anybody knows about good low ON resistance MOSFET suitable for making a direct drive driver?
What do other drivers use?
The MOSFET should be controllable via ATTiny13, have as low ON resistance as possible, fit on a 17mm driver board and be able to handle 5A+ in the range of 2.5-4.5V.
Yes there is digikey etc. = not available to me cost wise. So I need to find something either on eBay or in local stores. Widely used parts are preferred as they are easier to get.
It should drive a triple parallel Nichia 219 from a single lion cell with as little drop as possible ;)
Or is it too much for a them? They are safe to 4.5A and 6A peak. And I doubt the single battery would stay above the necessary voltage for these to draw more than 6A.
It’s a logic level N-channel MOSFET that comes on some of the direct drive XM-L budget lights. From what I’ve seen, it’s only available in an SO-8 package.
Featuers:
• –30V/-6A
• RDS (ON) =53mΩ@ VGS=–10V,ID=–6A
• RDS (ON) =68mΩ@ VGS=–4.5V,ID=–4A
• High Density Cell Design For Ultra Low On-Resistance
• Surface mount package:SOP8
Unfortunately 53mOhm is quite high I would say. And it goes down to 4A at 4.5V? Bummer. Fine for direct driving an XM-L, that’s what it was doing anyway with additional buck resistors.
IRL3803 is in my possession, but in the application we use it it was said to be best kept in the higher voltage range. I’ll check the graph for on resistance at 3V.
It should handle up to 10A at 3.0V, I would say the on resistance is 10-12 mOhm? (Would be 0.05V drop at 5A on the MOSFET, and 0.25W power to dissipate.)
Can’t find a graph for it. Another thing is that it’s a huge TO220.
Standard resitance is 6mOhm? Yeah that seems fine. I know there are lower resistance but hard to get MOSFETs.
I know IRL3803 is like past century these days, in the bigger packages. Anything better or similar with smaller footprint?
Will check the IRF7401
I have one in that range as well. IRF7905.
They work together, IRL3803 powers and IRF7905 breaks since they are open when the other one is closed.
It should really have lower voltage drop than simply using 12x 7135s = 4.2A.
How about the safety of such drive for the triple Nichias? Will it really limit itself at 4.5-5.0A? Will see I will have to check for that anyway before frying them to hell.
@3.0V it should do 20A, of course all these below 3.0V basically drop fast, but so does the output should get cut off by the IC anyway to save the Lion battery.
Half the price of IRL3803 here, $1 vs $2 for IRL3803, approx.
The ATTINY can only source 15 or 20mA (don’t remember off top of head) of current out of a port pin. The higher the gate-charge on a mosfet, the more current it takes to ‘turn it on’ (and conversely, turn it off). 10 or 20mA is NOTHING in the scheme of things when we’re talking about turning on the gates of Power MOSFETs so you want the absolute lowest Qg you can find. You’ll burn FAR more power as heat switching (PWMing) a high Qg FET with Low RDSon than you will switching a LOW Qg Fet with slightly higher RDSon. This is because the longer it takes to turn on the fet, the longer you remain in the linear region of its RDS curve where it makes massive quantities of heat.
PPtk
P.S. For reference, on my big light bar, I use 6 AMP Gate drivers. 6000mA compared to 15 or 20mA from an ATTINY.
Hmm yes, I was just looking at the time it takes to open and close but sure if it takes more power to turn it on than ATTiny can supply than yes it will spend too much time in the bad zone of being not closed and not open and burning to hell. Darn it. It’s easier when one has more power to work with, that’s why I ask here
I know I will appear like a noob but why does AMC7135 does not have Qg?
It does switch as well so where is the gate capacitance.
Yes the bigger the capacitance of the gate, the longer it takes for the poor ATTiny to charge it and then and only then it can fully open. The faster it charges and reaches the target voltage the better. At least when planning to use it the range of 4kHz+ I suppose.
I hate DigiKey and most electronics suppliers, there is so little useful filters and the results just return thousands of parts that are one worse than the other
PPTK: How about double the Qg of SIR424DP (22nc, 35nC)? SUB70N03-09P 45nc, 70nc
It’s fast too. But it dies when it goes near 3V, like really limits the output too much I think. Which means it raises Rdson and that means heat heat heat. So even if it had good Qg it would still suck I think.
So where could I get my hands on one or two SIR424DP?
Any source of them?
I'm not a driver guy by any means, but I think what's happening in this pic is that the (unidentifiable mystery part number) MCU is switching the 7136, and the 7136 switches the FET. 7136 is just acting as a relay to switch the high current. I think.
But, that driver didn't work very well AT ALL so it may not be the best example to try to learn anything from.
