On Thu, 07 Dec 2023 10:04:47 -0500, legg <legg@nospam.magma.ca> wrote:>On Wed, 6 Dec 2023 15:26:00 +0000, Clive Arthur ><clive@nowaytoday.co.uk> wrote: > >>I'm not an analog design expert, but needs must. >> >>I recently adapted a Doug Self audio amplifier design for use on a 60V >>single supply, and to go up to 100kHz with a working ambient temperature >>of -20'C to 180'C. > >No you haven't. Not using conventional components. > >RLI tested some plastic-package power mosfets at high temps. At 300c they turned on at zero gate voltage but recovered when they cooled off. At about 330c they failed hard. I probably desoldered stuff inside.
Power Amplifier for 100kHz.
Started by ●December 6, 2023
Reply by ●December 7, 20232023-12-07
Reply by ●December 7, 20232023-12-07
On Thu, 7 Dec 2023 15:26:52 +0000, Clive Arthur <clive@nowaytoday.co.uk> wrote:>On 07/12/2023 15:04, legg wrote: >> On Wed, 6 Dec 2023 15:26:00 +0000, Clive Arthur >> <clive@nowaytoday.co.uk> wrote: >> >>> I'm not an analog design expert, but needs must. >>> >>> I recently adapted a Doug Self audio amplifier design for use on a 60V >>> single supply, and to go up to 100kHz with a working ambient temperature >>> of -20'C to 180'C. >> >> No you haven't. Not using conventional components. >> >> RL > >Bugger! I could have sworn it was working at 180'C (along with all the >other parts of the system), but it seems you know better. I must have a >faulty oven. > >I'd better warn all the other downhole instrumentation companies too! > >But yes, selected conventional components, analog and digital. And yes, >I know that if you extrapolate the graphs, most of the parts de-rate to >negative power dissipation.We use D2PAK mosfets and lead-free solder, with relow temps around 240c. That works fine.
Reply by ●December 8, 20232023-12-08
On Friday, December 8, 2023 at 9:26:12 AM UTC+11, john larkin wrote:> On Wed, 6 Dec 2023 22:49:40 +0000, Clive Arthur > <cl...@nowaytoday.co.uk> wrote: > > >On 06/12/2023 21:19, Phil Hobbs wrote: > >> On 2023-12-06 10:26, Clive Arthur wrote:<snip>?> I used to build giant NMR gradient amplifiers. I used one opamp per > mosfet to make a sloppy fet into a nearly perfect device.Everything John Larkin puts together is insanely good. The insanity involved is all his. -- Bill Sloman, Sydney
Reply by ●December 8, 20232023-12-08
On 08/12/2023 02:45, John Larkin wrote:> On Thu, 7 Dec 2023 15:26:52 +0000, Clive Arthur > <clive@nowaytoday.co.uk> wrote: > >> On 07/12/2023 15:04, legg wrote: >>> On Wed, 6 Dec 2023 15:26:00 +0000, Clive Arthur >>> <clive@nowaytoday.co.uk> wrote: >>> >>>> I'm not an analog design expert, but needs must. >>>> >>>> I recently adapted a Doug Self audio amplifier design for use on a 60V >>>> single supply, and to go up to 100kHz with a working ambient temperature >>>> of -20'C to 180'C. >>> >>> No you haven't. Not using conventional components. >>> >>> RL >> >> Bugger! I could have sworn it was working at 180'C (along with all the >> other parts of the system), but it seems you know better. I must have a >> faulty oven. >> >> I'd better warn all the other downhole instrumentation companies too! >> >> But yes, selected conventional components, analog and digital. And yes, >> I know that if you extrapolate the graphs, most of the parts de-rate to >> negative power dissipation. > > We use D2PAK mosfets and lead-free solder, with relow temps around > 240c. That works fine.SiC is good too. When I first started working in this area, I was very surprised on my first day to see a colleague doing a crude temperature test using a hot air gun and a thermocouple, just checking before a long term test in an oven. I'm not giving anything away which isn't well known to those in the business by saying the part in question was an ordinary 8-bit PIC. Operating at 180'C. An 85'C part IIRC, though I suspect the only difference between that and a 125'C part is the part number. I've had PICs running at 200'C, though 180'C is the usual benchmark. Those involved have lists of components which they've tested. That takes considerable time and money so they don't readily reveal that information. -- Cheers Clive
Reply by ●December 8, 20232023-12-08
On Friday, December 8, 2023 at 9:54:36 PM UTC+11, Clive Arthur wrote:> On 08/12/2023 02:45, John Larkin wrote: > > On Thu, 7 Dec 2023 15:26:52 +0000, Clive Arthur <cl...@nowaytoday.co.uk> wrote: > >> On 07/12/2023 15:04, legg wrote: > >>> On Wed, 6 Dec 2023 15:26:00 +0000, Clive Arthur <cl...@nowaytoday.co.uk> wrote: > >>> > >>>> I'm not an analog design expert, but needs must. > >>>> > >>>> I recently adapted a Doug Self audio amplifier design for use on a 60V > >>>> single supply, and to go up to 100kHz with a working ambient temperature > >>>> of -20'C to 180'C. > >>> > >>> No you haven't. Not using conventional components. > >> > >> Bugger! I could have sworn it was working at 180'C (along with all the other parts of the system), but it seems you know better. I must have a faulty oven. > >> > >> I'd better warn all the other downhole instrumentation companies too! > >> > >> But yes, selected conventional components, analog and digital. And yes, I know that if you extrapolate the graphs, most of the parts de-rate to negative power dissipation. > > > > We use D2PAK mosfets and lead-free solder, with relow temps around 240c. That works fine. > > SiC is good too. > > When I first started working in this area, I was very surprised on my first day to see a colleague doing a crude temperature test using a hot air gun and a thermocouple, just checking before a long term test in an oven.The limitations on conventional components are mostly the packages, but not always.> I'm not giving anything away which isn't well known to those in the business by saying the part in question was an ordinary 8-bit PIC. > Operating at 180'C. An 85'C part IIRC, though I suspect the only difference between that and a 125'C part is the part number. I've had PICs running at 200'C, though 180'C is the usual benchmark.They aren't tested or certified for operation above 85C (for military grade 125C) because the testing costs money and reduces the yield.> Those involved have lists of components which they've tested. That takes considerable time and money so they don't readily reveal that information.If it was cheap or easy - or if there were enough interested customers - the manufacturers would do it for you, but charge extra for the certified parts. -- Bill Sloman. Sydney
Reply by ●December 8, 20232023-12-08
On Wed, 6 Dec 2023 15:26:00 +0000, Clive Arthur <clive@nowaytoday.co.uk> wrote:>I recently adapted a Doug Self audio amplifier design for use on a 60V >single supply, and to go up to 100kHz with a working ambient temperature >of -20'C to 180'C.How about reducing the _amplifier_ temperature range with a Peltier element ? This will: - increase component life time - simplify biasing However, there are several issues with Peltiers: - it doesn't tolerate strong vibration - sufficient extra power must be available to drive the element, often more than the power that you want to transfer out from the amplifier - the hot side can be well above 200 C if the ambient is hot, remember to dissipate both the amplifier losses and in addition the power for the Peltier The Peltier can be used to cool the amplifier in a hot environment. Reversing the Peltier current and it can be used to warm up the amplifier in a cold environment. Thus the bias design is simplified.
Reply by ●December 8, 20232023-12-08
On 08/12/2023 13:55, upsidedown@downunder.com wrote:> On Wed, 6 Dec 2023 15:26:00 +0000, Clive Arthur > <clive@nowaytoday.co.uk> wrote: > >> I recently adapted a Doug Self audio amplifier design for use on a 60V >> single supply, and to go up to 100kHz with a working ambient temperature >> of -20'C to 180'C. > > > How about reducing the _amplifier_ temperature range with a Peltier > element ? > > This will: > - increase component life time > - simplify biasing > > However, there are several issues with Peltiers: > - it doesn't tolerate strong vibration > - sufficient extra power must be available to drive the element, > often more than the power that you want to transfer > out from the amplifier > - the hot side can be well above 200 C if the ambient is hot, > remember to dissipate both the amplifier losses and in > addition the power for the Peltier > > > The Peltier can be used to cool the amplifier in a hot environment. > Reversing the Peltier current and it can be used to warm up the > amplifier in a cold environment. Thus the bias design is simplified.Not practical, I'm afraid. These instruments are in a tube (a pressure housing) to cope with over 1000 Bar, and the inside diameter is maybe 40mm. The mechanical shocks can be very severe too. Peltier modules are sometimes used for an individual small part, a camera chip for example, though I haven't used one. -- Cheers Clive
Reply by ●December 8, 20232023-12-08
onsdag den 6. december 2023 kl. 16.27.07 UTC+1 skrev Clive Arthur:>, and if I'd used say a rubber diode to get some quiescent > current, I think it would be very difficult to control Iq well enough > over the temperature range.tried how bad it is if you bolt bias transistor to TR6 and TR8?
Reply by ●December 8, 20232023-12-08
On Thu, 7 Dec 2023 15:26:52 +0000, Clive Arthur <clive@nowaytoday.co.uk> wrote:>On 07/12/2023 15:04, legg wrote: >> On Wed, 6 Dec 2023 15:26:00 +0000, Clive Arthur >> <clive@nowaytoday.co.uk> wrote: >> >>> I'm not an analog design expert, but needs must. >>> >>> I recently adapted a Doug Self audio amplifier design for use on a 60V >>> single supply, and to go up to 100kHz with a working ambient temperature >>> of -20'C to 180'C. >> >> No you haven't. Not using conventional components. >> >> RL > >Bugger! I could have sworn it was working at 180'C (along with all the >other parts of the system), but it seems you know better. I must have a >faulty oven. > >I'd better warn all the other downhole instrumentation companies too! > >But yes, selected conventional components, analog and digital. And yes, >I know that if you extrapolate the graphs, most of the parts de-rate to >negative power dissipation.E.M.Cherry's PA circuitry and their clones can form rugged designs, but they were never intended for data transmission. What's the format? Thermal compensation of quiescent biasing was a good trick, then, but you'd have to reconsider options over an extended range. Claiming to have done such a design without doing so is silly. You may have to satisfy yourself with something that doesn't work very well (or at all) at room temperature, if you stick with the limitations of Self's variation (intended to address inaudible distortion). Self-heating to within the range isn't out of the question, though inconvenient on the bench. RL
Reply by ●December 8, 20232023-12-08
On Fri, 8 Dec 2023 10:53:23 +0000, Clive Arthur <clive@nowaytoday.co.uk> wrote:>On 08/12/2023 02:45, John Larkin wrote: >> On Thu, 7 Dec 2023 15:26:52 +0000, Clive Arthur >> <clive@nowaytoday.co.uk> wrote: >> >>> On 07/12/2023 15:04, legg wrote: >>>> On Wed, 6 Dec 2023 15:26:00 +0000, Clive Arthur >>>> <clive@nowaytoday.co.uk> wrote: >>>> >>>>> I'm not an analog design expert, but needs must. >>>>> >>>>> I recently adapted a Doug Self audio amplifier design for use on a 60V >>>>> single supply, and to go up to 100kHz with a working ambient temperature >>>>> of -20'C to 180'C. >>>> >>>> No you haven't. Not using conventional components. >>>> >>>> RL >>> >>> Bugger! I could have sworn it was working at 180'C (along with all the >>> other parts of the system), but it seems you know better. I must have a >>> faulty oven. >>> >>> I'd better warn all the other downhole instrumentation companies too! >>> >>> But yes, selected conventional components, analog and digital. And yes, >>> I know that if you extrapolate the graphs, most of the parts de-rate to >>> negative power dissipation. >> >> We use D2PAK mosfets and lead-free solder, with relow temps around >> 240c. That works fine. > >SiC is good too.Maybe an SiC and a silicon fet will both fail whan the die bond solder melts. My concern with SiC is that they seem to have tiny die, hence high thetas. https://www.dropbox.com/s/hnu2b7qlfw98bwq/Cree_Chip.JPG?raw=1 vs https://www.dropbox.com/s/4nxm7m2q3j3buvc/ExFets.jpg?raw=1 That, and the horrible gate drive swings that they need. SiC only seems to make sense switching kilovolts.> >When I first started working in this area, I was very surprised on my >first day to see a colleague doing a crude temperature test using a hot >air gun and a thermocouple, just checking before a long term test in an >oven.Setting up a temp chamber is a nuisance. I use a cardboard box with some padding inside, a heat gun, and freeze spray on my bench, whenever I can. https://www.dropbox.com/scl/fi/ncxlgwgyvyoxexzmfqyk3/T660_Temp_Chamber.jpg?rlkey=oud1q89ygu5nafd2i5nym6jii&raw=1> >I'm not giving anything away which isn't well known to those in the >business by saying the part in question was an ordinary 8-bit PIC. >Operating at 180'C. An 85'C part IIRC, though I suspect the only >difference between that and a 125'C part is the part number. I've had >PICs running at 200'C, though 180'C is the usual benchmark.Maybe faster parts, with more timing margin, are sold as the extended temp parts. A test machine might test just one prop delay to pick parts with process margin.> >Those involved have lists of components which they've tested. That >takes considerable time and money so they don't readily reveal that >information.Bleeding-edge performance often involves violating datasheet abs-max ratings. It's a calculated risk. I like to test parts to failure or destruction. A margin of 2:1 over abs max voltage is normal and I've seen 5:1. The RF world is a special case! You can safely start at 2:1. I wonder if there is a philosophy about how to set abs max ratings.
