Keantoken's CFP cap multiplier

[maouna]

Hello.I ordered this 3.3V-12V In / +-15V Out Dual Power Step up converter to power my preamps from USB or batteries. Can i apply the K-multiplier at the output of step up converter?What modifications are needed for low drop K-multiplier supposing max output current wont exceed 100ma per rail?

+15V/-15V Dual Power Supply Module 3W DC-DC Step up Boost Converter 3.3V-12V In | eBay

 

[Destroyer OS]

Nothing, connect right to it.

But I'd want to put an inductor or some sorta filter in between, personally.

 

[keantoken]

If you want to add an inductor, most 5uH inductors are pretty good at blocking the upper end of SMPS noise. But they also tend to resonate with your supply lytics in the audio band. IE the same problem as lm317/337 regulators.

 

[RCruz]

Can I use KSA 1381 instead of 2SA1930 and KSC 3503 instead of 2SC5171 ?

These KS have 150Mhz Ft and lower Cob around 3pF

 

[RCruz]

The Ks are readily available and the 2SA not.

I must decide before ordering the boards because pinouts are reversed.

Also, would you please take a look at the layout.... there are a lot of diodes and I am wondering if it could oscilate.

 

[maouna]

Nothing, connect right to it.

But I'd want to put an inductor or some sorta filter in between, personally.

I was reading the page about K-multiplier The K Multiplier and there is a point that states:

''This regulator exhibits diodic output impedance. This means output impedance decreases with increased loading. The opposite is also true, which is why this circuit should NEVER be used with loads less then 25mA.''

My preamp draws about 18ma per rail.Should the circuit of K-multiplier be modified?

 

[Destroyer OS]

Two channels, 18x2?

You may need to add a little load if not. A capacitor with leakeage, resistor, something.

 

[maouna]

Yes just a resistor or a led with a series resistor...Can i replace 2SA1930 /2SC5171 with BD139/BD140 or there will be any degradation?Keep in mind my max current demand wont be above 150ma..

 

[RCruz]

Can I use KSA 1381 instead of 2SA1930 and KSC 3503 instead of 2SC5171 ?

These KS have 150Mhz Ft and lower Cob around 3pF

maybe other alternatives ?

 

[keantoken]

Capacitor leakage will usually be far too low to have any effect. Just add a load resistor at the output so that the total current will be over 25mA.

maybe other alternatives ?

C29's ground is polluted by C28. C29 ground can be any point before C15 ground, the closer the better. But if C29 ground is after C15 ground, oscillation is much more likely.

The decoupling caps next to your lytics should be around 2.2uF or larger not to reasonate. 5mm caps up to 10uF are available.

 

[keantoken]

Using the 1381/3503 is sort of a gamble. I really don't know how that will work out. Do you have 2SC4793/A1837?

 

[RCruz]

Thank you so much

Can I route C28, C29 and C15 grounds separately to -GND ?

 

[RCruz]

2SC4793LB-TF3T - Power Transistor 230V 1A

2SA1837LB-TF3T - Power Transistor -230V -1A

Profusion has the 2SC4793/A1837 parts

 

[RCruz]

I have rearranged the layout... now C15 gnd goes to C29 GND and than to -GND.... is this ok ?

 

[keantoken]

Those transistors are from UTS, not Toshiba. I don't know how well they meet the original spec.

Looks like C13 and C11 are swapped.

It looks like KM grounds are not routed with the KM outputs, which is not good EMC practice but may be a non-issue.

 

[RCruz]

Eagle yes you got thank you, I will swap the caps values.

You mean I should place the KM grounds over the KM rails ?

 

[keantoken]

That would be ideal, to reduce the loop area between rails and ground.

 

[keantoken]

It really depends on the layout, I think the most important thing is that there is a short path from the driver collectors to the zobel and drain grounds. So much of this is context-dependent, I can only make the most general comments, and I still may be wrong.

 

[RCruz]

The decoupling caps next to your lytics should be around 2.2uF or larger not to resonate. 5mm caps up to 10uF are available.

I was convinced the KM could support small films at the input and output without fear of oscillation.

The change you propose is to avoid oscillation or to not create other type of nastiness ?

 

[keantoken]

It is just my suggestion to prevent the film caps from resonating with the lytics. It has nothing to do with oscillation. No regulator can prevent this. But if you have found some kind of decoupling that you prefer by experience, you don't necessarily need me to justify it.