LM3445: Schematic confirmation

Hello Timsen,

The schematic is feasible.  There are no values and I don't know your LED voltage or current.  The schematic you have is the same as the datasheet.  I would look at LM3445EVM-695.  This includes EMI filtering, triac damping circuit as well as loading circuits to keep the triac from misfiring.  Interfacing to leading edge and trailing edge dimmers is difficult and may require some circuit adjustments.  There are many different triac and trailing edge dimmers, the behavior of them can be quite different.

Best Regards,

Dear Irwin：

       Q1: Could you please explain the functions of each part of the circuit in the schematic diagram of lm3445evm-695?

Q2: I need to meet the requirements of the front cut dimmer and rear cut dimmer, you say"may require some circuit adjustments". Can you provide me with circuit reference?

Thank you!

Hello Timsen,

The circuit connecting to the dim pin creates additional loading as the circuit dims deep.  The triac dimmer needs a certain current to maintain on state, this helps with this.  The capacitors from rectified AC to GND make this worse since they are supplying current as the voltage falls.

The Q4 circuit adds loading when the valley fill capacitor start taking over since current will not be from the input.  Again this is to create loading for the triac dimmer when the valley fill capacitors take over the source to the LM3445 as well as helping to discharge the capacitors from rectified AC to ground.

The Q2 circuit adds loading when the falling edge of the rectified AC has higher dv/dt on the falling edge.  This circuit is for reverse phase/trailing edge dimmers.  This helps discharge the capacitors to prevent the angle sense from becoming to wide (this becomes a positive feedback mechanism which causes the LED light output to oscillate).

It becomes a balance of minimizing loading (efficiency hit) versus operating with a wide variety of dimmers.  Watching current and voltage output of the dimmer when running the circuit will show if it is working correct or not.

Best Regards,