The DC / DC converter on the XL4015 does not regulate the voltage, how to protec

Hello,
I bought a DC / DC power supply system for XL4015 on a well-known website and I have a problem with voltage regulation. The problem repeats for the second time, previously I complained about the entire system at the seller and got a new one, working properly. The first and second system worked properly until I set 12VDC, I loaded it with a 21W / 12V bulb (about 1.7A), then I turned off the mains power of the entire system with this connected load and turned it on again then the bulb only flashed and burned out and the output was already voltage equal to input approx. 35VDC. To reduce the mains voltage, I used Trafo 230 / 24VAC (4A, 100VA), then the bridge rectifier at the OUTPUT from the bridge is 35VDC and I gave it to the INJ of the system.
I noticed that the stabilizer LM 317 and XL4015 used in the system get very hot even when idle, so I desoldered and placed them on large heat sinks and connected with wires. The LM 317, which has a current of 1.5A, replaced the LM 338 (5A). Unfortunately, it did not help either, because as I described, it was enough to take the power supply and reconnect it to probably damage the XL4015 with a current of 5A.
DC / DC power supply system data on the XL4015 provided by the distributor:
- input voltage 4 - 36V
- output voltage 1.25 - 32V
-current 4.5A (max 5A)
- max power 75W
- working temperature -40 +85 degrees
- efficiency 96% (max)
- frequency of 180 kHz
- short-circuit protection (limit 8A)
- voltmeter accuracy: +/- 0.05V
-Thermal protection
- no protection against reverse connection
LED display - voltage, current and power measurement.
Smooth regulation of the output voltage with a potentiometer
Input voltage measurement LED IN.
Output voltage measurement indication LED OUT
Ability to turn off the voltmeter with the left button
The ability to switch the measurement with the right button
1 - input voltage measurement
2 - measurement of the output voltage
3 - output current measurement
4 - output power measurement
5 - alternating display of all measurements.





I wanted to use this seemingly great circuit to build a "workshop" power supply so that certain parameters can be set. Unfortunately, a simple resistive load damages it. What am I doing wrong? How to check if the XL4015 is actually damaged?
The IN and OUT voltage measurement works, switching with the right button switches individual measurements, so probably the XL4015 has died, but why?
When I buy a new one, how to secure it so as not to replace it every now and then?

Hello, is 35V after load or not? I think that it is not a very good idea to put the xl circuit on the wires - rather you can give circuits as close to the coils and diodes as possible.

With the first system, everything was originally LM317 and XL4015 soldered on the board, they only heated up a lot, but in the situation as described (turning the power off and on again), the system stopped working, i.e. there is no possibility to regulate the voltage. So I replaced it with a new one. I checked the new one without desoldering it idle, then I desoldered it and mounted it on the heat sinks, I checked it idle. Then I substituted the 21W / 12V load, it also regulated. After trying to take and give power, it stopped regulating.

Added after 5 [minutes]:

belfegor1988 wrote:

Hello, is 35V after load or not? I think that it is not a very good idea to put the xl circuit on the wires - rather you can give circuits as close to the coils and diodes as possible.

I measured 35VDC without load.
Maybe I will actually buy a new XL4015 and solder it to the board and give it a solid heat sink. Because the lack of a large capacitor, e.g. 1000 - 2200uF behind the bridge, did not have a negative effect on this damage?

The capacitor will certainly not hurt. The one on the board will live longer. The question is is this the only damage, did the lm358 amplifiers survive, or the diodes, or something else?

eurotips wrote:

1R5 resistor

1.5 Ohm resistor to give only where? in series at the exit? If so, what power? As if I wanted to load the power supply max. 5A at a voltage of 30V and more, it would need approx. 150W +, i.e. 1R5 / 200W would be good?

The prices of power resistors are actually quite high: 1R5 / 100W - about PLN 20, 1R5 / 200W about PLN 55-60. At the beginning, for testing, I will think about 1R5 / 100W.

Hello, where do you get the 200W power from? Assuming a max current of 5A, a 1.5 ohm resistor in series with the bulb, we have a lost power of 37.5W.
edit in a similar converter, only without a display, giving an electrolyte capacitor to any of the 2 potentiometer leads, from voltage regulation, I had a slight increase in voltage when turning on the converter, only you need to check the polarity of the voltage there with a voltmeter.

belfegor1988 wrote:

where do you get the 200W power?

I assumed that at max output voltage: 32V and max. 5A current, the power in the event of a short circuit (e.g. accidental connection of the power supply terminals) will be 160W. because 32V x 5A = 160W. I have not found a 160W 1R5 resistor so the next one available is 200W. Hence the value.
As for the capacitor, thanks for the advice, good idea, but when I have a new XL4015, I will check the voltage on the U-adjustment potentiometer and I will plug the electrolyte, what capacity do you suggest?

So what current efficiency do you have 5A or I = U / R 32V / 1.5 ohms = 21.3A. Probably unrealistic, and try the capacitor experimentally - I didn't have a big one, I don't remember anymore. Just be careful that it doesn't explode on you.

Hello . Dzerat or after replacing xl4015 the problem has subsided or something else has fallen. I have the same output voltage without the possibility of regulation.

After replacing the XL4015, the problem resolved, nothing else fell. But after a few attempts, it turns on, despite adding a resistance in series with 1.5 Ohm / 100W, there was a repetition of the entertainment - the XL4015 fell again and did not respond to adjustment attempts. I gave up because this system is not suitable for unstable operation, i.e. when it is turned on and off under load.

I connected the resistor in series at the output, as you described in another post, but I also tried to put it in series at the input. in total "I arranged" 4 pcs. XL4015 and stopped trying. I wanted to have a laboratory power supply, but with this operation it is too big a risk that something important will suddenly get large Volts.

After 1, the XL4015 should not be on the wires, it is a pulse regulator for which a 5 cm cable already makes a difference. I have a power supply for the XL4015 and it had a short circuit at the output more than once or it was turned on with the load.

It was on the wires for a while, but after my colleagues' suggestions, I soldered it back to the PCB and added a powerful heat sink. After soldering during the tests as described above, unfortunately, after switching on, it broke - no adjustment possible and the voltage at the output is equal to the input voltage. My colleague kassans may have a different control system for the XL4015 and therefore nothing bad is happening?

After 1 then do not turn on the power supply with bulb load, the cold filament causes a large surge current which can kill the XL, after 2 measure the input voltage.

Subject not new, but I had the same and fixed it.
(1) because the voltage regulation did not work, but the CURRENT REGULATION WORKED, I assumed that the IC was working. I will add that I also connected the light bulb, as suggested by this forum, so I initially took into account that I burned it.
(2) one of the potentiometers (or trimmers) controls the voltage for me. Two of its legs are connected to each other (on the board), and the third should be connected to the xl4015 chip to the FB (feedback) pin. So the resistance measured with a multimeter between the third potentiometer foot and the second one on the stalak (FB) should show a short circuit (0.2 ohms for me).
(3) and did not show. There was something there, but a few kilohms and it changed depending on the capacitors' charge and the setting of the potentiometers. So WRONG.
(4) because I did not see any errors on the board and the place that I could fix, I connected the potentiometer soldering point and pin 2 of the chip (FB) with an external jumper.
(5) FIXED, EVERYTHING WORKS AS IT SHOULD.
(6) I imagine that because the PCB is double-layer, something after my soldering did not get in touch and hence the effect of the lack of voltage regulation. The jumper solves the problem.

The XL4015 Ci falls due to the smooth reduction of the supply voltage from the disconnected power supply - at some point the input voltage on the IC is lower than the voltage at its output and this causes its damage. The permissible negative (in relation to the mass) voltage of the XL4015 system is only 0.3 V, so it is easy to damage. The power switch between the power supply and the stabilizer will help.

Kris2711 wrote:

The power switch between the power supply and the stabilizer will help.

I know that I am digging up the topic a lot, but I was looking for an answer to this question. Is a switch, e.g. a rocker switch, sufficient, which will disconnect the positive pole between the power supply and the inverter in this case? Do you need to disconnect both poles?

Yes, single-pole positive power is enough.