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230ac to 5vdc

gregz0012

May 19, 2013
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I have put together a circuit to take mains 230vac down to 5vdc for use in phone chargers, USB hubs etc.

I plan to replace the LT1085-12 and LT1084-5 with cheaper versions, such as BA17805T etc. I'm using the 12vdc regulator to smooth the current before using the second regulator to reduce to 5vdc. However, is the second one necessary (ltspice shows a fairly wavy voltage output without the second one)?

I'm fairly new to electronics, so may have missed something.
 

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BobK

Jan 5, 2010
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You don't need 2 regulators. What you need is a larger capacitor where C1 is. Something like 1000uF.

Bob
 

gregz0012

May 19, 2013
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You don't need 2 regulators. What you need is a larger capacitor where C1 is. Something like 1000uF.

Bob

Thanks Bob, I've removed the 12v regulator and the capacitor in between the v regs, also increased C1 to 4700uF which seems to give me a stable 5vdc all the way up to 5 amps.

In LTSpice I have to add R1 to get the simulation to run, is R1 really necessary?
 

davenn

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Sep 5, 2009
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R1 is in the primary, no it shouldnt be there

Dave
 

CDRIVE

Hauling 10' pipe on a Trek Shift3
May 8, 2012
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That xfmr indicates Pri= 50uH, Sec: 400uH. I don't think so and may be why LT Spice is upchucking without the 1Ω in the primary. The input current will be in the ozone without it.

Chris
 

gregz0012

May 19, 2013
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That xfmr indicates Pri= 50uH, Sec: 400uH. I don't think so and may be why LT Spice is upchucking without the 1Ω in the primary. The input current will be in the ozone without it.

Chris

Your right, I couldn't find the values from my transformer so plugged in a set of numbers that get me the desired voltage.
 

CDRIVE

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Your right, I couldn't find the values from my transformer so plugged in a set of numbers that get me the desired voltage.

Your Transformer model appears to be modeled as Coupled Inductors. Does LT Spice provide a Transformer model also? Transformer models are modeled in terms of turns ratio,coupling (k) coefficient, Rprim, Rsec.

Chris
 

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gregz0012

May 19, 2013
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Your Transformer model appears to be modeled as Coupled Inductors. Does LT Spice provide a Transformer model also? Transformer models are modeled in terms of turns ratio,coupling (k) coefficient, Rprim, Rsec.

Chris
Unfortunatly not (see docs)
 

CDRIVE

Hauling 10' pipe on a Trek Shift3
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Put an Ammeter in line with the primary. With inductance that low I expect to see excessively high current ... especially if you shunt that 1 Ohm resistor.

Chris
 
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