Please check my LM317T schematic for errors.

SgtWookie

Joined Jul 17, 2007
22,219
My concern is there is no specifications given for desired performance.

It looks like you are expecting to get about 1.2v to ~22v out, but you didn't mention at what currents.

Keep in mind that this will work OK for moderate currents at 15v-22v, but you will have too much heat to get rid of in the regulator at low voltage out.
 

Wendy

Joined Mar 24, 2008
22,163
I would get rid of D6 and C3, you want the fastest response you can get out of this chip, and they would only slow things down regulation wise.

If C4 is an electrolytic (which is what is shown) it needs replaced with a non-electrolytic, this is because it is there to suppress possible oscillations. It is basically very similar in function to the sticky Decoupling or Bypass Capacitors, Why? You need a cap that can high frequency transients, which electrolytics can't.

C1 may be a bit small. I say may because without knowing the upper current limits it is impossible to tell. It fills in the gaps caused by the pulsating DC created by the diode bridge. The more current drawn from this circuit, the deeper the valley between the DC pulses. As long as these pulses are greater than the LM317 set point, the LM317 regulator will compensate.

Hope it helps.

20 years ago Radio Shack sold a PCB for the LM317. I used it and made a power supply that is virtually identical to yours. I did include a simple analog voltmeter, with a switch to add a X2 measured voltage function. If I were to do it again I would also add a ammeter.

Basic Bench Top Power Supplies

Power supplies are one of the few projects that are practical to DIY for a hobbiest. If you take good pictures you could even post it in the completed projects forum. Pictures aren't that necessary, but they are nice.
 
Last edited:

Ron H

Joined Apr 14, 2005
7,014
I would get rid of D6 and C3, you want the fastest response you can get out of this chip, and they would only slow things down regulation wise.
I don't know what it does to response time, but this circuit is recommended by TI/National. See fig. 3 in the datasheet.
The adjustment terminal can be bypassed to ground on the
LM117 to improve ripple rejection. This bypass capacitor prevents
ripple from being amplified as the output voltage is
increased. With a 10 μF bypass capacitor 80dB ripple rejection
is obtainable at any output level. Increases over 10 μF do
not appreciably improve the ripple rejection at frequencies
above 120Hz. If the bypass capacitor is used, it is sometimes
necessary to include protection diodes to prevent the capacitor
from discharging through internal low current paths and
damaging the device.
 
Top