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DER-865 Multiple Load Configuration

Posted by: gid204 on 07/21/2021


I'm trying to find a way to configure DER-865 with multiple load switch and dimming capabilities. Would anyone be able to assist in recommendations? Is there a way to do it without multiple LNK Modules.



Submitted by PI-Crumb on 07/22/2021


Here's an idea. Use one DER-865 to control the AC line (phase cut) for dimming. Hardwire external on/off or slider switches to other GPIO pins of the BLE module so that any changes to these switches can still control the main switch.

It is also possible to wirelessly transmit the signal just like how the DER is able to communicate with a phone. For that, it will require another BLE module that can pair with the main switch. This module does not have to be connected to the AC line so you don't need and LNKSwitch. You can use a battery to power this BLE if you want. In this approach, you may need to use a BLE mesh type of communication to be able to connect multiple BLEs. You can also try Zigbee.

Submitted by gid204 on 07/22/2021

Hi thanks for your response. I feel I didn't word my original question very well so I'll give it another go.

I want to implement this design to control on/off and dim 4 separate mains loads (lights). How would I connect these 4 loads to the Z2 pin of the LNK modules for zero cross detection on all four loads?

I’ve attached an image of my own solution based off a 2 load system, if you could provide feedback as to whether you think it this would work.



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3D7EE289-9039-4A6B-99B1-3061E83B2A2F.jpeg 239.84 KB


Thanks for the clarification. While the dimmer design can dim multiple loads simultaneously, individual dimming would require separate switch element (triac or Mosfet) and would require separate ZCD control.


My design currently incorporates 4 seperate switching elements (4 pairs of back to back MOSFETs).

I have connected each load to Z1 of the LNK3302 as show in my image attached in my previous comment.

The ZCD output (Q7 Drain) briefly turns off and this short pulse is what provides ZCD to the MCU. Am I correct in saying no matter what combination of the four loads I attach, I will only need a single ZCD output connected to the MCU for the zero cross detection.

I.e do I need a seperate ZCD signal for each load? - I don't I do....


hi. In 2-wire config, the ZCD is connected across the back to back FETs. When these FETs turn ON, then ZCD signal will go low. This is different in 3-wire config. Because the line and Neutral are stable, the ZCD will always work every half-line cycle.

In 2-wire, you need separate ZCD because if not, then you can't control each load individually. But if you dim the load simulataneously, then a single ZCD will suffice. However, if that is the case, you don't need separate FETs unless it's just to individually turn ON/OFF each load but you dim them simultaneously. Then a single ZCD could be fine.

I hope I was able to answer your questions. If not, please give a more detailed description on how each load will be turned ON/dimmed. Thanks.



Submitted by gid204 on 08/05/2021


Thank you for all your help so far!

Each load will be turned on/dimmed, separate from each other. So I am trying to work out the best way to configure this while keeping low load capabilities of no-neutral connection of DER-865.

Currently I have my setup configured as per the block diagram attached "Block Diagram_0.PNG". My main concerns are:

1. Do the common Source pins of each pair of switching/dimming MOSFET need to have separate references from one another?
I.e from my diagram, does GND1_ISO and GND2_ISO need to be separate or can they be combined?

2. If the above they need to be separate, is there any way to incorporate the discrete driving circuit while maintaining this?

3. The ZCD Output signal coming from the LNK3302D module should go low when either load 1 or load 2 is turned on (or both). Does this mean I will only need a single ZCD signal or have I got this completely wrong? If so can you recommend how I can incorporate two completely separate dimming circuits using a single LNK3302D module.

I'm not concerned about having a potentiometer. I plan on having just a single button per load, and configuring long/short presses via software to activate the dimming.


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Interesting configuration. I will have to get back on you after analyzing the circuit further. I assume it will be dimmed in trailing-mode only.

If possible would there be a way to send a private message (email perhaps) so I can share my schematic in a private manner?


Submitted by PI-Crumb on 08/09/2021


I would advise that you get in touch with the local PI FAE/Sales in your region if you want to share the schematic in private. We currently don't have a dedicated group of engineers that can support a more in-depth technical discussion with our customers. However, since the DER and the device (TNZ) are new, our FAEs may not have the experience to respond to your questions asap.

At this point, I think the schematic block you provided is good enough. 

To answer your previous questions, on item 1, a separate GND is needed. FETs have body diodes and that could provide leakage paths for the current to flow and will make it more difficult to control each branch independently. For item 2, I don't know. For item 3, yes, the ZCD signal will go low when any load is tuned ON. However, I advise that you make a timing diagram and/or simulation to determine what will happen to the ZCD at the positive and negative line cycle, and assuming you turn ON/OFF the load. I think your approach is feasible, but it could require some tricks on the software to be able to handle the varying logic seen by the ZCD as you dim and as the line cycle changes.

If you are going to simulate the circuit, you can just bypass Z1 and Z2 (treat it like a short circuit).

Thanks for all your help. I am going to have my design fabricated for testing and verification. Unfortunately sales aren’t responding to my emails regarding acquiring samples. I’ll have to order the LNK modules from my distributor which have a lead time of about 4 months.

Thanks again!