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Poles and zeros for two transistor forward?
Poles and zeros for two transistor forward?
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Old 26th September 2012, 05:23 AM   #1
treez is offline treez  United Kingdom
Join Date: Sep 2012
Default Poles and zeros for two transistor forward?


Can any reader list the poles and zeros for a two transistor forward converter?

i.e. for the power stage and modulator?

The control chip is UCC38C44

Vin = 385VDC
Vout = 80V
Load = 20 Ohms (maximum, heavyest load)
Switching frequency = 85KHz
C(out) = 940uF
ESR of Cout = 0.1 Ohm
L(out) = 186uH
Turns ratio (Ns/Np) = 46/50
Current sense resistor = 0.15 Ohms
Continuous conduction Mode.
Duty cycle at max load (20R) = 0.24

...its for Class B amp supply. (output is actually +/-40V, but lets call it 80V...i hope thats OK?
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Old 26th September 2012, 06:37 AM   #2
jan.didden is online now jan.didden  Europe
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It's over my head but TI has a free downloadable spice simulator for it's own products that will do this for you, called Tina.

jan didden
Music is dither to the brain; lets me think below the usual chaos - me
Linear Audio Vol 13 is out! Check out my Autoranger and SilentSwitcher
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Old 26th September 2012, 08:22 AM   #3
darkfenriz is offline darkfenriz  Poland
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Current loop: pole at Rsense and (Lout/turns ratio) i.e. R/2piL
Voltage loop: pole at Cout Rload i.e. 1/2piRC, zero at Cout ESR i.e. 1/(2*pi*ESR*C)
no tricks here.

Last edited by darkfenriz; 26th September 2012 at 08:32 AM. Reason: mistake
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Old 26th September 2012, 02:40 PM   #4
Terry Given is offline Terry Given  New Zealand
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yes. and given that Treez cant play with the current loop at all, might as well pretend its perfect, and treat the entire power stage as a transconductance. gm = delta_Iout/delta_Vcomp. thats pretty easy to work out - but dont forget the x1/3 from Vcomp to Vcurrentsense
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