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Common mode noise mitigation in offline power supplies – In offline power supplies, common mode emissions are best dealt with by using common mode chokes in conjunction with Y capacitors. However, do you agree that the “poor man’s” common mode noise reduction technique of using uncoupled inductors in both the live and neutral lines is also a somewhat worthy technique for mitigating common mode emissions? Read more

Connecting together solar panels output and AC-DC rectifier output? – I want to combine the power supplied by solar panels and power from an AC to DC rectifier. For that, is it possible to connect the solar panels output (210V, 6A DC) and a full-wave rectifier output (260V RMS) together? Read more

Precise high current sensing at 12.5 mV/A – I am designing a circuit where the requirement is to sense bi-directional currents from 0 to 50 Amps mapped from 0 to 5 V. I have chosen the LEM HAIS 50-P Hall Effect Current Sensor which offers a sensitivity of 12.5mV/Amp. To increase the sensitivity to 25mV A, I have an option to either place the gain stage first and then a unity buffer to connect it to the 12-bit ADC of the PIC24F that I’m using. Or else place the unity buffer first and then amplify the resultant signal to be connected to the ADC. Kindly suggest which would be the best suitable configuration to avoid any effects of nonlinearity or impedance mismatch. Read more

3.7 VDC to 50 VAC inverter for ringing old 1000 Ω phone bells – I have this old black rotary dial phone which I want to connect to a GSM module and microcontroller. The bells will ring at 24 VAC but they sound better with 48 VAC (no sound at 6 VAC). Inside the phone there is a schematic telling the bells has 1000 Ω resistance. I calculate that to 50VAC/1000Ω = 0.05 A, and 50VAC²/1000Ω = 2.5W. Now I want to make 50VAC from a 3.7VDC battery based on this inverter schematic with two MOSFETs. I have found this 1x240VAC to 2x18VAC 50mA transformer and when connected to a square wave of 3.7VDC at 50Hz it should give 240/18*3.7 ≈ 50VAC. On the battery side it should give a load around 2.5W/3.7VDC = 0.68A. Should I just choose MOSFETs which can handle 1A? Is that how it works with transformers and inverters or have I misunderstand/miscalculated something? Read more

Not using X2 rated capacitors in AC filter for offline SMPS? – You can find a million internet reports on X2 capacitors, i.e. https://ac-dc.power.com/system/files…-docs/an15.pdf
but none of them state if it’s an actual regulatory requirement for a capacitor from line to neutral upstream of the diode bridge to be an X2 rated one (in an offline SMPS).
I mean, surely it could be a ceramic and non-X2 rated? Read more

30W offline LED driver malfunctioning – We have an offline (240VAC) 30W offline LED driver with a high power factor. It is controlled by a microcontroller which dims it depending on light levels etc. The problem is that we are getting lots of noise issues with the operation. (eg sometimes it doesn’t dim when it should. We are not sure if the problem is with the code, or whether it is noise corrupting the circuit, or noise corrupting the microcontroller. Read more

Wifi Module effect on power IC measurement – I have a strange problem. We use in our application the power IC ADE7953 , and it gets its supply from a SMPS DC supply (1 A rated). It gives good measurement and it has no problem when it is connected alone, but when connecting WiFi module of our project to the same DC source, the power IC get blind in low current ranges (currents less than 20 mA), while it is still relatively good in high ranges. Are there any suggestions about how to eliminate or at least reduce this effect? Read more

Logic NPN switching PNP at 90 to 100 volts – I have a PNP switching 90 to 100 volts at 2 to 3 amps and an NPN at the logic level. The PNP is a IXTH48P20P that has a Gate-Source Threshold Voltage of -4 volts. I would like to know is what type of logic level NPN should I use to power on the PNP at say 10 volts and should i have opto isolation between the 100 volts and the 5 volts. Read more

Output device of a solid state relay – The switching device of an SSR can be a transistor, an SCR, or a TRIAC. Apparently, a transistor can be used for both AC and DC SSRs. I don’t understand how a transistor can both sink and source current in a transistor-based AC SSR? Read more

Power transformer software – Russian translation needed – I found this freeware and according to the website translation, it is supposed to be very good. I want to test it, but the program does not have any other language support. If there are any forum members who can help translate the entry fields it would be greatly appreciated. I will post links to the site once I managed to get it working. Read more