usign redundanct power transformer as CLC choke

[muddasirwaheedmalik]

I have a pair of 300VA toroid. 110V to 60-0-60V secondary. so the secondary has 300/(60+60)=2.5A capability.
If used in parallel the secondary will have 5A current capacity (RMS) without core saturation leaving the primary open.

1. the question is whether i can use it for CLC or CLCLC choke.
CLC two chokes in parallel , or CLCLC using each secondary in turn. ?

2. Can i use it in differnetial/common mode choke using both secondaries connected to C+ to C+ terminal and C- to C- terminal. ???

The supply design is for single ended Class A amplifier so ripple rejection is very critical here.

regards

 

[DF96]

You might be able to use it as a common-mode choke by wiring the secondaries in opposition so their is no DC flux to cause core saturation.

 

[AndrewT]

The 2.5Aac and 5Aac current rating are for AC current.

If you use the transformer as a choke you need to know the DC current rating.
IT WILL NOT BE THE SAME AS THE AC RATING.

 

[sawreyrw]

I would not put these in parallel without some series resistance to help balance the currents. A transformer cannot be used as a choke, because they will most likely saturate with any appreciable DC current.

 

[DF96]

The DC current rating will presumably be a bit higher than the AC rating, as there will be no skin or proximity effect to increase conductor resistance and no eddy current losses in the core. However, the DC currents will need to be fairly accurately balanced to avoid core saturation. Best to use only in circumstances where the circuit details guarantee DC balance e.g. secondary-rectifier-cap-CM choke - etc. If there are no other connections to the rectifier etc. then DC balance is assured by Kirchoff's current law.

 

[muddasirwaheedmalik]

I am really a bit confused here. I have seen old school car amplifiers regulard employing iron core small EI chokes for mains filtering at 12V. i.e 80A current is flowing through them how does it work then without saturation.

Ok. I agree the DC rating would be lesser due to conitnoues heating but should it not be same as that of RMS rating of Ac current ???

Help is neeeded i have these two spare toroids in metal cases salvaged from a sony vintage amplifier i hope i can make some good use of them. I am not sure of how to balance the two secondary windings for CMMMR??

 

[muddasirwaheedmalik]

can some one explain how to balance the secondaries. i have a pair of these from sony amplifiers. they are completely metal encapsulated. how can it be used in CMMR mode?

 

[sreten]

Hi,

Simple fact is you should never be doing stuff you don't understand.

Most of the time you won't understand the answers to your questions.

You work out what sort of inductors are used in SMPS's and why.

You work when you can use common mode and when you can't.

You work out the current rating of a transformer used as a choke.

You work out why CLCLC here simply cannot work properly.
(its an interesting problem as to what would actually happen ...)

(One of the answers in this thread is simply wrong .....)
(One of the answers in this thread is very misleading .....)

You work out why I can't be bothered to answer most of your
ill-informed questions, (answer - your not asking the right
questions - problem - work out what that actually means).

rgds, sreten.

 

[muddasirwaheedmalik]

agreeed. But i need solution to reduce hum to my pull push class A single ended amplifer.
for that i need to reduce the ripple at the mains. ????? how can i do do it else?

 

[abraxalito]

I am really a bit confused here. I have seen old school car amplifiers regulard employing iron core small EI chokes for mains filtering at 12V. i.e 80A current is flowing through them how does it work then without saturation.

Presumably the inductance is much much lower (fewer turns, thicker wire) so the core doesn't reach saturation. I just measured the secondary inductance of a 150VA toroid I have to hand. It was around 400mH but I suspect my LCR bridge was driving it into saturation because the loss was a bit on the high side. Does your circuit really need hundreds of mH inductance? That will look very high impedance at audio frequencies.

If you're building chokes then look into some cores based on no.26 material which is designed for this application - they're not at all expensive. It withstands higher magnetisation because its got a distributed air gap (its iron powder, not iron).

 

[muddasirwaheedmalik]

Ok. my plan is for 16A continous through the supply at 34 V single rail supply. Its a 600VA toroid with 10x10000uF capacitors.
can i use CRC , my plan is to keep the current 40000uF as first C then add R and then another C what could be the values of R and C ??? any guidance or thumb rule?

 

[abraxalito]

The transformer will overheat asked to produce that much (544W) continuously as the power factor of those caps will mean 600VA is easily exceeded.

 

[muddasirwaheedmalik]

I think you are referrring to the input transformer. sorry for typo 16A is the Ac current i would be ruuning at 4A per side thats 8A total. I hope that ruuning at continous half the power would be ok then. i.e. 32x8=256W and the tranformers is of an amplifier with 500w class B amplifier. any comments on its?

 

[muddasirwaheedmalik]

oh did i mention that no speaker coupling capacitor was used
some plans improvement.....using the secondary coil of out put transformer as CLC filter.
recifier diode noise cancellation with ceramic capacitors.
EMI filter for mains.
replacing the three 0.22uf electrolytic coupling capacitors with high quality metal film around 2.2 uF.

 

[gmphadte]

Go to the ESP site. There, u can find a psu circuit known as capacitance multiplier. May be, it will solve your hum problem.

I would first confirm the hum is sourced from the psu itself as there r other sources of hum like leakage from a transformer.

Gajanan Phadte

 

[DF96]

(One of the answers in this thread is simply wrong .....)
(One of the answers in this thread is very misleading .....)

Very helpful reply to us all.

As I said, the toriodal transformer could be used as a commmon-mode choke, which I think answers one of the OP's questions. Perhaps I should have added that a common-mode choke is not what is needed for PSU smoothing.

 

[grommeteer]

DF96: I am not good at explaining and English is not my native language. Could you please explain to the OP the difference between magnetizing current and load current. How load current is compensated by primary current and magn. current is not. I think he has problems understanding why a transformer with a high sec. current rating can be saturated by a very low current, be it AC or DC, that is "forced" through its secondary.

 

[DF96]

OK. In a transformer the magnetic flux generated by the primary current is largely cancelled by opposite flux generated by secondary current. This means that the core only sees a much smaller net flux. Using a transformer winding as a choke means there is no cancellation, so maybe only 5-10% of current rating is possible.

A common-mode choke achieves flux cancellation by sending the same DC current through two windings in opposite directions. The core only sees flux generated by the difference between the two currents. Note that another (RF) name for a common-mode (CM) choke is a current-mode balun.

PSU smoothing needs an ordinary choke, not a CM choke.

 

[nigel pearson]

If anyone is still interested the use of a toroidal transformer as a common mode choke can work very well . I did try the leap to a ferro-resonant idea . That is where one of the two coils is connected in shunt to a capacitor . Fascinating and everything got rather hot , it did start to work it should be said . The capacitors from memory were in the many 10's of uF . If anyone succeeded in this I would be more than very interested . Oneac UK had devices that claimed 1% THD in the past ( 50 Hz ) . CVT's may not work well with class B amplifiers ( D ) . I am told by the man who makes my transformers that CVT's are a black art to design . He was trained by the ex chief engineer of Partridge so is fairly reliable when saying this . 8KVA he does at the drop of a hat .

Voltage regulation : TRANSFORMERS
AGT 3000VA CVT | Power Conditioner | Critical Power Supplie5

 

[jcx]

DC current rated chokes may have air gaps where you can't easily see them in the finished product - under the bobbins/windings - so they only superficially appear to be built the same as transformers


reducing hum doesn't always require super low supply ripple - you could use a topology that has good supply rejection - just about any circuit except OTL low mu Triode

at your stated V you must be using SS which usually have high output conductance/low internal V feedback (it is high internal V feedback that gives triodes low mu) - should be able to have good supply rejection