Im using the MAX712 to charge 3X 3500 mAh NiMH's. On fast charge I charge at .875 mAh's. Im using a 12V supply to the charger circuit. I use 12V because I want to be able to charge the device off a car eventually.
As per the Maxim data sheet 'typical opperating circuit' Im using the a 2N6109 NPN transistor to controll the current flow into the batteries. pdf below.
http://www.onsemi.com/pub_link/Collateral/2N6107-D.PDF
I notice that the 2N6109 becomes very hot when charging. At the moment I have the pcb I designed running on the bench, I use a bulldog clamp as a make do heat sink. I have to fit the board into a tight enclosure so it would be easier not to have to use a heatsink.
How do I decide if I need a heatsink or not? Ive looked through the data sheet and cant see any obvious guide. I see there is refference to the devices power dissipation ability and opp. temps. Is there a way to work it out by formula? Can I simply leave it to run on the bench for a few days and if it keep going conclude it doesn't need a heat sink?
As per the Maxim data sheet 'typical opperating circuit' Im using the a 2N6109 NPN transistor to controll the current flow into the batteries. pdf below.
http://www.onsemi.com/pub_link/Collateral/2N6107-D.PDF
I notice that the 2N6109 becomes very hot when charging. At the moment I have the pcb I designed running on the bench, I use a bulldog clamp as a make do heat sink. I have to fit the board into a tight enclosure so it would be easier not to have to use a heatsink.
How do I decide if I need a heatsink or not? Ive looked through the data sheet and cant see any obvious guide. I see there is refference to the devices power dissipation ability and opp. temps. Is there a way to work it out by formula? Can I simply leave it to run on the bench for a few days and if it keep going conclude it doesn't need a heat sink?