Power electronic questions

Hello, i have some questions about my HV pcb.There’s things i use a lot on low voltage but i want to ask for HV.

1. I pass the 230Vrms through rectifier and have an 325VDC.I want a LED just for debug/display when its powered on.

I can use some resistor and common LED (Vf about 1.7V).Lets say (325-1.7)/10mA = 32.3kΩ. But as i calculate the W on resistor will be about 3WI can power the LED with lower current and use 1W resistor.Correct on above thinking;Or its better use some other (dunno) LED for those volts;

2. I will measure some AC currents with LTS-6NP.AC currents coming from 6 N-IGBT switching.Do i realy need low pass RC filter;And if yes, does an fitler with cut-off 1.5Hz will be ok for 10kHz switching;

3 I need an stable 15V supply.I am going to use an 230VAC-18V/20VA PCB-Transformer.After rectifier i will have about 25V.Will 7815 will working proper for currents below 1A or there will be issues;The big voltage difference and power dispiration troubles me.

High DC voltages like that have to be respected - you should be using a string of two or more high voltage rated resistors to drop down the the LED. Use a high brightness LED and you'll only need 1mA or so which will cure a lot of the heat issues. With high power high voltage DC any flash-over will be able to hold an arc continuously, even through a series resistor (ie without blowing a fuse), so don't be complacent.

25V down to 15V in a linear regulator at 1A will dissipate 10W, which is a lot.

You might do better to use a switch-mode 18V supply prior to the regulator? Or direct to 15V if you aren't worried about switch mode noise.

Hi, Please take the above advice, you do realise that even though it is rectified it is still electrically connected to the full force of the mains power supply.

230Vrms through rectifier and have an 325VDC

Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png? I hope you have at least a fuse in the AC circuit.

What is your project, what is the application?

Thanks ... Tom.... :)

There's an old version.

https://drive.google.com/file/d/0B_SOI_pGKecrTThDeTdfYVNJTWc/view?usp=sharing

I was taking the 12V from bench supply.Now the need for 15V supply and more current (drivers with more output current) makes me think about it.Also i need no decrease the components outside PCB,i found some PCB AC/DC converters 15V/4A but its a bit expensive.

I also was need 5V supply,but the current for 5V's opto and sensors is low.I think 7805 will be fine.I could use 2nd PCB converter but cost ++.

The part i cant solve,is the part of a LED to monitor the VDC.Even with low current,there will be so much heat.

The LED is important.

What exactly is the purpose of the LED monitor.

Is it simply to confirm the AC mains is connected or that the bridge rectifier hasn't blown up.

If the former then you could use either a miniature neon lamp (as used in mains switch indicators) or an LED with a reverse biased diode in parallel fed via a capacitor who's Xc is sized to deliver the mA the LED requires. The reverse biased diode prevents the LED being destroyed during the reverse half cycle. Note that the capacitor MUST be rated for direct mains connection ie class X or class Y. In fact, if you obtain a simple transient suppressor capacitor unit this may be capable of passing sufficient current to light your LED.

If it's the rectifier output you are interested in the neon concept can still be used.

I monitor the VDC via isolation amplifier.My MCU will handle the VDC over-under-voltage.

I just want a LED (or anything to inform) me that there's volt on VDC rain so i must care^2.Also will help me know there V on VDC rain cause of big capacitor value.

Hi, Okay why didn't you say you were building a Variable Speed Drive?

What is the power output?

Tom... >:(

Could handle up to 1kW.But i will run it for my 1/5HP motor.Its just for measures.

The LED will be just to know when the VDC rail has voltage.