SMPS CIRCUIT MEASUREMENTS - Page 1
Forum section: electronics / general

author: tb5byo
author_rank: Newbie
timestamp: October 11, 2024, 01:03:15 pm
content: Hello everyone. I have designed a circuit board that includes an SMPS circuit. This board controls a BLDC motor, and for motor control, it uses 310V DC power. The GND line shown in the schematic represents the entire ground line, meaning it is also connected to the microcontroller’s ground. To put it briefly, the ground line from the bridge rectifier is directly connected to the microcontroller.I set up the circuit, and it worked perfectly. However, when I tried to upload code to the microcontroller, I damaged the USB port and HDMI (very strange) input of my computer. When I tried to measure the SMPS output with an oscilloscope, as soon as I connected the oscilloscope’s ground crocodile clip to GND, a short circuit occurred, and the breaker tripped (I observed a short circuit just by connecting the ground crocodile clip).In your opinion, what could be causing this? Where am I making a mistake?

author: Sorama
author_rank: Frequent Contributor
timestamp: October 11, 2024, 01:11:00 pm
content: USB ground (pc side) is connected tot PE?There is probably a voltage between ground usb and ground you made with the probe crocodile.You could measure with dmm between those two points to verify.

author: tb5byo
author_rank: Newbie
timestamp: October 11, 2024, 01:33:11 pm
content: by the way i forgot to mention i am programming with stlink v2 device and that device burned.i apologize for my bad english but as far as i understand you are asking if the system zero points are equal? ​​i connected all gnds to the same line and there is no connection between gnd and PE (ground). i couldn't understand why my programmer burned. is it getting a reverse voltage from the GND line?

author: Sorama
author_rank: Frequent Contributor
timestamp: October 11, 2024, 01:58:47 pm
content: Was your programmer still connected to pc through usb and programmer to your device when you connected probe ground ?

author: dietert1
author_rank: Super Contributor
timestamp: October 11, 2024, 02:13:33 pm
content: Thank God you are alive!This is the classical situation where people use an isolation transformer.You need the transformer because mains AC isn't ground free. So the negative output of the bridge rectifier cannot be connected to Gnd without causing havoc.The mains isolation transformer can solve this problem. If you want to continue that project, get an isolation transformer of sufficient size. And get some electrician who understands about mains circuits before you kill yourself.Later, when you finished MCU development, the device can run without isolation transformer. But you need to remember that you always need the isolation transformer when you want to connect the STLink or the scope.I think that STLink with built-in isolation exists. That can be used for programming without the isolation transformer. But you still need the transformer to make scope measurements.Regards, Dieter

author: tb5byo
author_rank: Newbie
timestamp: October 11, 2024, 03:09:57 pm
content: No, I never connected the ST link and the oscilloscope at the same time, they both happened at different times.I actually had a minor electric shock.After I disconnected the card from the power supply, it crossed my mind for a moment that the capacitor would be full and I had a small shock