problem about wide range power supply design ( including original schematic)

Dec 25, 2006 7 Replies

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leelsuc 19 years ago

schematic:

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this design is to build a wide range voltage/current PS.

I don't know why the original designer chose the 2 ohm, 10 ohm, Darlington 100k ohm (what's this?), 1k ohm shunt ( just = 0.7 volt / leakage current from Q1 Emitter ), 330k ohm, and 100 ohm in seriese with LM317.

My only understanding is: since the input is high (230 volt DC rms or 230/0.707 volt DC peak), both Q1 & Q2 are in active mode.

there is no bleed resistor, why the designer put 2 ohm, 10 ohm serialed capacitors? try to filter noise as well as regulate DC voltage? how to choose them?

what does the 100 ohm use for ? to compensate phase???

This circuits will be operated < 25 mA, that's fine for single MPS U10, why use Darlington pair?

totally lost.

Thanks for your help.

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Robert Baer 19 years ago

The "pickoff" point for the collectors should be after the 2 ohm resistors (ie: at the 100Uf caps) for better filtering and safety; the

10 ohm resistor is of zero help. That 100K is the base pullup to drive the darlington pair. Yes, ther *should* be a bleed resistor for safety; a diode should be across the pass transistor to protect it if a capacitor is used at the output. BTW, what is supposed to set the output oltage and how is someone supposed to adjust that?

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leelsuc 19 years ago

The output marked as "HV" just below the "GND" in the figure, is stabalized at 160 volt DC and the DC current is adjustable from 5mA to

25 mA.

Robert Baer wrote:

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GPG 19 years ago

It is a CCS. The voltage is not stabilised or adjustable. The zener contributes an error and should be connected to out of the LM317 to remove this. The 330K bleed should be moved there also.

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Robert Baer 19 years ago

the question implied (1) how is the output voltage adjusted, and (b) how is it set; not a measured empirical value with an unstated load.

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Robert Baer 19 years ago

*now* there is some light on the subject; dim - but light nonetheless. seems the schematic needs a number of changes...

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leelsuc 19 years ago

LM317 will regulate the current only, thus the HV will maintain about 160 volt, there should be some extra positive voltage applied from the current regulating loop. The load varies with the applied voltage and current. HV ranges from 160 to 110 volt and current ranges from 5 to 25 mA which is determined by the LM317.

Robert Baer wrote:

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GPG 19 years ago

If the output is OC the voltage will be ~400V - Vz = 393V, if it is SC the output will be 0V

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