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NXP

Discussion in 'Home Brew' started by kopcicle, Jun 18, 2019.


  1. Rwb

    Rwb Sr. Member

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  2. kopcicle

    kopcicle Sr. Member

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    I can sum up the first one with
    MRF6VP11KGSR5
    935314866178
    Not Recommended for New Designs...
    That and with out a doubt that particular board is optimized for 88-108MHz
    The latter can be summed up with nearly the same.
    A 500 W to 600 W LDMOS power transistor for broadcast applications and industrial applications in the HF to 500 MHz band.

    The seller I know nothing of ...
     
    Shadetree Mechanic and Rwb like this.
  3. Klondike Mike

    Klondike Mike Sr. Member

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    Mmmm. Further study on some of his other products I find; "Suitable for Linear Application with Appropriate Biasing". Not a plug-&-play module. Additional work would need to be done before applying but could be a starting point on getting into LDMOS.
     
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  4. kopcicle

    kopcicle Sr. Member

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    Not really Mike. I have a 70w MosFet kit arriving on the slow boat where I intend to replace the IRF5xx with the MRF101's .

    What you missed in the above boards was their matching network being wholly unsuitable and not modifiable for HF frequencies. Well, not without such modifications that starting from scratch would be easier and cheaper.

    better would be https://qrpblog.com/2019/10/a-600w-broadband-hf-amplifier-using-affordable-ldmos-devices/
    At just a bit over 50 cents a watt it's a bargain. Even adding the low pass filter board it's still within $1/watt .

    I'll repeat that abusing the output side of these devices is not recommended however they will withstand an enormous amount of abuse. Mishandle the input even a little bit and they die.

    Another option is approaching RFMW or NXP directly for the MRF101 design essentials kit. This gives you a board , a heatsink, two MRF101AN devices and a place to start.
    https://www.nxp.com/products/rf/rf-...mrf101an-rf-essentials-kit:MRF101AN-START-KIT
    Look at it this way. Depending on the supplier you can get a kit for the same price that you can get two devices for .

    Mike , if you really want to dive in you have or I can provide my contact information again.
     
  5. Klondike Mike

    Klondike Mike Sr. Member

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    Nah. Just window shopping again. Kick'in tires. Take'n names. This project hasn't risen to the priority list yet. After seeing lots of garbage, one will be in a better position to recognize when something good comes along. Thanks.
     
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  6. Shockwave

    Shockwave Sr. Member

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    One thing I'll mention is all of the NXP "reference" boards I've seen are rated for CW or pulsed use and are designed to be as simple as possible with the least amount of parts used. While they mention linear applications and 100ma of idling current, the board only has a resistor and bypass caps to apply bias from an external circuit.
     
  7. kopcicle

    kopcicle Sr. Member

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    bias.jpg
     
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  8. Shockwave

    Shockwave Sr. Member

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    That's a good start but at the very least it would still need added voltage regulation. It may also require more than just a 1N4148 diode to properly track the thermal variations in linear operation. Although, I'm not familiar with the characteristics of this particular transistor, what I can say is it is more difficult to sense the die temperature through a plastic cased transistor.

    When this is right, you can set the IDQ for 100ma, apply a full power sustained carrier and as soon as the carrier is removed, the IDQ will instantly return to 100ma. It is not uncommon for the the IDQ to be noticeably higher until the die temperature cools.
     
    #39 Shockwave, May 17, 2020
    Last edited: May 17, 2020
  9. nomadradio

    nomadradio Analog Retentive

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    Nice. And I always thought FETs had a negative temp coefficient. And maybe that's just the resistance of the channel, not the behavior of the gate bias.

    Hmm.

    Seems to me putting two or more series diodes in the trimpot's ground return would increase the compensation. Each diode will add it's own increment. Seems like that would help. Mounting them across the face of the transistor body would improve response speed.

    Never have tried it.

    73
     
  10. Shockwave

    Shockwave Sr. Member

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    LDMOS FETs can have a positive coefficient (resistance increases with heat) at low drain currents and lower operating voltages, but at typical operating levels in the linear mode, the coefficient becomes negative (resistance decreases with heat). This seems more prevalent in higher voltage, power output devices and is the reverse of what we see with typical FET's.

    Mounting bias diodes across the face of a ceramic cased transistor works very well at accurately tracking thermal variations since the ceramic material reacts to changes in heat very quickly with respect to the die temperature. One you encase a high power die in plastic, there is an inevitable delay in the temperature transfer time through the case and the bias lags in its ability to quickly track these changes.

    If you're on a copper heat spreader, you can usually get away with mounting the diode to that spreader and close the the FET. When working with aluminum that has half of the heat conduction ability, you're back to the same type of lag in thermal tracking again. Most 50 volt devices can tolerate these variables while experiencing a maximum of about twice the normal bias current in worse case conditions and without going into a self destructive thermal runaway condition (provided that you're not over-driving it too).

    As transistor operating voltages increase beyond 50 volts, the chances of self destructive thermal runaway increase exponentially without a bias circuit and sensing that instantly tracks the direction and amount of change in the die temperature. Those higher voltages also cause the gate impedance to drop like a brick on high power devices. If you can match the RF drive to that impedance, you now have a new problem contributing to thermal runaway with very poor IMD and linearity.

    All conventional bias circuits can be modulated by any changes in this unusually high current RF drive level! Negative peaks of any modulated carrier will force the transistor into premature RF cutoff. Any positive modulation excursions of the DC bias beyond a few tenths of a volt, will instantly over bias and destroy the transistor. They jump into thermal runaway like a switch and even the complete removal of RF drive cannot break the cycle once it starts. These problems proved to be formidable tasks when designing the new line voltage operated linear pallets. They are very difficult to measure and trace due to all of the stray RF present within an energized circuit.

    To me, the most interesting question is how can the same device transition between a positive and negative temperature coefficient, just based on the voltage and current applied through it? The transistor manufacturer talks all about "holes" and "carriers" and how at a certain point one "layer" overcomes another and the coefficient inverts. To be straight forward, I'm still at a loss as to why all of that happens and am just thankful I've figured out the circuits to compensate for the transistor characteristics I've yet to fully grasp.
     
    #41 Shockwave, May 18, 2020
    Last edited: May 18, 2020
  11. kopcicle

    kopcicle Sr. Member

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    x4_mrf300.jpg x4_mrf300_LPF.jpg.jpg
     
  12. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    Wanted to pass along that issues with "Gate Capacitance" as well as Inductive Reactance to affect Rise and Fall times - so what you may be seeing as "negative" in the FET may simply be issue around the "Expansion" effects not of the fields present, but their thermal effects distorting the Die and therefore it's layout.

    That, along with Gate FET insulation - onto the dimensioning and then onto the spacing of layers and junctions...then adding to this are the problems with "zenering" (the protection device) of the base layer onto the (integrated) inherited traits of their junctions - the "negative" you see is more of the "avalanche" effect from the zener in the base substrate. It stays active through out the time it's "activated" unto when the power is finally switched off.
    • So you think Transistors are fun, at least they are physically junctioned together - MOSFET's are like a Peanut Butter Sandwich - Where's the Jelly when you need it?
    To activate that Zener - its a lot like a thermal detonator - you "push to test" <*click*> - then RELEASE to Detonate - Now what? You pull power before it self destructs - the inductive event on the output along with the capacitive surface the gate has, makes this a self-sustaining event until power is removed and the Zener can reset. You have to build in your own Self-protect feature in this matter - else the device will continue to stay latched and self-destruct.

    Seem this event happens a lot in 13N10's not because of reverse breakdowns, the Gates are failing...The 13N10
    "burn out" because of - I call it a distortion - a gate substrate "section" just plain opens up like a tear and the device is toast.

    VMOS or TRENCH FET designs are suffering a similar fate...
     
  13. kopcicle

    kopcicle Sr. Member

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  14. Shockwave

    Shockwave Sr. Member

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    Hi Andy,
    I've read about some of the things you've discussed here and actually think I've seen it before when I was working with other transistors in parallel. Without installing certain resistors in the gate circuit, one would latch on and burn up. The transistors I'm working with today also have very fast rise and fall times suitable for use into VHF. While I do not have enough internal knowledge of the transistor workings, manufacturers are claiming these parts will transition between a positive coefficient at lower output levels and invert to a negative coefficient at "more practical" power levels. I have definitely seen this on the bench prior to stabilizing the bias tracking, but have no real way of confirming the source.
     

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