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buck converter question

K

kell

Jan 1, 1970
0
I'd like to regulate the power through a load
using a basic buck circuit along these lines

14v
|
|
,-----+-------,
| | |
| | |
| | load
| | |
| | |
| | |
| | |
| '--|(---+
| |
| |
| )
| )
| )
| |
| |
'------|<-----+
|
|
|-'
PWM-----||
100kHz |-,
|
|
gnd


I have a junkbox toroid that I identified as mix 26
similar dimensions to Amidon's
iron powder toroid T-130 as spec'd here:

http://www.amidoncorp.com/aai_ironpowdercores.htm
wound with 12 ga solid copper wire for about 25 uH

I'll have about 20 amps going through the load.
The core should be able to support that much dc current,
according to Amidon's website.
My question: the 12 ga wire will present a lot of impedance
to the superimposed 100 kHz ac because of skin effect.
How much of a problem will that pose?
 
K

kell

Jan 1, 1970
0
By the way, you missed one very important power
component in this system. That would be the bypass
capacitor from the top of the load and its diode to the
bottom of the mosfet.

Right you are.
Thanks John.
 
J

John Popelish

Jan 1, 1970
0
kell said:
I'd like to regulate the power through a load
using a basic buck circuit along these lines

14v
|
|
,-----+-------,
| | |
| | |
| | load
| | |
| | |
| | |
| | |
| '--|(---+
| |
| |
| )
| )
| )
| |
| |
'------|<-----+
|
|
|-'
PWM-----||
100kHz |-,
|
|
gnd


I have a junkbox toroid that I identified as mix 26
similar dimensions to Amidon's
iron powder toroid T-130 as spec'd here:

http://www.amidoncorp.com/aai_ironpowdercores.htm
wound with 12 ga solid copper wire for about 25 uH

I'll have about 20 amps going through the load.
The core should be able to support that much dc current,
according to Amidon's website.
My question: the 12 ga wire will present a lot of impedance
to the superimposed 100 kHz ac because of skin effect.
How much of a problem will that pose?

It will cause some additional wire heating, but it may not
be a problem. The main wire loss comes from the DC
component of the current, which is the largest component, by
far. By the way, you missed one very important power
component in this system. That would be the bypass
capacitor from the top of the load and its diode to the
bottom of the mosfet. It is more important than the
capacitor across the load.
 
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