Put a scope on the MOSFET gate and you'll see the PWM clear as day. I doubt there's any current sense or other feedback into the PWM chip but the best tools would have some flavor of that.
The halfway decent cordless tools implement battery charge smarts too. It seems obvious to me that this will eventually be integrated into the tool itself although many current variations put it into the battery pack (for rapid recharge this makes some sense as you need to sense the cell temperature) or more traditionally just current-voltage- limited wall warts.
I don't see any obvious charger functionality on that little PCB.
On Fri, 21 Jan 2011 21:12:00 +0000, Richard put finger to keyboard and composed:
The "313" marking on the MOSFET may be a YWW date code. This would be consistent with the marking on the PWM controller. ST markings often have a code letter before the YWW. IIRC, this letter indicates the country of manufacture. I'd say the part marking is probably D4 or D4v, depending on how it is laid out.
I'm wondering whether both part markings are house codes rather than regular marking codes. Maybe "D" stands for "Drill", and perhaps the "4" indicates a 4 amp device ???
- Franc Zabkar
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