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Hi all
From searching the messages, I find that the?TN0106 is a preferred substitute for the BS170.? Yes?? No?? Where's a good place to get 20 or so ... without buying counterfeits or devices with a reversed pin-out?
DigiKey has them, but I'm not happy with their price, even if free shipping may be available.
Thanks in advance, and 73 Jim N6OTQ
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In my opinion.?
I think it is most likely that bad SWR resulting in high voltage transients is probably the cause of most BS170 failures.? The SWR protection may not be fast enough to protect against such transients, particularly if caused by an automatic antenna tuner.? Hans did include provision for zener protection (D503 & D504)? but did not provide the diodes.? I used?IN4756A (47V) from a $15 kit of zeners.
Regarding heat dissipation, the majority of heat from these small plastic MOS FETs is actually through the leads.? Unfortunately there is little published information on their thermal model.?
??
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Jim,
I have no source recommendation , just two comments:
- TN0110 is identical to TN0106 but with a higher drain breakdown voltage: 100V v 60V
- Both have a pinout which is reversed relative to BS170. It is the only pinout available.
JZ
Hi all
From searching the messages, I find that the?TN0106 is a preferred substitute for the BS170.? Yes?? No?? Where's a good place to get 20 or so ... without buying counterfeits or devices with a reversed pin-out?
DigiKey has them, but I'm not happy with their price, even if free shipping may be available.
Thanks in advance, and 73 Jim N6OTQ
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Hi Jim,
I am using 4 x TN0110 in QMX. They are more forgiving by having higher voltage. I am running them at +14V without any trouble. But I am not taking any risk with VSWR higher than 1.2:1 hence also no ATU!
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73 Bojan S53DZ
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John, Bojan, You are both right, and I mis-spoke (also mis-searched).? It was the TN0110 ... but ... which suffixes?? Does it matter?? If not, where should I buy from, if not DigiKey?? Price matters, as does shipping cost,?as does my time to enter a BOM in several vendor's order?page.? DigiKey is easy ... I can wait for my?check to clear their?accounting department.? I know how to fix the reversed pin-out.? Also easy, with a piece of 0.120" Cu or Al.
Next -- is there a page in the builder manual that shows the 47V Zener diode mod for the QDX? ? I'm seeing now that I should?have printed out some emails?from the group a few months ago. ?
Thanks for all useful and on-topic answers, and 73 Jim N6OTQ ?
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I bought the TN0110s from Mouser.?TN0110N3-G-P002
IIRC there was no real difference in the suffixes that mattered. Same leads, etc.?
I've never seen anything official on putting Zeners on the finals on the QDX, just some testing I believe Hans did of a diode across L14.?
I chose to do the diode across L14 on both of my QDXs so far after losing a set of BS170s w/o a diode.
-Nate
N8BTR
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All,
The issue with the QDX is it does not have a key shaping function.? Because of that, there is a very large voltage spike at the abrupt end of the transmission cycle due to the magnetic field built up in L14.? Adding the diode prevents the field generation, much like a diode on a relay coil shorts the kickback current.? The diode across L14 would not handle any voltage caused by SWR mismatch.??
Adding the Zeners on the drains of the BS170s should handle both.? One or the other of the mods should be done as that end-of-cycle spike I have measured at over 120vols, though for an extremely short time.
One possibility for the L14 diode to help with SWR is that the failure is caused when the SWR voltage feedback coincides with the end of the transmission spike.? Adding the Zeners will not help with heat-caused failures that bad SWR can cause.? I have seen very different power measurements between an OCFD and a 50ohm dummy load.? The OCFD read 6+ watts, while the dummy load was 4.6.
Here is a reference on using Zeners to protect output transistors:
As stated in the article above, the best practice is to prevent the SWR mismatch from occurring or to minimize the impact by reducing power.
73
Evan
AC9TU
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Hi Evan,
A few months ago you had observed that the BS170 failure rate on QMX was far less than that on QDX, and had suggested that it was testimony to the efficacy of wave shaping on QMX preventing the end-of-transmission spike.
Well, more time has passed and your observation continues to hold up very well. QMX Wave shaping does appear to have made a tremendous difference in BS170 mortality. Good!
For those planning on using TN0110 or TN0106 in QDX:
Those transistors switch off more rapidly than BS170 does. That makes it even more critical that the L14 commutation diode be used as the fast switching speed can drive the Ldi/dt spike to over 200V !
73 JZ KJ4A
On Fri, Apr 5, 2024 at 12:10?PM Evan Hand < elhandjr@...> wrote: All,
The issue with the QDX is it does not have a key shaping function.? Because of that, there is a very large voltage spike at the abrupt end of the transmission cycle due to the magnetic field built up in L14.? Adding the diode prevents the field generation, much like a diode on a relay coil shorts the kickback current.? The diode across L14 would not handle any voltage caused by SWR mismatch.??
Adding the Zeners on the drains of the BS170s should handle both.? One or the other of the mods should be done as that end-of-cycle spike I have measured at over 120vols, though for an extremely short time.
One possibility for the L14 diode to help with SWR is that the failure is caused when the SWR voltage feedback coincides with the end of the transmission spike.? Adding the Zeners will not help with heat-caused failures that bad SWR can cause.? I have seen very different power measurements between an OCFD and a 50ohm dummy load.? The OCFD read 6+ watts, while the dummy load was 4.6.
Here is a reference on using Zeners to protect output transistors:
As stated in the article above, the best practice is to prevent the SWR mismatch from occurring or to minimize the impact by reducing power.
73
Evan
AC9TU
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Would someone kindly remind me why the substitutes for the BS170?
Are the originals hard to find? Are alternatives considered to be an improved choice?
I currently perceive the BS170 as being fairly common and cheap.
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Tony S., AC9QY,? first identified TN0110 and TN0106 as potential replacements for BS170.
This is what he found attractive:
- lower threshold voltage - higher avalanche voltage (TN0110 = 100V) - better case thermal resistance
The pinout reversal was annoying but folks have found ways to cope with that.
JZ KJ4A?
On Fri, Apr 5, 2024, 5:55?PM Franz Niedermeyer via <wholeflaffer= [email protected]> wrote: Would someone kindly remind me why the substitutes for the BS170?
Are the originals hard to find? Are alternatives considered to be an improved choice?
I currently perceive the BS170 as being fairly common and cheap.
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The BS170 substitute is because the QDX gets very unhappy with over-voltage on the finals, no matter where it comes from.? If it comes from an unexpected SWR spike, the BS170s can emit their magic smoke with ease.? The QCX and QMX are less likely to explode than the QDX, but they can still do it.? Now, most of us won't run at an unacceptably high SWR on purpose, but accidents happen.? Especially with the QDX, stiffer finals like the TN0110 on the original build can save the work needed to replace the finals. ?
If you socket the finals, you still have most of the cooling, because most of the heat is radiated from the leads ... socketed finals expose more lead than finals soldered directly to the board. ? When I get the good replacement finals and get around to building a QDX, you'll see what I'm talking about.? I'd be farther along with this, except that my liver transplant work-up has kept me away from my soldering iron since before Christmas. ??
73 Jim N6OTQ
On Fri, Apr 5, 2024 at 4:55?PM Franz Niedermeyer via <wholeflaffer= [email protected]> wrote: Would someone kindly remind me why the substitutes for the BS170?
Are the originals hard to find? Are alternatives considered to be an improved choice?
I currently perceive the BS170 as being fairly common and cheap.
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Jim and Jz,
Thank you for some good explanations of why not the BS170.
73,
-Franz, N3HFS
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Jim?
¡°most of the heat is radiated from the leads ... socketed finals expose more lead than finals soldered¡±
Would love an authoritative ?source for all this ^
(thin steel wire is a horrible heatsink material even if it successfully gets hot?
thin shiny wire is a poor heat radiator form
sockets carrying significant current /voltage will go intermittent when exposed to thermal movement (but probably ok for a year or two ) notice their total absence in most pro equipment since this was first discovered in the late70¡¯s /80¡¯s?
Epoxy isn¡¯t a fabulous heat conductor but the case heat path has a lot more area to work with and it¡¯s absolutely clear that a copper heatsink attached to the case receives and radiates heat?
finally - over dissipation is not the failure mode and heat sinking won¡¯t protect from voltage spikes ???¡á?. )
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On 06/04/2024 09:50, Bruce Akhurst wrote: Jim
¡°most of the heat is radiated from the leads ... socketed finals expose more lead than finals soldered¡±
Would love an authoritative ?source for all this ^ Various semiconductor data sheets explain the leads are the primary heat sink.
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Can you post a link to one that claims that for a TO-92 package?
JZ
On 06/04/2024 09:50, Bruce Akhurst wrote:
> Jim
> ¡°most of the heat is radiated from the leads ... socketed finals expose
> more lead than finals soldered¡±
>
> Would love an authoritative ?source for all this ^
Various semiconductor data sheets explain the leads are the primary heat
sink.
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can the 47v zeiner diode protection be applied to the qcx variants?
--
regards,
Bryan, N0LUF
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¡° Various semiconductor data sheets explain the leads are the primary heat sink¡±
I¡¯m not familiar with that manufacturer or part number ??
We are talking about a specific manufacturer and part here and the manufacturer specifies Tja in free air around the case making no specific reference to lead length or termination. In completely different (mostly SMD) devices board transfer is a dominant method - as they often have little hope of airflow, broad cross section leads and close to zero lead length where this is to be the main thermal design plan
Back to BS170 - It IS is clear that at least one of the wires (not all 3) is potentially a thermal link to the chip and if the leads are short or well ventilated then you have a thermal path of sorts to the board but with a tiny cross section and surface area out of the TO92 body and using steel which is a bad heat conductor too.
That wire will show up as hot close to the case but in this case please don¡¯t confuse ¡®hot¡¯ with sufficient heat flow to heatsink the entire device
Meanwhile the entire chip is enclosed in a far larger thermal path to ambient air and in a typical installation that will be the bigger heat path. Impossible to give a % as someone with a very hot board in a very cold case or vice versa will be along.
I have found that enclosing TO92 packages in a copper or aluminium surround or clip in results in the surround or clip getting reasonably hot while demonstrably acting as a heat path to ambient. This is probably why TO92 case heatsinks are sold ..
I have only done this (TO92 case heat sinking) in QRP+5w and U3S projects where they run continuously, and the ambient air can reach 40c or more in summer. This is precautionary as I want average Tj below 90C for longest reliability. I have 3 radios run like this and all are still on their original BS170s
However for new readers let me remind everyone that overheating (clumsy soldering aside) does not appear to be a common failure mode while transient voltage excesses does.
Heatsinking won¡¯t help with transients
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Bravo, Bruce! An excellent post.
JZ
On Sun, Apr 7, 2024, 4:57?AM Bruce Akhurst < bruce@...> wrote: ¡° Various semiconductor data sheets explain the leads are the primary heat sink¡±
I¡¯m not familiar with that manufacturer or part number ??
We are talking about a specific manufacturer and part here and the manufacturer specifies Tja in free air around the case making no specific reference to lead length or termination. In completely different (mostly SMD) devices board transfer is a dominant method - as they often have little hope of airflow, broad cross section leads and close to zero lead length where this is to be the main thermal design plan
Back to BS170 - It IS is clear that at least one of the wires (not all 3) is potentially a thermal link to the chip and if the leads are short or well ventilated then you have a thermal path of sorts to the board but with a tiny cross section and surface area out of the TO92 body and using steel which is a bad heat conductor too.
That wire will show up as hot close to the case but in this case please don¡¯t confuse ¡®hot¡¯ with sufficient heat flow to heatsink the entire device
Meanwhile the entire chip is enclosed in a far larger thermal path to ambient air and in a typical installation that will be the bigger heat path. Impossible to give a % as someone with a very hot board in a very cold case or vice versa will be along.
I have found that enclosing TO92 packages in a copper or aluminium surround or clip in results in the surround or clip getting reasonably hot while demonstrably acting as a heat path to ambient. This is probably why TO92 case heatsinks are sold ..
I have only done this (TO92 case heat sinking) in QRP+5w and U3S projects where they run continuously, and the ambient air can reach 40c or more in summer. This is precautionary as I want average Tj below 90C for longest reliability. I have 3 radios run like this and all are still on their original BS170s
However for new readers let me remind everyone that overheating (clumsy soldering aside) does not appear to be a common failure mode while transient voltage excesses does.
Heatsinking won¡¯t help with transients
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?
Bryan Curl
Apr 6? ?#120489? ?
can the 47v zener diode protection be applied to the qcx variants?
?
?
Not unsurprisingly this has been queried at a few points and I think I remember someone saying they had done it but without much detail .? ?
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A few things are different on the QCX series?
?
Probably the most important is that the QCX radios, when run within their published limits don't seem as prone to these types of failures (and of course use a different design).? ?
?
I think Hans would be the first to say that any 'speculative' modification runs a risk of creating another problem or fault mode as a side effect especially if implemented ad-hoc on several versions of the respective boards with components from many sources.
My QCX radio beacons have transmitted countless WSPR cycles (on 8.5V at the PA? for about 3 W out at the BNC )? but along the way this includes several hours into a collapsed antenna? (storm)? and an open circuit (some idiot in charge ?) without any apparent issue.? ?
I'm very aware though that the user is the main protection feature on these sets but currently think that caution on higher operating voltages is a better precaution if you want one. .
?
?
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Bruce and Bryan,
Both the QCX and QMX series of radios have key click filtering that reduces the end-of-transmission spike that I believe is killing most QDX BS170s. The combination of high SWR and that last spike exceeds the limits of the BS170. If that is correct, adding the Zener(s) to the QCX or QMX will not hurt but will most likely not protect all SWR issues. A bad SWR can cause a high current or high voltage. The Zener protects against voltage failure.
73
Evan
AC9TU
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Bruce Akhurst