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Electronics Forum / Basics / November 2005forward converter duty cycle question
Looking at the forward converter topology illustrated here: http://schmidt-walter.fbe.fh-darmstadt.de/smps_e/edw_hilfe_e.html They specify a maximum duty cycle of 50%. Is this predicated on N1 and N1' having an equal number of turns? It seems to me you get a longer duty cycle by reducing the number of turns on N1'. > Looking at the forward converter topology illustrated here: > http://schmidt-walter.fbe.fh-darmstadt.de/smps_e/edw_hilfe_e.html > They specify a maximum duty cycle of 50%. > Is this predicated on N1 and N1' having an equal number of turns? > It seems to me you get a longer duty cycle by reducing the number of > turns on N1'. I think it's to keep the transformer from saturating. John > > Looking at the forward converter topology illustrated here: > > http://schmidt-walter.fbe.fh-darmstadt.de/smps_e/edw_hilfe_e.html [quoted text clipped - 6 lines] > > John I know. The magnetic field needs time to collapse. I'm asking does the mag field collapse faster with fewer turns on N1'. >> > Looking at the forward converter topology illustrated here: >> > http://schmidt-walter.fbe.fh-darmstadt.de/smps_e/edw_hilfe_e.html [quoted text clipped - 9 lines] > the mag field collapse faster with fewer > turns on N1'. Yes. However, note that the transistor's drain voltage would then be Vin+(N1*Vin/N1'). The series diode on the secondary would also see higher voltage (Vin*N2/N1'). John > Yes. However, note that the transistor's drain voltage would then be > Vin+(N1*Vin/N1'). Ouch. > Yes. However, note that the transistor's drain voltage would then be > Vin+(N1*Vin/N1'). That means when N1=N1', drain voltage is 2Vin. I didn't know that. >>Yes. However, note that the transistor's drain voltage would then be >>Vin+(N1*Vin/N1'). > > That means when N1=N1', drain voltage is 2Vin. I didn't know that. You must have missed it. 5th paragraph below the schematic it says... "Due to this the transistor drain-source voltage steps up to Vds > 2Vin when the transistor is turned off." Sorry. John |
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