AC DC grounding problem - Page 1
Forum section: electronics / projects

author: nimit393@gmail.com
author_rank: Contributor
timestamp: December 05, 2013, 06:06:16 am
content: i am applyong 230vac across collector and emmiter of the IGBT and a PWM is applied to the gate for controlling the power.my question is that where should the return path of DC PWM be connected as the positive end obviously goes to the gate.Should it be connected to neutral of AC voltage or i need some other circuitry??

author: Psi
author_rank: Super Contributor
timestamp: December 05, 2013, 01:00:46 pm
content: as far as i know you cant switch AC with a IGBT (unless this is a special AC IGBT module)Perhaps you mean a solid state AC relay? They normally have an LED as the input so are isolated.

author: nimit393@gmail.com
author_rank: Contributor
timestamp: December 05, 2013, 05:10:53 pm
content: 2 igbt in anti parallel config can be used to completely block or switch AC.

author: Andy Watson
author_rank: Super Contributor
timestamp: December 05, 2013, 05:18:23 pm
content: To the emitter of the IGBT, i.e. the gate operates with respect to the emitter as reference.

author: nimit393@gmail.com
author_rank: Contributor
timestamp: December 05, 2013, 07:04:48 pm
content: thanks

author: nimit393@gmail.com
author_rank: Contributor
timestamp: December 06, 2013, 04:50:35 am
content: but my DC supply is derived from ACso eefectively shorting return of DC and AC neutral would short out a diode in bridge rectifier.

author: minime72706
author_rank: Frequent Contributor
timestamp: December 06, 2013, 04:56:05 am
content: An IGBT has a gate just like a MOSFET and since an ideal MOS gate doesn't draw DC current, you'd typically use some fairly large resistor value to ground as the return path.This advice may or may not work in your particular situation, but it seems logical to me. You can use a pretty high value, but you don't need to go nuts.

author: nimit393@gmail.com
author_rank: Contributor
timestamp: December 11, 2013, 05:22:30 pm
content: i am finally getting chopped AC wave as my output but there are two problems1)smoothening of AC waveform2)as im chopping the AC waveform i'll get lower output voltage...what if i need voltage greater than input...i.e. boost for AC

author: minime72706
author_rank: Frequent Contributor
timestamp: December 11, 2013, 10:19:37 pm
content: So your DC control signal is derived from a mains-powered circuit that is on the secondary side of a transformer, yes? I've never used a IGBT before (though I just received some today for a capacitor bank) but I am pretty damn sure that you'll need to isolate the bastard with a 2N35 or something similar.I hate this particular problem because it appears all the time and makes things more annoying than they seem like they'd ought to be ...

author: nimit393@gmail.com
author_rank: Contributor
timestamp: December 12, 2013, 06:05:05 am
content: i got over the prob by connecting igbt across bridge...so igbt always sees DC and AC load is easily controlled.Though the problem of getting a smooth waveform from chpped AC still persists.Thought of Capacitors but getting large value Caps ...hvnt tried it for line voltage (230VAC) but works for smaller AC voltages

author: nimit393@gmail.com
author_rank: Contributor
timestamp: December 12, 2013, 09:56:32 am
content: switching pulse given by function generator works perfectly but when it is given via op-amp (as it will be required for interfacing with controller) it does not work as suppllies of op amp need to be shorted with IGBT circuit.Help!

author: minime72706
author_rank: Frequent Contributor
timestamp: December 14, 2013, 11:22:44 pm
content: Can you take any photos or draw a limited schematic of the region of the circuit in question?