serial led display driver powering mosfets for high ampage effects

[mikebot]

Figuring out a circuit using an MM5451 to drive leds and some mosfets to supply up to 1 amp at 12 or 24v to fire stage effects to simulate damage to bot.
MM5451 pdf url: http://www.micrel.com/_PDF/mm5450.pdf

I can drive the mm5451 sink driver from arduino with an existing library, so using mm5451 is set  (an alternative could be 5891 source driver but I really want the mm5451 as I have a few) but not sure of the circuit and SOR board members seem to know their stuff. (not all circuit shown for arduino and leds)

I think I can drive the IRF7316 or IRF7306 direct from arduino rather than via a bjt, but do you think I would be best driving all the leds by bjt as the MM chip can only sink 15mA max on each channel when they are all active and they will all be on at times.

mosfet pdf url: http://www.irf.com/product-info/datasheets/data/irf7316pbf.pdf
alternative mosft pdf url: http://www.irf.com/product-info/datasheets/data/irf7306pbf.pdf

The diodes are in case it get used to drive small inductive loads (simple motors). Also shows indicator leds on effects pins.

The 5451 has brightness control via resistor r_bri or pwm via jumper jp1 and io pin 7.

Microcontroller power is 5v but effects are driven by 12/24v, is the mm5451 protected from over voltage by ciruit?

Effects (somke puffs and sparf hits) need 500mA to guarantee fire, but would like to have overhead on ciruit, hence 1 amp requirement.
Effects url: http://www.hfmgroup.com/professionalsupplies/flash.html

Thanks for looking

[Soeren]

Hi,

I think I can drive the IRF7316 or IRF7306 direct from arduino rather than via a bjt, but do you think I would be best driving all the leds by bjt as the MM chip can only sink 15mA max on each channel when they are all active and they will all be on at times.

I would just use TIP120 (BjT power Darlington devices).
They have a current gain of more than 3,000 at 1A collector current and close to 2,000 at 500mA, so they only require a base current of 334µA for 1A (250µA for 0.5A).
A 10kOhm resistor from the drivin pin to the base is (all that is) needed.

[mikebot]

Thanks for the reply Soeren.

I made a mistake in my post, the mosfets are driven by the MM5451 which are current sinks, so I suppose that would mean using the compliment TIP125? I am using the MM5451 as it is a serial port driven latching chip that uses 3 O/I pins to drive 35 channels.

I don't have room for TO-220s as the pcb is only 81 x 53mm with 12mm headroom, has other components and connectors for the LEDS, which is why I was looking at the SMT Mosfets. Is there an alternative?

Cheers

[Soeren]

Hi,

I made a mistake in my post, the mosfets are driven by the MM5451 which are current sinks, so I suppose that would mean using the compliment TIP125? I am using the MM5451 as it is a serial port driven latching chip that uses 3 O/I pins to drive 35 channels.

Oh, I should have caught that - my bad.
Well, yes and no. A PNP device on the 12V (or 24V) line should not have its base connected to a line that switches between 0V and +5V, as it'd be on all the time.
A PNP is on when the base is around ~0.7V (~1.4V for Darlingtons) lower than the emitter.

I don't have room for TO-220s as the pcb is only 81 x 53mm with 12mm headroom, has other components and connectors for the LEDS, which is why I was looking at the SMT Mosfets.

You don't have room??
You live in an extremely small apartment or what?  (I bet your toothbrush is foldable then )
Any reason you cannot have twice the PCB area... Or ten times that?

First you design the circuit, then you find out what area it takes with a reasonable component placement and only then you select a box for it.
If there's not enough room for something, somebody screwed up the line of decisions (like when a foolish designer placed an LED a very inaccessible place in a telephone from a world renowned Danish HiFi manufacturer *coughB&Ocough* making a heck of a strain on the engineers that had to redesign the entire electronics layout)

Is there an alternative?

Allways (except with death and taxes).
You could use MOSFETs or BjTs as you like, as long as they're connected the right way.
You need to run the MM5451 off +5V (it can run off +4.5V to +12V) to keep it working with the Arduino. To go from a sink going from +5V to 0V, to a 12V (24V) driven device, you need a small signal transistor to invert the output.

Something like this:


Or... Use a P-ch MOSFET or a PNP Darlington with a zener diode in the input like this: