This week’s top power electronic posts from EDAboard.com

Two different grounds, one transformer — On switched mode power supplies….I have seen many circuit block diagrams where the ground connections on either side of the transformer have different symbols….I would assume this means the grounds can’t be connected together to maintain the galvanic isolation of the secondary side from the mains for safety; so what do you normally do with these two grounds when they both need to be grounded but can’t be connected? Read more.

Generating sine waves the easy way — It can be difficult to generate a sine wave with a power circuit. Here is one of the easiest methods. It takes a microcontroller which has at least two PWM/CCP modules. To get a sine wave we will need two SPWM signals. These two signals will generate sinewaves after filtering with an L-C circuit. But between this signal and the filters must go some kind of transformer. To switch the transformer we need MOSFETs. Usually an H-Bridge will do the work. Read more.

When a SMPS blows fuses — I have a PCB from an arcade machine power supply that occupies four PCBs in total. The arcade machine pops fuses. I traced the fault to one PCB that takes a 120-V input and (I think) outputs 5 V. (I measured the 120 V, and the wire terminal has a small 5-V sticker on it, so I assume it’s ±5 V and two ground wires). When I got the machine, the fuse was already blown and is soldered onto the PCB. I replaced the largest capacitor on the PCB, then I added a new fuse and it immediately blew, so I suspect something else is wrong! I removed the bridge rectifier and tested it out-of-circuit with a multimeter. The reading began at roughly 3.00 and started to count towards an open circuit. Read more.

From square wave to sine wave — I have made an inverter using linear topology. It takes 12 Vdc and outputs 220 Vac, 100 VA. But of course it produces square waves (50 Hz). I want to know how to convert this square wave into a pure sine wave (using a reference sine wave). I have searched the Internet but I haven’t found any useful data…Read More

Why a gate-drive transformer? –On page 25 of the LTC3722 datasheet, it says that bootstrap high side drive ICs such as  the LTC4440 can be used when input voltage is less than 80 V. This implies that if above 80 v, gate drive transformers are needed instead. Why do they say this? Bootstrap high-side drive ICs are used with 400-V (post PFC) input voltages and there’s no problem. Read more.