LNK419 33W driver
hello,i am using lnk419 driver ic for getting 33W output but i am not getting desired output i am attaching schematic of driver please suggest me where i am going wrong.the changes i have made is that i have removed R20 and short base and emitter of Q2 .by doing so only i was getting some output. problem is we are getting very high voltage that is of 120 v instead of 48v and so our led output is fluctuating and instead of R14 and R17 we have used preset of 100k and by reducing its value we getting desired current but not desired voltage so please kindly suggest me what can be done.
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we are using LED load only and we are getting desired output current . But by giving ground to Base of transistor Q2.which is not logical true .
If the load is LED, the output voltage should be fixed by the LED itself.
The Q2 is the part of latching over voltage protection circuit by pulling down bypass pin voltage in the open load condition.
yes . but our problem is that we are getting very high voltage about 120 V on
no-load condition when we are giving ground to base of Q2.and if we dont give ground to base of Q2 then we are not getting any voltage at output or at bias winding of x'mer neither at load condition nor at no-load condition .
please kindly help me out what can be done.
awaiting for your immediate reply
It seems to me that the OVP threshold level is too low.
It is necessary to incrase the OVP sensing zener voltage,VR1, higher until the OVP circuit will not be triggered in normal operating condition.
ok. i tried increasing my zener vpltage upto 47V but still facing the same problem can you please suggest me upto what level should i keep my zener voltage .
thank you
accepting your fast reply
As I mentioned in my previous reply, you need to increase the zener voltage until OVP will not be triggered in normal operating condition.
ok, thank you will try doing that.
hello,i tried as u said ,i have increased zener voltage upto 56V,but still facing the same problem,we are still not getting ovp i.e we are getting output only by giving ground to base of Q2.
please give some immediate solution....
How about 100 V zener?
What is the bias voltage when Q2 is shorted?
Could you attach your schematic again?
the voltage across collector and base is 5.8V when we short base and emitter of Q2
i am hereby attaching my schematic.please give me some solutions we are still not getting
we are getting output voltage of above 120v when base and emitter of Q2 is short on no load condition.and if we are not shorting base and emitter we are getting 0V on no-load and on-load condition.what should be done?where are we doing mistake?
Now by using zener diode of 120V we are getting 0v output.
Now by using 120V zener diode we are getting upto 150V output on no load instead of 48V that also after shorting base and emitter of Q2.else we are getting only 3V output on no-load
please can i get your num or something so that i can have fast communictaion.as i am facing many problems.
• Desired Output voltage 48V and 700mA
Results after implementing the given design
• Voltage at R2,D2,C4 is 240-315Vdc
• Voltage at D of LNK419 is 240-315Vdc
• Voltage at V of LNK419 is 14V
Output Voltages when Zener voltage =33V and R20 is removed
• Voltage at output on no-load is 0V when base and emitter of Q2 is not shorted
• Voltage at output on no-load is upto 150V when base and emitter of Q2 is shorted
Output Voltages when Zener voltage =75V and R20 is removed
• Voltage at output on no-load is 0V when base and emitter of Q2 is not shorted
• Voltage at output on no-load is 120V to 150V when base and emitter of Q2 is shorted
• VCE of Q2 and Q1 is 5.8 V when base and emitter of Q2 is shorted else it is 0V
Output Voltages when Zener voltage =120V and R20 is removed
• Voltage at output on no-load is 2-3V when base and emitter of Q2 is not shorted
• Voltage at output on no-load is 120V-150V when base and emitter of Q2 is shorted
• VCE of Q2 and Q1 is 5.8 V when base and emitter of Q2 is shorted else it is 0V
What is the bias voltage, V at C5, when Q2 base shorted?
What is the voltage on C6 when Q2 is shorted?
it was 5.8V
Does frequency affects the output in this circuit and if yes then in what way?
i mean voltage at c5 and c6 is 5.8v
The minimum bias voltage should be higher than 15V.
5.8V at C5 and C6 is too low.
It is necessary to increase the bias winding of the transformer.
ok.thank u
Our circuit is now running succesfully by mounting components on another pcb as told by PI techinical support.I just wanted to know that how mounting of components on appropriate pcb affects the output and circuit.
The load should be either LED itself or CV mode elctronic load.
LinkSwitch-PH is the constant current controller, not constant voltage controller.