High voltage DC-DC converter power supply filtering

[pavjayt]

Hello,

I am designing a PCB which holds components such as a DC-DC high voltage converter (12VDC to [0-500VDC]) alongside a dual output DC converter which run off the same input supply.

The voltage outputs from all there are used to drive a sensitive equipment like an APD. I would like to design this PCB so that I can minimize any noise at the input and output of these converters. I added that components that the high votlage converter manufacturer has suggested using their evaluation board, but they also suggest to add extra filtering to improve performance.

Any suggestions?

thanks

 

[crutschow]

I would follow the manufacturer's recommendations for board layout, since the layout is critical to minimizing noise. If you need really low noise you may need to add an LC output filter and/or perhaps common-mode chokes at the input and output to reduce ground noise.

 

[pavjayt]

Thanks for your reply. Actually I am not sure what values I have to use to implement/add those components to the schematic. Do you have any recommendations on that?

 

[crutschow]

Do you know the switching frequency of the DC-DC converter and what maximum level of noise you can tolerate?

 

[pavjayt]

Do you know the switching frequency of the DC-DC converter and what maximum level of noise you can tolerate?

The datasheet for the power supply states thats it operates at 100-250KHz frequency (CA05N). There is no specifications on noise level tolerance in the PAD spec sheet. But I would like to keep it as reasonable as possible without going extreme on filtering.

thanks

 

[pavjayt]

I am thinking of using this series chokes, but not sure what value I should pick for input and output. Any suggestions or better options?

 

[crutschow]

I am thinking of using this series chokes, but not sure what value I should pick for input and output. Any suggestions or better options?

Those are dual winding common-mode chokes with one winding in the power line and the other in the common line. They are intended to minimize common-mode ground noise and do not reduce ripple voltage when connected as a common-mode choke.

 

[pavjayt]

Those are dual winding common-mode chokes with one winding in the power line and the other in the common line. They are intended to minimize common-mode ground noise and do not reduce ripple voltage when connected as a common-mode choke.

Thanks for your reply. That's good to know that they are not suited for our application. Do you recommend any other types from a good manufacturer?

 

[crutschow]

Thanks for your reply. That's good to know that they are not suited for our application. Do you recommend any other types from a good manufacturer?

Coilcraft and Panasonic are two good manufacturers I know of.

 

[pavjayt]

Coilcraft and Panasonic are two good manufacturers I know of.

Do you have any recommendations on the Part#s (values) of chokes that I can use on the input and output side of my HV power supply S1 in my schematic along with an LC output filter?

thanks

 

[crutschow]

Since you want to "minimize" the noise and don't have a specific noise value target, then it's rather a guess as to what you need. Generally you select the inductor with the largest inductance value, sufficient current rating, and sufficiently low series resistance that will fit in your available space,

 

[ronv]

Here is a filter that should knock down the ripple. It's a little hard to say because the supply already has a filter, but it might be worth a try. Just a little resistor sized inductor should work.

The 12 volt supply looks pretty good with the 120Ufd at the input to the HV supply, but if you like you could use 2 in parallel.

 

[pavjayt]

Here is a filter that should knock down the ripple. It's a little hard to say because the supply already has a filter, but it might be worth a try. Just a little resistor sized inductor should work.

The 12 volt supply looks pretty good with the 120Ufd at the input to the HV supply, but if you like you could use 2 in parallel.

Thanks for the schematic, currently my HV output looks like below. Should I add your components in addition to those or just add only the inductor?

 

[pavjayt]

I will try to find something in that range and will try Ron's suggested value too.

thanks

 

[ronv]

You should take out your resistor and cap and replace it with the circuit above.

 

[pavjayt]

Thanks Ron, I updated the schematic. Could you suggest me of any changes that would make it better?

 

[ronv]

You need to remove the 50 ohm resistor R4 as it would load down your supply.
You don't show what your input power supply is (12 volt), but if all it runs are these 2 supplies you would probably be better off without the diode or input resistors. In any case 100 ohms is way to big. (.1 amps X 100 ohms = 10V) If you want to use the diode because of high ripple from your bulk supply the cap needs to be much larger - say 6800 Ufd. so it can supply the current between ripple peaks. But unless there are other loads causing ripple on the input you would be better off just adding the extra cap to the supply and leaving out the diode.

 

[pavjayt]

You need to remove the 50 ohm resistor R4 as it would load down your supply.
You don't show what your input power supply is (12 volt), but if all it runs are these 2 supplies you would probably be better off without the diode or input resistors. In any case 100 ohms is way to big. (.1 amps X 100 ohms = 10V) If you want to use the diode because of high ripple from your bulk supply the cap needs to be much larger - say 6800 Ufd. so it can supply the current between ripple peaks. But unless there are other loads causing ripple on the input you would be better off just adding the extra cap to the supply and leaving out the diode.

R4 is supposed to be 250K as you had in your circuit above, just forgot to change its value. The input is 12V DC regulated supply and the outputs are HV (0-500VDC Regulated) and +/-5V 1W isolated Murata power supply. I will make the changes to the circuit as you suggested and test it. I had the diode just for reverse polarity protection.

thanks

 

[pavjayt]

Hi Ron,

I updated the schematic as attached. Removed the input resistors, changed R4 to 250K as you have shown in your circuit. I had the diode just for reverse polarity of the input supply protection. The input 12VDC supply is a linear regulated power supply which I guess wont be having much ripple noise. Do you think its better to use 6800uF cap on the input?

thanks

 

[ronv]

Sorry, my bad. I put the 250k in to simulate the load. You should leave it out as it takes all the supply current.
Sure, ok the diode & caps are fine. I think it will be as quiet as a mouse.