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Choosing transformer core
- Thread starter ytsoc
- Start date
at the moment i'm waiting for some prices , but i think i've settled on TX42/26/13-3C90 at 35khz with 5 turns in primary , and by my calculations about 200mT , in this case power loss is at 100mw/cubic cm so a total of 1W is disipated in the core(if i calculated corectly).
Now i'm thinking about other parts like input/output capacitors and mosfets.
For output current of 6 amps i was planning on using 6 680uG caps rated at 1.4Amps ripple current , (don't know if ripple current of capacitors is related to output current).
Also for input capacitor , i'm not sure what value should i use.
As for the mosfets i'm searcing for some less used models/brands to avoid buying counterfits. I found these: AP9990GP-HF-3TB but i'm not shure how they compare to the traditional irf 3205.
They seem better but some specs are at lower currents so i don't know how they scale
Now i'm thinking about other parts like input/output capacitors and mosfets.
For output current of 6 amps i was planning on using 6 680uG caps rated at 1.4Amps ripple current , (don't know if ripple current of capacitors is related to output current).
Also for input capacitor , i'm not sure what value should i use.
As for the mosfets i'm searcing for some less used models/brands to avoid buying counterfits. I found these: AP9990GP-HF-3TB but i'm not shure how they compare to the traditional irf 3205.
They seem better but some specs are at lower currents so i don't know how they scale
FERROXCUBE - TX36/23/15-3F3 - FERRITE CORE, TOROID, 3F3
14.7v, 30khz, 1600G, Ae .975 = 7.85 Pri turns.
Use 8 turns, 22awg, 10 strands.
10 strands on primary will fit, 11 strands will be tight.
Secondary 50vdc, 10vdc min voltage, 2 volts drop on bridge = 42 turns
Use 42 turns, 22awg, 2 strands.
2 strands on secondary will fit, 3 strands will not.
In the first TN example i do not think i had enough current capability for the primary. For that primary i took 300W / 14V = 21.4A
For this example i got a little more scientific.
300W / worst case voltage 10v = 30A
Next you have to increase the 30A to account for push pull efficency, my best guess is 70% worst case, and 90% best case.
8 pri strands is good for 30A, and a maximum of 10 strands will fit, so i would just go with 10 strands.
14.7v, 30khz, 1600G, Ae .975 = 7.85 Pri turns.
Use 8 turns, 22awg, 10 strands.
10 strands on primary will fit, 11 strands will be tight.
Secondary 50vdc, 10vdc min voltage, 2 volts drop on bridge = 42 turns
Use 42 turns, 22awg, 2 strands.
2 strands on secondary will fit, 3 strands will not.
In the first TN example i do not think i had enough current capability for the primary. For that primary i took 300W / 14V = 21.4A
For this example i got a little more scientific.
300W / worst case voltage 10v = 30A
Next you have to increase the 30A to account for push pull efficency, my best guess is 70% worst case, and 90% best case.
8 pri strands is good for 30A, and a maximum of 10 strands will fit, so i would just go with 10 strands.
“TX42/26/13-3C90 at 35khz with 5 turns in primary
200mT
power loss is at 100mw/cubic cm so a total of 1W is disipated in the core(if i calculated corectly).”
Armatures like us should not exceed 160mT. Leave the high Gauss levels for seasoned professionals and people with dumb luck.
200mT
power loss is at 100mw/cubic cm so a total of 1W is disipated in the core(if i calculated corectly).”
Armatures like us should not exceed 160mT. Leave the high Gauss levels for seasoned professionals and people with dumb luck.
“For output current of 6 amps i was planning on using 6 680uG caps rated at 1.4Amps ripple current , (don't know if ripple current of capacitors is related to output current)."
I am not the expert on these questions but i would also make ripple current at least as large as my output current. Also you need capacitors rated for high frequency and current paralleled across your electrolitic’s.
“Also for input capacitor , i'm not sure what value should i use."
Rule of thumb 3uf per watt, so 900uF minimum.
“As for the mosfets i'm searcing for some less used models/brands to avoid buying counterfits. I found these: AP9990GP-HF-3TB but i'm not shure how they compare to the traditional irf 3205.
They seem better but some specs are at lower currents so i don't know how they scale”
If you buy from a large electronics distributor you will get good parts. I am also learning how to select mosfets so i can not give specific advice. But low RDS on is good, and use several devices to spread the load out. Also watch the gate capacitance, lower is better.
Most people screw up the output. They leave out the output inductor. It makes the power supply unstable and inefficient. I have found that calculating the output inductor is difficult and i am still trying to figure out how to do it properly.
I am not the expert on these questions but i would also make ripple current at least as large as my output current. Also you need capacitors rated for high frequency and current paralleled across your electrolitic’s.
“Also for input capacitor , i'm not sure what value should i use."
Rule of thumb 3uf per watt, so 900uF minimum.
“As for the mosfets i'm searcing for some less used models/brands to avoid buying counterfits. I found these: AP9990GP-HF-3TB but i'm not shure how they compare to the traditional irf 3205.
They seem better but some specs are at lower currents so i don't know how they scale”
If you buy from a large electronics distributor you will get good parts. I am also learning how to select mosfets so i can not give specific advice. But low RDS on is good, and use several devices to spread the load out. Also watch the gate capacitance, lower is better.
Most people screw up the output. They leave out the output inductor. It makes the power supply unstable and inefficient. I have found that calculating the output inductor is difficult and i am still trying to figure out how to do it properly.
Of course i'm far from understanding the magnetics involved in smps so i'll try and keep B at least under 180mT so 6+6 turns, altough some people use cores even at 240mT.
Capacitors will be hi freq type altough cheap ones(samxon/samwha)
As for counterfits...well i'd rather be sure , as i can't say for sure that my local store will get the parts exclusively from tme/farnell.
Some of the important specs of a mosfet are, as you said Rds gate capacitance(lower means that the mosfet requires lower current to switch) output capacitance and the switching caracteristics : rise time , fall time , Turn-On/Off Delay Time.
As for the output inductor i have no clue , i'll have to look into it
Capacitors will be hi freq type altough cheap ones(samxon/samwha)
As for counterfits...well i'd rather be sure , as i can't say for sure that my local store will get the parts exclusively from tme/farnell.
Some of the important specs of a mosfet are, as you said Rds gate capacitance(lower means that the mosfet requires lower current to switch) output capacitance and the switching caracteristics : rise time , fall time , Turn-On/Off Delay Time.
As for the output inductor i have no clue , i'll have to look into it