Strange behaviour of modded TC421

Zacksi

New member
Hello there, I need some help and will appreciate if someone could give me a hand to understand an issue with mode TC421 that I have.
So I have this "standard" configuration of TC421 + LDD700H to control 3W Leds . I'm using 5 of the MOSFET's gates and there is an oukward situation:
- if 4 of the 5 channels (no matter which) are set to 100% everything works fine. As soon as the 5th channel is set to something above"¦ let's say 5 %, the intensity of all channels is suddenly decreased to something like 2-3% of their capacity.
The power supply for the Leds and the TC421 is 350W MeanWell one connected with a bulk convertor to supply 12v to TC421
- The other issue I saw is - when a channel is enabled on TC421's site but there is no load on it(not connected to led series) all the other enabled/connected channels start flickering and the intensity is again something like 2-3 % of their capacity, no matter what is set on the TC421.

Do you have any ideas what could cause that? I have additionally put 10K resistors on the PCB connected to the V- input and the PWM in order to avoid constant on of the LDDs.
 

Zacksi

New member
Unfortunately not. No matter if there is 1 or multiple LDD per channel the behavior is the same.
So what I did is to leave a LDD with no load on one of the channels which I will never use. On some of the other channels I put 2 ldds and that works flawlessly. I really have no idea what could be the reason.
 

oreo57

Active member
Unfortunately not. No matter if there is 1 or multiple LDD per channel the behavior is the same.
So what I did is to leave a LDD with no load on one of the channels which I will never use. On some of the other channels I put 2 ldds and that works flawlessly. I really have no idea what could be the reason.

Really odd. I'm not an electronic geek by any means but ran an old tc-420 for quite some time.

A couple of times I had weird channel issues.. not like yours but sort of unexplained.
I usually just re-soldered the gate wire.
Or just fiddled and it worked again (hard to explain)
This odd behavior was only on one channel though. Didn't impact any of the others if I remember correctly. TC-420 was retired for a bluefish mini eventually.

Things I'd check:
Make sure you are getting the 5v (at 100%) on the gate wires.
It's possible it's 3.3v but those are the only 2 choices.

Could be a current issue I suppose.. either on the buck converter or to the gate.

Not sure how your "fix" actually works.

Power supplies and I suppose drivers can go into "limp mode" where the lights pulse if there is a short or another "anomaly".

Maybe just a faulty 421.
 
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