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walid

BJT power supply

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Guest Alun

Sorry, I misread you last post, I'm the one who needs my eyes testing. ;D

I already knew I could've used a P-channel MOSFET, but they have a larger on resistance.

I was wrong earlier when I said I don't need a fast op-amp, I do because the MOSFET is connected as a source follower so I wouldn't getr any voltage amplification, but I would if I used the P-channel idea which would have a better transient response.

By the way couldn't you think of a cheap, faster, low power op-amp with a low saturation voltage? ;D

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Hi Alun,
This is a linear regulator so the on resistance of its Mosfet doesn't matter unless it is drawing about 40A or more, but then the poor thingy would melt anyway.
I selected the MC34071 because it is the same as the MC33171 that you used except it is faster (10V/us), saturates with a lower loss and can output higher current. At Digikey it is cheaper than yours. Isn't it nice that the dual version of both ICs costs exactly the same as a single one of yours.
Looky, looky again. ;D

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Guest Alun

Hi Alun,
This is a linear regulator so the on resistance of its Mosfet doesn't matter unless it is drawing about 40A or more, but then the poor thingy would melt anyway.

Yes I know, but a lower on resistance means a lower dropout voltage.

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Guest Alun

Any low current constant voltage source such as a shunt referance made with a zener diode and resistor,  or a voltage referance IC such as a a band gap referance.

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Guest Alun

To make people think. ;D

No seriously, often things like voltage referances and current sources aren't shown because they can be any of many things. Here it could've been a zener diode and pullup, band gap reference such as the LM113 or the programable shunt regulator TL431A. The person using this circuit can decide and choose which type of volatge referance is best for thier application.

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