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.

LM2678 voltage regulator

aPowerSupply.com — Sun, 29 Jan 2012 14:34:30 +0000

The LM2678 series of regulators are monolithic integrated circuits for a step-down switching voltage regulator capable of driving up to 5A loads with excellent line and load regulation characteristics. High efficiency (>90%) is obtained through the use of a low ON-resistance DMOS power switch. The series consists of fixed output voltages of 3.3V, 5V and 12V and an adjustable output version.

LM2678 12vdc 5amp voltage regulator schematic

LM2678 features

Efficiency up to 92%
Simple and easy to design with (using off-the-shelf external components)
120 mΩ DMOS output switch
3.3V, 5V and 12V fixed output and adjustable (1.2V to 37V ) versions
50μA standby current when switched OFF
±2%maximum output tolerance over full line and load conditions
Wide input voltage range: 8V to 40V
260 KHz fixed frequency internal oscillator

LM2678 applications