SMPS has a failed power transistor. One measures ok but getting hot, the other measures zero resistance across any terminal.

New SMPS arrived, and has a different IC. it is a 7500BD. Am i able to limit current with this also?

 

Am i able to limit current with this also?

Unfortunately that device shows no explicit current limit input, so I can't tell how they may be limiting the current on that module.

 

altering pin1 at their "typical application" by an avg. output current might work ... but the result is not too well predictable as the diagram shows -- the AND gate is no any way coordinated with the NOT gate ???

 

Thanks! I will use this one for the supply with my 741 based circuit i posted earlier.

 

https://forum.allaboutcircuits.com/attachments/current-limiting-circuit1-jpg.204776/

Would someone with more circuit knowledge than i check to see if my circuit is ok?
I an not getting any current limiting atm. the 4 Resistors on the the 3055 collectors are .1 ohm for balancing

 

Sorry, but I only work from circuit schematics and I'm too lazy to try to draw one from your wiring diagram.

 

Would someone with more circuit knowledge than i check to see if my circuit is ok?

there are load of ways to limit the current --and/or-- limit/fold-back the SC (short circuit) condition . . .
. . . but they all come with the head ache . . . they tend to

• start oscillating (←if such condition is ok it must be controlled over all possible I/O currents/-voltages conditions)
• shut down the supply
• have excessive current bursts at certain conditions
• limit the (otherwise) possible max output current
• make the startup or recovery from SC complicated to design properly
  this one may require to alter (change/modify) your existing circuit completely
  the circuit acts as a whole -- and thus everything depends on everything (it's not that you change a few things and it's done ... it's more like you change few things and need to redesign the rest of the circuit)
• etc. ...

↑▲↑ to manage all that ↑▲↑ you need to define precisely your expected supply resopnse to all possible conditions . . . a lot of work . . . but not impossible to achieve

 

Hi, I am needing to build a new variable current limiting power supply for electroplating.
Previous one went up in smoke (its in a harsh environment)

With 40A at 12V, current limiter should be able to dissipate 480W of power.
So,
A. Use 8 transistors 2N3055. Every transistor will dissipate up to 60W.
B. Use fan cooled heatsink LA 17/150 24V with low thermal resistance = 0.07°C/W.
C. Mount by four 2N3055 on both thick sides of heatsink.
-----------------------------------------------------------------
At 40°C ambient air, heatsink will heated to ~74°C (40 + 480 * 0.07).
At 74°C 2N3055 can dissipate 80W max, so 80 - 60 = 20W. Good spare.

--------------------------------------------------------------------
LA 17/150 24V
Fan / Force Cooled Heat Sink,
Hollow Fin Aggregate, 0.07 °C/W,
120 mm, 122 mm, 150 mm, 237 m³/h
Price £177.00

-------------------------------------------------------------------------
ADDED:

 

I have the 2n3055s on a large fan cooled heatsink.
I will build another with 8 transistors. Which may need more than the BD139 to drive them all. Thats not priority ATM.

Just wanting the current circuit to work.
Do i need a -neg supply to pin 4 of the 741 to make it work? Or have i missed something else?

 

Tempting Danko!
But!
My previous experiences with this type of chinesium electrics hasnt been blessed with reliability.

My circuit above did work, might not be efficient but its simple! Does anyone have any sugggestions on it? can it be improved?

Dont diss these Chinese supplies. For the price buy one and give it a try. Ive got something similar and am happy wit it. Your going to spend a lot more than $US63 trying to cobble together a circuit. Just remember that you want 480W of power so you are going to need a pretty big ass power supply in front of this buck converter.

 

Circuit in post #28 designed in free software LTspice, DOWNLOAD_LTspice.
Resistors R1...R8 and R12 are 5W.
Potentiometer U2 better to use multiturn, wirewound.
For example, with 5-turn pot, it is easy to select any load current from 200mA to 40A by one knob.

5-turn resistor:

7486R1KL.3
7480 Series 1 kOhm 7/8 in Bushing 5 % Precision Potentiometer
US $17.09

ADDED:
Voltages in circuit:

 

I built this power supply.
But not getting any output. Question on the 2N3055s. I measure approx 12V on the Emitter, 11.6V on the Base and 1.5V on the Collector. I have isolated them all and measured them independently, same values.

With only the Emitter connected i still get 11.6V 0n the base. Dodgy components? they are new.

 

I built this power supply.

considering the power output capability you can consider yourself lucky for not getting any output
you should test it damn carefully better with multiple fast blowing fuses to all critical power paths

 

Problem solved. resistor in wrong place.

Lucky is getting it working! Works very well now.

 

Lucky is getting it working! Works very well now

Congratulations on your achievement!

 

A Huge thankyou for Danko spending the time to design a new working circuit!

 

Simplicity way (with loss of efficiency %) - 2N3055 two pieces parallel with larger emitter "measure" resistor, what voltage is measured by Zener or reciproke zener or other transistor or anything else, to regulate those 3055 base current. Extraordinary cheap method within zero USD expenses. Circuit similar to this www.google.com/url?sa=i&url=https%3A%2F%2Fmyelectrons.com%2Fmosfet-tl431-ldo-linear-voltage-regulator%2F&psig=AOvVaw0Wozdpii4HBaguVt9YUXrB&ust=1589267690745000&source=images&cd=vfe&ved=0CAIQjRxqFwoTCKjxveehq-kCFQAAAAAdAAAAABAD

Wiser way - to copyate the Danyk.cz circuit for 60V 40A CVCC SMPS (basis UC3842) just trimming the voltage to some 15-18V but boosting the current to some 100. But this is the project costing few tens of USD and demanding a week to solder.
www.danyk.cz/reg60v_en.html
www.danyk.cz/svar_en.html