Landyacht's Flame-O-Watt (A thought)

Question

When installing the new transistors...After bonding (screwing them) to the heat sink...You DID use a DMM and insure with a resistance check that the continuity between the metal -tab- of the replacement TO220 transistors and the heat sink was open circuit, right? The tab is where the device has a hole for a screw to pass through and clamp the device to the heat sink.

landyacht318 · Answer

I ordered the same transistor that failed. It was not a T0220.
I linked the exact product in the cheapowatt thread

There was no hole in the transistor. There was a screw inbetween transistors. A threaded flat bar pulled the transistors tight to the heat sink.

I did not bust out the DMM.

I was just using my new solder sucker gun pulling components out of cheapowatt circuit board. Practice. Much easier than using solder wick, but still a technique required. More practice needed.

mexicowanderer · Answer

Ping here is measured with a sundial. Cannot access sites with data cross reference. Sounds like the C.O.W. transistors may be JFETS.

landyacht318 · Answer

Fairchild specs wrote:Manufacturer:	Fairchild Semiconductor	Product Category:	Transistors Bipolar - BJT	RoHS:	RoHS Compliant Details	Configuration:	Single	Transistor Polarity:	NPN	Collector- Base Voltage VCBO:	700 V	Collector- Emitter Voltage VCEO Max:	400 V	Emitter- Base Voltage VEBO:	9 V	Collector-Emitter Saturation Voltage:	1 V	Maximum DC Collector Current:	12 A	Gain Bandwidth Product fT:	4 MHz	Maximum Operating Temperature:	+ 150 C	Mounting Style:	Through Hole	Package / Case:	TO-3P	Brand:	Fairchild Semiconductor	Continuous Collector Current:	12 A	DC Collector/Base Gain hfe Min:	8	DC Current Gain hFE Max:	40	Maximum Power Dissipation:	130 W	Minimum Operating Temperature:	- 65 C	Packaging:	Tube	Series:	FJA13009TU	Factory Pack Quantity:	30	Part # Aliases:	FJA13009TU_NL	Unit Weight:	0.225789 oz

mexicowanderer · Answer

Excellent, current rather than voltage controlled.

Bi polar Junction transistor. Difficult to parallel without using resistor across emitter. Requires less driver current.

Rather than try and reinvent the wheel I would LOVE to see how MeanWell addresses the issue. Which type of transistor did they select for your unit...Type and possibly paralleling. A transistor ID and count would reveal much.

Single BJT IMHO have a fatal flaw in a high current switched power supply. They are severely limited by Vf that can easily exceed 1 volt. Thirty watts of saturation is insane. Explains why the driver circuit in your experiment smoked as well as the BJT. But I'll have to wait to see what circuit/transistor choice (amperage or voltage control technique) the MeanWell uses.

Patience Mex, Patience.

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