die4drive getting hot problem

[badger1666]

hi
i am using a die4drive modded by robin for blu-rays and 445nm
i am running it on 9v as per instuctions and 5v to modulation input
set bias to just lasing and
i have only set drive to 300ma but it get very hot within a minute
any ideas as to whats going wrong ??

[-bart-]

... not having a heatsink ??

(supply voltage - diode voltage)*diode current = ~1,5 W of heat.

Lower your supply voltage in such a way that max power and lineair modulation is maintained.

I haven't tested linearity yet, but supplyvoltage = diode voltage + 2,5 V worked fine for me so far with the die 4 drive.

Problem is that there are not much smps in between 5V and 9V, most do have a pot to adjust the voltage +/-10%. In your case lowering the voltage to 8V will give you ~1W of heat.

[andy_con]

chris you should alway heat sink your die4diver.

maybe simon could post pics of his heat sink mod?

[badger1666]

i have the die4drives bolted down the heatsink the projectors built on ,trouble is the pcb dont sink heat to well , anyone have any ideas how i can drop 2v off the 9.5v supply i am using ?? mayby a big fat resistor but i have no idea what one to use ?

[p1t8ull]

That mod was to mechanically connect the drain tab of the FET directly to the heatsink rather than through PCB cooling by drilling out the contact area behind the device and inserting a brass disk the same thickness as the board.
Worked, but milling machine required if driver obliteration is to be avoided

How warm is the driver and the heatsink actually getting Chris? The IRLR3105PBF FET is good for 175C junction temp, so with a case temp of <100C it should be quite happy..

[badger1666]

hi simon
its hot enough that 2 secs with my finger on the case and i go ouch
if they can be happy at them temps
then no worries but i might just bond a ram chip sink on to the fet case as just as a little extra cooling

[catalanjo]

i have the die4drives bolted down the heatsink the projectors built on ,trouble is the pcb dont sink heat to well , anyone have any ideas how i can drop 2v off the 9.5v supply i am using ?? mayby a big fat resistor but i have no idea what one to use ?

Much better looking with 3 or 4 BIG FAT DIODES
(also works better than a resistor cos voltage drop wont change with current draw !)

cheers

[drlava]

You've come across the reason why the FlexMod P3 is built with a directly heatsinkable transistor. However you could probably use thermal glue to attach a heatsink to the top of the transistor on that driver and it will help to some extent.