I drew a 24v to 5v circuit board and it gave a short circuit warning when connected to a 24v power supply.

练习时长2.5月

I drew a 24v to 5v circuit board and it gave a short circuit warning when connected to a 24v power supply. [Copy link]

 

Figure 1: Schematic diagram of 24V to 5V voltage regulator circuit [attach]689645 [/attach] Figure 2: PCB diagram

Figure 3: Welding

Problem description: Connect 24v DC power supply through +24v and GND pads, SMAJ28A tube sparks (probably it), power supply prompts short circuit warning, guess the reason is that SMAJ28A tube is broken down and causes short circuit

What I modified:

1. Replace SMAJ12A with SMAJ28A

2. The original schematic used mp2315s, which was replaced with mp2315gj-z, and the package is ACGP

Could you guys help me figure out the reason?

chunyang

Check if the TVS is connected in reverse. This device is usually not necessary and can be left unconnected. Also pay attention to the polarity of the input voltage and do not connect it in reverse.

练习时长2.5月

chunyang posted on 2023-4-11 16:45 Check if the TVS is connected in reverse. This device is usually not necessary and can be left unconnected. Also pay attention to the polarity of the input voltage and do not connect it in reverse.

I first found the cathode wire on the TVS tube, and placed the positive pole on the other side at the ground end. I measured the input voltage with a voltmeter at the beginning, so it shouldn't be reversed.

吾妻思萌

Is the polarity connected in reverse? The voltage should be designed with a margin of 1.5 times.

chunyang

Practice duration 2.5 months Published on 2023-4-11 16:59 I first find the cathode wire on the TVS tube, and put the positive electrode on the other side on the ground end. I measured the input voltage with a voltmeter at the beginning, so it shouldn't be reversed.

Test it with a meter first. If you confirm that the power supply and TVS are not connected in reverse, it only means that there is a short circuit problem in the circuit. But the short circuit problem will not cause the TVS to spark, so if what you see is true, there must be reverse connection.

qwqwqw2088

At first glance, it is obvious that the picture was drawn using Lichuang's software and device library.

lugl4313820

Before testing, use a multimeter to check if there is a short circuit. Use a programmable power supply to supply a small current to see if it is normal, then increase the current to test. If you start with a large current, you may be a little too confident.

秦天qintian0303

chunyang posted on 2023-4-11 19:40 Test it with a meter first. If it is confirmed that the power supply and TVS are not connected reversely, it only means that there is a short circuit problem in the circuit. But the short circuit problem will not cause the TVS to spark...

I guess I have drawn something similar before, so I am more confident.

hahajing

It is recommended to increase the protection voltage of the TVS tube. If the layout is not good, the output end will be triggered incorrectly, and the positive and negative copper foils of the input terminals should be kept away from each other.

led2015

When I encounter a short circuit, I usually measure it first, then replace the components one by one.