Thank You John, I have both sil-pads and mica thermal pads. Now I know which to use when I really need to remove the heat. I always enjoy your videos.

Thanks for this test. I've been wondering which was actually better, and now I know. Now I can send amps out on the road with more confidence in them holding up better once I change any fitted with silicone pads, to mica pads.

Great test, saved me a lot of time, never doubt about mica thermal conductibility, harder to find though...thanks!

Thanks for the experiment. It's nice to have some data behind the choice.

One learns something new every day. Thanks!

Very good demonstation and presentation results !

I have heard that mica contains aluminium compunds, so that might improve its thermal characteristics. The new thing that I learned from this video is that mylar film or kapton tape can also be used as heatsink isolators......thanks for that.

Thanks for a very well presented video.

Thanks for this test

Shocker for me re Sili - pad. Great vid thanks!

Nice video - very useful!

vERY informative, I wonder how the newer sil type pads compare.

Cool test. Thanx.

Thanks, this information is useful.

Great video mate👏Are ceramic insulators good as well, or how they compare to the mica and silicone?

Perhaps someone else already asked this, but I wonder if there's a difference in the electrical resistance between those different thermal pads, which might make using a sil pad necessary if extreme electrical isolation is needed. I imagine testing the resistance of each of those different thermal pads might be pretty difficult, and as you said, thermal and electrical conductivity are usually strongly related to one another, so there likely will not be any big surprises in the results.

That was interesting. Thankyou.

My gut feeling was right, mica rules!

Wow, amazing to watch the temperature rise so fast. Very enlightening. I assume a bipolar transistor that could handle the power would rise even faster?

@SianaGearz

5 жыл бұрын

No, he's forcing the MOSFET to dissipate 15W in this test, using its linear mode and not taking advantage of its low voltage drop, since it's forced to drop about 15V in here anyway. If you had a resistor in such package, it would perform the same, and the BJT would too. Normally when you're creating a switching device you use either in saturation and MOSFETs will tend to have lower dissipation in low voltage scenarios than BJTs.

Hi John, yeah I figured mica would be best, but how much trouble would it be to use no insulator, and insulate each heat sink from each other?

@JohnAudioTech

5 жыл бұрын

It could be done with hardware to isolate each heat sink. It isn't done in consumer products because of the extra cost plus the large voltage across the heat sinks. The large TO-264 transistors I will use in the final amp have such a large thermal pad area that mica will suffice.

How hot does the heat sink get? Does a small fan help in any way? How long until the heat sink gets HOT?

Question: Why some transistors cannot be direct mounting without isolation pads? Thanks

Any thoughts how would perform sil-pad with thermal paste ?

I have a smps power supply its 12 v and 30 amp the transistor heat can I put the transistor direct with the heat sink without use isolation

Kapton tape has always done better for me than those soggy silicone pads.

Kapton tape is also often used in speaker voice coils and transformers, at least that's what I remember from back in the 80's and 90's. Hey, I spy with my little eye, an E-Circuit USB car charger. Did VWestlife's video ealier today inspire a trip? Just kidding. Good info on the isolation pads. SilPads seem like their forte would be for low dissapation devices.

@JohnAudioTech

5 жыл бұрын

I spied that charger at my local DT a couple weeks ago during my swing through the store. Video coming soon!

Thanks sir.

At first glance it looks like if there is no possibility to do a direct connection to the heat sink, with the thermal compound naturally, a good ventilation will more likely be mandatory. I guess this would pretty much explain why we have fans almost everywhere ensuring proper air flow.

so it would just better to use only a transistor and the heat sink with some paste between? It is easier for me to separate other components from the heat sink than fight with the heat :/ What would you recommend? I need to increase the performance of my hoem built power supply because the transmormer and other components are very efficient but the regulator is the wekaest part here because it gives me only 0.6 A before shutting down which is sometimes not enough (usuelly it is ok when I use 100 mA) but sometimes I need a better performance and actually buying another regulator is not the case as even 5 A regulator has almost the same thermal ratings!

Isolate Each Transistor / Heatsink ?

thank you!

I'd have said your initial temperatures were all ambient i.e. 70 deg F / 21.1 deg C. Impressive for Mica though with a Delta T of 29.4 Deg C.

if one doesn't care about isolation (in low voltage circuits) what about using cpu thermal paste?

When we reparing smps that time only testing time we chek mosfet without sitsink ??? It's blasting??? Please sir how chek gate voltage

Does the "Thermal Grizzly Minus Pad 8" 0.5mm thick thermal pad work better than mica and thermal grease?

@tonyj7205

3 жыл бұрын

I wouldn't mind sending you a package or I've even seen "fujipoly XR-m". Their spec sheet shows to have more thermal conductivity and electrical insulation than mica and thermal paste. Never used it but it seems worth it on upgrading something people would want to keep for a long time.

can you use CPU thermal paste for MOSFET?

Sorry John I forgot to ask. What maximum temperature would you consider the practical 'ideal' taken on the device case There a hundreds of articles on KZread and Google giving complex and often confusing design criteria. For every 10C (50F) you halve the life of a device. Not one that I can find says keep your device case below (for example) 60C (140F). I know this is a very rough and ready method but if I can't keep my finger on it it's too hot. That's about 60C (I have an infrared thermometer) - and hurts. Even EEVblog in an old video says it's whatever you feel is right. I did pop a TIP35C because one of the thin mica layers (with thermal paste) had broken off half way across it. I do understand this is putting you in an awkward spot but please - GO FOR IT. Regards

@JohnAudioTech

5 жыл бұрын

In his power amplifier design book, Bob Cordell said pretty much the same thing about the finger test. I've always felt that if the heat sink is too hot to touch for more than a couple seconds then it is inadequate for the job. The long answer is more complicated. The thermal resistance of the die to the metal tab in the package to the package to heat sink interface, the heat sink's ability to dissipate the thermal energy and ambient temp all play a roll. Keeping the junction temperature well below maximum by providing a low resistance thermal path is key. There is no specific answer other than the cooler, the better. A good example of thermal design is LED bulbs. The A style LED bulb designed to have the same shape as the incandescent counterpart doesn't lend itself to dissipating heat very well. Some of these bulbs run at 100 Deg C or more in open air. When the consumer puts the bulb in a fixture with restricted airflow, the bulb runs even hotter and has a short life. The pressure of keeping the price low and making the bulb last long could potentially lead to better components that withstand heat.

@jp-um2fr

5 жыл бұрын

@@JohnAudioTech Thanks for the reply John. It sounds like my 60C figure is good enough. It's pretty obvious that there are so may variables an exact answer is almost impossible to obtain. There is even - 'Correction factors for passive thermal devices due to altitude'. I wonder if one should include the height of the table ? Your words 'the cooler the better' are spot on. I have 12 x TIP35C's running in 2 banks of 6 from 2 x 36V - 8.5A transformers in parallel. 6 x 60mm fans. I have set them to start up at 45C and run flat out by 60C. That's an awfull lot of watts to get rid of but so far apart from the that one TIP35 popping it all seems to work quite well. Please don't ask why I have made this thing because I don't know. Thanks again John - best answer in 2 years

noted direct and huge ,,, is best

Something possibly useful (for me): quasi-(electrically)-conductive thermo-pads; TI calls for multiple LM338s (10/15A Power supply) and 0.1 ohm resistor(s)... between tab/output... "direct-mounted" to heatsink, with 0.1 ohm thermal pad, making the heatsink the current plane.. perhaps I'm just building another bonfire ;-)

can you recommends me an amplifier board for 2 speakers of 5w and 6Ω, from ihome iw2 speakers. i try with tda7297 ,but seems to be too poweful. maybe i need some filters?

@rogerwalter2500

5 жыл бұрын

PAM 8403 or 8410

Thanks

Please make a video on TDA8954 classD amplifier. I recently found on Aliexpress. It's around 15$ only for 420w mono. I think it's very cheap for the price. But I've no setup to scientifically test like yours. Hope you'll interested on slightly higher wattage amplifiers. Also interested on stereo version as well. Thank you.

@JohnAudioTech

5 жыл бұрын

I will certainly look into that one.

@arunbalakrishnan8978

5 жыл бұрын

@@JohnAudioTech Thank you 😍

Got to the cat hair and had to give a thumbs-up. Been there.

I checked the datasheet for this transistor, which states Rds(on) = 22 mohms, wouldn't power dissipation be only (1A)^2 * 0.022ohms = 22mW?

@argcargv

3 жыл бұрын

John is operating the mosfet in its saturation region not in its ohmic region. The transistor is biased such that there is about 15v dropped across the transistor which at 1 amp will produce 15 watts of dissipation. If the transistor was biased into the ohmic region (with a higher bias voltage) then the power supply would be largely dropped across the resistor instead and the current would be much higher than 1 amp.

@blackz06

2 жыл бұрын

Rds(on) will be at a higher Vgs than what's being ran here. Check the stats for the resistance and see what I mean...

I only use mica pads, thermal grease, and a big ass heat sink. It never fails

@JohnAudioTech

5 жыл бұрын

Like they always say, "No heat sink is too large".

I recommend these: Ceramic - www.amazon.com/gp/product/B00MOCFFHU/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1 Mica is great too.

11:21 oo thank you really appreciate it as I am european :D ;)

wouldn't the 1R resistor be better on the Drain pin, why/why not?

@JohnAudioTech

5 жыл бұрын

It has the similar function as the emitter resistor on a BJT. It provides some negative feedback to the circuit.

I used copper anti-seize compound in a pinch and that stuff worked better than the paste i had that came with a processor i got a while back... the stuff is very conductive and dont recommend it on aluminum heat sinks because dissimilar metals and galvanic corrosion, use the aluminum anti-seize compound.. the stuff mechanics use on bolts... that gets everywhere if you touch it.. lol.. try it out for yourself.. like 6$ for enough of it to paint your entire body with, twice.. ha!

Hi John, found this and needed it for 12 x TIP35C. Mica can be split down to very thin sections. Good video as usual, goes well with this down to earth article. sound.whsites.net/heatsinks.htm Mica - sound.whsites.net/heatsinks.htm#s8

what abt arctic grease

Its not isolated when you screw it down without a sleeve and nonconductive washers...

Thermal compound wasn’t used on the sil pad bad idea

Yea but once you put a screw in it, it electrically connects the heatsink.

@JohnAudioTech

5 жыл бұрын

I use a nylon shouldered washer for isolation

@pointedspider

5 жыл бұрын

@@JohnAudioTech ... Well that would be the answer. From my experience, manufacturers usually just use thermal paste, probably for cost reasons...but, I also noticed the heatsink is grounded. Also most transistors have a positive potential in the tab. I never paid much attention to the isolation. I must try some experiments. thanks

7:25 a Gay Stopper?