shitty chinese psu kit

[magic]

I suppose it could work as D6, that diode is just sitting there under reverse bias.
The PSU would even work without it, but it protects it from externally applied negative voltage which could damage things.

Beware that schottkys leak more than silicon diodes, check the datasheet "reverse characteristic". Leakage may even be a few mA for some large diodes close to their peak reverse rating.

[m3vuv]

I have 5 of these,would 5 of then be ok for 20a at say 5v?,or do i keep the 2s1047 trannys fitted at the moment( originals were tip 3055 types.

[m3vuv]

LINK DIDNT WORK,heres the data sheet,am i correct in thinking they are no good in non switching applications?

[magic]

ISC / InChange Semiconductor and SavantIC transistors are made of 100% pure Chinesium semiconductor material.
Rumor has it that even their replacements of "linear" transistors have SOA inferior to the originals (and SOA is rarely specified in their datasheets even if it should).

It's probably crap. It may work with low input-output differential.

[xavier60]

The TIP35C BJTs I used in my bench PSU came from this Aliexpress seller, https://www.aliexpress.com/item/32539913063.html?spm=a2g0o.order_list.0.0.21ef18022M3Ta4

[m3vuv]

Morning all,i have just got this working,with one issue,it puts out 6a max,i assume thats down to the current sense resistor value,would that be R19? TIA.

[xavier60]

Morning all,i have just got this working,with one issue,it puts out 6a max,i assume thats down to the current sense resistor value,would that be R19? TIA.

The Emitter resistors summed together are used foe current sense.
It it's going into CC mode, the LED should light up.

[m3vuv]

So should i double r15+r 16 then for double the output?

[xavier60]

So should i double r15+r 16 then for double the output?

Altering R15 and R16 wont help. Is it going into CC mode? Or is it a drive problem?

[m3vuv]

seems a drive issue as the cc led doesent illuminate.

[xavier60]

seems a drive issue as the cc led doesent illuminate.

With it still loaded to 6A, confirm that the  opamp outputs are both close to 12v.
Starting at the anode of D5, measure the voltages at every point along the drive path.

[xavier60]

If the voltage measurements dont show any obvious fault, try reducing R4 by about half.
Q1's current gain might be too low.

[m3vuv]

Well at the moment,it has 4x buw49 pass transistors ,the 2sd1047 trannys(aliexpress junk!) went sc at 21v 5a output,at the moment it will output 36v max at 3a,i havent reduced r4 yet for more drive,i notice the 7812 must be about 80 deg c,it gets to hot to hold your finger on!,i guess if i reduce r4 that will put it under more load and kill it?.

[xavier60]

Well at the moment,it has 4x buw49 pass transistors ,the 2sd1047 trannys(aliexpress junk!) went sc at 21v 5a output,at the moment it will output 36v max at 3a,i havent reduced r4 yet for more drive,i notice the 7812 must be about 80 deg c,it gets to hot to hold your finger on!,i guess if i reduce r4 that will put it under more load and kill it?.

The few milliamps through R4 isn't a great load for the 7812. What is the input voltage and is it powering anything other than shown in the schematic?

[m3vuv]

The input to the 7812 is 22v output is 12.1v,there is nothing connected on it apart from whats on the schematic.

[xavier60]

There should be about 10mA load, very little. Is the opamp getting hot?

[m3vuv]

No both opamps are cool and seem to be working ok,everything seems fine apart from the lack of output current,seems to max out at about 2a, i am using a 1 ohm 100 watt resistor,am i correct in thinking 5v into that should draw 5a?.,as i said i get about 2 max,no mater where the current pot is.

[m3vuv]

I just unplugged the led,if i wind the voltage up i get about 5a at about 11.5v,couldnt go any more as wires got hot on my leads and grabbers!

[xavier60]

No both opamps are cool and seem to be working ok,everything seems fine apart from the lack of output current,seems to max out at about 2a, i am using a 1 ohm 100 watt resistor,am i correct in thinking 5v into that should draw 5a?.,as i said i get about 2 max,no mater where the current pot is.

Yes, 5V across 1 ohm will cause 5A of current.

[m3vuv]

I have some 1 watt 1k2 resistors,would it be safe to try one of those in place of r4,or is that pushing it?

[xavier60]

I just unplugged the led,if i wind the voltage up i get about 5a at about 11.5v,couldnt go any more as wires got hot on my leads and grabbers!

If disconnecting the LED causes increased current output, it indicates that there is a problem with the CC control side.
Is the LED faulty in some way? It's important that the LED functions a a good diode for the PSU to work properly.

[m3vuv]

well it ligts up! lol,has a 2.122v drop using the diode test on my fluke,its a red one from my junkbox.

[xavier60]

I have some 1 watt 1k2 resistors,would it be safe to try one of those in place of r4,or is that pushing it?

Yes, try it. Although it's the wrong fix. You either still have a fault in the control circuit or have transistors with unusually low current gain or maybe a faulty one hogging drive current. Or a wiring mistake. For example, a bad collector connection to one of the output transistors.
Test carefully  with the CC disabled by leaving out the LED.

[m3vuv]

Well,i just tested the led that came with the kit,its way brighter and has a vf of 1.97v,could that be the issue?,everything else looks good.

[xavier60]

Also, Oscillations can be the reason for odd PSU behavior. Best checked with an oscilloscope.