Senior Member
Joined: 27/09/2008
Location: AustraliaPosts: 190
| Posted: 08:57am 30 Nov 2009 |
Hi Bob,
My congratulations on the excellent presentation of your MPPTdevice.
As someone who has been tinkering with similar circuits for some time, there are a couple of things that I have found by bitter experience that might be of interest.
The low value caps in parallel with your 100 MF electros should not also be electros. Electros exhibit a relatively high internal impedance, and will not bypass the high frequency switching noise that your mosfets will generate, probably causing some local interference. This is more particularly so as your circuitry is not surrounded by metal. Ceramic capacitors are best for this, but anything other than an electro will be much better.
AS Dinges has indicated, the circuitry that you use to switch the gates of your mosfets looks as though it will be a bit too slow, probably causing the heating that you note. Mosfet gates are like capacitors, they require a low impedance in the switching circuit to charge or discharge them quickly to turn them on and off.
My partcular favourite for this is the 4050 hex non inverting buffer, with all of the elements paralleled. This both charges and discharges the gates very quickly. A word of caution though, it is possible to do this too quickly, destroying the mosfet. For this reason, you need a series resistor in series with each gate. Something of the order of 50 Ohms is a good starting point.
Keep up the good work!
Regards
Don B