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Need mofset final and companion part info

D

dss56

Active Member
Sep 27, 2010
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Hi All

I was looking into the attached picture the EN369FN it shows a part change someone marked. Can someone verify what is the correct part to use. 230k or 20k resistor

Also cant find 230k resistor and 320k resistor can they be replaced with 240k and 330k resistor or do i need to use correct values to make.
320k = 2 x 160k
230k = 220k +10k
How critical are the values?

thanks

corrected one en369fn.jpg
 

dss56 said:
They are not made anymore hard to find
Click to expand...
Who did the red line on the schematic?

230 Kohms is not a standard value in 5% or 10% tolerances. If you go to the 1% precision resistor you will have better luck.

You could take a 220k and in series add a 10k resistor. That is a resistor/diode if they red lined one part there should have been an adjustment to one of the other resistors.
 
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Not me that is my question hope someone here made 1 and had the correct resistor they used
 
You'd be safer to OBSERVE the FN-Hybrid design.

Why?

RF interacts with this part.

So you can use the "diode and Resistor" of your choice - per diagram, but you really should also use a "trimmer" pot of 20K and verify the properties you need are being produced, not just taken for granted. As posted by Leap Frog, your voltage can vary due to other factors you need to consider...so use the Trimmer of 20 K to "adjust your drive" and develop a profile or swap parts until it can be safely operated in the environment it's used in.

But as shown, and in my own experiences - they don't correlate back to anything but - "Use What Works For You" principle. Meaning: The value of shunt you use, plus the diode/series resistor and entire design including the INPUT CAPACTIANCE - being the capacitor that is used to send / join the Driver - these factors come into play.

The 1230 is capable of generating a Turn-On voltage to supply the gate of an EN-2030 - but it REQUIRES power to drive it, and converts some of that power into a DC relative value. It works a lot like Carrier Detect in the final AF section of IF out into a Diode Detector - an Audio and DC value from the Carrier is obtained thru the process, but it (the MOSFET) also looks like a capacitor to the DC value - and MODIFIES the DC (smooth's it out much like any cap would do) to a HIGHER value - add that if you apply Audio - too much and it'll pop - generate a hot gate and blow up.

That word "Relative" is just what it means - you only get so much useful "work" from something without changing that something into something THAT YOU CAN'T USE.

It's why we are here talking about that "shunt" resistor - you can try 20K but if it (MOSFET) blows, I am here to warn you, not console you - that the input signal presence can re-rectify within this gate drive system - turning it into a "tank" circuit of energy that can cause the part to latch on until the RF drops off - meaning you will turn on the MOSFET but it'll will act like a switch and simply stay on, not produce RF - just turn on a DC value and take all the power the AM regulator is sending it and sends it to ground until the part blows, pops, like a fuse. The Gate is an INSULATOR - and the RF Diode is a one way valve - Audio plus RF can make the bias voltage generated, and applied RF levels from the preceding stage, exceed the recommended Gate drive voltage of +/- - 20V P2P. It's works like a high-speed switch, but you need to find the trigger voltage to make the RF work as the switching event and let the waves rise and fall as they may - it have a VERY NARROW/SMALL/TINY/MINISCULE KNEE of linear operation - if any.
 
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I sometimes just use a regulated bias supply (w/ a choke) with an adjustable voltage regulator, and circumvent the whole "companion component", the voltage present at the "Gate" pin turns on the device.

As Andy pointed out, a variable resistor offers the advantage of adjustability, but you'd have to take care not provide too much bias voltage, or the MosFet will pop, potentially exploding in pieces.

The Voltage required will not be same for all MosFet devices, but generally around 3.6 V +/- 0.1 is okay for most of the common ones used as finals, the ERF2030, IRF520, FQP13N10.
The "VGs On voltage" is the figure to look for in the datasheet.

Best Regards
 
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dss56 said:
So use the 20k resistor
Click to expand...
I would. Did you see all of the calculations that were done to verify the resistor value.
As LeapFrog suggested the variable regulator like LM-317 would work very well. I have a mosfet amplifier in the works and I am going to use the LM-317 for an amp that will be fairly close to 1000 watts.
Test and set your voltage before firing the amp up. Be sure not to exceed the voltage for your particular FET's.
I hope your fets are matched with the on voltage.

LM317-typical-adjustable-regulator-ckt.png


http://www.datasheetcatalog.com/datasheets_pdf/L/M/3/1/LM317T.shtml
 
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Hello Everyone,

Sorry to post gain but how many mA does it take to bias the fet? I was considering heat dissipation on the 317 and what it may have to endure with an input of 13.8 volts regulated to 3.8volts. This was topic talked about in my ham group this evening.
 
That is a fair question, it doesn't take much current.
Of course it will dissipate more heat the higher the input voltage.

The reason I can say that it doesn't take much current without giving you an actual measurement, is because I've gone down the lazy path on some of my personal projects and have actually powered the regulator off of the 8 Volt (TX only) rail, if the current demand was very high I'd except the the TX switching transistor to give up, but that hasn't happened. MosFet are voltage controlled devices and shouldn't require much current from the gate voltage source.

I usually mount the regulator on the chassis, near the driver/final area, it doesn't produce a lot of heat as it is only functioning while in transmit mode, from a switched 8 Volt source.
I don't think the MosFet should always be "on", maybe I'm incorrect here and that doesn't matter.
 
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LeapFrog said:
That is a fair question, it doesn't take much current.
Of course it will dissipate more heat the higher the input voltage.

The reason I can say that it doesn't take much current without giving you an actual measurement, is because I've gone down the lazy path on some of my personal projects and have actually powered the regulator off of the 8 Volt (TX only) voltage rail, if the current demand was very high I'd except the the TX switching transistor to give up, but that hasn't happened.

I usually mount the regulator on the chassis, near the driver/final area, it doesn't produce a lot of heat as it is only functioning while in transmit mode, from a switched 8 Volt source.
I don't think the MosFet should always be "on", maybe I'm incorrect here and that doesn't matter.
Click to expand...
The input impedance to the FET is extremely high(There should be Zero current continuous, only gate charging) Current flow would be dictated by how many stages, and the resistor setup around the gate. I always use pull down resistors to assure the transistors will not "Latch up." 220 K ohms or higher down to 10 K ohms depending on circuit use.
 

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