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Topic: rectified AC phase control (Read 9739 times) previous topic - next topic

dgueorguiev

Yes, I follow this recommendations , but I have  negative pattern for gate signal. I check voltage with my multimeter and is showing   Vgs= +5.6V . This make me decide to try with the coil, because i have no explanation were this negative wave is produced at the Mosfet GATE. I connect the coil between + of the bridge and drain of the mosfet and source to the "-"of the bridge. Is this correct or I am wrong again?

wvmarle

Yes, I follow this recommendations , but I have  negative pattern for gate signal.
At which stage do you see this negative pattern? How do you see it? You say your multimeter gives a positive signal.

Switching capacitors produces negative voltage peaks, and that's what you're doing: that MOSFET gate is also a small capacitor. You charge VGS up to about +12V, then you switch the optos, pulling the gate to 0V, and with it the source to -12V. Of course this very quickly charges back to 0V, switching off the MOSFET, and you're likely to measure some halfway point of this voltage.

Quote
I check voltage with my multimeter and is showing   Vgs= +5.6V .
Which is an averaged voltage, as your multimeter is not following the peaks. You're not supplying a constant voltage to the gate, so a multimeter can never give a reasonable number here.

In testing I'd leave out the coils and the voltage at its minimum until confident everything else works. This as it keeps damage to a minimum if things go wrong. Also the coil with its kick-back when switching can cause interference. Also go step by step, making sure it works before you move on. So if you see something odd, make sure you understand what's going on before connecting more stuff.
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

dgueorguiev

Hi , every one. I received  new prob for my Oscilloscope and now i have two again.
But my disasters continue .My rectifier bridge get in smoke and same time my variable transformer start making strange noise and output voltage drop. the fuse on step up TR#3 burn. I decide  to use regular suply voltage supply  119V AC which is at my place ,but I can not get full wave rectified image (see attached photo. I keep changing the bridges with new ones ,but same result . I am afraid something happened to my oscilloscope . I am on DC settings for probe 1 , and AC for probe 2 . I have 5 new
 KBPC5010 -  Bridge Rectifier Diode, KBPC Series, Single, 1 kV, 50 A, Module, The one it burn was KBPC2510(25A)

dgueorguiev

 see attached photo : this is with half wave rectified 119V AC ,without coil ,channel 1 is set to 20V DC  and showing voltage at Mosfet gate . Probe at gate,  GND at source of MOSFET.
 channel 2  is set to100V DC and show voltage across resistor 1.5K(which I use instead of coil L2). I do not see pulse I was expected across the resistor. There only small cut of tip of the positive portion of the wave representing on channel 2. I have  0A trough the resistor.Look like the Mosfet is not switching at all. What could be the problem?

dgueorguiev

I change U1(4N25 ) with new one (4N35) and have amps passing trough the Mosfet (0.15 A),but I still have no pulses I expect for the DC going trough resistor. See attachment. on channel 1 I have monitoring Gait voltage for Mosfet ( going from+9.81V to - 62V ), and on chanel2 DC going trough resistor. every thing on the side of the ARDUINO commands to optocouplers is like I expected and luckily nothing change since first photos I posted for this part of the schematic . What I can do next ?

wvmarle

I see a square pulse - that's the Arduino's signal?

What to do next.... check your wiring, very carefully and thoroughly, as I suspect there's something wrong. A solder bridge or so, maybe a part that's connected wrong - something at least.

The schematic that I designed should keep the gate voltage (referenced to GND) to about 0-12V. The voltage you report are too high for your MOSFET: most can handle no more than +/- 25-30V on the gate, referenced to the source pin. More than that will kill a MOSFET.

Actually without the MOSFET in place you should be able to see the VGS pulses. That should be the output of the two optocouplers. Back in #101 you reported some good values for that. Make sure that hasn't changed - it's what you provide to the gate that counts.
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

dgueorguiev

Hi everyone, I have checked everything and I monitoring on ( photo jpg) signal from ARDUINO on pin1 of U1 on channel 1(setting  5V). I monitoring on channel 2 signal on pin1 of U2 (setting 5V) looks normal.
On photo(1)jpg you can see I am monitoring on channel1 voltage on pin4 ofU1 and channel 2 monitoring pin4 ofU2. This is looking totally wrong. Why this is happening to me? I do not see how it will switch on the MOSFET and how it will drain the charge at gate of MOSFET to switch off. I do not have any load or MOSFET in the schematic and I am waiting for new rectifier bridge ,because the one I (received 10 Each),do not give me full wave rectified picture. See on right upper corner of the oscilloscope,  I have register -68V .Both probe ( channels)are set to monitoring DC

TomGeorge

#142
Jan 14, 2018, 12:33 am Last Edit: Jan 14, 2018, 12:38 am by TomGeorge
Hi,
Can you post a new up to date schematic please.

Can you mark on it where you are connecting the scope probes and the gnd clip of the probes when you show a multi channel scope diaplay.

All your scope patterns are of little help if you have a circuit with parts of it floating or biased with respect to the the
main reference point, where ever that is.

You must be aware that ALL of the scope probes' gnd clips are connected together and to gnd of your mains supply.

This may explain you blowing up probes and rectifiers and other components.


Quote
Yes, I follow this recommendations , but I have  negative pattern for gate signal. I check voltage with my multimeter and is showing   Vgs= +5.6V .
Where did you have the gnd probe of the scope connected for the negative pattern

Vgs = +5.6V would be correct as your reference is the MOSFET source.

Can I suggest before posting your images,  you use a graphics editor, like PAINT and add some text pointing to what each trace is, some of  your images you cannot read the CH numbers.

Thanks... Tom.... :)
Everything runs on smoke, let the smoke out, it stops running....

dgueorguiev

Sorry for this  bad drawing. Like I sed I get back to original drawing , but for the test I do not connect L2 (or any resistor) and I did not connect the MOSFET.When I  draw,  I sow that it is bad Idea to monitoring Pin4 of U2, because this is directly connected to the GRD (or "-" of the bridge)

TomGeorge

#144
Jan 14, 2018, 03:16 am Last Edit: Jan 14, 2018, 03:17 am by TomGeorge
Hi,
Thanks...
Ops circuit.


Tom.. :)
Everything runs on smoke, let the smoke out, it stops running....

TomGeorge

Hi,
Your scope should have the provision to do    Ch1 minus Ch2 trace.
Can you see what that displays please.

Thanks.. Tom... :)
Everything runs on smoke, let the smoke out, it stops running....

dgueorguiev

I went to math,A-B(channel 1-channel 2) and I have strait line  at "0" V, see attachments

aarg

Your scope setting must be wrong. The difference signal is bull.
  ... with a transistor and a large sum of money to spend ...
Please don't PM me with technical questions. Post them in the forum.

TomGeorge

#148
Jan 14, 2018, 06:25 am Last Edit: Jan 14, 2018, 06:26 am by TomGeorge
Hi,
Make both channels the same V/cm.
And  both channels DC coupling.

Tom... :)
Everything runs on smoke, let the smoke out, it stops running....

dgueorguiev

I set Chanel1 at scale 50V ,Chanel2 at 50V ,and math scale 10V, after that I lower to5V and going down steps up to100mV .No changes to Math line  "0"V strait line.

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