hyland psu questions

[p.larner]

on the schematic,it looks like u3+u2 have a negative feed on pin4 and the +ve supply on pins7,how do i measure the negative supply to them?,also can i feed the+ve opamp rails from say an 7812 reg,or wll that screw up the operation of the psu?,it seems the max voltage on the opamps is on the edge of what a tl081 can take.

[Jwillis]

You measure the op amp power rails relative to the common ground.
If you pre-regulate the positive supply rail to the op amps to 12V then the maximum output voltage will be aproximately12V.

[p.larner]

so where are the common grounds?,on u3 do i measure between pins 4 and 7,i am trying to work out how too see if the -ve rail is working,but not sure what points to probe.

[p.larner]

can 741 opamps be used ok in this?.

[p.larner]

anyone.

[Jwillis]

Connect your negative probe to the common ground that I labelled  on the schematic. Probing the pin 7 on U1, U2 or U3 with the positive probe  will read a positive voltage. Probing pin 4 on U1, U2 or U3 with the positive probe will give you a negative reading. Because the positive rail and negative rail voltage are relative to the common ground. The Common Ground is the 0V potential of both the positive rail and the negative rail.
If you measure between  pin 7 and pin 4 you get the added voltage of both the positive rail  and negative rail.


A 741 op amp would work. I've also dropped in a LT1637 which is just as slow as the 741 and it works fine without further modification. Using any op amp with ±22V supply works way better than the TL081CP suggested for the design. 
Since your dealing with DC (0Hz), then op amp parameters such as Slew Rate, Unity-Gain Bandwidth and Phase Margin become unimportant. A slow op amp will work just as well as a fast op amp at DC or (0Hz)

Are you building the kit or just using the circuit diagram for your own scratch build? What is the VA and Secondary Voltage of your transformer? How many Amps do you require? How much ripple voltage is exceptable? Some changes to the input filter circuit may needed depending on requirements. 

[p.larner]

let me explaine,a couple of years ago i brought the remains of a farnell psu,it had the main transfo removed,the control board i removed but kept the filter cap (22000uf) and the 6 2n3055 pasas transistors on there heatsinks,the transfo i have fitted is from a ham psu like in the pic,i want to use the hyland kit to drive/control the pass transistors already fitted to the farnell remains,i have done away with the rectifier diodes on the hyland board and am using a 30amp off board bridge rectifier.

[kevin.gibbs]

It is better to see which op-amps are in the original circuit and then choose a replacement. If you do not have data about resistors, Zener diodes, and capacitors, repeating the circuit may become a problem.

[p.larner]

its a cheapo aliexpress kit i am using with the tl081 opamps. but i have a selection of opamps i can use.

[CaptDon]

Why no spaces after the commas in your sentences? Are you a non-native typer of english?

[Kleinstein]

can 741 opamps be used ok in this?.

AFAIK the plan is based on an old circuit from a electronis magazine and originally was using 741. So the 741 would be fine.
The TL081 is only OK for a lower voltage (e.g. < 20 V transformer).

The PCB of the kit has a slight problem with the ground layout. The ripple from the filter cap couples to the current control loop. This can be fixed with a few badges if needed.

[p.larner]

my transformer outputs about 19v unloaded, reads 40.7v on the filter cap after the bridge rectifier unloaded,is that ok for a 741 not taking into account the minus rail of 5v?.

[Gyro]

No. Read the datasheet.

[p.larner]

Hi chris,i found some MC34071AP ic's, would they be ok?.

[Jwillis]

let me explaine,a couple of years ago i brought the remains of a farnell psu,it had the main transfo removed,the control board i removed but kept the filter cap (22000uf) and the 6 2n3055 pasas transistors on there heatsinks,the transfo i have fitted is from a ham psu like in the pic,i want to use the hyland kit to drive/control the pass transistors already fitted to the farnell remains,i have done away with the rectifier diodes on the hyland board and am using a 30amp off board bridge rectifier.

 


Your PALSTAR PS-30M power supply is/was  0-15V 30A Max design. The transformer has 2 secondaries. One for high current to the power transistors and one for control circuit, which will likely be low current. Both secondaries  may not have the same current rating.
Can you post a picture of just the transformer secondary wires.
Voltage measurements need to be taken of each secondary separately to identify the transformer properties and limitations. From looks of the picture below, there appears to be a high current secondary and a low current secondary. The transformer looks to be around 400VA to 500VA. That would put the high current secondary at around 15V to 19V at best.
If the 2 secondary windings have vastly different current ratings you cannot connect them in series and expect to get 30A without burning out the low current secondary.
You may not be able to get full advantage  of the hyland board because of the transformers limitations.

I added a circuit diagram of the original PALSTAR PS-30M.

[p.larner]

Its the high current secondarys i am using,the raw ac unloaded is 19v, For some reason i get 40.5v when i connect the filtercap to the bridge rectifier output!, It seems too high to me?.

[Jwillis]

Its the high current secondarys i am using,the raw ac unloaded is 19v, For some reason i get 40.5v when i connect the filtercap to the bridge rectifier output!, It seems too high to me?.

Ok.
The unloaded 40V is probably the low current secondary. That would work out to be around 25V to 28V from that secondary. The current  would probably be rated for around 1A.
The High current secondary is probably around 19V at 30A.
So using with the hyland you can expect theoretically around 0v to 15V at 30A using the high current secondary. For that amperage some modifications would be needed to the hyland since the current limit is set for around only 3A. If you only want 3A then a direct drop in would work.
If you modified the hyland board to run on the low current and passed the high current separate then you can achieve better stability and a cleaner output. Pretty easy to do. I think I have a modified circuit diagram of the hyland already drawn that does just that if your interested.     

[p.larner]

the widings i am using are the thick heavy secondarys,the aux secondarys are unconnected,my plan is to use a low value 100w current sense resistor,i have also found some mc34071p opamps to try in this in place of the tl081 parts,with 40v on the filtercap and the -5v, its still 1v over the opamps 44v rating,should i use say a 4v zenner n the - rail charge pump?.

[Jwillis]

Something is not right if your getting 40V after the rectifier and filter capacitors supplied by the 19VAC secondary. With a 19VAC secondary you should be getting only about 27VDC after the filter capacitors.

[xavier60]

Not certain if this applies here. A capacitive load on one of the secondary ends can cause a voltage boost.

[Jwillis]

Not certain if this applies here. A capacitive load on one of the secondary ends can cause a voltage boost.

The bridge rectifier for the high current secondary has parallel caps with the diodes. Would it be plausible that a diode is open and one of the caps is causing the rectifier to act as a doubler? I've not worked with that type of rectifier or what voltage would be expected.
 

[coromonadalix]

the palstar psu does not have a good current sensing for the current limiter 

it sniff out a portion of the current shared by tr3  ...  not god to me,   i never saw that ...


filtered dc passed thru an full bridge rectifier calculation is :   Ac  x 1.414 = xxx

[Jwillis]

the palstar psu does not have a good current sensing for the current limiter 

it sniff out a portion of the current shared by tr3  ...  not god to me,   i never saw that ...


filtered dc passed thru an full bridge rectifier calculation is :   Ac  x 1.414 = xxx

From what I understand, He's using the remains of the original PS-30M without the control circuit. Just the transformer rectifier and filter caps. But your right about VAC x 1.414 = Peak DC voltage after rectification and filter caps. This is why the measured 40VDC doesn't make sense.

[floobydust]

A relative of treez? The troll voltage seems too high.
The Palstar filter cap rated 35V, hopefully it does not go bang, probably a good idea to keep one's face away from it- if the voltage measurements are real.

edit: high quality CapXon parts - DUCK

[IanB]

Your PALSTAR PS-30M power supply is/was  0-15V 30A Max design. The transformer has 2 secondaries. One for high current to the power transistors and one for control circuit, which will likely be low current. Both secondaries  may not have the same current rating.
Can you post a picture of just the transformer secondary wires.
Voltage measurements need to be taken of each secondary separately to identify the transformer properties and limitations. From looks of the picture below, there appears to be a high current secondary and a low current secondary. The transformer looks to be around 400VA to 500VA. That would put the high current secondary at around 15V to 19V at best.
If the 2 secondary windings have vastly different current ratings you cannot connect them in series and expect to get 30A without burning out the low current secondary.
You may not be able to get full advantage  of the hyland board because of the transformers limitations.

I added a circuit diagram of the original PALSTAR PS-30M.

Remember the OP does not have the original transformer. In fact the only thing that remains of the original power supply is apparently the box, some pass transistors and filter caps. Everything else is missing or removed. So any reference to the original schematic is void.

We do not know the details of the replacement transformer, what windings it has, or what size it is. There is no picture of it and no specifications given.