Palomar ERF-2030+

I know this thread is old, but has anyone figured out how to drive these ERF2030+ parts yet? I've tried them in a handful of different radios and the only thing I've ever gotten them to work decently in was the Connex 4400 Turbo. And it took quite a lot of fiddling to get it working.
They are definitely not drop-in replacements. A big issue is the gate capacitance. The average IRF520 has a static Cgs of approximately 400pF. The ERF2030+ are up around 1100pF. The Cgd seems to compound the issue. I honestly don't know how some of these guys are getting them to work as good as they do. I'm no expert, but if I were choosing a power switching FET to use in an RF application, I don't think these are what i would go with.

That's really crazy high.

Nobody wants to use a REAL RF MOSFET like the RD16HHF1
Not enough "watts"

Funny that you'd bring that up. I was just talking to a couple people in a YouTube comments section about that the other day. I have quite a few of that family of FETs and they are spectacular. I use the RD00HHS1, RD06HHF1, RD16HHF1, and the RD100HHF1 FETs in my homebrew projects. I'm sure the RD70HHF1 is a good part also, but the 100 is only $3 more, so I've never bothered trying them. I've been considering prototyping a custom transmitter chain in one of my CBs using these devices. I like the RDx6HHF1 devices though. The tabs are the source connection, this means no isolated mounting needed, and it minimizes internal inductance on the source pin which allows better gain at higher frequencies.
I was just curious if anyone happened to figure out a good way to drive the 2030+ since I have 8 of them laying here collecting dust. I've only seen a couple people able to show them outputting clean power, and they don't show anything since they're trying to sell you stuff. On a side note, if you think the Cgs of the 2030+ is high, I measured just over 3000pF of static Cgs on the ERF9530s. I know these numbers drop with Vds applied, but that's insanely high for a 100W device. I guess I'll stick to the RD and other real RF devices, they have tons of published data and good examples of how to use them in different applications.

Eldorado828 said:

I've got a handful and they've been pretty useless to me as well. I've had the same question as you but have yet to find any suggestions. Until then I've been got a bag full of fishing weights..

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Get one of these from eBay. You can find them for under $20.00.
It will tell you the gate voltage, and capacitance and the on resistance.
I have one and use it all the time. It can help you match Bipolar transistors as well.

Andy,
No thermal runaway on FETS! The following article comes from:

https://www.onsemi.com/pub/Collateral/AND8199-D.PDF

© Semiconductor Components Industries, LLC, 2014January, 2014 − Rev. 11Publication Order Number:AND8199/DAND8199/D Thermal Stability of MOSFETs A variety of applications use hot-swap controllers, often to increase the reliability of a system. However, a failure inthe hot-swap circuit would defeat that purpose. When you use MOSFETs in their active region to control current, suchas you would for a controller that operates in a constant-current mode of operation, they have an inherent failure mechanism. In this mode, the MOSFET can get hot spots and fail, long before the device exceeds its Safe Operating Area (SOA) ratings.Engineers have long understood that MOSFETs are positive temperature coefficient devices. Therefore, as the temperature of the device increases, the resistance increases.In other words, higher temperatures result in lower currents.This fact is important if you want to operate MOSFETs in parallel. With a good thermal path between devices, the positive temperature coefficient reduces the current in the hottest device and forces more of it to flow in the cooler device, thereby avoiding thermal runaway.

Also the DC biasing circuit needsto be constant voltage, not constant current.

Keep your pearls.

That's likely why Qixiang has the metal plate and thermal pad over the front of the devices in the Stryker and Anytone.
A lot of amplifier designs that employ MOSFETs also have an aluminum bar across the front of the devices to clamp them down and provide another path for heat.

Andy, that is a whole lot of writing there, and I'm not really getting what you're trying to say here.
The diode to ground in the bias circuit of a bipolar transistor isn't there to define the class of operation, it's there to provide rudimentary thermal tracking for the bias current. The base-emitter junction of the transistor and the p-n junction in the diode both have a negative temperature coefficient (NTC) and as they both heat up the voltage drop across the p-n junction drops causing more current draw. In theory, the diode will pull current away from the b-e junction as they both heat up and prevent the b-e junction from drawing more current and causing a thermal runaway. This is why those diodes are held to the transistor with thermally conductive glue. Bipolar operation isn't really relevant to the problem with these mosfets though.
I get that the impedance and RF isolation of the gate biasing circuit can be an important factor when using Mosfets, especially when the gate has a non-symmetrical (distorted) drive signal. If the impedance of the bias supply is too high, or not properly decoupled from the RF, a non-symmetrical drive signal can cause the gate bias voltage to drift away from it's steady-state point and can change the operating class of the FET, sometimes this is minimal, but I've seen it both collapse the bias voltage and push it to the point where the FET never turns off. In the Qixiang based/derived radios (Strykers, Anytones, ect.), there is a reversed biased (in relation to the bias voltage) 1N4148 diode in series with a low value resistor (330R for the finals and 820R for the drivers I think) across the gate-source connection. I think this is supposed to provide a small amount of DC voltage offset across the capacitor that is driving the gate, essentially providing a slight increase in bias point when RF is present vs. when there is no signal at the gate. I've never actually tried scoping the gate with and without this D-R in place to see if there is an offset change, so this is purely speculation. The biasing setup still isn't the issue I'm/we're facing with driving these 2030+ FETs though.
When you drive a mosfet gate with a really fast rising edge, which a 27MHz sine wave has, you get a step in the gate voltage as the FET begins to turn on significantly. This is caused by the miller effect of the gate-drain capacitance. With the gate voltage rising so fast, this will cause the drain voltage to fall very fast as the FET turns on, the Cgd will cause the falling drain voltage to pull charge away from the gate and causes a step in the rising edge of the gate voltage. Now, mosfets are voltage controlled devices, but due to the capacitance of the gate, combined with the miller effect, driving the gate very fast requires a significant amount of current to get through that stepping point without having a step occur. This is something I've dealt with when building switch-mode power supplies. In my Connex 4400 Turbo, I was able to provide this current in the amp section by adding an additional turn to the primary of the input transformer (total of 3 turns). This allowed me to drive the 2030+ gates hard enough to eliminate the step in the gate signal, minimizing distortion, and allowed for 80W PEP with only 4W PEP input signal. Getting this type of drive without the use of a transformer in a single ended configuration has been out of my reach though. I'm not too super concerned, as I do have other options to use in my radios. My posting here was merely a curiosity if anyone ever figured this out. As I said earlier, I'm absolutely no expert, and there is obviously something I'm missing, but it's nice to know that I'm not the only one having the same exact problem with these things.

Tallman: The thermal runaway on FETs is kind of hit or miss these days. It depends on what FET technology you're working with. Older FET designs like the IRF510/520/530 were like you described with PTC, allowing easy current sharing and gate biasing for RF applications. Many of the newer switching FET technologies actually have NTC and can suffer from thermal runaway just like a bipolar transistor. I was just reading about this the other day and I think it had something to do with the evolution of how the gate was designed and what materials were used in the gate's construction. It's pretty easy to tell what kind of FET you have. Put it in a test jig and apply a constant biasing voltage to the gate while measuring the drain current. As the FET heats up, the drain current will either fall or rise depending on the generation of FET tech that is used inside that device. I believe these 2030+ FETs have the NTC type gate design, but I haven't set them up and measured them.
Those cheap component testers are pretty nice for quick device measurements. I used a similar one at a friend's house and I'm awaiting mine to be delivered.

Eldorado: They were cheap, so I'm not super worried about it if I never make use of them in another radio. The 4 in my Connex 4400T work fine, but it took more work to get them there than it would have taken me to match out a set of IRF520s and go that route. I've built a couple homebrew amateur radio rigs and amplifiers, but never anything that was presentable or could be used in a mobile application. I mentioned earlier about maybe prototyping an RDxxHHF1 TX chain into one of my CBs just to see if I could get it to work and keep it cool. Sort of like the old Connex 4300HP with the 2SC2290 as a final. In addition to brainstorming that prototype, I've also been brainstorming designing my own mobile 10/11m mobile rig with a 2 x RD100HHF1 amp section built into it. Not a strap-on like the RCI based radios, but built into the main board like a Cobra 200GTL with the 2 x 2SC2290. There is a lot of stuff I'd have to learn to build this, such as ANL and Noise Blanker circuitry designs, and other things that are great in a mobile, but not really necessary in a base rig. With the cheap and easy availability of professional custom circuit boards from China, and the ease of frequency generation you can get with a simple micro-controller and something like a Si5351, I think I could roll my own experimental prototype mobile rig.

I guess my ass better get to work. If I come up with anything worthy of sharing, I'll post it up on the forums here. It seems like you guys have a pretty cool community here.

- Brad, KC3MOP

Eldorado828 said:

Hmmm when will Ranger and all its derivatives adopt it ?

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It's hard to tell. I've seen the RCI based radios fall off significantly in quality control over the last couple years. I don't see them doing any type of innovation unless something within changes. When was the last time they put out anything with a new design? Wasn't the last evolution of their main board design with the 2950/2970DX based radios? I mean, all of their designs are based off of the same basic circuit blocks, but I've not seen any improvements made by them in quite a while. I think moving their entire product line over to SMD components and catching up with better quality control would be a start. But who am I to judge?

- Brad, KC3MOP

I took the first two posts down because no one sees this like I do...

So I'll take a different approach and I will consider my participation in this thread final...because for many people this might help them understand the issue of trigger and stiffening the voltage because you have to use the current passing thru the circuit to reapply the voltage taken from it by the Gate...

I'm tired of getting into Vulcan mind-melds....

Re-view this pic...


NOTICE WHERE THE ADJUSTMENT POT IS...ACROSS RAIL TO GROUND!

There are several methods but this one is the voltage adjust on the ground lead.

Several manufacturers are doing it this way - where Galaxy is concerned - their "stoichiometry" relied on the impedance across an known reference to ground. IT was fixed, as in a Fixed resistor. THEY VARIED THE VOLTAGE ACROSS IT from source side (Driver) - not across the leads of the Gate to ground.

The other makers use a simple series of diodes as the wattless dropper that will adjust the voltage to the Gate from their appearance in the circuit across the gate to ground thru a fixed resistor in series with it - the Diodes are providing a built-in thermal tracking but also a built in voltage divider that each diodes own inherited voltage drop across its' junction causes the voltage drop to LOWER values when hot, but recover, restore up to about .6 volts when cold.


The above is the thermal effect of the diodes that can allow the gate to sustain a thermally equalized voltage tracking that keeps the Gate in the Class you want it to be in.

Fantastic if all you know and use are parts that work with this...Galaxy kept their discrete design and for that I'm thankful but the rest of the world - eh?

But everyone else moved on and now uses these pots across the gate - so your "window" is far more adjustable.

There are other things I've noticed including a type of shift in the Bias recovery that @blasphemy000 (Blasphemy000) is seeing - I don't know how to describe it but you are seeing it too.

That was and is why I posted the above to help others - if those "others" wish to answer the question then I still stand by my statements - "I Will Not Interfere!" - This is simply due to the fact that what I have to repair, is done by my boss and their way - following manufacturers design - anything else will not make the radio acceptable repair under warranty - it's not me here folks - it's my ability to try and inform others that "Manufacturers tell you to - do it there way or the highway" - and they will treat you as such.

It's that simple!

If you have better idea, talk to the manufacturer - don't preach to me about your experience - it's not going to do any good - it's not about me - I'm trying to save bandwidth.

You don't have to believe me, in fact you can do what you want - but the wise are the ones that learn from others mistakes - and their own. I'm trying to help people here from making those mistakes - and you can solve this problem one of two ways, right or wrong. To them? It doesn't matter. Because (when it comes to service) the MANUFACTURER determines that outcome - so review the "adjustable" and see for yourself.

Andy, it's not that I don't believe what you're saying, it's that i don't really understand what you're meaning. The image in your post with the 3 diodes in parallel with the trimmer; what type of radio is that from? I'd like to look up the entire schematic diagram to get a better view of what around it.
As far as the stock Galaxy mosfet biasing goes, the dual finals are fed bias through a 47K resistor fed from the 8V TX rail, into a 100K resistor to ground. There is a 100K trimmer in parallel with the 100K fixed resistor to vary the shunt resistance thus changing the voltage. There is a 100nF bypass cap to ground then the voltage is connected to the gate with a 1K resistor. The driver FET has a different bias setup in which the trimmer is fed at the wiper with the 8V and it's a very touchy adjustment that tends to drift. I reconfigure it to work like the finals so that the trimmer goes to ground. It's easier to adjust and doesn't drift as much. I get how thermal tracking improves the operating point stability.

My question is, how does this discussion about biasing stability fit into being able to drive the gates of the 2030+ FETs while overcoming the strong Miller effect these specific devices have? The people that put these FETs into radios like the Stryker 955 and the Anytone 6666s can't be adding a bunch of extra biasing circuitry to the radios. There's just physically no room on the board. I just don't get it.

I believe that was an Anytone Radio...not sure if it's the AT-6666 or AT-5555

The idea here with the "Bias stiffening" was to help you find a point of operation that the ERF will produce the wattage you're looking for.

The concepts are from another project I've been working on for the effort of MOSFET biasing...

What I'm finding in the "threshold" realm is the requirement of having a little more current to provide the voltage feed to keep up with the demand of the FET gate needing steady platform of power (in this case - Voltage) to handle the switching it has to deal with and the amount of RF that's there.

So in some ways you need a higher voltage - but not a lot of power behind it, which equates to the impedance the Gate is using for threshold - or those 4.7K or 1K resistors showing up - they want to feed the Gate but not have a lot of RF affecting the Bias circuit let alone the Bias circuit using the Capacitance the Gate exhibits as a means to smooth out the very signal you're trying to amplify.(acting like a filter)

So when you mentioned the Galaxy - you can easily see the problem lies in the voltage presence "falling" and basically being washed away - incurring the power losses because the Gate to Bias impedance is too high to be effective against strong RF yet allow for some work to be performed when in SSB modes. You need more of a voltage presence to force the Gate "on" threshold - so you have to change the divider to apply more current to flow thru the circuit - and on top of that - allow for the voltage to stay within acceptable levels - a.k.a = not to cause latching. You're not forcing more power into the Gate per-se - the impedance is there for the isolation - but you need to keep the voltage presence possible for the Gate - even when it's flooded with RF - like Zero-Point bias settings - strong enough in presence to maintain that threshold.

IRF 520 Galaxy uses in this older design, has limitations - even in this current design - so you can also see these effects AMPLIFIED in a device like the ERF2030+ which used to be an acclaimed drop-in replacement for it's AN2030 series from EKL. Only the 13N10FQP seems to survive with limited success due to it's constraints with power level and window - the dynamics of the power delivery system and the required capacitance level extremes (High farad for low-level SSB signal drive linearity and then the flat topping effects of AM and excessive over modulation killing the 20V P-2-P windows these parts have on their Gates from the very same level of capacitance blowing up the gate thru perforation) generate the other half of the problem. But, the IRF 520 is idealized part to survive in place, but it's the 13N10's response that people desire.

So - How I Look At It - the concept of "Constant current" seems to be needed - at least from what I see - for as you mentioned, the Diode, with 330 ohm and 820 ohm parallel across the other two - you get something that works for AM but it takes away power from that RF energy - skewing some of it, to a point of where it pinches up. It simply can sound bad.

So to take care of that - many "Simple-ton" radios of AM mode only (Read RK56 Uniden 880, and now New Cobra 29) are BIASING using TX voltage thru a divider to make the Gate operate - fine if you're only in AM or even FM modes, but lousy for SSB use. Now, they use 4.7K and in some instances of the later revisions - even an adjustable pot - seems to be the new standards.

That previous post section was the whole purpose of applying the Gate regulation - let the part (7805) see some of the loading the Gate requires to maintain a "set-point" voltage - much like an Offset - to keep the Gate working and track the thermal profile.

You are having a problem with getting the ERF2030+ to work in these radios - as my experience has already revealed - it can get you burnt in the pocketbook to make these parts even respond like the originals' did. What I found - was to make the Gate stronger to supply voltage by applying a divider principle of current flow using lower values then "tap" the mid-point and make the Gate to Ground side of this divider adjustable in voltage presence not for current but for the recovery of voltage that "swings" under loading condition that seem to occur in the typical CB radios' output network

We know the Gate doesn't take the power, but it's working against a flow of power underneath it - it's that power that influences the "Gate" effect as an inverse to it's operation. So in a way, the gate reflects the power "glitches" flowing across Drain to Source - you just have to keep the "rudder" steady. The problem is exacerbated when you have higher working voltages slowing down the processing abilities as well as increased capacitive effects you have to remove. The dielectric or insulation used, and it's thickness, for the Gate; is adding to the complexity of the switching times and the need for better die designs for power dissipation.

And we haven't even got to the Admittance issues yet...that's another story for later...I mentioned an effect you can see in scoping the region in both Gate and output - they are subtle but can reveal problems in coupling to the next stage or output network tank circuit.

As a secondary note the R(t) function in this circuit sets a level of sensitivity to apply the changes in power the thermal properties the diodes exhibit - so lower resistance means lower effective power "swing" in thermal (swamping) profile - while the higher R(t) function sets the Diodes to Increase this voltage swing effect in the Thermal profile.

I guess I'm working on a different level - because I'm seeing the various ways people have tried to modify the Bias schemes in the older Galaxy-class radios and as I repair them I have to keep track of what was done and undone to re-do the sections back to stock - and if they can even be made serviceable again. That can be a heartbreaker for a guy whom has a passion for radio and CB - just not thrilled with the idea of having to take out the garbage and clean up their mess only to have the determination made if it's salvageable or not. They are not being made anymore - sad to see some just get thrown into a pile - period.

I say throw that junk in the trash and use 13N10’s or 520’s. There’s a reason why most radios are coming with 13N10’s and not those 2030+.

The PLUS stands for extra headache and BS. They gave companion parts for the original 2030’s and now nothing for the Plus versions.

Yeah, I'm not going to get upset about not being able to use 8 FETs that were like $1/each. I'm also not going to spend any more of my time fussing with them trying to figure out how to make them work. It's not worth my time. I'm not a technician, I'm a hobbyist with some test equipment, and it's much easier for me to use devices like the RDxxHHF1 family that have publicly available datasheets and application notes that I can use as references. Sure, they're more expensive per device, but they're also specifically designed for RF applications.