LNK410 flickering on dim & work without clampling

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Hi, everybody

I desing on PI a power supply for 28v output 2.85A, with follow results

1.- with blocking diode connected have 5v output (clamping voltage)not work
2.- with diode disconnected have 24v 2.5A pretty close, but working nice
3.- with dimmer (triac)& (no clamping) its flickering and have a loud buzz noise, erratic from 100% to 15% then turn off.
 
I need a help to see what is going on, a do something to fix the troubles, the most wear is that is working without clamping.
without load reading is 70V ??
 
Proyect included
 

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LinkSwitch-PH_EE4028.uds370.5 KB

Hi

At first sight, the blocking diode voltage is too low (120 V). try blocking diode around 180 volts.

70 volts no load???! maybe there is something wrong with feedback.

if you still had a problem let us know. tnx

Hi,

I been working with this changing diferents diode volts, I start with 180 and output goes dowm, same with 200v.

I change the D1 FR257 for the IN4937, and works with the 120v blocking diode, but at no load follow be high output(65v)

with same conditions I change de R16 (118kOhm)for a 195kohm, with better regulation ( to comment, to get this I put a  variable resistor), question, is possible to use the feedback as dimmig way?

But the output at no load is being high(60v), is the output regulation going to be needed?

thank in advance.

Hi,

LNK-PH is CC only driver. The OVP handling is done by sensing the bias voltage and pulling down the FB to trigger auto-restart. I attached the schematic taken from one of LNK-PH DERs (DER-278) and you'll find the extra circuit for OVP (D7 to Q1). VR2 sets the OVP point based on the bias voltage.

Modulating the feebdack resistor does impact the output current setpoint so in that sense it can be used in dimming. However, take note of the usable range (between 20 uA to 200 uA) in order to prevent auto-restart or pulse-skipping.

For the blocking diode, 120V diode is too low. Try 180V to 200V. You can even remove the R-C. Please refer to the attached schematic as reference.

 

 

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