Electronics > Beginners
Help choosing components for a power supply
David Hess:
--- Quote from: derationalize on February 01, 2020, 03:26:15 am ---LM109 is $17 a piece. LM317 is 0.58 cents on Mouser. I figured I could just order a quantity of them and have some jellybean components for future projects. I have to keep the cost of this project down lest it would not be worth the effort.
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Those specific parts are not required. It works fine with an LM317, a PNP transistor and perhaps a couple cheap diodes replacing the JFET, and your favorite operational amplifier. Last time I did it with a 7805 regulator and LT1007 operational amplifier but I had to add external frequency compensation networks.
--- Quote ---I have a few TIP4CG transistors sitting in a scrap bin. If I recall those can handle quite a bit. Is that a bit overkill? Also, is a 4800uF electrolytic big enough for the main cap? Should I use any polyfilm caps in that circuit? Should I worry about using cheap carbon film resistors?
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TIP4CG? TIP4?
Carbon film resistors are fine for the preregulator. They may be acceptable for the output divider depending on the requirements for output voltage accuracy.
The series preregulator could be implemented with a power depletion mode MOSFET with the gate tied to the output of the regulator.
Jwillis:
--- Quote from: David Hess on February 01, 2020, 02:22:56 am ---A MOSFET or IGBT could be used but a bipolar transistor has a much better cost per die area which is proportional to power dissipation which is what matters.
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I'm thinking in terms of very high currents (20 A to 100A) and high voltages (50V to 100V) for very specialized industrial applications.
David Hess:
--- Quote from: Jwillis on February 01, 2020, 10:13:35 am ---
--- Quote from: David Hess on February 01, 2020, 02:22:56 am ---A MOSFET or IGBT could be used but a bipolar transistor has a much better cost per die area which is proportional to power dissipation which is what matters.
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I'm thinking in terms of very high currents (20 A to 100A) and high voltages (50V to 100V) for very specialized industrial applications.
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Bipolar transistor still have a cost advantage even when extras for drivers are required to supply the base current. More of them have to be used in parallel but more devices should be used anyway to lower case to heat sink thermal resistance. Their drop in current gain at high currents is not a problem because multiple devices are needed to handle the power dissipation anyway.
MOSFETs and IGBTs will still require drivers to handle their high gate capacitance. There is no advantage to using IGBTs instead of MOSFETs unless they are available with higher power ratings.
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