more hardware if necessary (need to keep the wife aggro down). The 74HC595's were at the edge of what the system might draw so I figured the TPIC's would add a healthy safety factor. Again, Thank you.

Don't forget the [u]maximum[/u] current an AVR arduino pin can take is 40mA so ensure you don't go over this (and preferably half that). If you have many strips then get the pin to drive a transistor that drives multiple others.

Oh yeah. Time to break out the datasheets. Smoking chips tends to increase wife aggro. Thanks again.

Why aren't you using PWM into the TPIC6B595 OE pin for brightness control? EACH TPIC6B595 can sink 150mA. HC595 only designed for 8-9mA.

Just to be clear, if I use PWM on the OE pin (pin 9, G-bar on TI's datasheet) that will effectively do what I want? TBH I trust what you're saying, I just want to make sure that I'm reading the datasheet correctly and matching it to what you're saying so that I don't screw it up. This will make the design a bit easier.

Thank you for the info on the HC595. I now know that they were far from the edge of what my system will draw. 150 mA is about 30-50 mA more than I'll need.

Last note, I love your website. It's been very useful to me, and will be useful in the future when I attempt my next major project (a crossfit timer).

Yes applying PWM to the output enable will in effect dim all the LEDs attached to that shift register.I think you muddied the waters by talking about a FET, that is not part of the soloution to your problem.

That’s why I asked on this forum. While I’m glad that my concept “would” work, which means I’m not a complete idiot, I knew that if a simpler and more elegant solution existed, I would be told about it.

, which means I'm not a complete idiot

It's a bad term, like most here, you/we just need more practice.

Crossroads, I noticed in one of your projects BobuinoRev17/12digit_2relay_drive_sch.png, You tied SRCLR to the 5V line (with a filtering cap to ground). Some of the other examples I've looked at tie it to a control pin. Wouldn' t tying it to VCC keep SRCLR high and prevent clearing the shift register? Or is that the best way to set it up? Thank you.

Crossroads, I just noted a different thread where you explained everything. You make me wish I was still living on the Cape.