How it works? - Electronic Circuits Projects Diagrams Free

wkyong · 30th April 2008, 02:29 AM

Pls see attached ,can anyone explain how R1 & Q1 contribute to this high current power supply?

dknguyen · 30th April 2008, 02:36 AM

THe resistor is making a feedback loop for Q1 so it is dropping the extra voltage across it the same way the LM is dropping extra voltage in order to produce a lower, regulated voltage. Q1 and R1 are like an amplifier that is in parallel with the LM to increase current output. A1 is using the LM's regulated voltage in own feedback loop to imitate and assist the LM in current output capability.

audioguru · 30th April 2008, 02:52 AM

The transistor is turned off and the regulator regulates low load currents.
When the current in the load increases then it also increases in the regulator and when it causes 0.7V across the 3 ohms resistor (0.7V/3 ohms= 233mA) then the transistor turns on and passes any more current.

If the output is shorted then the current will be extremely high and the transistor will be destroyed. A second transistor can be added to limit the max current.

Hero999 · 3rd May 2008, 06:47 PM

You are not using the LM78xx to it's full potential change the resistor to 0.75

hm: to work it a little harder and take some of the stain off the transistor. Of course, if you're using this for a high input-output voltage differential then stick with the 3

hm: as the LM78xx limits the current to about 250mA at differentials over 15V.

The p

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Similar Threads
Title	Starter	Forum	Replies	Latest
Is this Cicuits Works ?	AboZakaria	Alternative Energy	11	10th June 2008 09:25 AM
My button works like magic, I only have to hover my finger over it	jimfraseruk	Micro Controllers	31	13th August 2007 08:42 AM
How this circuit works	fugrammer	General Electronics Chat	15	25th October 2006 03:57 PM
Randomness of 16F84 program - sometimes works somtimes doesn	FusionITR	Micro Controllers	10	28th February 2006 10:06 AM
what works in the simulator does not work on hardware???	spyghost	Micro Controllers	7	26th May 2004 12:15 PM

30th April 2008, 02:36 AM	(permalink)
dknguyen	THe resistor is making a feedback loop for Q1 so it is dropping the extra voltage across it the same way the LM is dropping extra voltage in order to produce a lower, regulated voltage. Q1 and R1 are like an amplifier that is in parallel with the LM to increase current output. A1 is using the LM's regulated voltage in own feedback loop to imitate and assist the LM in current output capability. __________________ NO, that picture isn't me so don't bother asking if we can be friends.

30th April 2008, 02:52 AM	(permalink)
audioguru	The transistor is turned off and the regulator regulates low load currents. When the current in the load increases then it also increases in the regulator and when it causes 0.7V across the 3 ohms resistor (0.7V/3 ohms= 233mA) then the transistor turns on and passes any more current. If the output is shorted then the current will be extremely high and the transistor will be destroyed. A second transistor can be added to limit the max current. __________________ Uncle $crooge

3rd May 2008, 06:47 PM	(permalink)
Hero999	You are not using the LM78xx to it's full potential change the resistor to 0.75hm: to work it a little harder and take some of the stain off the transistor. Of course, if you're using this for a high input-output voltage differential then stick with the 3hm: as the LM78xx limits the current to about 250mA at differentials over 15V. The p __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez