Saturday, October 21, 2017

2SK669 thresh hold

My build was over driving. I lowered the Vcc and it would function but it just wasn't right. When i made the model I used a BSS123 and changed a couple of the parameters. The thresh hold was at 1.6volts so my design was forward biasing the the amp into saturation. I took 5 2Sk669's from the parts bin and made a jig to test them. All 5 were on at 1 volt. Then I looked at the datasheet an the 0.9 typical was making me ask where did 1.6 volt come from? I have some datasheets from different brands. Could I have gotten that from one of them? Anyhoo, I changed the Vth to 1.0 in the model lib. I had adjusted the bias on the test amp and it is better with the lower bias.
The simple fix is to adjust your model to 0.9 volts.

.model 2SK669 VDMOS(Rg=3 Rd=2.4 Rs=1.8 Vto=1.0 Kp=1 Cgdmax=.1n Cgdmin=.01n Cgs=.1n Cjo=.03n Is=2.8p Rb=3 ksubthres=.1 mfg=Fairchild Vds=50 Ron=20 Qg=1.4n)

I set Vto=1.0 

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