delabs Circuits

Thursday, September 28, 2017

Mains Stability and Supply Regulation

I have problem with my power supply... . The power supply uses LM317 and TIP2955 and the unstable AC net here causes the output to drop sometimes below 5V. The normally output is 13,5V. I like to look at your schematics to improve my power supply.

Mail from WV

See some circuits here ...

See the Insides of a DIY Ham Radio Power Supply

DIY Ham Radio Power Supply

You have to ensure at least a min of 15V AC to the Bridge or diodes on transformer. Only if a DC of around min 17V is available at input DC of 13.5 can be managed by this circuit. This circuit will not boost a voltage from a lower value for that you need Switching Boost Supplies.

Use AC Voltage Stabilizers or ServoStabilizers to maintain a stable AC Supply.

WorkBench Dual Power Supply
LM317 - Simple Workbench Dual Power Supply

delabs

.....I like to compare with my schematics from our power supply. We have something very strange.. the backup battery takes over and don't cause a voltage drop when I disconnect power supply from 220V AC lines.. but the backup battery can not anticipate the disturbances in the 220V AC lines and gives a very short power drop at the output..

We have sometimes very short power drops at the output of the power supply.. Do you have any idea what is wrong? The transformer is 16V AC 3A
Reply from WV

You can double the size of filter caps at input. use something like 10,000uF, if you draw 3A a 10000uf across the input rectifier may help. Or you have to use a battery of 12V after the LM317. So that the battery can supply the short outages.
delabs

But that is exactly my problem, we have a large battery after the power supply of 13,5V 5,5Ah, but it doesn't help to avoid the powerdips after the power supply..
Reply from WV

I feel you have a ground loop problem, The wires to the battery seem thin. I feel the potential across a ground wire must be lifting up when mains fluctuates.

The PCB ground plane may be thin or absent, check all ground and supply wires. Make all supply wires and Tracks thick and radiate from a center copper lug reference. Both positive, negative and ground tracks reinforce with lead or copper braids. Use decoupling caps at every stage.

delabs