JSR04 adjusted for +12 volts, LM431 = 6 V and gain of 2.
The negative side +5 volts, LM431 = 2.5 V, gain of 2
1.244 base-emitter T9 is way too much. You are not measuring between pin 6, IC7 and ground?
Max voltage base-emitter is 0.6-0.75 V
Are you getting approx 8-9 volts out? If yes, it's a sign of a dead or not working opamp.
Voltage:
Pin 7?
Between pin 2 and 3 and down to ground?
Pin 6?
Over R45 (should be 2.50 V if the LM431 is working.)?
Across R25? Should be approx. 1 volts)
Please notice also that the LM337 and LM317 don't have the same pinout so LM317 won't fit at location of IC2 or IC4. I might have forgot to tell you that.
Hi P-A,
I am not sure how much of my original e-mail response you have seen, so I will include it here:
>Re the 12v positive ½ of the JSR 04
>
>I have 1.244 volts base emitter of T9
>The voltage drop across R11 is0.35volts
>
>The LM431 voltages are 3.89 volts between R31 and the IC and 0.96volts
>
>R33 = 1k
>R39 = 1k
>R31 = 2k2
>R43 = 1k5
>R45 = 1k
>
>R43 is not used, however P3 is still in the circuit.
>
>It is worth noting that the 12v supply was working with all of the
>above resistor values before I shorted the unstabilised raw voltage
>output with the regulated side ie. Output 12 with pins 9,10 and 11.
>
>Currently I have replaced a couple of the ICs as you suggested and have
>managed to get the led to light and get 8.6 volts out, although I am
>sure that some components still need replacing!
>
>Re the 5v positive ½ of the JSR 04 modified from the – output
>
>I am only getting 1.5 volts DC output from an input of 13.5 volts DC
>unregulated
>
>I have used the LM317 with careful re-working of the PCB to copy the +
>half of the board, and wonder whether this is the cause of the very low
>output voltage, presumably I require different values for R14 and R16?
>
>Thank you in advance of your help with this.
The op-amp seems to be getting power and I am getting 8.6v output, so I will look to change the op-amp initially and see if this helps.
Have you measured the things I suggested? The opamp may not be dead.
I have already replaced the op amp and can now confirm that the problem is not with the op amp. The only difference now is a slight reduction in the output voltage at 8.1 volts.
I will now measure the areas you requested
OK..
I have now taken readings for the following
T9 output to pin 6 on the op amp voltage is 1.27v
the op amp pins have the follwing voltages
1. 4.04v
2. 4.09v
3. 3.91v
4. nc
5. 0.62v
6. 1.27v
7. 7.99v
8. 7.99v
the voltage over R45 is 0.97volts (this should be 1/2 of the target output voltage)
the voltage across R25 is 1.09volts
hope this helps
This may a symptom of too small values around LM431.
I may have missled you here because I have changed the values. See rather the newly upload schematics.
At startup and with a LM431 you must unsure that the LM431 has a _higher_ voltage than the feedback until the opamp gets active.
From readings now the inverting input has a higher voltage than the non-inverting. This will create a latchup or "lacthdown"
The easiest for you is to connect 2.2k in parallel to R31 just to check. If this was the problem you know that you have to change the ratio.
!!!!!!!!!
you are right!
I now have 20v output with a 2.3k resistor in parallel with R31
I quickly checked the voltages around the op amp and have 19 volts supply with 10+ volts output.
FYI I also tested the PS with a 47 ohm 10watt resistor and observed a drop in the output to 16.5 volts
what do I now need to do?
Brad
How much voltage do you now have on pin 3? It should be 6 volts.
pin 3 has 10v, which explains the 20 output, athough I am not sure what alternative resistor values will be needed for 12v. The value of r31 is currently 800 ohms
I have a similar "latching" problem with the 5v (from the -12 side) output, with less than 1.5 volts measured at the output. Is it worth trying a 2.3k resistor across r32 to see if this makes a difference to the output. r32 is currently 470 ohm.
If you load the 20 volts output, do you get a stable voltage? If yes, the regulator works but the reference is set wrong.
Hi P-A, when I load a 47ohm resistor across the 20v output, this causes the voltage to drop to 16v which does not fluctuate
Brad
How about the voltage across R45? Is it 2.5 volts?
Pin 2 and 3, IC7? A couple of mV across the pins?
The output, pin 6, does it change anything?
Hi P-A
Re The 12v + output section:
2.5v is drop is seen across r45
Pin 6 on ic7 measures 13.3v with no load and increases to 15.1 volts when the 47 ohm resistor is placed across the output
pins 2 and 3 have 0.5mv pd which increases to 630mv with that 47 ohm load.
The LM431 seems to work since you have 2.50 Volts between anode and ref but can you tell me which values you have around the LM431? You should have 6 volts so I'll suspect some error there in values.
Do you have 2.45-2.55 volts, probably 2.495-2.505V
I have just tried turning the wiper P3 down and have managed to reduce the output down to 13.6v which remains stable with the 47 ohm resistor on the output!
i have 470R on r47, 1k5 on r43, and 1k on r41 and r45
this 1/2 of the power supply will be used to replace a SLA battery so 13 volts should not be a problem, out of interest if I wanted to reduce the output to 12 volts which value/ resistors should I change?
RE. 5 volt output (from altered 12 neg side)
what do I need to do to get the 5v section of this PS working, I tried a 2k2 resistor across r32 and this did not change the output voltage
The gain of the LM431 should be 6/2.5 = 2.4
This means R43/R45 = 1.4 If you also use P3 and 41 (which is option) you must include them in "R45".
One way to determine that the LM431 is working properly is to measure the voltage between anode and ref, should be very near 2.5 volts.
Do you have a stable output voltage now but at a bit more than 12 volts?
Is the output voltage at pin 6 around 5-9 volts?
Can you tell me how the 5 volts side is built?
Can you tell me which voltages you have?
everything looks good on the 12v + side
I have 2.5 v across the input and reference on the LM431
I do not see a change to the output voltage with a 47 ohm resistor connected across the outputs
Pin 6 measures 6.5 volts
The output does drop from 13.6 volts to just under 12 volts when I put 22 ohms across the terminals - is this correct?
Re the 5v 1/2 of the board
The components have all been reversed with the exception of the pre regulator which is an exact mirror of the 12v positive side including LM317T pre regulator and pcb re-working.
If you load under the current limitation limit and you have a constant voltage, then you have a working regulator.
if you have 1 ohms as shunt you'll get approx. 600 mA out.
For the 5 volt section, make sure your LM431 is properly flipped and when it works you will have 2.5 volts across REF and ANODE.
Make sure all electrolitic caps are turned right.
Check also the opamp.
If you use LM317 bear in mind that LM337 isn't pin kompatible, check how the difference is.
Re The 5v section
Hi P-A,
this is getting really confusing...
i have taken a lot of time to check the pcb and components and found 1 error with the designations on the pcb screen print. R44 and R46 are transposed which meant that the ref out from the LM431 was being taken to ground via the 470 ohm resistor. I have now corrected for this but have not observed any changes to the output voltage. The voltages measured on the LM431 are 1.37v on both K and ref.
Would the regulator have been damaged by taking the ref output to ground via the 470 ohm resistor?
What do I need to check now?
I have also just noticed that R12 gets hot very quickly - definately too hot to touch and that is without a load! R12 drops 2.2 volts - does this help diagnose the problem?
Have you GND on pin 7 and minus something on pin 4?
Changed all transistors?
LM337 patched due to different pinning?
Hi P-A
The op amp has been rewired so that pin 7 is + supply, directly from R20 and pin 4 is gnd. I have checked both of these and they are OK.
I have used an LM317T as the preregulator and have carefully reworked the traces so that I have an exact replica of the 12v positive 1/2 of the board. I am getting a good 9-10v before the pre-regulator.
I have reversed all of the elec capacitors and the transistors and ICs except the LM431 which required some additional work to get the connections as per your sugestions. The LM431 has the centre pin to ground and the reference output linked back to the Cathode via R44 @ 470 ohms.
HELP!
9 V in is too little if you have a preregulator. 10 V or more is better.
I'm afraid I have done the sketch a bit wrong. It may work with R20 used but it will work better with R22. Exclude C26 (or have it), put a wire in R18 and D10.
How much voltage do you have out?
hi P-A
I have altered the supply for the op-amp which is now taken from the post pre regulator output via r22 @ 47 ohms. the op amp is getting 1.9v on pin 7 now.
The dc output is now 1.07 volts!!!
I am measuring 7 volts before R12, which drops 2.4 volts across R12! - R11 on the 12 volt 1/2 of the board is getting 26 volts and only drops 0.4v - R12 gets very hot very quickly - could this help diagnose the problem, surely R12 should not do this when there is no loading on the power supply.
I have again double checked all of the components on the pcb. IC2 is a re wired LM317T with R14 and R16 values of 1k0. the following parts have simply been turned around on the pcb to work with the + supply T2,T8,T10, the LM431/ IC10 has been reworked with the centre pin to ground and the reference output tied back to the Cathode via a 470 ohn resistor. I have used a BD139 for T4 as the pining is identical to the + half of the supply and the power supply for the op-amp has been reversed.
The led was illuminated but this has now stopped working as well.
do you have any more ideas, I keep checking the pcb, looking for any mistakes ect, but have just come to a complete standstill.
I do wonder about the minimum voltage for the pre regulator, but believe that the 0-9-18 transformer used should be giving at least 10 volts on the 1st winding as the 2 connected in series are producing 26v.
You might exclude or reduce R12 due to low raw voltage.
In order to get on track:
Use R20, short R18, short D10. Omit R22
Remove DZ1 and solder in a PNP like T10. Connect a pot to the base in series with 1 k (protection) so you can get a variable voltage. You can use the raw voltage to drive the pot.
Adjust the base voltage between 0-5 volts. Do you get 0-5 V out? If you do get a variable voltage, this section is working. If the opamp is still consuming more current than expected, remove T10. Better now?
If the power section is working, how much voltage do you have at the opamp inputs? Around 2.5 volts? 0.5 times the output at pin 2 (feedback) and exactly 2.5 volts at pin 3 (reference voltage).
H2 must be lit when the output section is working.
Hi P-A,
thankyou,
If you remember I have fitted op-amp ic connectors, so it is easy for me to swap or remove the op-amps. When I remove the op-amp on the 5v section I get 8.6 volts out and the input voltage increases to 12v. with 0.12v drop across R12. I have also tried to power the 5v op amp with the supply from the 12v side which is over 13v and only observed a 0.4 volt increase to the out put and one single flash from the led.
Before I do as you sugest is there anything else worth trying, I think that the problem may not be with the op amps power consumption because there was no improvement when using the 12v op amp supply.
Is it worth making an exact copy of the 12v working side ie. resistor values ect. and get that working first, and then make the sdjustments to get 5cv dc out?
Of cource you can make a 12 volt section but since you have trouble it's important to rule out the different sections. When you are troubleshooting you must have a strategy.
Hi P-A
Finally got to around to having a closer look at this project again......
The faulty component was the T4 transistor and I now have 4.13 volts regulated output which drops to 2.7 volts when I connect a 10 watt 47 ohm load resistor. The H2 LED is not illuminated and only has .3 volts across its terminals. R32 is supplying 2.61 volts to the LM431 regulator.
I just need that final push to get this PS up and running.
Cheers
Brad
I'll get back to you in two weeks. I'm on vacation.
Hi P-A,
I hope you had a relaxed and enjoyable break!
any ideas regarding this PS project?
Brad
Quote from: builder bradHi P-A
Finally got to around to having a closer look at this project again......
The faulty component was the T4 transistor and I now have 4.13 volts regulated output which drops to 2.7 volts when I connect a 10 watt 47 ohm load resistor. The H2 LED is not illuminated and only has .3 volts across its terminals. R32 is supplying 2.61 volts to the LM431 regulator.
Can you measure the voltages around the AD825? The LM431 should have 2.5 volts and 2.61 is a tiny bit too much. Have you paid attention to the polarity of the LM431? Anode and cathode must be switched and ref must be tied to cathode.
Which transistor types do you have right now?
Could you possibly take a couple of closeup photos? (not more than 2 MB please)
Hi P-A
Thank you!
when I chacked the Op amp voltages I immediately noticed that it was not getting enough voltage, then I remembered that I had cut its supply during some of the previous tests and had re-routed a supply from the +12v op amp side.
As soon as I corrected for this i got exactly 5.00 volts!!!!!!
quick test show a drop in output to 3.66 volts when a 12 ohm resistor is connected across the output, is this ok?
Brad
Good that you finally manage to get 5 volts out of the regulator :D
The voltage should be constant within a couple of mV's when it regulates properly.
When you increase the load and get a voltage drop you can have this:
Not enough input voltage and this means including the voltage ripple.
Not enough headroom for the opamp output due to the DC shifter (the LED or zener). I'll guess you feed the opamp with more than 5 volts so this should be a problem.
Not enough base current for the output transistor
Thank you,
The voltage drop is still a problem and when the Power supply is connected to the squeezebox the voltage also fluctuates.
The AC supply is 10v which produces 9v unregulated. I am still concerned about the voltage drop across R12 which is 1.48v and the amount of heat that is generated by R12 - R11 on the 12v+ side only drops .3v and is cool to touch.
The Opamp used is an NE5534 which is powered by 5.7 and this drops to 4.8v when the load is connected.
The LED is still not illuminated - I am getting .32v across the LED terminals.
I know that I am almost there now, just need to sort this final thing
5,7 volts for NE5534 is a bit low accordning to datasheet which says 6 V but ought to work. Remember though that a NE5534 isn't verified by me. AD825 works.
You must also unsure that the incoming voltage is 8 V (can be measured by an oscillscope) at least as a very minimum and if you don't use the preregulator if if you do it's 11 V.
Hi P-A,
I am using a 9-0-9 transformer with the PS, configured to provide a nominal +9 and +18v AC suppply for the +5 and +12v regulators. Is it possible to power the 5v PS from the +18 turn of the transformer, this would certainly deal with the low voltage preoblems!
9 VAC should give you 11-13 V I should guess. One way to find out if 9 VAC is to little for you is to test the 5 V regulator with 18 VAC in.
The value of R10, R12 is dependent of how much current your load take. If you can't "afford" much there, just short them.
I tested with the 18v AC supply and saw quite a large improvement. The 5v output only dropped by about .2v with the 12ohm load, so I have now removed/shorted the R12 resistor and now see a similar voltage drop with that 12 ohm load.
Just trying the 12 ohm load on the 12v side also causes a large voltage drop down to 8v. i have shorted the 12v side equivalent resistors, but do not see an improvement.
I think I may have the answer, but just want to check if I am on the right track.
On the original schematics you indicated the required parts for this project and included one load resistor and diode for each half of the power supply ie. R8 and D8, which only utilises one half of the AC cycle. Surely I need a full bridge rectifier here for each half of the PS?
I could easily modify the board to provide full wave rectification - would this help with the voltage drop problem?
You can use halfwave rectification. The only thing to think of is maybe more smoothing capacitance since you have only one voltage pulse during a mains cycle.
Your AC source, is it weak? How many VA is the transformer rated?
The transformer is rated at 50VA/2.78 amps. our mains supply is nornally pretty good here in terms of voltage, always around the 230v mark. I do not have access to a scope so there ius no way of really knowing if there are any other problems with the mains.
I do want to get this perfect as I am planning on powering the JSR06 with balanced AC power at a slightly lower mains voltage - around 225volts
The disadvantage of halfwave rectification is:
More (double) smoothing capacitance
More harmonics going out to the mains
More losses in the transformer ... but this is more present if the load is heavy in relation to the size of the transformer.
In your case you have 50 VA but how heavy is your load really?
Well......it would be very easy to add an extra 2 diodes and resistors for full wave rectification, so I guess i will do that anyway, your PCB is v.flexible in that area. I will just change the pcb tracks to suit, is it absolutely neccesary to include the capacitor across the resistor and diode in the rectifier 1/2 that I am going to add?
I originally wanted to build a PS that could supply battery-like currents, if demanded, to cope with transients ect. I guess you are right about the "actual" power requirements, although the original voltage drop I was seeing would not provide enough power in any situation.
If the transformer has two separate secondary windings it's possible to fullwave rectify, otherwise not. Winding with center tap will not do.
The Transformer used has 2 x 9v windings that are separate, although thay are joined at the centre tap for the 9v supply, with the second winding connected in series to give 18v. The start of the first winding is 0v and it would be this point, or somewhere on the ground plane that I would connect to a 4watt 1 ohm resistor and diode for the 2 x additional sides of the bridge rectifier.
oh s***t
I have another problem with the -5 volt section. R8 has always run very hot, certainly too hot to touch, and it was dropping 1.4 AC across this 1 ohm resistor. I tried to connect the ps up today and was suddenly measuring almost 12volts out of the 5 volt side, the odd thing here is that R8 is now not getting hot.
any ideas here?
This is getting really silly now. I have built loads of diy project, withou any problems - I for example the 2 x jsr06 power supplies that I built earlier this year were completed in 2 days and worked 1st time around.
I am at the point where I think I may just build 2 x linear PS with basic regulators and smoothing caps. This is really frustrating as I know how good your designs are I just want to get this working.
ok
I have now taken some more measurements of the 5v section
regulated output 10.6v (was 5v dead, I have got not idea what has gone wrong except that R8 is no longer heating up)
un regulated 13.1v
AC in 10.1v
op amp pins
1 7.1v
2 4.1v
3 3.4v
4 gnd 0v
5 .6v
6 1.2v
7 11.2v
8 11.2v
the LM431 has 2.5v on both its Anode and reference
HELP!
When you had it working, what exactly did you do in order to break the regulator?
R8 and the other series resistors must be tuned for the load and the unregulated voltage.
Can you check the voltages around the transistors. Only 1.2 volts out from the opamp and still 10 volts out indicates that T10 might not be working.
Thank you,
I really appreciate your patience with this.
I tested an additional IN5407 diode connected in series with a 1 ohm resistor from ground to the 5v supply, effectively using R7 and D7, to create what I thought would be the other 1/2 of the rectifier circuit.
This involved a little reworking of the board, but I was confident that there this was done correctly.
It certainly does seem that this has caused the failure of one half of the PS, its just strange as I also did the same thing on the +12v section and this is still working!
Is the PS working properly now?
Hi P-A
no the 5 volt section is still not working. The problem is the overvoltage output which seems to have been caused by my attempt to create full wave rectification by adding an extra diode and resistor as described in my last post.
I have a number of spare transistors and regulators, so its no problem to test by simply swaping out any suspect components. You mentioned that IC10 may be faulty - are there any other parts that I should check if replacing IC10 does not fix the problem.
thank you
Brad, I recommed you to make the rectification according to my directions. You can't make a fullwave rectification with a center tapped transformer and dual voltages out.
Did the 5 volts work? What did you do when it stopped working?
If the opamp is in a socket pull it out and take a resistor (1-10 k) from the base of T10 and short to ground. If the transistors are working the output voltage should go from "high" to almost zero (1-2 volts max). When the voltage is high you should also get 2.5 volts from your LM431.
Hi P-A
congratulations on the new forum - looks good!
I removed the op amp and connected a 5k resistor between the base of t10 and gnd, as sugested, and did not see a change to the output voltage.
I am running the rectification exectly as you sugested, it was when I tried to add the extra diode and resistor that I developed the high voltage fault on the 5v section.
Now when the opamp is removed you can easily check weather the transistors are alive or dead. If T10, base is grounded you must have 0.7 volts across base-emitter, if not dead. Check also the other transistors for these 0.7 volts. Does the LED's shine? You should disconnect the preregulator also becasue it won't work without the opamp.
I traced the fault to T10 and I now have 5v output - but it keeps jumping up to 11v and then after a few seconds it goes back to 5v
I am concerned about the high temperature of R8 - this really looks like something is drawing a current somewhere. T10 is also getting very hot and I wonder if this shuts down because of the temperature, causing the voltage change from 5v to 11v.
The op amp gets slightly warm, but no other components seem to be affected.
R8 should not get particular hot without a load.
The thing that the output is 11 volts for a while may have to do with the opamp. Did you have this problem before?
The current consumption with no load should be 30-50 mA, not enough to make R8 hot.
wow, that was a quick reply.
I am not sure if I had the voltage changing problem before as I did not really get round to testing the PS before it stopped working.
The hot resistor problem has occured from day 1
I have plenty of components now, so I am happy to really push this PS to get it working perfectly. I have just placed an extra 1 ohm resistor across R8 to see what changes that made and within a few seconds T10 destroyed itself
The op amp is the same as on the 12v side and I have not observed any voltage fluctuation
If you have the opamp in a socket, remove it for a while and test the transistors only.
First not part should be warm or hot with thwe base of T10 grounded via a couple of kohms.
Active transistors should have 0.7 volts across base-emitter.
If you connect a pot as a voltage divider to T10 (variable voltage) you should also get a rather stable output voltage even with a moderate load. Both LED's should shine.
How much AC voltage (ripple) do you have at the raw DC voltage? Should be rather little.
Have you disconnectred the LM317 (if you use it)? Will only work IF you have a workong feedback via the oapmp.
I haven't tested that NE5534 works proberly at 11 volts as supply voltage and only 5 volts out so I can't garantee that.
I have just tested the transistors with T10 transistors base connected to ground with a 2.2k resistor and measured .69v on all transistors between base and ground, so they all appear to be working.
I have also taken the pre regulator out of the circuit, just to be sure.
I am still having heat issues with R8, I do wonder if this is the op amp?
here is a link to a local supplier and their web page for op amps, if you sugest an alternative from this list I will visit their local shop and buy one tommorow to try and see if that solves the problem:
http://www.maplin.co.uk/search.aspx?MenuNo=464&MenuName=OP%20Amps&FromMenu=y&criteria=OP%20Amps&doy=13m9&worldid=3
I'm not sure a CA3140 will work but you can try.
About the R8, value?, how many volts across it, both AC and DC voltage?
I measured 1.4v Ac across R8 previously, I am unable to do so again as T10 has just blown again, and I am not sure about the DC reading.
when I put T10 to ground via that 2.2 ohm resistor I measured 0.7 volts across all ot the bc337 and bc327 transistors except the bd140 (T4) transistor which measured 1.6v - is this correct?
Have you really checked the transistor types?
NPN for the current limting and series transistor and _PNP_ for the drivers. The same kind of types as for the +12 V section.
as far as I can see all the transistors are correct.
Originally in order to change the negative section over to positive you sugested that I reverse all of the transistors in your updated schematic.
recently I replaced all of the transistors in order to try to fix this problem and then changed all of the transistors to the same type as the + section, obviously being mindfull of their orientation.
... but you mention BD140? I'll hope you are using BD139 for a positive regulator.
BC327 = PNP should be used for the drivers (two of them)
BC337 = NPN should be used as current limiting transistor
BD139 = NPN should be used as series transistor
the section is now working - I had previously swapped the bd139 for a bd140 (reversed) as I misunderstood your instructions to "reverse" this component in the schematic.
I now have +5.01 volts out which does not drop, even with a 12 ohm load connected
BUT the 12v section is still buggy, I am seeing a 4volt drop with the 12 ohm load connected to the 12v outputs. I have almost 27 volts unregulated, so there is plenty of headroom. I have tested all of the transistors for the 0.7v difference and they all seem to be working.
I'm glad you finally got it working. You can experience weird phenomia when you swap npn-pnp as you may have noticed.
Good work!
For the 12 volt, when the voltage starts to drop, measure the voltage across T3/T5. When it is starting to change you have reached the limit. One way to increase the "headroom" is to decrease the series resistors at the rectifying diodes. Test with the load you plan to use and some more, but not _much_ more.
I have measured the 12v section with various loads and have observed the following
unloaded regulated output 13.27 v
12 ohm load causes 4 v drop
15.5 ohm load causes 2 v drop
23.5 ohm load does not make a difference to the output
so, from the readings I can see that I am ok up to 560ma, maybe a little more, but certainly not 700ma.
the unregulated supply voltage dropped from 27v to 22v when I added the 15.5 ohm load, so it apears that the regulator is strugling to supply the current and not the transformer.
what can i do to get closer to 1000ma, or more?
would larger capacitors help in this case?
even under load there is no temperature increase
It seems that the section before the regulator not is what you ought to have.
Since you have halfwave recification you must have twice the amount of smoothing caps but first, how must does your AC voltage drop when you load?
You must tune three parts:
1 AC voltage in
2 The resisitance of the series resistors
3 Smoothing capacitance
Those three parameters determines the lowest voltage into the LM317 including ripple, don't forget that.
I measured 0.6v drop in the AC supply voltage with that 12 ohm load connected, so I guess that I need to look at the caps.
I have just replaced the 4700uf x 2 main caps with 2 x 22000uf and tried the 12 ohm load. Unfortunately I am still seeing exactly the same voltage drop with that 12 ohm load. I have .5 ohms in series at the moment - could this be lowered any further?
Brad
Where do you have the voltage drop? Have you adjusted the series resistors at the diodes? The original values were 2.2 ohms and 10 ohms and as you can see you must how lower values if you want to take out a larger current. See also post 69.
ok!
I was originally using a 1 ohm 4watt resistor at R5 which has now been reduced to 0.5 ohms by placing another 1 ohm resistor in series - this has not made any difference to the output under load.
I see 19 volts ac input which does not drop when I load up the output with a 12 ohm resistor. I am getting 27 volts dc at the + side of diode D5 which does drop to 23 volts with the 12 ohm load.
PS. The power supply looks great I have 30mm heatsinks on the regulator and the transistor with 4 x 30mm diameter x 30mm high 22000uf supply capacitors - it really looks the part, if only I could get higher current output!
Which value does R27/R29 have?
Current limitation at 0.7/R27 => 1 ohms => 700 mA
1 A = 0.68 ohms
R29 is currently 1 ohm
Ok, then. You will get 650-700 mA as max current.