Hello.
I'm having trouble with this datasheet PSU.
The original schematic is from the LH0044 datasheet, for a
"Precision Dual Tracking Regulator", but I'm using (2) OPA27's instead.
Here is the LH0044 datasheet (schem, pg. 6)
http://www.techno-star.biz/transistors/LH0044CH.pdf
Here is what I built....the upper opamp gives me a nice +15v....but the lower opamp only gives me the values shown in red.
The green-blue are the transistors I'm using.
The +17. -17, 0v input is from my bench psu (@ 400mA).
All pins check out OK.
Is the lower opamp's pins reversed ?? ....that's all I can think of.
(I've swapped opamps, and transistors, no change)
???
I'm having trouble with this datasheet PSU.
The original schematic is from the LH0044 datasheet, for a
"Precision Dual Tracking Regulator", but I'm using (2) OPA27's instead.
Here is the LH0044 datasheet (schem, pg. 6)
http://www.techno-star.biz/transistors/LH0044CH.pdf
Here is what I built....the upper opamp gives me a nice +15v....but the lower opamp only gives me the values shown in red.
The green-blue are the transistors I'm using.
The +17. -17, 0v input is from my bench psu (@ 400mA).
All pins check out OK.
Is the lower opamp's pins reversed ?? ....that's all I can think of.
(I've swapped opamps, and transistors, no change)
???
Hmmmm,...
I see this is a typical IC opamp regulator, and is real close to the one shown in Walt Jung's article,
http://waltjung.org/PDFs/IC_Regulated_Power.pdf
.....except that the way the transistor is connected on the negative side of the supply (fig. 5 from Walt's article) He shows an NPN , not a PNP as in my schematic.
Im still looking for an instance of a schematic where a PNP is used on the neg. side, to figure this out.
=RR=
I see this is a typical IC opamp regulator, and is real close to the one shown in Walt Jung's article,
http://waltjung.org/PDFs/IC_Regulated_Power.pdf
.....except that the way the transistor is connected on the negative side of the supply (fig. 5 from Walt's article) He shows an NPN , not a PNP as in my schematic.
Im still looking for an instance of a schematic where a PNP is used on the neg. side, to figure this out.
=RR=
The lower opamp cannot have its +IN tied to its positive supply pin, this is outside the input common mode range. This supply pin must be at least 4V higher than the inputs. Run the lower amp's pos supply from a higher voltage than GND, you could either use the +17V unregulated or the +15V regulated. The amp will survive up to 44V total supply voltage (if it's a Burr-Brown OPA27), so this no problem.
There is no short circuit protection / current limiting, you will fry the transistors when an output is shorted.
BTW, do you need the pos to neg tracking feature for a specific reason?
- Klaus
There is no short circuit protection / current limiting, you will fry the transistors when an output is shorted.
BTW, do you need the pos to neg tracking feature for a specific reason?
- Klaus
The 10k resistors are well matched, I checked before and after being soldered.
Klaus, Yes. That helped.
Actually, I put a 5k resistor between the +IN pin and ground.
Now I'll check the amperage on the outputs, see if they're equal.
I may still have to connect the +V pin to somewhere else (??)
But I wonder why the datasheet schematic would be shown as not working....??....either it is wrong, or there is something different/special in the original LH0044 part ?
What protection would you recommend ?
=RR=
Klaus, Yes. That helped.
Actually, I put a 5k resistor between the +IN pin and ground.
Now I'll check the amperage on the outputs, see if they're equal.
I may still have to connect the +V pin to somewhere else (??)
But I wonder why the datasheet schematic would be shown as not working....??....either it is wrong, or there is something different/special in the original LH0044 part ?
Just to try something new......
What protection would you recommend ?
=RR=
Hell, that original schematic in the LH0044 spec sheet is wrong indeed. So much for datasheet circuits 
Those are always to be taken with caution since those are usually simplified to the bare bone, just showing the essentials.
There are opamps that allow the inputs to be at or even slightly beyond the supplies, the LM324 is a typical old-school example, albeit only for the negative rail. But neither that LH0044 nor the OPA27 are of this type. So, just tie the +-supplies to the +-power input and it should work.
The reason why Walt Jung uses a NPN also for the neg supply is that the LM395K is not a simply transistor, it's a more complex circuit in disguise, featuring current limiting etc, but there is no PNP version of it. This one is hard to kill, compared to a normal transistor. Note he also shows the neg regulator opamp (LM301) with its +IN tied to the +supply which in this case works, the LM301 can handle that condition.
Current limiting, there are many options. Simple one: series resistors on the circuit input, lower input capacitors (less than the outputs caps which could be increased -- and stay away from LowESR types) and more rugged transistors like BD139/140, on a heatsink. Or some active scheme around the transistors, sensing the current with a shunt resistor in the emitters and using that with another transistor to steal base drive in case of overload (this would be similar to the scheme often seen with power amplifiers).
- Klaus
Those are always to be taken with caution since those are usually simplified to the bare bone, just showing the essentials.There are opamps that allow the inputs to be at or even slightly beyond the supplies, the LM324 is a typical old-school example, albeit only for the negative rail. But neither that LH0044 nor the OPA27 are of this type. So, just tie the +-supplies to the +-power input and it should work.
The reason why Walt Jung uses a NPN also for the neg supply is that the LM395K is not a simply transistor, it's a more complex circuit in disguise, featuring current limiting etc, but there is no PNP version of it. This one is hard to kill, compared to a normal transistor. Note he also shows the neg regulator opamp (LM301) with its +IN tied to the +supply which in this case works, the LM301 can handle that condition.
Current limiting, there are many options. Simple one: series resistors on the circuit input, lower input capacitors (less than the outputs caps which could be increased -- and stay away from LowESR types) and more rugged transistors like BD139/140, on a heatsink. Or some active scheme around the transistors, sensing the current with a shunt resistor in the emitters and using that with another transistor to steal base drive in case of overload (this would be similar to the scheme often seen with power amplifiers).
- Klaus
KSTR said:Hell, that original schematic in the LH0044 spec sheet is wrong indeed. So much for datasheet circuits
- Klaus
I must have "faulty datasheet" radar......in THIS thread earlier this week, I found two more. (starting at the beginning, and then again, at post #19)
I'll try connecting the +V of the negative supply opamp, to the +power input.
But I'm curious, is that better than the method I used to get the circuit working (the 5k resistor, described 2 posts above) ?
With the 5k, the outputs do give me 100mA per side, with a 150 ohm load per side, with the +-15v output staying stable.
You've been much help, btw.
=RR=
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