VERIABLE POWER SUPPLY - Electronic Circuits Projects Diagrams Free

TPS · 22nd January 2004, 06:31 PM

IS IT USEFUL TO ANY ONE?

Sebi · 22nd January 2004, 07:12 PM

The 22uF in feedback loop not a good idea: the circuit respond very slowly for output changing.

panic mode · 22nd January 2004, 10:23 PM

Another problem is non linear output. About half of turn on the
potentiometer will make only ca. 1/2Volt change on the output
(from 1.2 to 1.7).
Make sure that potentiometer end connected to 100 Oh resistor
is shorted to wiper.

panic mode · 22nd January 2004, 10:28 PM

I don't see why you need 1/2Watt (500mW) rating for 100Ohm
resistor. It will never see even 15mW but sure it doesn't hurt to
oversize.

panic mode · 22nd January 2004, 10:30 PM

The miliamp meter should have shunt.

Roff · 23rd January 2004, 01:24 AM

Quote:

Originally Posted by Sebi

The 22uF in feedback loop not a good idea: the circuit respond very slowly for output changing.

The National datasheet recommends this cap for reduction of ripple from the input.
Feedback is not dependent on having impedance from adj to GND. Consider that you can ground the adj pin and make a 1.25v regulator. Feedback occurs because the circuit attempts to maintain 1.25v between the output and adj., independent of the impedance between adj and GND.
If you use this cap, National recommends a 1N4002 (any of the 1N400x series should work) from output to adj, cathode to output.
The unlabeled capacitor from input to adj in the schematic above should NOT be used.

TPS · 23rd January 2004, 06:29 PM

missing Velue of capacitor is 10kpf please revew the circuit

Sebi · 23rd January 2004, 08:41 PM

Right, Ron: i've also found it in my catalog, but - as You wroted - also need a diode. But all application show the potmeter between adj. and GND pins, not as voltage divider...

Optikon · 24th January 2004, 06:05 PM

Quote:

Originally Posted by TPS

missing Velue of capacitor is 10kpf please revew the circuit

use your 103 capacitor from input to circuit ground instead.

With the others suggestions implemented, this supply will work.
It has the following disadvantages:

1) It is linear so it suffers from very poor power conversion efficiency.
2) Power output will be limited by the LM317 - put it on a heat sink and you can get more bang for your buck.
3) other than bulk smoothing caps, no efforts are made to reduce noise conducted from the line - but you might not care about that noise

Someone Electro · 25th January 2004, 11:58 AM

Only that LM317 wod be a litle usefull to me.

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22nd January 2004, 07:12 PM	(permalink)
Sebi	The 22uF in feedback loop not a good idea: the circuit respond very slowly for output changing.

22nd January 2004, 10:23 PM	(permalink)
panic mode	VENERABLE POWER SUPPLY Another problem is non linear output. About half of turn on the potentiometer will make only ca. 1/2Volt change on the output (from 1.2 to 1.7). Make sure that potentiometer end connected to 100 Oh resistor is shorted to wiper.

22nd January 2004, 10:28 PM	(permalink)
panic mode	I don't see why you need 1/2Watt (500mW) rating for 100Ohm resistor. It will never see even 15mW but sure it doesn't hurt to oversize.

22nd January 2004, 10:30 PM	(permalink)
panic mode	The miliamp meter should have shunt.

23rd January 2004, 08:41 PM	(permalink)
Sebi	Right, Ron: i've also found it in my catalog, but - as You wroted - also need a diode. But all application show the potmeter between adj. and GND pins, not as voltage divider...

25th January 2004, 11:58 AM	(permalink)
Someone Electro	Only that LM317 wod be a litle usefull to me. __________________ Il give you shocking experience.