LM317 power supply - Page 2 - Electronic Circuits Projects Diagrams Free

bananasiong · 8th January 2007, 02:08 AM

If I don't use the center tap, then the frequency is lower (60 Hz) but not twice of the incoming frequency. So I need a larger capacitor right? But I don't get a 12000 µF from the lab, the maximum I think is only 1000 µF so I have to buy it

audioguru · 8th January 2007, 02:46 AM

Use a 4-diode bridge rectifier module for 120hz full-wave rectification. The center-tap and one end is 12VAC and end to end is 24VAC.
1000uF will create 2Vp-p of ripple when the circuit has a 235mA load and way too much ripple when the circuit has a 1A load. Use two 4700uF, three 3300uF, five 2200uF or one dozen 1000uF capacitors in parallel.

ljcox · 8th January 2007, 07:36 AM

Quote:

Originally Posted by bananasiong

If I don't use the center tap, then the frequency is lower (60 Hz) but not twice of the incoming frequency. So I need a larger capacitor right? But I don't get a 12000 µF from the lab, the maximum I think is only 1000 µF so I have to buy it

It does not matter whether you use 2 diodes and the centre tap or a rectifier bridge. Either way it is full wave rectification.

So if your mains frequency is 60 Hz, then the output of the rectifier will 120 Hz in both cases.

Only half wave rectification will result in 60 Hz.

mvs sarma · 8th January 2007, 09:20 AM

Hi,
For a variable power supply, it is always better to have theree rages with secondary tapped at three ranges (0-12-18-24) and switched, thereby minimizing power loss across the device(LM317). Use of single winding whethwr with or without center tap, and working at low output with high currents --we deifinitely waste power and further we try to cool the device ba a fan, to incerase wastage.

I had seen bench top power supplies that have automatic switching of secondary tap as you try to incerase out put voltage adj POT. They have used relays.

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8th January 2007, 02:08 AM	#16
bananasiong	If I don't use the center tap, then the frequency is lower (60 Hz) but not twice of the incoming frequency. So I need a larger capacitor right? But I don't get a 12000 µF from the lab, the maximum I think is only 1000 µF so I have to buy it __________________ bananasiong

8th January 2007, 02:46 AM	#17
audioguru	Use a 4-diode bridge rectifier module for 120hz full-wave rectification. The center-tap and one end is 12VAC and end to end is 24VAC. 1000uF will create 2Vp-p of ripple when the circuit has a 235mA load and way too much ripple when the circuit has a 1A load. Use two 4700uF, three 3300uF, five 2200uF or one dozen 1000uF capacitors in parallel. __________________ Uncle $crooge

8th January 2007, 09:20 AM	#19
mvs sarma	Hi, For a variable power supply, it is always better to have theree rages with secondary tapped at three ranges (0-12-18-24) and switched, thereby minimizing power loss across the device(LM317). Use of single winding whethwr with or without center tap, and working at low output with high currents --we deifinitely waste power and further we try to cool the device ba a fan, to incerase wastage. I had seen bench top power supplies that have automatic switching of secondary tap as you try to incerase out put voltage adj POT. They have used relays. __________________ Regards, Sarma.