shorting mosfets

[russlk]

Thanks for the info, guys. I have some more experimenting to do.

[russlk]

I slowed the turn-on time down from 100nS to 500nS and I am not destroying any more transistors. The efficiency is 84% which is just as good as when the transistors were shorting. Thanks for the input.

[Joseph]

Russ, that is how I gradually got to where I am, along with help from application notes from the International Rectifier Web site.<p>Be sure to keep the mosfet, transformer, power supply loop as small in physical size as possible. Also remember your mylar bypass capacitors where needed in that power portion of the circuit. Use good bypass/storage capacitors like ceramic or tantalum to stiffen the power output peaks to the mosfet gates in the gate drive circuit, and keep them very close to the mosfet drivers. <p>I thought I would like to comment about the IRF7343 and how it ties in with my _total disdain for SMT technology_. That component and ocasionally the lesser powerful IRF9952, which since only is half as "hefty" as its cousin, the IRF7343 are the only surface mount devices I use. I put up with them because they perfectly complement the through-hole version of the IR2113 mosfet driver. Those SOT-8 devices are perfectly sized so that each of the two drain leads of the P-ch and N-ch line up with the + and - power supply pins of the IR2113. This alignment permits those dual mosfet devices to be soldered directly onto the power supply pins of the _through-hole_ version IR2113, or for those circuit board users, directly next to the IR2113. This extremely close proximity cuts down on stray circuit inductance and noise. It also permits circuit which takes up little space.

[Joseph]

>>I slowed the turn-on time down from 100nS to 500nS and I am not destroying any more transistors. The efficiency is 84% which is just as good as when the transistors were shorting. Thanks for the input.<p>Thanks for the feedback. I forgot to suggest increasing the gate resistors to 100 0hms, but if you just slowed the turn-on times and kept the turn-off time relatively fast, that is even better than just increasing the gate resistance for both switchings.

[russlk]

I have gotten to like SMT, out of necessity. The drivers I am using are SOT-23-6, rated for an amazing 3.5 amps.

[Joseph]

If SMT were not the "in thing", they would make the same component in the old style long, strong leaded packages. I may like to start a thread on why SMT is going to kill the art of anolog electronic design, especially for the DIYer. Digital may not matter since computers can design something that is based on ones and zeros.<p>[ August 11, 2003: Message edited by: Joseph Meisenhelder ]</p>

[russlk]

I worked at Sprague Electric 20 years ago, we were using SMT then, hand soldering formed To-92 transistors, chip caps and formed TO-220 and 14 pin DIPs. We did not use the "gullwing" form, but cut the leads short and butt soldered them to the pads. Some production lines used screened solder paste and a "hot plate" with teflon coated fiberglass belt to reflow solder the parts.

[Joseph]

If one is going to surface mount, then that is how I like it, with standard components with formed leads. I actually am not for drilled boards though I don't like tiny SMT parts. When the parts are mounted on the same side as the traces, then the circuit can be followed without losing orientation by having to flip the board over.