Power supply circuit » Stabilized

L165 symmetrical power supply

aPowerSupply.com — Mon, 14 May 2012 06:43:14 +0000

The compact 5 pin L165 IC general a stabilized symmetrical power supply from a single asymmetrical power supply. The output voltage is however, half of the input voltage. One needs to add the ripple filter capacitors C1, C2, C3 and C4 and some resistors for setting the symmetry. In constructing the circuit, place the capacitors C1 and C2 as close to the IC as possible.
On the other hand, place the capacitors C3 and C4 close to the output jacks. Make sure that the circuit lines on the pcb are properly dimensioned to handle high current levels. Current levels up to 3 amperes can flow through the circuit. Additionally, provide a proper heatsink for the L165 IC.

The L165 IC can also be viewed as a voltage amplifier. It amplifies the voltage appearing at the junction between R1 and R2.
One cas also replace the IC with TCA1365. However, when using the TCA IC, pins 3 and 4 have to be connected together. Also connect a 220pF capacitor between pins 5 and 6.

Symmetrical power supply schematic

Symmetrical supply printed circuit layout

Variable Power Supply with UA78G/UA79G

aPowerSupply.com — Fri, 11 May 2012 05:37:38 +0000

A stable variable power supply with an adjustable output voltage from 5 volts to 30 volts can be easily constructed with the regulator ICs UA78G or UA79G. These ICs differ from the common three-terminal regulator since their output voltages are adjustable by a voltage level at their control inputs. The maximum current delivered by these ICs is 1 ampere.

The unregulated voltage must be at least 5 volts higher than the desired output level to maintain stability. The input voltage however must not exceed 40 volts. The maximum dissipation of the IC is 15 watts.

The variable power supply circuit presented here is designed to give maximum voltage level of 28 volts. If P1 is replaced with 25K potentiometer, the regulator can deliver up to a maximum of 30 volts. Capacitors C1 and C2 stabilize the IC and they must be connected as close as possible to the IC terminals.

The IC UA79G delivers negative voltage level. Take note that the two ICs have different terminal connections.

UA78G/UA79G power supply circuit diagram

Variable power supply PCB layout

Voltage regulator

aPowerSupply.com — Tue, 24 Apr 2012 22:33:26 +0000

Voltage regulator IC’s, with 3 pins, from LM7805 and LM7812 series are excellent for usage in voltage regulator circuits. If you need higher currents, up to 3 A, you must add a complementary transistor, T2 in this schematic. In a normal design, in case of a shortcircuit, the power dissipation can be very high. This problem can be solved using the voltage regulator design presented bellow. Through electronics tehniques, when shortcircuits occurs this circuit design reduces the maximum current consumption when the output voltage drops.

At this voltage regulator prototype the maximum current, with output shortcircuited it was only 0,5 A, so no overheating occured.
In this dc voltage regulator circuit, T1 is for current limitation. As soon as the voltage on the R2+R3 becomes higher than 0,6-0,7 V, T1 opens, which leads to a reduction to zero of the T2 base current. The voltage at which the shortcircuit protection starts to act, is given by voltage sum on R2 and R3. R3 and R4 resistances form a T2 voltage divider.

Shortcircuit protected voltage regulator schematic

This is LM7805 5V dc voltage regulator circuit diagram has not been tested.

Universal power supply circuit

aPowerSupply.com — Fri, 20 Jan 2012 10:33:21 +0000

This universal power supply contains, beside the bridge rectifier, a voltage stabilizer (78xx) and a pnp power transistor. This combination allow a load current up to 5 A. As you know a voltage stabilizer in a TO-220 package can deliver up to 1A. The additional power transistor takes the load current of about 200mA.
The transformer voltage must be greater with 4V than DC stabilized voltage. C1 is calculated for 1A/1000uF, so at 5A C1 must have 4700uF. Both, transistor and voltage stabilizer must be mounted on a heatsink.