K1259/J200 pairs - report on testing - Page 1
Forum section: electronics / repair

author: keland_uk
author_rank: Contributor
timestamp: August 01, 2021, 07:47:15 pm
content: ok I have sourced some K1259 and J200 MOSFETS from cricklewood in the uk (https://www.cricklewoodelectronics.com/)its for a repair of a Sony TA-3000ESI have a Peak DCA proJ200 givesP-Ch Enhancement mode MOSFET Red-D Green-S Blue-GVgs(on)=1.421V at Id=4.99mA and Ig=0µA Vgs(off)=0.941V at Id=5.1µAgm=45.1mA/V at Id=3.0mA to 5.0mA Rds(on)<1.0Ω at Id=5.0mA and Vgs=8.0V with body diodeK1529 givesN-Ch Enhancement mode MOSFET Red-D Green-S Blue-GVgs(on)=2.423V at Id=5.04mA and Ig=0µA Vgs(off)=1.775V at Id=4.8µAgm=38.5mA/V at Id=3.0mA to 5.0mA Rds(on)<1.0Ω at Id=5.0mA and Vgs=8.0V with body diodeVgs off for the 4 off J200's are 0.941, 0.914,, 0.878 and 0.910VVgs off for the 4 off K1529's are 1.775, 1.698, 1.791 & 1.862VSo the K1259's are within spec of the Y variant (Vgs off range O: 0.8- 1.6 Y: 1.4 to 2.8 from datasheet)So the J200's are not! They look like O variant (Vgs off range O: -0.8 to -1.6 Y: -1.4 to -2.8 from datasheet)(mind you the DCA75 says +ve voltages, spec sheet says -ve.....so the question is1) Does it matter as long as N-N and P-P reasonably matched?2) I have read you match N to N and P to P on amplifiers. What is the max difference in mV3) RTFM, (i've just read it) DCA75 can drive the gate between 0V and 8V, evidently no -ve voltages, and implies MOSFET's don't care if +ve or -ve on gate!) Is this true, and would the +ve Vgs(off) be different to the -ve Vgs(off) values?Ctt attached, also photo of transistors

author: Kleinstein
author_rank: Super Contributor
timestamp: August 01, 2021, 08:49:04 pm
content: The amplifier seems to use only 1 P and 1 N channel FET per channel. In this case there is hardly any need for matching. Matching would mainly be needed if more FETs are used in parallel. Then it is matching N to N obvious as the N's would be in parallel. Rather good matching would help - maybe within some 20 mV. It is still problematic and needs extra care.There is no need to match the Vth of the N and P side. The relevant number there would be the sum (without the sign). This would effect the threshold and will usually need adjustment anyway if the FETs are changed. So even very different (e.g. 3 V) thresholds for left / rigt channel would not matter.Ideally one could like a similar Ggm at a higher current (like 100 mA or 1A), but this is usually wishfull thinking as P channel fets usually have a lower gm for a similar size. So the circuit should be OK with a difference there.

author: keland_uk
author_rank: Contributor
timestamp: August 01, 2021, 10:48:51 pm
content: Many thanks, I had seen the bit about parallel MOSFETS and matching them, it's good to know that in this instance not super relevant.

author: Audiorepair
author_rank: Frequent Contributor
timestamp: August 01, 2021, 11:03:39 pm
content: I have to say that if I were Cricklewood Electronics, I would be mightily miffed at being accused of possibly selling fake transistors.Did you not notice what you did?

author: magic
author_rank: Super Contributor
timestamp: August 02, 2021, 05:40:17 am
content: Reputation of the vendor is pretty much everything without much more extensive testing. If you are unlucky, a fake part could appear similar and then blow up under load.Note that Vgs(on) is specified for 0.1A current in the datasheet and the gm plot begins at 30mA, but you are testing at a few mA.

author: keland_uk
author_rank: Contributor
timestamp: August 02, 2021, 02:33:57 pm
content: well said, no intention of a slur. Sometimes even vendors are hood winked :-(, I've changed the title.mea culpa