LM3450 PWM only

Andrew: Can you show us your schematic? David Zhang

Hi David, I am using the LM3450AEV230V30/NOPB evaluation kit.
I have removed the Buck .
but would like to remove the flyback section.
I am only interested in the PWM decoder section.

Andrew:
It is an overkill if you just want to use LM3450 for the PWM decoding. You can use LM555 timer to do the job.
David Zhang

Hi David, As in converting a phase cut triac signal to PWM?
If you have a circuit please send it.
Thanks

Andrew:
You can use the angle sense circuit of LM3445. It is much simpler than LM3450.
David Zhang

Hi David, Ok I will look into this. Thank you.
The LM3450 has a 500Hz PWM output which is preferable.
Is it possible to run the LM3450 without the flyback circuit? or am I wasting my time?

Andrew:
LM3445 PWM signal is 5.9KHz. Yes, you can run LM3450 without the flyback circuit. But you don't want to design a product using LM3450 as a triac angle decoder. It is too complicated and too expensive for just a decoder.
David zhang

Hi David, Is the LM3445 PWM signal is a noisy or clean? 5.9KHz is pretty high I would have to reduce this.
I will look at the LM3445. Thanks
But could you advise on how I would make the LM3450 work? I have the hardware already.

Hi David, Have had a look at the LM3445 and the ASNS is 100Hz @240V and follows the phase cut signal. 

Is there a chance I can receive help with the LM3450?

Andrew:
If you just want to use the angle sense function of LM3450, you can power LM3450 VCC with a 15V DC. The circuit does not shut down unless VCC reaches under voltage.
David Zhang

Hi David, Using datasheet SNVA485B is there any other sections of the circuit that I need to connect? I am following Fig16 dimmer decoding circuit. What else do I need connected.
Thanks

Andrew

Andrew:
Besides the circuits in Figure 16, you also need the bias circuit to provide 15VDC for VCC.
David Zhang

Andrew:
Sorry. One more connection you need to make. The FB pin can not be floating. It needs to be connected to Vref through a resistor divider to set voltage to 2.5V.
David Zhang

Hi David, Are you not meaning Vadj to Vref via resistor divider? FB to GND via resistor.
If possible could you send me a schematic .
Andrew

Andrew:
I suggest you connect FB pin to 2.5V. The easiest way to get 2.5V is from Vref using a resistor divdier.
David Zhang

hello, i am design traic dimming decoder so, i need only PWM signal in output , please halp me to give the schematic sand me schematic on vaibhavpatel46@gmail.com

Hello,

I just wanted to let you know I have forwarded this to the best person but many people are out on vacation at the moment. Please have some patience and hopefully you will have an answer next week.

Regards,

Clint

Hello,

I can try and help you figure this out. How are you using the LM3450, as a power factor controller from rectified AC? What are you doing with the dimming pins on the part? I see some of the history of this post, is this still relevant? Are you just using this as a triac dimming decoder?

Thanks,

Yes I would like to use this as a triac dimming decoder.
I just require it to produce a PWM signal.
It does have a PWM output but I couldnt work out how to run the IC without the the secondary circuit.

I had given up as damaged two dev boards in the process.

If your confident that this can be done I will have another go.

Thanks for your help.

Hello Andrew,

If you are not using any of the controller it seems it should be fairly straight forward.  It will need VCC (possibly derived from rectified AC via a pass MOSFET if Hold is needed), a resistor divider from rectified AC for detecting the triac duty cycle, Vadj tied to Vref if not adjusting phase dimming range from default and possibly Isns and Hold (connected to the VCC generating MOSFET source) if there is enough EMI capacitance holding up the voltage causing incorrect decoding and the associated FLT1 and FLT2 components depending on the information you are trying to get.

Perhaps, if you are trying to use the EVM, something is not getting disconnected that needs to be disconnected in your situation.

Are you using this information to power another driver that controls dimming?

Thanks,