ElectricGod
10 MW
The mosfets arrived today.
My bench is grounded. There's a long section of 2"x2" angle aluminum across the front edge of the bench. It has a 16 awg wire going to earth ground. My arms rest on it and I touch it often. Rolling up to my bench and coming in contact with that aluminum angle is easy and natural and hard to avoid doing. This grounds out any static I may build up on me and keeps the bench top from building up any static. Never the less, I lay the mosfets on an anti-static bag that is in contact with the aluminum strip. This is done because mosfets can be damaged by static discharge.
People have scoffed before and claimed there's no way a $30 Chinese component tester can tell you squat about a part and do it reliably and accurately. I disagree. I can do these exact tests with my expensive DMM and a bench power supply and get very close results and take 10X longer to do it. I can pull out my milliOhm meter and check Rds. I have the expensive test gear to test with! Why would I test the mosfets the hard way when I already know the results from the component tester are going to be pretty close to the same? I'm NOT...that's just stupid to bother spending an hour to set up my test gear and another hour testing mosfets. My $30 component tester from China can tell me the exact same thing in seconds! Scoff, complain, whine all you want. I already know the $30 parts tester is doing the right thing and where it is off and by how much. You are biased if you think this inexpensive tester can't do the job. IT's NOT true and you don't actually possess the facts! You are stating your opinions. I'm stating actual facts from my own tests. I actually tested to be sure. What did you do? Oh that's right, postured, whined and complained, but didn't actually do any test work to prove me right or wrong. You know who you are!
OK...enough...getting off the soap box! LOL!
I'm looking for 3 things on my component tester.
1. Does the mosfet work? Does the component tester even recognize it as a part and if so what kind? In this case...N-E-MOS or N-channel, enhanced mosfet.
2. Turn on voltage or Vt. This is the voltage needed at the gate to make the mosfet fully turn on. I want Vt to be the same across all mosfets. The spec sheet says Vgs(th) is typically 2.5v and max of 3.2v. Looking at the graph of actual turn on voltages, I see that it's really at about 3.2 to 3.3 volts. Looks like the $30 tester hit the mark! All mosfets tested at 3.2 or 3.3 volts except one at 3.4 volts. I think I can trust this tester so far.
3. Uf is the voltage drop across source to drain. I want Uf to be the same across all mosfets. Lower is better. Uf is based on an internal precision voltage source in the component tester. This voltage source is placed across Source to Drain and a series resistor. The voltage on the mosfet is then measured. Higher Uf indicates that Rds is higher. Lower Uf indicates lower Rds. There's another graph that plots the gate voltage and voltage across Source to Drain. The 25C (cold mosfet) line at 3.2-3.3 volts on the gate shows about 700mV across Source to Drain. I read 571mV on my component tester. I already know it's internal precision voltage source is a little low. This skews my results down by 60mV on the component tester. As a result, It does read Uf a little low. So then 571mV + 60mV = 631mV. The graph says 700mV, I say 631mV...39mV difference. I'm NOT worried! The $30 Chinese parts tester does what I could do in 10X more time with my expensive test gear in a couple of seconds!
When done with the first test run, I had 3 piles of mosfets. I'm just looking that they all work and what Vt is. I want mosfets that all turn on at the same voltage. In this case, that was 3.2v, 3.3v and a single mosfet at 3.4v. This is pretty good! I've bought loads of AOT290's and had far worse results on this exact parts tester.
This is after the second test run. In the tube and on top of it are all the 3.3v mosfets. This time I'm looking at Uf. I now know all the turn on voltages or Vt. Do they also have the same voltage drop across Source to Drain? Again...doing this same test on AOT290's or Chinese mosfets, I got lots of variation. In this test all the 3.3v mosfets also had the same Uf of 571mV. The outlier (center most single part) at 3.4v Vt also has a Uf of 571mV. The mosfets with a Vt of 3.2 volts has 2 of them that had lower Uf than the rest. That's the left 2 single mosfets. One is at 569mV and the other at 570mV. The lower right pile is all the rest of the 3.2v Vt mosfets that have a Uf of 571mV. That means 28 of the 30 mosfets have the same Rds. Out of 30 mosfets 3 were different than the 2 groupings. Since the motor controller will supply more than 3.3v to turn on the mosfets, I'm not overly worried about the small Vt differences. However, the 12 mosfets that go in this controller will have the same Vt. I will use 12 mosfets with Identical Uf in the controller. Fortunately there are plenty that can work. Since there are 12 that have a Vt of 3.2v and Uf of 571mV it's a good grouping to use in the controller. I could also use 12 from the 3.3v grouping, but there are 15 of those. The three mosfets that don't match up will get used for something less critical...like a BMS or a mosfet switch.
Conclusions:
1. Chinese mosfets are just awful. I've tested many on my parts tester and I see Vt and Uf all over the place for same model mosfets from the same source. Commonly the test results and the spec sheet are way different.
2. I don't know if AOT went through a bad spell about 2 years to 18 months ago and their quality control was horrible. I haven't bought any AOT290's since then. However I saw Vt and Uf vary a lot. I bought 100 AOT290's from digikey and Arrow over 3 orders and at different times over about a year. I forget the exact quantities now in each order, but something like 45, 30 and 25. I tested all of them on my component tester shown above. The Vt And Uf readings were pretty inconsistent across the 100 mosfets. I ended up with 8 piles. To get 18 for a single controller meant taking the single largest pile and then part of similar piles to populate a single controller. 12 more went into the 12 fet currently in the Currie. Those were picked first and they all matched each other, but not the spec sheet. A few of those 100 mosfets actually matched the spec sheet. Most didn't.
3. These TI mosfets are far more consistent. .2v difference in Vt and .002v difference in Uf and 27 of the 30 fell into 2 groups...that's pretty darn good! And more importantly they are all pretty darn close to the graphs in the spec sheet.
My bench is grounded. There's a long section of 2"x2" angle aluminum across the front edge of the bench. It has a 16 awg wire going to earth ground. My arms rest on it and I touch it often. Rolling up to my bench and coming in contact with that aluminum angle is easy and natural and hard to avoid doing. This grounds out any static I may build up on me and keeps the bench top from building up any static. Never the less, I lay the mosfets on an anti-static bag that is in contact with the aluminum strip. This is done because mosfets can be damaged by static discharge.
People have scoffed before and claimed there's no way a $30 Chinese component tester can tell you squat about a part and do it reliably and accurately. I disagree. I can do these exact tests with my expensive DMM and a bench power supply and get very close results and take 10X longer to do it. I can pull out my milliOhm meter and check Rds. I have the expensive test gear to test with! Why would I test the mosfets the hard way when I already know the results from the component tester are going to be pretty close to the same? I'm NOT...that's just stupid to bother spending an hour to set up my test gear and another hour testing mosfets. My $30 component tester from China can tell me the exact same thing in seconds! Scoff, complain, whine all you want. I already know the $30 parts tester is doing the right thing and where it is off and by how much. You are biased if you think this inexpensive tester can't do the job. IT's NOT true and you don't actually possess the facts! You are stating your opinions. I'm stating actual facts from my own tests. I actually tested to be sure. What did you do? Oh that's right, postured, whined and complained, but didn't actually do any test work to prove me right or wrong. You know who you are!
OK...enough...getting off the soap box! LOL!
I'm looking for 3 things on my component tester.
1. Does the mosfet work? Does the component tester even recognize it as a part and if so what kind? In this case...N-E-MOS or N-channel, enhanced mosfet.
2. Turn on voltage or Vt. This is the voltage needed at the gate to make the mosfet fully turn on. I want Vt to be the same across all mosfets. The spec sheet says Vgs(th) is typically 2.5v and max of 3.2v. Looking at the graph of actual turn on voltages, I see that it's really at about 3.2 to 3.3 volts. Looks like the $30 tester hit the mark! All mosfets tested at 3.2 or 3.3 volts except one at 3.4 volts. I think I can trust this tester so far.
3. Uf is the voltage drop across source to drain. I want Uf to be the same across all mosfets. Lower is better. Uf is based on an internal precision voltage source in the component tester. This voltage source is placed across Source to Drain and a series resistor. The voltage on the mosfet is then measured. Higher Uf indicates that Rds is higher. Lower Uf indicates lower Rds. There's another graph that plots the gate voltage and voltage across Source to Drain. The 25C (cold mosfet) line at 3.2-3.3 volts on the gate shows about 700mV across Source to Drain. I read 571mV on my component tester. I already know it's internal precision voltage source is a little low. This skews my results down by 60mV on the component tester. As a result, It does read Uf a little low. So then 571mV + 60mV = 631mV. The graph says 700mV, I say 631mV...39mV difference. I'm NOT worried! The $30 Chinese parts tester does what I could do in 10X more time with my expensive test gear in a couple of seconds!
When done with the first test run, I had 3 piles of mosfets. I'm just looking that they all work and what Vt is. I want mosfets that all turn on at the same voltage. In this case, that was 3.2v, 3.3v and a single mosfet at 3.4v. This is pretty good! I've bought loads of AOT290's and had far worse results on this exact parts tester.
This is after the second test run. In the tube and on top of it are all the 3.3v mosfets. This time I'm looking at Uf. I now know all the turn on voltages or Vt. Do they also have the same voltage drop across Source to Drain? Again...doing this same test on AOT290's or Chinese mosfets, I got lots of variation. In this test all the 3.3v mosfets also had the same Uf of 571mV. The outlier (center most single part) at 3.4v Vt also has a Uf of 571mV. The mosfets with a Vt of 3.2 volts has 2 of them that had lower Uf than the rest. That's the left 2 single mosfets. One is at 569mV and the other at 570mV. The lower right pile is all the rest of the 3.2v Vt mosfets that have a Uf of 571mV. That means 28 of the 30 mosfets have the same Rds. Out of 30 mosfets 3 were different than the 2 groupings. Since the motor controller will supply more than 3.3v to turn on the mosfets, I'm not overly worried about the small Vt differences. However, the 12 mosfets that go in this controller will have the same Vt. I will use 12 mosfets with Identical Uf in the controller. Fortunately there are plenty that can work. Since there are 12 that have a Vt of 3.2v and Uf of 571mV it's a good grouping to use in the controller. I could also use 12 from the 3.3v grouping, but there are 15 of those. The three mosfets that don't match up will get used for something less critical...like a BMS or a mosfet switch.
Conclusions:
1. Chinese mosfets are just awful. I've tested many on my parts tester and I see Vt and Uf all over the place for same model mosfets from the same source. Commonly the test results and the spec sheet are way different.
2. I don't know if AOT went through a bad spell about 2 years to 18 months ago and their quality control was horrible. I haven't bought any AOT290's since then. However I saw Vt and Uf vary a lot. I bought 100 AOT290's from digikey and Arrow over 3 orders and at different times over about a year. I forget the exact quantities now in each order, but something like 45, 30 and 25. I tested all of them on my component tester shown above. The Vt And Uf readings were pretty inconsistent across the 100 mosfets. I ended up with 8 piles. To get 18 for a single controller meant taking the single largest pile and then part of similar piles to populate a single controller. 12 more went into the 12 fet currently in the Currie. Those were picked first and they all matched each other, but not the spec sheet. A few of those 100 mosfets actually matched the spec sheet. Most didn't.
3. These TI mosfets are far more consistent. .2v difference in Vt and .002v difference in Uf and 27 of the 30 fell into 2 groups...that's pretty darn good! And more importantly they are all pretty darn close to the graphs in the spec sheet.
