10W LED Driver misbehaves

1) Try disabling the OVP (remove D4) to see if it goes away
2) When this is happening, pls. observe the Drain voltage (to see what kind of swtching it does), and the bias voltage (C6).

Disabling D4 did not help.

I suspect C9

If I use a 47uF/16V, percentage of problems reduce drastically... Instead if I use a 47uF/63V, I see the problem is more prominent.

I also noticed that by physically discharging the C9 cap and then turning back ON brings the LEDs ON again.

What is so critical about this capacitor? What is the series resistor (R8) for?

Thanks
Roopesh

Ref: http://www.powerint.com/sites/default/files/product-docs/tophx_family_datasheet.pdf

CONTROL (C) Pin Operation

When the CONTROL pin voltage VC reaches approximately 5.8 V, the control circuitry is activated and the soft-start begins.

When I start, the voltage at this control pin is far less than 5.8V... the voltage is very slowly increasing and it takes not less than 3 to 4min to reach around 5.8V before the internal control circuitry is activated...

But why is this happening???

The DC voltage at the drain terminal is more than 300V ...

When rectified DC high voltage is applied to the DRAIN pin during start-up, the MOSFET is initially off, and the CONTROL pin capacitor is charged through a switched high voltage current source connected internally between the DRAIN and CONTROL pins.

Is it the internal current source not pumping enough current which is why the capacitor charging so slow???

Do you have any instruments connected between to the C pin when it takes minutes to re-start? When you say it takes several minutes to re-start, is this with the AC power connected?

When you short C9 and it re-starts, that means the device is latched off via the V pin latch feature. If zener D4 is disconnected and it does this, it could be latching off due to noise - try placing a 10 pF capacitor between the V pin and the S pin. This capacitor must have short prongs, and is directly connected to the V and S pins.

Can you post a pdf or gif of the layout, and/or a photo of the prototype?

It is possible that the reason the PSU shuts down after running for several minutes, is that when your output diode D2 gets hot, its reverse recovery may become so severe that the Drain current initial turn-on spike is causing the TOP-HX to prematurely terminate its pulses and so it shuts down. To test this, heat the output diode with a small-nozzled heat gun and see if you can induce it to shut down. In any case, the FR series diodes are generally too low performance for the output diode. Pls. try using a UF series diode.

Likewise, for D3 the BAV21 is a better, lower cost choice.

I have slightly different situation here. This LED driver has never shutdown by itself... it keeps working fine continuously... Problem is observed only when I intentionally turn OFF and switch it back ON immediately. So, I guess we can rule out possibility of D2 getting hot. However, I have now replaced FR Diodes with UF4007 diodes.

After Off and then ON, and the LEDs don't come ON, I use my Fluke 179 DMM to monitor the behavior across C9 (not C pin). I see that the voltage is much below 5.8V. The LEDs come ON only when this voltage exceeds 5.8V. (As I said earlier, it takes 3 -4mins for the voltage across C9 to reach 5.8V)

Introducing a 10pF cap between V pin and S pin has not helped.

Yes, When I say it takes several minutes to re-start,it is this with the AC power connected...

Anymore suggestions?

here are the attachments.

If during failure there is still some output voltage then try looking at drain switching current and find out what amplitude of switching current is. Also check to see if supply is in auto-restart - that is burst cycles of pulse followed by long off interval. If auto-restart is ocurring you may be in power limit I would shorting out resistor from X-pin pin to ground. Also try increasing value of output current sense resistors R7 and/or R13 to reduced output current somewhat to see if problem goes away.
Check to see if problem is L-pin related. Remove D4 and see if problem goes away. If it does you may need to increase the value of zener and then recheck OVP function. If you do not need OVP then simply remove D4 permanently. Since this is an LED driver operating in CC the voltage sense clamp on seconndary already gives you protection so it is debatable whehter you even need this circuit. But first verify this is problem.

If during failure there is still some output voltage then try looking at drain switching current and find out what amplitude of switching current is.

There is no Drain Voltage at all. May be because the C pin voltage is much below 5.8V

Also check to see if supply is in auto-restart - that is burst cycles of pulse followed by long off interval. If auto-restart is ocurring you may be in power limit I would shorting out resistor from X-pin pin to ground. Also try increasing value of output current sense resistors R7 and/or R13 to reduced output current somewhat to see if problem goes away.

The preset problem is not related to this... however, I had this problem earlier and was solved once I changed R7 and R13 Values to 6.8E and 2.2E respectively

Check to see if problem is L-pin related.

Sorry, please elaborate

Remove D4 and see if problem goes away. If it does you may need to increase the value of zener and then recheck OVP function.

Removing D4 is not solving the problem

Since this is an LED driver operating in CC the voltage sense clamp on seconndary already gives you protection so it is debatable whehter you even need this circuit. But first verify this is problem.

I will consider this once the present problem is resolved.

hello rupesh, r u placed in india, i can support you for free ..pls let me know if you wish.Mail me at prasunkuls9@gmail.com anyways, try changing D4 as 12V zener + 15V zener must work..

hello rupesh, r u placed in india, i can support you for free ..pls let me know if you wish.Mail me at prasunkuls9@gmail.com anyways, try changing D4 as 12V zener + 15V zener must work..