What is "Rds(on) Test Voltage Vgs" parameter of a MOSFET? - Page 1
Forum section: electronics / beginners

author: hkBattousai
author_rank: Regular Contributor
timestamp: June 16, 2014, 11:53:30 am
content: I was looking for a MOSFET inthis page. There is a search parameter called "Rds(on) Test Voltage Vgs". What does it imply? I didn't hear a parameter like this when I was studying MOSFET transistor back in the time. Can you please explain it to me?

author: sleemanj
author_rank: Super Contributor
timestamp: June 16, 2014, 11:55:50 am
content: It is the voltage Gate to Source which was used when determining the stated Rds(On)

author: hkBattousai
author_rank: Regular Contributor
timestamp: June 16, 2014, 12:17:31 pm
content: Ah, just as I guessed. Thank you.

author: rob77
author_rank: Super Contributor
timestamp: June 16, 2014, 12:18:00 pm
content: Rdson is the lowest possible resistance between drain and source pins - and you have a correlated Ugs voltage for that Rdson. in other words.. if you apply that Ugs voltage between gate and source you will get that low Rdson resistance.there are 3 important Ugs volatges for each mosfet1. Ugs threshhold voltage - the voltrage needed to start "opening" the drain-source channel.2. Ugs "saturation" voltage - the one when you reach the lowest Rdson between drain and source.3. max Ugs voltage - beyond this value the gate insulation might (and actually will) break down (irreversible process).

author: hkBattousai
author_rank: Regular Contributor
timestamp: June 16, 2014, 12:20:14 pm
content: Thank you very much. It is very clear now.

author: jlmoon
author_rank: Unknown
timestamp: June 16, 2014, 08:10:11 pm
content: Quoteand when the magical smoke starts to appear - sometimes anyway!

author: woodchips
author_rank: Frequent Contributor
timestamp: June 19, 2014, 10:59:32 am
content: If you don't mind a slight diversion, FETs aren't something I know much about.In the thread about questions on relays there is mentioned a FET with a carrying capacity of 150A and Ron of 2.5mohm. Made by Infinion so must be right, but seems incredible to me, is this the typical technology that has been reached now?

author: rob77
author_rank: Super Contributor
timestamp: June 19, 2014, 11:26:43 am
content: Quote from: woodchips on June 19, 2014, 10:59:32 amyes, and it went even further than that already

author: Psi
author_rank: Super Contributor
timestamp: June 19, 2014, 11:35:15 am
content: how about 260A continuous <2mohms Rds and only costs $2http://www.digikey.com/product-detail/en/IRLB3813PBF/IRLB3813PBF-ND/2118485

author: Kremmen
author_rank: Super Contributor
timestamp: June 19, 2014, 11:52:49 am
content: One thing that i find curious/strange/unrealistic is exemplified with this component: Continuous Id of 260A in a TO220 package. The package leads are roughly 1 mm square, not significantly more. That means the current density in the leads would be a whopping 260 A/mm2which is frankly ridiculous. In the context of electric installations, this would exceed the maximum permissible wiring current density by some 20x. I hesitate to think what it would take to keep everything cool enough not to catch fire...But hats off to IR engineers for managing to create the chip inside. No mean feat, that.

author: lgbeno
author_rank: Frequent Contributor
timestamp: June 19, 2014, 11:59:40 am
content: 8420pf gate capacitance, wowI did also see Alpha & Omega had a sub mOhm fethttp://www.aosmd.com/pdfs/datasheet/AON6500.pdf

author: fmaimon
author_rank: Unknown
timestamp: June 19, 2014, 12:01:26 pm
content: Quote from: Psi onTodayat 08:35:15 AMTO220 packages can only handle about 75A without melting their pins. If somehow you can find a way for the pins to handle more current, 260A in a 1.95 mR is 132W. You will have a hard time dissipating that! Then the junction will heat up to more than 150 oC and the Rdson will rise more than 1.5 times, so your dissipation is now 200W.So no. You can't drive any TO220 packaged MOSFET, or even a TO247, to anything like that continuosly.These low Rdson are just for lower power dissipation, not higher current handling. For that, you parallel the transistors.

author: woodchips
author_rank: Frequent Contributor
timestamp: June 19, 2014, 09:13:04 pm
content: My limited experience of high power DC circuits is in plant. Even something as low power as solenoid hydraulic valves I have used 2.5 sq mm cable. Then to DC traction at 30-40A and up to DC hydraulic pumps at 120-150A, but then you are using 16 sq mm cable.How on earth do you connect a TO220 device to 16 sq mm cable? They are so out of scale with each other that there seems to be a physical strength limitation at the boundary between transistor and cable. I have used the large transistors with M6 screw down terminals, and even they look too small at 100A.Anyone done this for real and can offer some design hints please?

author: rob77
author_rank: Super Contributor
timestamp: June 19, 2014, 09:24:34 pm
content: actually the TO220 leads can withstand such a currents during pulses of few milliseconds, but from the MOSFET point of view the few millisecond pulse is considered as continuous current

author: Jope
author_rank: Regular Contributor
timestamp: June 20, 2014, 02:35:45 pm
content: Regarding the current ratings of MOSFETs, International Rectifier has an application note about that topic:Continuous DC Current Ratings of International Rectifier’s Large Semiconductor Packages