TPS92314 PMP4448

Hello,

I am not an expert with this part.  The compensation capacitor on the EVM is 33 uF.  This is causing the turn on delay.  The datasheet has no information on how to calculate the value, it states that in most applications 4.7 uF is acceptable.  The larger capacitor probably has to do with universal input on the EVM.  They can try and reduce the compensation capacitor but need to verify it is stable for all operating ranges they desire.

Thanks,

Irwin

Hi PAN-M,

You can try to reduce the value of C4 and R6+R7, such as 10 uF, 50 kohm + 50 kohm.

Best Regards,

Jason

Hi PAN-M,

Before changing the R10, what is the max output voltage? I don't think R10 effects the ouput  too much.

This is a constant circuit and the max output voltage is set by Vcc-OVP or Vzcd-OVP. Cause Vcc-OVP is 38 V ( max ),  we cannot get 52 V with this circuit. 

Fortunately, there is another solution. Please refer to  PMP4362.

Regards,

Jason

PAN-M,

You can set C4 a smaller value ( try 4.7uF or 2.2uF ), but you need to make sure the circuit can startup successfully. The power stored in C4 supplies tps92314 during startup.
Also, you can continue to reduce R7 + R6, but you need to evaluate the power loss, it effects the efficiency.

Regards,
Jason

You can also add a start-up circuit similar to the drawing below.  Many of the triac dimmable EVMs or PMPs have these circuits.  I would also disable the start-up MOSFET when the supply powers up otherwise the IC bias will always be from the start-up circuit.  This will charge the bias capacitors much quicker than possible with an RC.  At 240 VAC input if the resistors are a total of 100 Kohms it will dissipate 0.4 watts continuous, an efficiency drop of 2-3% at your power level.  If this is for triac dimming C4 needs to be large enough to hold up during the dimmer off-time or it can be separated with a diode so it does not have to charge at first turn on leaving a smaller capacitor in place of C4 for faster turn on.

This also needs to be tested when turning on when dimmed very low.  It takes longer for the supply to come up when deep dimming and may not start if C4 is too small.  If you need a circuit with a MOSFET for quick turn on I can come up with something.

The circuit below is cut from an older LM3445 design:

It didn't paste the circuit so you can see it here:

www.ti.com/.../snva429c.pdf

The circuit is Q1 and the components around it.

Thank you for support, Jason.

If adding the resistance in attached file, isn't it possible to increase the LED voltage?

TPS92314nonisoLED_2.pptx

Regards,
PAN-M

Hi,

That isn't a good way, cause there is power shipping on this link. But you can try to increase R5, 510 ohm may be a good start point.

There is a reference design, PM7695, 48V/140mA. Please refer the attached.

PMP7695.pdf

Also, it's needed to modify R8 & R9, and increase the voltage tolerance of C11.

Regards,
Jason