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reverse phase dimmer

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hhhsssmmm

New Member
Hello

Im building a 1kW reverse phase dimmer (230VAC) using PIC MCU and a power MOSFET. This dimmer is designed for the dimming of ELECTRONIC transformers only. Enclosed is my circuit schematic.

Details of the power MOSFET (Q) in use are as follows....

# Manufacturer: INFINEON
# Manufacturer Part No: IPP60R099CPA
# Transistor Polarity: N - Channel
# Voltage, Vds Typ: 600V
# Current, Id Cont: 31A

The inductor and capacitor combination in the schematic is an RFI filter.

I simply wish to have my complete schematic cross checked for any mistakes so that the circuit can work as a reverse phase dimmer. Please can someone go through my schematic and kindly suggest any improvements that might be required. If there is any mistake, then please also point out and suggest the necessary fix.

Thank you
Haseeb
 

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KMoffett

Well-Known Member
Why are you bothering with the optocoupler since you are tying your -HV to the optocoupler transistor's emitter and the PIC's common. Just use a NPN transistor and base resistor. But, if you are looking for isolation, you need to break the connection between the emitter and the PIC. And, it would be wise to make sure the 15v supply is also isolated from the PIC circuit.

ken
 

ccurtis

Well-Known Member
The varistor has me wondering. Let's say the varistor conducts because its trip voltage is exceeded, for whatever, if any, reason. If it is exceeded by more than the maximum gate voltage of the FET then it seems to me the FET is in trouble.
 

hhhsssmmm

New Member
okay I get your point

I will definitely want to keep the PIC isolated from the HT side. I hope this also solves the voltage exceeding problem for the DB3 DIAC (varistor).

Therefore I have redone the circuit diagram. It is enclosed with this reply.

As you can see that this time I have removed the 15V regulator IC and instead placed a 15V zener diode from the +ve DC 230V. The PIC is now isolated completely from the HT side.

Will this provide me with the 15V to turn on the MOSFET gate? Im a little confused on the resistor R2. Does it need to be there? If I take it out will I still have 230V DC across the DRIAN and SOURCE of the MOSFET?

thankyou

haseeb
 

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KMoffett

Well-Known Member
Haseeb,

Where did you get this circuit or design idea? There too many things wrong. I am not close to an expert in this area, though I have built similar control circuits. So, I feel that I can not continue to try to correct even the faults that are obvious to me. I do not want to place you a risk. Sorry.

Ken
 

ccurtis

Well-Known Member
That looks worse yet. I would like to know where the circuit came from, too. I don't understand why the diac is there in the first place. My inclination to is get rid of it.
 

hhhsssmmm

New Member
okay people....

the diac is now also gone....please see the new diagram enclosed.

this circuit is actually for the dimmming of 12V halogen lamps via transformer couple. But the transformer on the HT side will be an electronic transformer.

Because these transformers are capacitive load in nature (V lags I)...therefore....for these types of transfromers, i have read on the internet that you need a reverse phase dimmer to achieve flicker free dimming....and one achieves this via Power MOSFET or IGBT etc....essentially a transistor....not a TRIAC. In reverse phase dimming you turn on at the zero crossing and turn off in between the phase set according to your desired dim level.

I already have a PIC based leadiing edge dimmer (TRIAC based) that works perfectly with wire wound transformers for the dimming of 12V halogen lamps.....but i observed that with leading edge dimmers, Electronic transformer loads are not good to control.....since leading edge dimmers are good for pure inductive loads (V leads I) such as wire wound transformers.

Obviously non of this is a problem to mankind had all loads been pure resistive in nature where V & I are in phase....but unfortunately thats not the case and im having to deal with the V & I leading and lagging problems....

Sure enough I can get away with this headache by doing a cheap fix (on my leading edge dimmer) such as putting a resistive load ballast (5W to 100W light bulb) across the load. This brings V & I in phase....but the resistive load is a cheap (poor mans) fix and not a professional approach.....that is why the dimming logic has to be altered completely.

So now please can you help?

thank you
haseeb
 

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hhhsssmmm

New Member
Hello and thank you for the diagram:)

My questions now are.....


1) I wish to avoid using another 15V DC supply, either via regulator IC or power supply etc. So can I use a high power 15V zener connected across the +ve 230DCV and the collector of the opto transistor?

2) Do you or anyone else know that can I also get dimming performance from a reverse phase dimmer for a WIRE wound transformer?

Thank you
Haseeb
 

duffy

Well-Known Member
The only transformers I know of that aren't wire wound are piezo transformers, and that's probably a little more exotic than you are working with.
 

KMoffett

Well-Known Member
I'm wondering if the "electronic transformer" is actually a switch mode power supply. A phase controlled dimmer in front of that wouldn't be a good idea. And dimming halogen lamps will darken the inside of the envelope, and shorten their lives.

Ken
 
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duffy

Well-Known Member
Yeah, halogens need that high operating temp to deposit metal back on the filament. Putting a lamp dimmer on a switching regulator is just a bad idea.
 

andy257

Member
I dont mean to hijack this thread but what is an "Electronic Transformer"?
 

ccurtis

Well-Known Member
1) I wish to avoid using another 15V DC supply, either via regulator IC or power supply etc. So can I use a high power 15V zener connected across the +ve 230DCV and the collector of the opto transistor?

Judging from the datasheet for the FET, you can get by with the 5V supply, you have already, in place of the 15V supply. You can't connect the 15v zener as you describe because the FET's source is not referenced to the neutral of the mains. Side note: I am assuming that your +5v supply is derived from a transformer connected to the mains, which isolates its return from the mains, also. If that is not the case, the circuit will not work.

2) Do you or anyone else know that can I also get dimming performance from a reverse phase dimmer for a WIRE wound transformer?

I'm sorry. I don't follow the question.

With regards to the halogen also, at less than 180 deg phase output, the halogen sees pulsating DC (a single polarity) with the circuit. I don't know how halogens hold up to that.
 
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