Peer-to-peer, engineer-to-engineer questions and answers from the EDABoard.com engineering community around power electronics. Click the “Read more” link and follow the entire conversation and maybe add your two cents by logging in to EDAboard.com

Ground problem cause SPI to fail – I have designed a power electronic inverter. The DC link is supplied by single phase grid by a diode bridge. The control section is supplied by an isolated DC link. The problem is that when I connect negative bus of the DC link to the GND (isolated from the grid) of the control board’s power supply, the SPI communication between the control board and IO board failed. Read more

High side driving with 0 to 100% duty cycle – I’m trying to optimize the performance of a class D modulator for a transmitter. This is basically a buck converter with active free-wheeling rectifier, or in other words, a plain simple half-bridge. The supply voltage to the half bridge is 50V. I need a 30 kHz signal bandwidth. To make the lowpass filter reasonably simple and achieve enough suppression of the carrier, I’m using a 200kHz PWM frequency. I need the circuit to work as linearly as possible over the full 0 to 100% pulse width range, in order to get an output covering the full range from zero to as close to 50V as possible. A linearity like 0.1% would be completely satisfying. Somewhat worse is still acceptable. Not finding any PWM IC that performs well enough, I made my own PWM circuit using fast comparators and op amps. Read more

Dell 255W PSU 8.3V on source power MOSFET – I’m trying to fix this Dell 255W PSU, I think the fuse was broken and I replaced it, then I tried to power up the unit but didn’t work on output rails. So, I measured the voltage on the high power side and I think the power MOSFET isn’t working, The drain receives 316V from the high voltage capacitor, the gate is 8.3V from the switcher IC and on the source I found 8.3V, so I thought the MOSFET was broken. Is my guess right? Read more

DC/DC Buck/Boost converter – So one of my classes this semester wants me to design and build a DC/DC Buck/Boost converter. Personally, I have no idea where to start with this. If someone could provide me with some sort of roadmap to follow, I would very much appreciate it. I am planning to use a MOSFET to act as my switches and a MOSFET driver as well. Where can I find whether a certain driver would work with the MOSFET I plan to use? I am planning to use an IRFZ44N by the way. Read more

450V rated linear regulator suffers high voltage spike to its input – We are using a 450V rated LR8 linear regulator in our offline product. If the product happens to get switched on at mains peak then the LR8 gets a voltage of 600V peak at its input (as in the scope shot attached). However, if we put a 100nF X2 capacitor across live/neutral, then the peak voltage applied to the LR8 is 500V. However, the peak duration is longer even though its less voltage(as shown in attached scope shot). Which is less harmful to the LR8? Do you think there could be long term damage due to these overvoltages? Read more

DC-DC converter with high power density – Can anyone suggest suitable DC-DC converter topology for converting 300 V to 50V with isolated output power of 2000W at higher efficiency and less size. Read more

Welding machine (need circuit explain) – Hello, I would like, if anybody knows, to help me to understand the circuit of inverter welding machine. There are two points.
1. On the following picture, I have marked on red cycle an ultra fast diode near to MOSFETS? What is the rule of this?

2. On the following picture I have marked on red cycle a group of 6pcs BYV52 diodes. What is the rule of these? Read more

Power factor corrected LED driver couldn’t be this highly efficient? – We dispute efficiency claims of 89% in the datasheet of this 40W Phillips Xitanium outdoor offline LED driver (Xi LP 75W 0.2-0.7A SN 230V S240 sXt). However, when we opened it up, we found it was a L6562 controlled Boost PFC stage, followed by an L6562 controlled isolated Flyback stage. There is also a Viper controlled little Buck converter to provide bias power. The Boost PFC output capacitor is a 22uF, 450V electrolytic. This surely could not be 89% efficient? Read more

Speed motor control without PWM by potentiometer – I have a question. Can I control the speed of 12 V DC motor by LM293 IC and Variable resistor? I want to do this without PWM and just by a variable resistor. Read more

SMPS transformers without datasheet – I purchased an SMPS transformers online, but they did not come with the datasheet. They are of several sizes: PC40/EE8.3; PC40/EE13; PC40/EE16; PC40/EE19; and more. The manufacturers do not seem to have datasheets for them. It’s difficult proceeding with the power supply design. Read more