Why is it necessary to design power bricks to get too hot to handle?

Why do the power bricks, that plug into products consumers use everyday, get so incredibly hot!? I've resorted to using a pot holder on work bench when I have to plug my laptop in to charge the battery while I use it. Yes, I understand that there is a maximum charging current level necessary for recharging the battery. But, I have worked with engineers who meticulously designed products to run cooler and more efficient. Granted, it took a while to get the product done. But, it was incredibly reliable and wouldn't have created interesting burn marks on my work bench.

Sounds like bad design, or at least a design with lots of corners cut to trim every possible penny from the production cost.

People buy on price too often, or don't have means to compare quality so are only left comparing price. When consumers demand cheap things and don't care whether they are crap, that's what manufacturers will make.

Dell's 90W bricks are of this persuasion. I am actually quite impressed at the temperatures they can run to without malfunction or failure. I occasionally find a blanket or other random junk covering my laptop supply and the case temp is far too hot to hold. Over 5 years periodic abuse and 24/7 operation, the supply is still ticking. Why do they have to run that hot, I don't know, but the fact that they can run that hot is really the impressive part. On top of that the size of the newer thin supplies is even more impressive.

Size and cost and reliability; there are design specs for each.

If the reliability target can be achieved with a rather warm circuit then there is no problem from that standpoint.

For consumer equipment EN60950 (and others) specify the maximum surface temperature for a consumer item.

Thank you Dave, I think I'll have to measure the temp of my brick to see whether it is staying within the guidelines.

Let me give you a different slant..... All designs in the commercial arena are designed around costs and savings. If the power supply that barely meets the needs of the unit is cheaper then the one that meets and exceeds the needs, the company normally opts for the cheaper solution. And sometimes they specify a power supply that does not meet the needs and has a calculated failure point built into the expiration of the warranty.

I know...I am fully skeptical of all business types.

Bob,

UL60950,Information Technology Equipment - Safety - Part I, 4.5.4 Table 4C, Touch Temperature Limits specifies a maximum temperature of 95 deg C for Plastic and Rubber External surfaces of equipment that may be touched.

Which is really, really hot when you consider 1. that is barely below boiling water and 2. it takes only a few seconds to scald at 63C, and scalding is virtually instantaneous at 70C (when you have firm contact).

Fortunately a tap with a dry finger can tell you it is too hot to be touched without getting burned, even at 95C. But it is my personal policy that any power supply I design runs much cooler than this, and that any power supply I got with a laptop or monitor gets replaced if it gets that hot.

How many hear are old enough to remember overheating Commodore 64 power supplies? Rather than put a fan on mine, I sanded the top off down to the potting epoxy and epoxied a big aluminum heat sink onto it. Ran nice and cool after that.