One of my friends asked. Can we build the switching dc power supply circuit with 2 transistor? The applications IC that Sometimes is difficult. A some number IC is hard to find. and very expensive. When considering Applications for some time. We do not need to use a high current. and have sufficient space to install circuits. The selection use the transistors. Therefore as an alternative to saving, and extremely value for money.
How it works
In Figure 1 it is design of the switching regulator, which is a step down dc converter converts the voltage from 15-20 volts to a voltage of 12 volts.
The important components is T1 act as switching and has a common components The main are L1, D1 transistors, NPN+PNP Acted to feed back to each other. Increased frequency generators or to Makes the switch to run continuously. Only in this circuit of coil is not up because there is a voltage detector with C2, R4 and zener diode D2(C12) to control the voltage
When we apply dc current to this circuit the transistor T2 causes bias because the current flow through R5 to bias makes T2(BC550) into the current conduction Impact to the T1.(2N2905) Makes T1 has current flow into the emitter pin to base pin.
To send the current to pass through the introduction of T2(BC550). This case therefore equivalent to T2(BC550) a unit to control bias T1. Makes, T1(2N2905) apply current to the collector to the the coil L1. However, because the base pin of T1 has zener diode set the voltage value constant. It is determined the constant voltage of 12 volts. When the output voltage rise to 12 volts. As a result, to Makes up with the emitter voltage of T2. It is the same point. As a result, T2 turn off. Stop conduction. And, providing T1 stop conduct current, too.
Now the coil will start providing current., To accumulate at C1 with a rectifier D1(BTA43). And when compared an electrical potential to ground. To the left of L1 negative voltage and the current of L1 has gone. Working new round will occur.
If we consider this system. Found that the performance of this circuits by more than 90% of quite.
This circuit is not design PCB. If you do not want to design own PCB. Or use universal PCB Board that difficult.
I would recommend a DC Converter Power Supply Buck Step Down Regulator In:4-40V Out:1.5-35V. It is a DIY Kits available for use. I hope this guide is helpful for you.
Although the circuits are is not the same. It can be switching DC regulator as well.