120v SMPS without using input voltage doubler

[hanair]

I just built my first SMPS to convert 120v to 45-0-45v for my audio amplifier. It works fine and I tested it with 100w 110v Incandescent bulb. it is based on the standard IR2143 circuit (EI33 core with 20+20 turns primary and 12+12 turns secondary). The oscillator is running at about 50 kHz. The circuit uses the standard voltage doubler (120v/240v switch) to produce 340v rectified at the input capacitors.

I am wondering what would it take to make it just 110v without using the voltage doubler?

Will changing the number of primary turns to 10+10 take care of that? Should I change the 2143 frequency as well? Or any other changes?

Thanks for the help!

 

[hanair]

It is IR2153 not IR2143
I don't see a way to edit my post.

 

[MicrosiM]

I just built my first SMPS to convert 120v to 45-0-45v for my audio amplifier. It works fine and I tested it with 100w 110v Incandescent bulb. it is based on the standard IR2143 circuit (EI33 core with 20+20 turns primary and 12+12 turns secondary). The oscillator is running at about 50 kHz. The circuit uses the standard voltage doubler (120v/240v switch) to produce 340v rectified at the input capacitors.

I am wondering what would it take to make it just 110v without using the voltage doubler?

Will changing the number of primary turns to 10+10 take care of that? Should I change the 2143 frequency as well? Or any other changes?

Thanks for the help!

I am not sure if I understand your question correctly, your SMPS fed by 110VAC or 240VAC?

 

[hanair]

Thanks for the reply MicrosiM.

My SMPS is fed 120v and is using the standard 120/240v switch (which acts as a voltage doubler, so after rectification DC input becomes around 340v). What I am trying to achieve is to run it at 120v without using the voltage doubler, so that th DC input would be about 170v (full wave bridge rectifier instead of voltage doubler). That will make the input capacitors much smaller in size and the transformer with fewer turns (thus larger diameter wires for input). Since I am using 20+20 turns for the input winding as it is now, I should be able to use 10+10 turns for input with half the input voltage, correct? but I am wondering if that would require a change in switching frequency as well. Or may be other modifications to the circuit which I am not aware of.

 

[KX36]

Yes, it should be the case that you can run directly off the 120Vac input without a voltage doubler by adjusting the turns ratio. As long as you meet the minimum absolute number of turns on the primary to avoid saturation or whatever core loss in the transformer you deep appropriate, you have to do the maths to work out what that is for your core. Of course, it won't work right on 240Vac any more.

 

[hanair]

Thanks KX36. I am using standard EI33 ferrite core found on the standard computer ATX power supply. I do not know how much variability can there be with differnet EI33 ferrite cores from various manufacturers. Is it simpler to calculate to see if 10+10 turns at 50kHz is within the limits of core parameters?

 

[KX36]

Without a datasheet you should probably go to an effort to characterise the core to see where it will saturate etc. If you know the exact core material it's a lot easier. Others here are a lot more familiar with using salvaged cores than me, I just buy new cores bobbins etc.

50kHz is a relatively low frequency. Perhaps see if you can get it around 70-100kHz.

 

[wally7856]

This is the best data i have been able to find over the years.

EI33

3C90

Ae 1.18 cm^2

Ve = 7.91 cm^3

WaAe = 1.579 cm^4

transformer switches at 35khz

Bobbin Dim from Alibaba
Winding width = 16.3mm = .6417"
Winding height = 9.8mm = .3858"

TL494
Rt 6 18K
Ct 5 1nF
70khz / 2 = 35khz

 

[hanair]

Without a datasheet you should probably go to an effort to characterise the core to see where it will saturate etc. If you know the exact core material it's a lot easier. Others here are a lot more familiar with using salvaged cores than me, I just buy new cores bobbins etc.

50kHz is a relatively low frequency. Perhaps see if you can get it around 70-100kHz.

I bought the core/bobbin from Aliexpress and there was no datasheet. Where do you buy core and bobbin from?

 

[hanair]

This is the best data i have been able to find over the years.

EI33

3C90

Ae 1.18 cm^2

Ve = 7.91 cm^3

WaAe = 1.579 cm^4

transformer switches at 35khz

Bobbin Dim from Alibaba
Winding width = 16.3mm = .6417"
Winding height = 9.8mm = .3858"

TL494
Rt 6 18K
Ct 5 1nF
70khz / 2 = 35khz

I will surely try to calculate the minimum frequency with those parameters. BTW, why did you mention that 70kHz/2 = 35kHz? Does it mean that by halving either Rt or Ct we can get 75kHz?

Thanks!

 

[wally7856]

"why did you mention that 70kHz/2 = 35kHz?"

This.

TL494
Rt 6 18K
Ct 5 1nF
70khz / 2 = 35khz

Was taken from an ATX power supply schematic. The control chip runs at 70khz and the half bridge runs at 35 khz. From what i understand this is a typical operating frequency for these power supplies.

 

[KX36]

If it is 3C90 as wally suggests, that's capable of up to 200kHz. I typically start off at 100kHz and see where I end up.

IIRC, the TL494 has alternating outputs so each output fires once for every 2 clock cycles and you have to set the oscillator to twice the switching frequency. I personally wouldn't recommend TL494 for new smps designs as its a general purpose PWM IC. And compared to ICs designed for smps it's got a few quirks and lacks a few desirable features. It's obsolete and if you want to use voltage mode control, the SG3525 is really the most basic IC to use. I'd usually recommend current mode control though except in half bridge converters.

 

[hanair]

"why did you mention that 70kHz/2 = 35kHz?"

This.

TL494
Rt 6 18K
Ct 5 1nF
70khz / 2 = 35khz

Was taken from an ATX power supply schematic. The control chip runs at 70khz and the half bridge runs at 35 khz. From what i understand this is a typical operating frequency for these power supplies.

I use IR2153 and the 50kHz is the switching freqency. I think in my case that is the same as the operating frequency of the transformer.

If it is 3C90 as wally suggests, that's capable of up to 200kHz. I typically start off at 100kHz and see where I end up.

Is there a way to determine what frequncy is the best for a specific configuration, by changing the switching frequency and measuring output?

 

[wally7856]

KX36, the 3C90 is a guess on my part. The EI33's are used by the millions for computer power supplies and appears to be there main use. Ferroxcube only sells the EI33 with 3C90, so i assume they are targeting the largest market of computer power supplies.

 

[wally7856]

“3C90 is capable of up to 200kHz. I typically start off at 100kHz and see where I end up.”

KX36, around 100khz you enter litz wire or copper foil territory. That is kind of sophisticated stuff for us toothless hillbillies. Litz wire is almost impossible to buy and copper foil has to be cut down from a sheet and is almost as hard to buy.

 

[hanair]

“3C90 is capable of up to 200kHz. I typically start off at 100kHz and see where I end up.”

KX36, around 100khz you enter litz wire or copper foil territory. That is kind of sophisticated stuff for us toothless hillbillies. Litz wire is almost impossible to buy and copper foil has to be cut down from a sheet and is almost as hard to buy.

I am not sure if you can use the kind of litz wire listed in ebay. Instead, I used multiple strands of 26AWG - 3 each for primary and 6 each for secondary. I wound the output in bifilar fashion (12+12 turns for symmetrical output) so I had to wind 12 strands at the same time! 12 turns of 12 strands was not too hard to handle.

 

[wally7856]

Hamair, how much power are you trying to get out of your SMPS.

 

[hanair]

I am shooting for about 300-400W RMS output at +/- 45 to 50v. It is actually for a Class-D audio amplifier rated at 300+300W RMS.

 

[wally7856]

That is a lot of power to get out of that little core. Are you going to cool it with a fan? And how did you fit all of that secondary wire on the bobbin in one layer, it must be all scrunched up, do you have a picture.

I would not get rid of the voltage doubler. You would then need 2x the current because your voltage would be 1/2.

 

[hanair]

That is a lot of power to get out of that little core. Are you going to cool it with a fan? And how did you fit all of that secondary wire on the bobbin in one layer, it must be all scrunched up, do you have a picture.

I would not get rid of the voltage doubler. You would then need 2x the current because your voltage would be 1/2.

Yes, I was planning to use a fan. Do you think even 200W is too much for EI33? Since audio power is usually much lower in real use than the max RMS, these may not run at the stated power all the time. May be I should have two separate transformers each with 200W.