PMP5732 based design

Hello,

Is there any reason that you want to add that capacitor?

Will the capacitor be added between the EAOUT pin and ground?

Regards,

Victor

Hello,

The capacitor will be added between the EAOUT pin and Ground - YES.

Reason: There is an increase in input power factor and decrease in ATHD

The below values are as a result of adding a capacitor for the output – 37V @ 1.4A

Due to that above values whether any effect on the performance of driver.

Regards,

Rajasekaran         

Hello Rajasekaran,

If you are not using features like fast dimming, it is fine to add a capacitor to EAOUT pin as it will lower the slop which will increase the PF and lower the THD. But make sure the capacitor value is small. It may false trigger the OVP if the EAOUT pin is not pulled low fast enough (pg.8 in data sheet). I think the capacitor value you use should be fine.

Regards,

Victor

Hello,

Thanks for your solution provided to us.

Regards,

Rajasekaran

Hello Victor,

1. Please suggest a formula for calculating the RC snubber value for the secondary diode.

2. When we using the same design for 36V/1A, the power factor slightly reduces as well as current harmonics increases. how to recify it.

Hello Rajasekaran,

 1. Which is the secondary diode you are talking about, D8?

 2. Since your output power is reduced more than 40%, I think the transformer will have some impact on the PF and THD. But I need to check that.

 Regards,

Victor

Hello Victor,

1. Secondary Diode - D5 ( MUR1020CT)

2. We planned to use Pi filter in the output section instead of capacitor filter. Please suggest the Pi filter values with the calculations. ( Pi filter - C, L, C )

Hello Victor,

I am awaiting for your reply.

Hello Rajasekaran,

For both snubber and Pi filter, you should know what frequency you want to remove.

1. Snubber, you can try with 10nF capacitor with a hundred Ohm resistor to compare the result before and after you added the snubber. Then base on the result to adjust the resistor value. But be aware that a snubber will reduce efficiency.
2. Pi filter, f=1/(2*pi*(L*C)^0.5). Maybe you can start with 1uH with 100uF and then adjust the values after you compare the result.

However, designing a snubber or Pi filter that fits for your system will consume a lot of time in doing experiment.

Best regards,

Victor

Hello Victor,

Thanks for your solution.

I will try it.

2. Since your output power is reduced more than 40%, I think the transformer will have some impact on the PF and THD. But I need to check that.

Dear Victor,

Awaiting for your reply.

Normally, higher power will have better PF and THD. That’s why the PF reduces and THD increase after you change your output to 36V@1A. But I think it is OK as long as the PF and THD are still in your requirement as the change is not significant.

Well, you can adjust the input EMI filter and transformer to get a slight enhancement in PF and THD if you insist. As a trade-off, it may affect the EMI of your circuit.

Hello Victor,

We have two Queries.

1. Please provide the magnetic details for 36V / 700mA using the same circuit. ( Because by using the same magnetic design if reducing the current the ATHD and PF are reducing).

2. Can we use the same circuit for 36V / 1.75A by increasing the transformer size and the Mosfet (8A, 800V, TO-220FP).

Thanks & Regards,

Rajasekaran.S

Hello Victor,

Please help us.

Awaiting for your reply.

Thanks & Regards,

Rajasekaran.S