This is a simple multi voltage step down converter circuit. You can set multiple DC Output Selection 3V, 6V, 9V by the selector switch. It is a fixed 200mA Regulator. Though it is very easy, it still interesting for learning. Sometimes you may use it.
This circuit will generate a smaller DC output voltage from a larger DC input voltage.
It is quick and simple to make. By changing the value of the Zener diode. The circuit can universal adapt to provide other output voltages.
The working circuit
The multi voltage step down converter circuit
This circuit has a difference from the Zener diode regulator circuits. First of all, we use many the Zener diode in series. A chain of 3V Zener diode, this increases the output by +3V for every diode using.
It can maintain the regulated Vout in many level, as we choose on the selector switch.
- 3V the voltage across only from ZD1
- 6V volts ZD1+ZD2 (3+3)
- 9V, the voltage across ZD1+ZD2+ZD3 (3+3+3)
- 12V the voltage across ZD1+ZD2+ZD3+ZD4 (3+3+3)
Next, Suppose that the 15V input voltage flow to a resistor-R1, the base of Q1 2N3904. To bais Q1-2N3904 works. Then, the large current flow from collector to emitter of Q1 to the output.
At the same time, the series of Zener diodes also connect to the base of Q1.
Thus, the output voltage has the stable. And the current is higher than using an only Zener diode.
Final, Capacitor-C1 will smooth (filter) the pulsating voltage at the output power supply into a steady direct current (DC).
Parts you will need
Q1- 2N3904 – 0.4A 40V NPN transistor
?You may use BD139 to increase the output current more than 0.5A
R1 – 1K 0.5W resistors
ZD1 to ZD4 = 3V 1W Zener diodes
C1 – 470uF 25V Electrolytic capacitor
?We are sorry in the circuit. We’re wrong, it’s not 4700 uF.
But you can use it no problem. Just it expensive than 470uF only.
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