# power supply using lm317

#### Tonyr1084

Joined Sep 24, 2015
7,251
Looking over the post I see I got some numbers a little mixed up. Instead of 41.345 it should have been 41.543 VAC RMS

PP would still be 58.742 And my 41.543 comes from the reading on XMM2. The ORIGINAL screen shot showed XMM2 as 44.073 VAC RMS. Whichever is correct, multiply that figure by 1.414 (the reciprocal of a 45° sine).

Last edited:

#### Syed Naqvi 7

Joined Oct 14, 2015
14
See if this clears things up for you:
.....
View attachment 103659
Thank you so much for your precious time.You have explained it in a lot better way.
Now I am using two scopes and getting the correct graph.
Thanks once again.

#### Syed Naqvi 7

Joined Oct 14, 2015
14
Thank you all of you for helping me out of this problem....

#### Syed Naqvi 7

Joined Oct 14, 2015
14
I need a bit more favor...
I want to know which components in multisim are which?
i'm using transformer TS MISC VIRTUAL and DIODE VIRTUAL and I want to know about the values of components and which o use when....suggest me any link for it

#### hp1729

Joined Nov 23, 2015
2,304
See if this clears things up for you:

TP (Test Points) 1 & 2 are your 220 VAC input. The input is read as an RMS voltage (Root Mean Square), NOT P to P (Peak to Peak). TP 3&4 are your output from the transformer and are 41.345 VAC RMS. The P to P (or PP) value is 58.742 VAC PP. Your meter will read the RMS value while the scope will display the PP value. If you're being confused by seeing nearly 60 VAC PP on the scope - don't be. That's what it should look like.

TP 5 to 7 show the rectified voltage. You're getting close to the PP value because C1 is storing up to the PP voltage. Thus, you get nearly 58.742 VDC. Remember, it's been rectified and will be slightly lower than the AC PP value. The reason is the voltage drop through the diodes (the bridge rectifier). TP 6&7 are your regulated output test points.

Instead of using a two channel scope - try a single channel. Set it to DC coupling and connect it to TP 3&4. Just like Crutschow has said a number of times before - you WILL get a pure sign wave. NEXT, connect the scope to TP 5&7 You will see the PP value close to a straight line. You should see some ripple because the rest of the circuit is drawing down C1. C1 is your input buffer. C2 is your output buffer. C1 stabilizes the incoming signal from the AC ripple and C2 stabilizes the output making up for sudden spikes in the drain current of your load (the LED). It stops transient spikes from affecting components further down the line.

Put your meter XMM1 on the output (TP 6&7) and adjust the value of RP1 (Potentiometer) to the desired output of your circuit. This WILL work. You WILL see the sign wave as expected on 3&4. You WILL see 58.742 VAC PP. Your regulator will see approximately 58.742 VAC DC. Your output will be what you set it to be.

View attachment 103659
Input voltage is too high for the LM317. Maybe use LM317HV?

#### KeepItSimpleStupid

Joined Mar 4, 2014
5,088
It's Magic Smoke not blue smoke - Go get yourself a sticker https://www.adafruit.com/product/691 and read the Wikipedia article referenced.

You need to know these technical terms!