I know this is old post. I read almost all the comments. Funny indeed.

This is a DIY project. Some DIY is not logical, just for the hell of it. The designer is experimenting. Help him.

If you have a better mouser trap, publish it and show us how.

LOL, Maxim (an IC maker) actually, in Application Note 1923, does just that (150mW output from phone line, off-hook, using ICs Max253 and Max667).

Back to 7805. Per spec, the designer needs input capacitor and output cap. on 7805 for proper operation.

When drawing more than 20mA, it will be 'off-hook' and the phone line DC Voltage will drop to 7.5V-6.2V. At 6.2V the low side, 7805 is unable to output 5V. 7805 needs about 2.5V drop-out (Vin-Vout). Recommend to use a low drop-out (<=1.2V) linear regulator, or build a discrete regulator.

Since it is off-hook, there will be no high Voltage ring signal (90Vrms AC). Surely he has to be careful at the moment hooking his kit to the phone line. Maybe just happen to be a call coming in, and the 90Vac will fry the 7805 and possibly the device connected to it.

There are ways to fix this. Let's make it work rather than criticize.

You can connect up to 5 old type phones to phone line (5xREN). If you have Fiber Optics from the street side, like me, then the DC is from a battery backup panel (UPS + maintainer/charger), at your house! You can then even connect more load! If you later cancel phone line service, you can use it any which way! You own the battery backup panel. I'm told battery replacement is my cost+labor.

IMO, I would do on-hook DIY though.

That is, drawing less than 20mA. Then protection circuit ahead of it to prevent high ring Voltage intrusion. A low power 5V-out buck converter will do (Step-down switching regulator: from high to low Voltage).

48Vx18mA=0.86W, 80% efficiency to 0.86Wx0.8=0.69W, 0.69W/5V=138mA. Not bad!

And it can connect to phone line 24/7 without affecting phone operation (call out, receive calls).

Not just for charging, 138mA is plenty for lighting LEDs. 0.69W can power LEDs to 55 Lumens. Suitable as bedside light or bedside book light.

Compared to this DIY, 5Vx75mA=0.375W. Nearly double the power!

DIY project for fun! Help to improve it!