dimmer probelm urgent pls help

[takbbb]

my mcu drive the above dimmer in 12Vac

however the gate signal is greatly affect by the triac

and it's lost in control .

The gate and the MT1 signal are so low in impediance (abt 50-100 ohm)
and the MT1 signal feedback on the triac gate termianl. . .

how to solve it?
thx!!

p.S. if R3 is not added, the 2N3906 will break down
for unknown reason . . .




Added after 8 minutes:

the link is the waveform

the above is measured at triac gate signal !! which completely different from my mcu waveform in below one

the below is from my mcu leg output without tirac

so do any can help me ?

thx a lot

 

[FvM]

if R3 is not added, the 2N3906 will break down for unknown reason . . .

Look sharp and write obvious instead of unknown.

Actually, you have two options:
1. Connect DC power supply GND with Triac A1 terminal. Requires either an isolated supply or rearrangement of the AC load.

2. Use an optotriac for triggering

If you don't see the problem, study known operational example circuits and check, how they connected DC supply and AC circuit.

 

[takbbb]

thx for ur reply

but can you elaborate more ?

1)"Look sharp and write obvious instead of unknown."
Why say so?

2)Connect DC power supply GND with Triac A1 terminal. Requires either an isolated supply or rearrangement of the AC load

why do that>?

 

[FvM]

May I answer with counterquestion? How did you connect your DC supply with the AC power?
The connection isn't shown in your schematic. What's the return path for the current through R3?

 

[takbbb]

thx Fvm again~

the ac and dc connection are on above
i draw most of it as i guess you know the main principle

==>What's the return path for the current through R3?
thur R2 ?

My main reference is on that **broken link removed**
of Figure 2

the main differemce is that the ref use MCU to direct fire the triac

 

[FvM]

So you basically have connected DC GND to AC L.

In this case, the said solution of connecting triac A1 to DC GND can work. The AC load has to be connected between AC N and triac A2 instead (move up in the schematic).

 

[takbbb]

thx i 'll try tmr and i'll post the result and problem if any ~

thx for help~

 

[takbbb]

then why R3 is needed to add ?

 

[FvM]

R3 is required for current limiting, also with correct DC ground to A1 connection.

 

[takbbb]

halo again

i try the result and post in below

purple line -> measure @ triac gate /gnd
yellow -> my mcu output to gate
blue -> voltage across the triac

it seems that half of ac have prbolem (blue line)
the positive half of ac was on (which should be off? that is when my mcu leg is low
there should be ac waveform

however the positive was missing that also imply the driver part still have probelm!??


and the waveform @ gate terminal is very stange


pls advice if anyone can help~

 

[pranam77]

hai Takbb, I had posted a triac driver in may old post. "&highlight=" The circuit is of a light chaser. But consider the MCU is used as an dimmer in your case. Triac driving circuit may help you. But i strongly think you need to use a separate regulated Power with 7805 for your MCU. and use the triac as in the link provided. Hope it helps.