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Old 13th September 2013, 01:55 PM   #11
macboy is offline macboy  Canada
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Just saw the notes about voltages, and I agree with Katieanddad about the headroom. You need more than 33 or 34 V at the input if you want to have 30 V @5 A at the output. Generally more headroom is required when using a transistor boosted circuit. You will likely need to reduce the output to something like 27 V or get a different transformer.

Another option may be to use low dropout regulators. But you would need to use a few in parallel, and I don't know how well they behave like that (LDO regulators are tempermental at the best of times).
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Old 13th September 2013, 01:58 PM   #12
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Originally Posted by macboy View Post
Your circuit has errors and will not work as intended. Have you tried simulating it?
Yes i did and it worked quite fine actually.

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You have mis-connected some things on the output side of the LM337.
Like what exactly?

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Try a google image search for something like LM337 high current or LM337 transistor, and you will find plenty of working examples of what you tried to do here.
Did that but all i can find was the lm317 circuit or the positive half of the power supply.
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Old 13th September 2013, 01:59 PM   #13
macboy is offline macboy  Canada
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Originally Posted by sghr220 View Post
Sorry i didn't understand the Vbe part
VBE is Voltage across the base-emitter junction of the transistor (Q7 in your schematic). You will need to find what VBE should be at 5 A output current (a.k.a. IC) by examining the datasheet for the 2SA1943. (Hint: Toshiba datasheet, page 3, "IC - VBE" graph).
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Old 13th September 2013, 02:06 PM   #14
macboy is offline macboy  Canada
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Unfortunately, simulations often don't find common mistakes like flipping the emitter and collector. Plenty of simulated transistors work very well backwards. Most real BJT transistors work to some extent backwards, but not well.
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Old 13th September 2013, 02:09 PM   #15
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You will likely need to reduce the output to something like 27 V or get a different transformer.
I can do just fine with +-25 to +-27 voltage output at 5A.
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Old 13th September 2013, 02:09 PM   #16
macboy is offline macboy  Canada
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Originally Posted by sghr220 View Post
Did that but all i can find was the lm317 circuit or the positive half of the power supply.
Try googling:
lm337 high current site:electronics-diy.com
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Old 13th September 2013, 02:11 PM   #17
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VBE is Voltage across the base-emitter junction of the transistor (Q7 in your schematic). You will need to find what VBE should be at 5 A output current (a.k.a. IC) by examining the datasheet for the 2SA1943. (Hint: Toshiba datasheet, page 3, "IC - VBE" graph).
Measuring the voltage between the base and emitter in the simulated circuit gives -0.99V.
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Old 13th September 2013, 02:13 PM   #18
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Unfortunately, simulations often don't find common mistakes like flipping the emitter and collector. Plenty of simulated transistors work very well backwards. Most real BJT transistors work to some extent backwards, but not well.
Fortunately they do.
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Old 13th September 2013, 02:15 PM   #19
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Try googling:
lm337 high current site:electronics-diy.com
Thanks for the pointer, but can the 3055/2955 be swapped with the Sanken pair. And also what about the capacitors arrangement and values.
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Old 13th September 2013, 02:23 PM   #20
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You need to address the transformer before you think about the caps. The transformer is just not adequate in this circuit unless you dispense with the regulator.
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