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Old 14th September 2015, 08:40 AM   #41
Zen Mod is online now Zen Mod  Serbia
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Originally Posted by nashbap View Post
......

Now could you help me to figure out from this how to calculate the turn on Vgs needed for the IRFP240 fet which I believe is about 4.5V?

Thanks. Nash
Vgs needed for common FW range of Iq is around-ish 4V
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Old 14th September 2015, 10:03 AM   #42
nashbap is offline nashbap  United States
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Originally Posted by Zen Mod View Post
Vgs needed for common FW range of Iq is around-ish 4V
ZM what I meant is how does this circuit produce the approx 4Vish ?

I understand that the voltage across the 5k pot is the same as the zener voltage and that the current thru the pot is 1.36ma as per your example but how does this translate into getting the desired Vgs?

thanks again.

Nash
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Old 14th September 2015, 11:37 AM   #43
palstanturhin is offline palstanturhin  Finland
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Quote:
Originally Posted by nashbap View Post
ZM what I meant is how does this circuit produce the approx 4Vish ?

I understand that the voltage across the 5k pot is the same as the zener voltage and that the current thru the pot is 1.36ma as per your example but how does this translate into getting the desired Vgs?

thanks again.

Nash
The trimmer is the voltage divider for the Zener voltage.
You take the gate voltage for the mosfets from the trimmer viper.
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Old 14th September 2015, 12:37 PM   #44
nashbap is offline nashbap  United States
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Originally Posted by palstanturhin View Post
The trimmer is the voltage divider for the Zener voltage.
You take the gate voltage for the mosfets from the trimmer viper.
OK but it goes thru R9/10 and R11/12 before reaching the gate. So how does one calculate the Vgs ?

thanks. nash
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Old 14th September 2015, 12:47 PM   #45
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just do it

it's pretty obvious .... from pot viper to gate there is no significant current , so voltage at wiper is practicaly same at gate
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Old 14th September 2015, 01:31 PM   #46
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just do it

it's pretty obvious .... from pot viper to gate there is no significant current , so voltage at wiper is practicaly same at gate

OK got it. Thanks. Nash
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Old 16th September 2015, 05:58 AM   #47
audiok is offline audiok  Hong Kong
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My I use LU1014D at the output stage ?
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Old 16th September 2015, 06:08 AM   #48
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Lu1014d is depletion mode mosfet. You would also need to cascode to dissipate power.
You would need to completely change the circuit to make it work
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Old 16th September 2015, 06:21 AM   #49
audiok is offline audiok  Hong Kong
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Thanks you comment.
Would you please show me the cascade circuit.

Thank you.
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Old 16th September 2015, 07:19 AM   #50
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Look at Zen 8. Probably best to look at that first, as it directly relates to lu1014d.
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