Anything wrong with this linear PSU design? (now selecting parts)

[blackdog]

Hi,


If you want to start by builiding a test circuit of your design, de LT1007 is realy fine, i see no problems.
But! do not use a "slow" power section, this give a to big phase lag and to keep it stable you must use large capacitors to compensate.
Trap for young players, many designers make the same mistake 
Stay away of 2N3055 ect, use somthing as the 2SC5200 and de PNP 2SA1943 these are cheap(by real ones) and good. (Toshiba, Faichild)

Buffer capacitor, aboud 2000 a 2500uF per Ampere, 6800uF for a 3 Ampere power supply is "normal"
You may use 10.000uF for a 3 Ampere power supply, it will give you less ripple.
The bigger the buffer capacitor, the more dissipation you wil have in the transformer and rectifier bridge.

Be aware that is you buy a 5 Ampere transformer, you can only use about 60% of the max current of this transformer continuously...


Kind regarts,
Blackdog

[Powermax]

Hi,


If you want to start by builiding a test circuit of your design, de LT1007 is realy fine, i see no problems.
But! do not use a "slow" power section, this give a to big phase lag and to keep it stable you must use large capacitors to compensate.
Trap for young players, many designers make the same mistake 
Stay away of 2N3055 ect, use somthing as the 2SC5200 and de PNP 2SA1943 these are cheap(by real ones) and good. (Toshiba, Faichild)

Buffer capacitor, aboud 2000 a 2500uF per Ampere, 6800uF for a 3 Ampere power supply is "normal"
You may use 10.000uF for a 3 Ampere power supply, it will give you less ripple.
The bigger the buffer capacitor, the more dissipation you wil have in the transformer and rectifier bridge.

Be aware that is you buy a 5 Ampere transformer, you can only use about 60% of the max current of this transformer continuously...


Kind regarts,
Blackdog

Thanks! My final design should be capable of 5A continuous if I can find a suitable transformer with enough tabs. This is proving to be a challenge, I may need to wind my own. I get that I can take advantage of the ripple to reduce power dissipation as the RMS voltage is smaller. It's a cool technique! At 3A, my complementary darlington drops 1V. Higher than expected, then that paired with the 0.25 shunt means I will probably have 3V dropout minimum. I might be able to reduce it if my complementary darlington saturates, which can occur when the voltage looking into the "collector" of the complementary darlington is a smaller voltage than the voltage being driven from the op amps.

I am using an MJE2955 as the pass transistor, GBP is only 2MHz, which might be part of why line regulation is not the best. A switching preregulator will probably require the use of a higher speed more modern transistor.

But no one can deny the sheer awesomeness of the classic 2N3055, with that 3mm² dye inside!

[Powermax]

last post above I have posted my prototype beta (alpha was breadboard) circuit. It's not finished yet, I have yet to solder in some current sources and sinks. Unfortunately the metal film resistor I have are all 100PPM/*C. And the ancient carbon composition 10% resistors are probably worse. Does temp-co matter when resistors are used as dividers? If they are identical resistors, I'd expect simalar changes in all the resistors, which means that the actual division ratio stays roughly the same even as the resistance of the individual resistors change with temperature.

I picked the values for this prototype to allow voltages between 0 and 15V, and currents between 0 and 3A. The current was tricky because finding 2 resistors with the right ratio was very difficult. I ended up picking 274K and 16.2K.
Also how can I easily achieve a negative 5V voltage rail with jellybean parts? The closest thing I have is a charge pump (MAX680) on hand but it runs of a 5V supply, not a 20V supply, and generates both a +10V and -10V rail, 10mA max. Useful for low power analog amps and stuff powered from a digital rail, but I don't know if I want my -5V rail at -10V, or if I want to use the 78c05 (surface mount 7805) which I am using as a voltage reference to power this chip. It may cause noise on the 5V rail, and significant power dissipation.(30mA max draw from the MAX680 * (20-5) = basically half a watt.)

[Kleinstein]

One can reduce the dropout a little, if one uses separate diodes and filter capacitor for the base drive. With input tap switching you might want that anyway to have a constant supply for the OPs.

Faster transistors can make the supply faster, but than you already get to a range where the layout is important. It can be layout and parasitics that makes the difference between a stable circuit and an oscillation of the sziklai stage. So you need to measure real world and maybe tweak the circuit, both for the complementary power stage and the loop adjustment.  With a slow 2N3055 or similar you are in a more predictable range and still fast enough for a power supply.

With more than about 2-3 A one might have to consider a second power transistor and thus power sharing resistors. Than these can be used for the extra fast current limit.

Usually the drop on the shunt and power sharing resistor is something like 200-500 mV each. With more drop the heat dissipation will get rather large and thus self heating gets a problem.

For the negative supply one can use a kind of charge pump, but driven from the mains AC. This is a kind of votlage doubling rectifier. The voltage can be rather high, but to a certain extend it can be adjusted by using the right size capacitors. The extra current through the capacitors is usually at a different time from the main current pulses - so it will not add much to the transformer AC current. Charge pump chips are notoriously noisy as they produce a lot of spikes, so I would avoid them if possible.

[blackdog]

Hi Kleinstein,

Try to think more positive, not backwards in design...
He can use his LT1007 opamp's and like you say 2 power sections to distribute the heat, if you do it like i say, 2 extra resistors in the sziklai stage, than its stable, no problemo!
The design dont have to be so fast as my schematic to be good, The LT1007 is a good opamp for a low noise, low Ri power supply.

Powermax
Do not neglect my remarkse about the loopgain and the phase margin!
Why do you think i tell you, to not use the 2N3055.
Yes i know, there are 1000 designs with LM234/LM741 and 2N3055, 1970 electronic's...

If you use more modern stuf like the LT1007 (also old but very good) en modern power transistors, you wil get a low noise and a low Ri powersupply thats not to difficult to build.
Use about 50uF/Ampere output capacitor, for your 5 Ampere design this would be 220 tot 330uF, 50 or 63V and good of quality! say Rubicon brand, lager give you a better dynamic responce but also larger piek currents in your D.U.T. if something goes wrong.

A tip, go read about loopgain and phase margen in power supply design, much more important than the DA converter.
Without good stability of the design, your DA converters are not important 

If you use Google translate, read my measurements and remarke's on this Dutch website www.circuitsonline.net.

The original design CO-2016 Power Supply
https://www.circuitsonline.net/forum/view/130041/1/co+0

My modifications of the CO-2016 design
https://www.circuitsonline.net/forum/view/131554/1/co+0

My power supply design page on the circuitsonline.net forum(large)
https://www.circuitsonline.net/forum/view/110029/1/co+0

Topic on the same Forum of a friend of mine: Gertjan, He also did a lot of measurements on power supplies.
https://www.circuitsonline.net/forum/view/130792

Happy reading 

Kind regarts,
Blackdog

PS
Sorry for my bad English, it is not my native language and I am dyslexic.
So bear with me.

[Powermax]

One can reduce the dropout a little, if one uses separate diodes and filter capacitor for the base drive. With input tap switching you might want that anyway to have a constant supply for the OPs.

Faster transistors can make the supply faster, but than you already get to a range where the layout is important. It can be layout and parasitics that makes the difference between a stable circuit and an oscillation of the sziklai stage. So you need to measure real world and maybe tweak the circuit, both for the complementary power stage and the loop adjustment.  With a slow 2N3055 or similar you are in a more predictable range and still fast enough for a power supply.

With more than about 2-3 A one might have to consider a second power transistor and thus power sharing resistors. Than these can be used for the extra fast current limit.

Usually the drop on the shunt and power sharing resistor is something like 200-500 mV each. With more drop the heat dissipation will get rather large and thus self heating gets a problem.

For the negative supply one can use a kind of charge pump, but driven from the mains AC. This is a kind of votlage doubling rectifier. The voltage can be rather high, but to a certain extend it can be adjusted by using the right size capacitors. The extra current through the capacitors is usually at a different time from the main current pulses - so it will not add much to the transformer AC current. Charge pump chips are notoriously noisy as they produce a lot of spikes, so I would avoid them if possible.

I built up the prototype, made a optional removable daughterboard for a MAX680 charge pump, and on the output I can see the sharp periodic transients from it down around the 100mV range. My prototype uses LM741's and draws a lot of quiescent current (about 150mA, due to the saturated current error amp with its inputs far apart voltage-wise.) I have a selectable jumper pin on it to select either whatever inverting supply I choose, or to give it a proper negative supply externally. My layout is a bit of a mess at the moment due to the very small perf boards and complex circuit, and many mistakes that required soldering re-work. I have yet to debug the current error amp (as it did not appear to work initially) hopefully it's just that the trim is bad on it.

Luckily because LM741 and LT1007 and OP27 all have simalar pinouts, I should be able to use any one of them. I mounted pots and connected pins5 and 8 together to one end, and pin 1 to the other, this will allow me to null out the voltage offset for precision.  I think this will be necessary on the current error amp.

[Powermax]

Hi Kleinstein,

Try to think more positive, not backwards in design...
He can use his LT1007 opamp's and like you say 2 power sections to distribute the heat, if you do it like i say, 2 extra resistors in the sziklai stage, than its stable, no problemo!
The design dont have to be so fast as my schematic to be good, The LT1007 is a good opamp for a low noise, low Ri power supply.

Powermax
Do not neglect my remarkse about the loopgain and the phase margin!
Why do you think i tell you, to not use the 2N3055.
Yes i know, there are 1000 designs with LM234/LM741 and 2N3055, 1970 electronic's...

If you use more modern stuf like the LT1007 (also old but very good) en modern power transistors, you wil get a low noise and a low Ri powersupply thats not to difficult to build.
Use about 50uF/Ampere output capacitor, for your 5 Ampere design this would be 220 tot 330uF, 50 or 63V and good of quality! say Rubicon brand, lager give you a better dynamic responce but also larger piek currents in your D.U.T. if something goes wrong.

A tip, go read about loopgain and phase margen in power supply design, much more important than the DA converter.
Without good stability of the design, your DA converters are not important 

If you use Google translate, read my measurements and remarke's on this Dutch website www.circuitsonline.net.

The original design CO-2016 Power Supply
https://www.circuitsonline.net/forum/view/130041/1/co+0

My modifications of the CO-2016 design
https://www.circuitsonline.net/forum/view/131554/1/co+0

My power supply design page on the circuitsonline.net forum(large)
https://www.circuitsonline.net/forum/view/110029/1/co+0

Topic on the same Forum of a friend of mine: Gertjan, He also did a lot of measurements on power supplies.
https://www.circuitsonline.net/forum/view/130792

Happy reading 

Kind regarts,
Blackdog

PS
Sorry for my bad English, it is not my native language and I am dyslexic.
So bear with me.

Thanks for your input blackdog!

One of my unspoken requirements is to find a use for some of the junk I have collected. I have over a handful of 2N3055's (about 15), 10 more MJE3055's, and 11 MJE2955's. I also have a few mid power transistors like TIP31C, TIP42, TIP41C, and a few high voltage ones too. If I was to buy more transistors in the future I'll certainly keep this in-mind.

I did read an excellent tutorial / article from All About Electronics that discusses the topic of frequency compensation. It's interesting although I don't fully understand the procedure to actually do it.

[Powermax]

I just found a bunch of AD517JH op amps, in that sexy metal TO-99 package!  I wish these packages still existed today! They look so great!

They are astonishingly fast at a whooping 0.1V/uS, have insane GBP clocking in at a blistering 250kHz!

Actually these specs are laughable! But I'm sure given that they are ancient relics of the past, I think they are actually pretty good on the precision specs. About 75uV offset, and the noise rating is only about 3 times higher than the LT1007. Those specs are more respectable. Of course I have no idea what any of this stuff means, I'm just a DIY'er Ah well.

[David Hess]

My prototype uses LM741's and draws a lot of quiescent current (about 150mA, due to the saturated current error amp with its inputs far apart voltage-wise.)

That does not seem right.  Maybe something is oscillating?  Didn't you add clamps to prevent the error amplifiers from saturating?

One of my unspoken requirements is to find a use for some of the junk I have collected. I have over a handful of 2N3055's (about 15), 10 more MJE3055's, and 11 MJE2955's. I also have a few mid power transistors like TIP31C, TIP42, TIP41C, and a few high voltage ones too. If I was to buy more transistors in the future I'll certainly keep this in-mind.

The modern but still old jelly bean fast TO-220 power transistors are the D44/D45 series.  The MJE182/MJE172 series or MJE243/MJE253 make good fast driver transistors if you need something beefier than the 2N4401/2N4403.

Fast transistors are wasted on a general purpose bench supply though because of long external lead lengths.  Release the 2N2955/2N3055 and TIPs of war.

I did read an excellent tutorial / article from All About Electronics that discusses the topic of frequency compensation. It's interesting although I don't fully understand the procedure to actually do it.

Look up how to perform transient response testing using a pulse/function generator and oscilloscope.  It takes less time to substitute a couple of capacitors and resistors than to run a simulation to find values which will need to be changed anyway.

I just found a bunch of AD517JH op amps, in that sexy metal TO-99 package!  I wish these packages still existed today! They look so great!

They are astonishingly fast at a whooping 0.1V/uS, have insane GBP clocking in at a blistering 250kHz!

Actually these specs are laughable! But I'm sure given that they are ancient relics of the past, I think they are actually pretty good on the precision specs. About 75uV offset, and the noise rating is only about 3 times higher than the LT1007. Those specs are more respectable. Of course I have no idea what any of this stuff means, I'm just a DIY'er Ah well.

Walter Jung's book mentions the AD517.  He says it is a laser trimmed version of the AD508 which itself is sort of a super beta 308 but with precision enhancements.  To me, it looks like AD's version of the OP07 which is a trimmed OP05 and that is how I would treat it.

The AD517/OP07 has much lower bias current than an LT1007/OP27 so it has higher voltage noise but lower current noise.  That makes it useful with higher source impedances where the LT1007/OP27 would be noisier.  The difference is roughly 30k versus 3k.

Be careful about using these operational amplifiers because unlike the 741, they have low voltage shunts across their inputs limiting their differential input voltage range.  The input source impedance can limit the differential current preventing damage.

[Powermax]

My prototype uses LM741's and draws a lot of quiescent current (about 150mA, due to the saturated current error amp with its inputs far apart voltage-wise.)

That does not seem right.  Maybe something is oscillating?  Didn't you add clamps to prevent the error amplifiers from saturating?

Yeah, I didnt add them yet. That was total current draw including current draw from the charge pump. So its probably double what it should be. The MAX680 was powered from the 78c05 reference, so its not acvurate. I dnt know how efficient the charge pump is.

One of my unspoken requirements is to find a use for some of the junk I have collected. I have over a handful of 2N3055's (about 15), 10 more MJE3055's, and 11 MJE2955's. I also have a few mid power transistors like TIP31C, TIP42, TIP41C, and a few high voltage ones too. If I was to buy more transistors in the future I'll certainly keep this in-mind.

The modern but still old jelly bean fast TO-220 power transistors are the D44/D45 series.  The MJE182/MJE172 series or MJE243/MJE253 make good fast driver transistors if you need something beefier than the 2N4401/2N4403.

Fast transistors are wasted on a general purpose bench supply though because of long external lead lengths.  Release the 2N2955/2N3055 and TIPs of war.

I did read an excellent tutorial / article from All About Electronics that discusses the topic of frequency compensation. It's interesting although I don't fully understand the procedure to actually do it.

Look up how to perform transient response testing using a pulse/function generator and oscilloscope.  It takes less time to substitute a couple of capacitors and resistors than to run a simulation to find values which will need to be changed anyway.

Thanks for the lead, I'll check it out!

I just found a bunch of AD517JH op amps, in that sexy metal TO-99 package!  I wish these packages still existed today! They look so great!

They are astonishingly fast at a whooping 0.1V/uS, have insane GBP clocking in at a blistering 250kHz!

Actually these specs are laughable! But I'm sure given that they are ancient relics of the past, I think they are actually pretty good on the precision specs. About 75uV offset, and the noise rating is only about 3 times higher than the LT1007. Those specs are more respectable. Of course I have no idea what any of this stuff means, I'm just a DIY'er Ah well.

Walter Jung's book mentions the AD517.  He says it is a laser trimmed version of the AD508 which itself is sort of a super beta 308 but with precision enhancements.  To me, it looks like AD's version of the OP07 which is a trimmed OP05 and that is how I would treat it.

The AD517/OP07 has much lower bias current than an LT1007/OP27 so it has higher voltage noise but lower current noise.  That makes it useful with higher source impedances where the LT1007/OP27 would be noisier.  The difference is roughly 30k versus 3k.

Intresting! I'll need to find a use for these 40 or so parts!

Be careful about using these operational amplifiers because unlike the 741, they have low voltage shunts across their inputs limiting their differential input voltage range.  The input source impedance can limit the differential current preventing damage.

Oh yeah, the annoying antiparelell diodes. Would using 1K resistor  (or a source with that minumum impedance) on the inputs fix that? My full design should avoid that anyways but good to be safe then sorry!

[Powermax]

Here is a picture of the almost completed circuit! It is still problematic, some reason the main pass transistor failed, not sure why, so I rebuilt the complementary darlington. I ran out of solder before I finished it, ended up desperately using disregarded blobs of solder in my cleaning steel wool and lots of flux to finish the job lol! Surprisingly that worked better than expected.

[Powermax]

I think I might go for a classic TL431 it has an acceptable temp co, can be precisely tweaked,  and has so many uses in analog circuits. The other day when looking at stuff relating to crystal set radios, I saw a "single transistor" amplifier with a very high gain using this chip. Given the price I might buy several along with some LML334's to have on hand.

[not1xor1]

If you use Google translate, read my measurements and remarke's on this Dutch website www.circuitsonline.net.

The original design CO-2016 Power Supply
https://www.circuitsonline.net/forum/view/130041/1/co+0

My modifications of the CO-2016 design
https://www.circuitsonline.net/forum/view/131554/1/co+0

Hi

I would like to simulate your PSU with LTSpice

I'm particularly interested in the preregulator
I already made a rough simulation using an LT1083 as post regulator, but
now I would like to simulate the whole circuit

can you provide a link to the most recent schematic?
thanks

[David Hess]

Walter Jung's book mentions the AD517.  He says it is a laser trimmed version of the AD508 which itself is sort of a super beta 308 but with precision enhancements.  To me, it looks like AD's version of the OP07 which is a trimmed OP05 and that is how I would treat it.

The AD517/OP07 has much lower bias current than an LT1007/OP27 so it has higher voltage noise but lower current noise.  That makes it useful with higher source impedances where the LT1007/OP27 would be noisier.  The difference is roughly 30k versus 3k.

Interesting!  I'll need to find a use for these 40 or so parts!

They would be good as part of a reference circuit.  They are not quite as fast as a 741 but certainly fast enough for a general purpose power supply if clamps are used.  The annoying part about them is that with a metal can package, they are not exactly direct substitutes for parts in DIP packages.

Be careful about using these operational amplifiers because unlike the 741, they have low voltage shunts across their inputs limiting their differential input voltage range.  The input source impedance can limit the differential current preventing damage.

Oh yeah, the annoying antiparelell diodes. Would using 1K resistor  (or a source with that minimum impedance) on the inputs fix that? My full design should avoid that anyways but good to be safe then sorry!

With the clamp circuit where the output pulls the inverting input to follow the non-inverting input, this is not a problem.  Otherwise series resistors can be used to limit the current if the existing feedback or non-inverting network have too low of an impedance.

This is more of a problem with the LT1007/OP27 because they work best with low impedance inputs which makes it difficult to limit the current.  With your AD517s, that is no problem at all.

[Powermax]

Walter Jung's book mentions the AD517.  He says it is a laser trimmed version of the AD508 which itself is sort of a super beta 308 but with precision enhancements.  To me, it looks like AD's version of the OP07 which is a trimmed OP05 and that is how I would treat it.

The AD517/OP07 has much lower bias current than an LT1007/OP27 so it has higher voltage noise but lower current noise.  That makes it useful with higher source impedances where the LT1007/OP27 would be noisier.  The difference is roughly 30k versus 3k.

Interesting!  I'll need to find a use for these 40 or so parts!

They would be good as part of a reference circuit.  They are not quite as fast as a 741 but certainly fast enough for a general purpose power supply if clamps are used.  The annoying part about them is that with a metal can package, they are not exactly direct substitutes for parts in DIP packages.

Be careful about using these operational amplifiers because unlike the 741, they have low voltage shunts across their inputs limiting their differential input voltage range.  The input source impedance can limit the differential current preventing damage.

Oh yeah, the annoying antiparelell diodes. Would using 1K resistor  (or a source with that minimum impedance) on the inputs fix that? My full design should avoid that anyways but good to be safe then sorry!

With the clamp circuit where the output pulls the inverting input to follow the non-inverting input, this is not a problem.  Otherwise series resistors can be used to limit the current if the existing feedback or non-inverting network have too low of an impedance.

This is more of a problem with the LT1007/OP27 because they work best with low impedance inputs which makes it difficult to limit the current.  With your AD517s, that is no problem at all.

Cool! I might take a look at the pinouts and see if I can substitute it. Currently I am having issues with the reference portion of my supply. I have killed a small SMD 7805 regulator (probably from accidental reverse polarity)  and substituted a LM317T into it. Not the best line regulation (I can see an LED literally changing brightness in CC mode with input voltage.(!) but it had killed a 1K pot to adjust voltage, and I am suspicious if the part is damaged or not working properly. Soldering rework on phenolic is a real PITA!!!

-----------

Also, I noticed my complementary darlington was pickup paranormal activity!!! (ohhh)!  well, acting very strange to say the least. I noticed that in emitter-follower config going into an old green LED, the LED would flicker like there was a bad connection or noise pickup even with the base shorted to ground. I scraped and scraped away at the PCB material trying to eliminate soldering gunk between the pins of the MJE3055, but it still seems intermittent at best. Any ideas?

[Kleinstein]

Those complementary darlingtons are somewhat prone to oscillation and if just at the edge, they might pick up RF noise. Just the two transistors are usually just an the edge - so minute extra inductance or capacity can make the difference. To reduce the tendency to oscillation, have a resistor at the emitter of the NPN and make sure the input impedance is not to high. So something like 1 K and 1 nF in series to ground might be a good idea, even if this slows down normal operation.

One might use a normal darlington instead of the Sziklai pair. With a slightly higher supply for the drive side there is not more drop.

[Powermax]

Those complementary darlingtons are somewhat prone to oscillation and if just at the edge, they might pick up RF noise. Just the two transistors are usually just an the edge - so minute extra inductance or capacity can make the difference. To reduce the tendency to oscillation, have a resistor at the emitter of the NPN and make sure the input impedance is not to high. So something like 1 K and 1 nF in series to ground might be a good idea, even if this slows down normal operation.

One might use a normal darlington instead of the Sziklai pair. With a slightly higher supply for the drive side there is not more drop.

I'm not convinced it's a parasitic oscillation, given the chaotic nature of it (the LED is flickering like as if it was a really crusty connection) but I don't know what it could be. The first NPN transistor should not have had anything to do with it, it's job is to turn ON the PNP, not off. I didn't add the pullup resistor to the PNP pass transistor so it's base was left floating. My guess is that something was causing small currents to enter it. Leakage from some source.

I might choose to use a darlington in the more final design, because I have 12 2N3055 transistors in the annoying but classic TO-3 package. The only problem is heatsinking. Finding cheap heatsinks large enough that can mount TO-3 is hard. CPU heatsinks are cheap and readily available. I do have 3 of these nice aluminum cast moldings which you can mount a TO-3 package to, and bolt the whole thing to a large flat surface for heat sinking, so I might use these things! I got them out of a 5V 10A linear Lambda power supply. It was a defective unit and was gutted to turn it into a 12V unregulated supply. It had 3 pass transistors in it, and a very weird looking wirewound resistor with 3 seperate 0.3 ohm elements. I didn't reverse engineer the supply but surely these were the balancing resistors for the unit.

[Powermax]

What do you guys think of the MAX5215 / MAX5217? They seem nice, not the very cheapest but seem more than good enough.

INL is Integral Nonlinearity, and DNL is Differential Nonlinearity, and the MAX5217 has a maximum of 4LSB error. Does this mean the output could be as much as 4 counts off? This would translate to (15 / (2^16)) * 4LSB = 0.915527mV maximum error in the output? If so, I think that would be acceptable, still within 4 sig figs, only 1 least significant figure off after rounding.

What's the diff between those and the MAX5216 / MAX5216 parts? Banner specs seem equivalent at first glance.


Also, if I want to make low noise supply, should I avoid trimmers? I read that pots are notorious for poor thermal coefficients and noise.

[Powermax]

Also, is it possible to order resistors such that I get an assortment of all the common values? Resistors are surprisingly expensive when you need to order 2 of those, 3 of these, 1 of that, etc...

[Powermax]

Also, as for "high speed" I have bought these PHE13009 transistors for a flyback driver, but found out they were basically unsuitable due to the difficulty of a strong gate drive and high Vce even when saturated. (something like 4V or so!) Would these be any better than the MJE2955/3055?

[ZeTeX]

Also, is it possible to order resistors such that I get an assortment of all the common values? Resistors are surprisingly expensive when you need to order 2 of those, 3 of these, 1 of that, etc...

Nobody really orders resistors the same amount they need, when you order a resistor, generally most of them are like 0.01$ per one so people just buy 25 of them (even if they need 1 for the project) and slowly they start having a collection.
what I did because of reasons is I went to taydaelectronics.com and ordered most of the 1/4W 1% resistors in 10 quantity, tayda doesn't just throw all the resistors in a bag, they separate all the resistors and put them in a small neat zip-lock bag with a sticker that says the resistance of the resistors in the bag.
like this:

so its much easier to assort them.

The resistors are OK quality, defiantly use-able, but "vishay" brand cheap resistors are better as they have thicker legs and usually more accurate then the 1% specified.
maybe if you want to get high quality resistors from known distributors but without ordering tons of values you will never use (even though they are cheap) go to tayda website, and look at all the resistors value and choose the one you think you would need in the future and just search them in digikey or something, this way you will never miss a value instead of just going to site and searching random values outwith knowing if they are E12 / E24 and so on.

Just don't get the cheap eBay kits, they are horrible and messy.

[Kleinstein]

The max5215/5217 are quite similar chips: one is 14 Bit resolution and the other one 16 Bit. Due to the similar construction the accuracy (INL relative to output range) is similar and thus the 16 Bit version provides not much extra accuracy.  I don't think the 14/16 Bit versions are binned parts, it is more like same technology parts with the 16 Bit version possibly a little newer as an upgrade option.

[David Hess]

Also, if I want to make low noise supply, should I avoid trimmers? I read that pots are notorious for poor thermal coefficients and noise.

Configure the circuit using series and parallel resistors so that the trimmer adjustment range is small.  Then the trimmer's uncertainty is reduced.

Also, as for "high speed" I have bought these PHE13009 transistors for a flyback driver, but found out they were basically unsuitable due to the difficulty of a strong gate drive and high Vce even when saturated. (something like 4V or so!) Would these be any better than the MJE2955/3055?

The PHE13009 should work fine but its high speed will make local oscillations more likely.

[Powermax]

Also, if I want to make low noise supply, should I avoid trimmers? I read that pots are notorious for poor thermal coefficients and noise.

Configure the circuit using series and parallel resistors so that the trimmer adjustment range is small.  Then the trimmer's uncertainty is reduced.

Cool, will do. To reduce noise, I should also use trimmers on the non-inverting input side, not part of the feedback, that way I can tack on a small capacitor on the output of the pot to smooth out noise (?)

Also, as for "high speed" I have bought these PHE13009 transistors for a flyback driver, but found out they were basically unsuitable due to the difficulty of a strong gate drive and high Vce even when saturated. (something like 4V or so!) Would these be any better than the MJE2955/3055?

The PHE13009 should work fine but its high speed will make local oscillations more likely.

Even in the darlington config?  I can't make a complementary darlington as it's not a PNP transistor anyways.

[David Hess]

Also, if I want to make low noise supply, should I avoid trimmers? I read that pots are notorious for poor thermal coefficients and noise.

Configure the circuit using series and parallel resistors so that the trimmer adjustment range is small.  Then the trimmer's uncertainty is reduced.

Cool, will do. To reduce noise, I should also use trimmers on the non-inverting input side, not part of the feedback, that way I can tack on a small capacitor on the output of the pot to smooth out noise (?)

It should not matter if the adjustment range is minimized.

For an ADC and DAC controlled design, it should be possible to arrange for only the reference voltages into the ADCs and DACs to be trimmed which gets the trimmer circuits out of the frequency compensation path and allows them to be filtered as much as you want.

Arrange the trimmer circuits so that if the wiper goes open, the output voltage or current change is either limited for drops to zero.

Also, as for "high speed" I have bought these PHE13009 transistors for a flyback driver, but found out they were basically unsuitable due to the difficulty of a strong gate drive and high Vce even when saturated. (something like 4V or so!) Would these be any better than the MJE2955/3055?

The PHE13009 should work fine but its high speed will make local oscillations more likely.

Even in the darlington config?  I can't make a complementary darlington as it's not a PNP transistor anyways.

Since the PHE13009 and all similar high voltage transistors that I know of are NPN, that will limit you to using it as the output transistor.  The only reason to use this type of transistor is because you have a bunch available; a new design would use something like the lower voltage D44/D45 series which are available in both types.

I would not worry so much about the output transistor configuration unless you are trying to get the last bit of performance; instead use what you have available.