0 High Efficiency 5V converter using LM2671 IC

The circuit step down  DC (8V - 40V DC) to 5V DC. The circuit can deliver up to 500mA current. It can be used to power 5V rated devices and chargers specially those using USB port as power source.

5V converter schematic

Part List:
C1 - 47uF electrolytic capacitor rated 50V
C2 - 100nF Mylar or ceramic
C3 - 47uF electrolytic capacitor rated 16V
D1 - 3.3A, 50V Schottky Rectifier, IR 30WQ05F
IC - LM2671-5.0 IC
L1 - 68uH inductor (500mA minimum current)
Vin - 8V to 40V DC

6 12V to 3V buck converter

There are many ways of converting 12V to 3V. You can use regulator IC, transistors, zener diodes and many more. The problem of these converters is very low efficiency and most of their power is converted to heat. A dc-dc converter is a need in this case.
The circuit below is a simple buck converter that converts a 12V DC (usually from battery) to 3V DC. The heart of the circuit is the 555 timer IC that controls the Mosfet and the entire circuit. This converter can deliver a current up to 5A at a 3V load. Current can be made even higher if Q1, D1, and L1 are replaced with much higher current capacity.

buck converter diagram

To make the output voltage more regulated, you can add the circuit below across the converter output.

regulator circuit

Part List:
R1 - 5 kilo ohms 1/4W
R2 - 2.7 kilo ohms 1/4W
R3 - 1.2 kilo ohms 1/4W
R4 -  just remove (its a dummy load)
C1, C2 - 100 nano-Farad capacitor
C3 - 2200uF electrolytic capacitor rated 16V
Q1 - IRF9530 or any similar P-channel Mosfet (10A current min)
D1 - SR506 or any diode rated 6A min (SCHOTTKY preferable)
L1 - 1mH Inductor minimum 6A current rating
555 - LM555 IC
Regulator circuit (optional)
      Dz - 1N5223B or 2.7V zener diode min 1/2W
      R - 120 ohms 1W
      Q - 2N3055, TIP41C or similar NPN transistor

555 pins

2N2222 pins

IRF9530 or PMOS pins

10 12V to 5V converter (555IC + Mosfet)

Buck converter circuit powered by a 12V battery down to 5V DC. Circuit is controlled by 555 timer IC that is operated in monostable mode.  The circuit is similar to 12V to 5V converter using BJT transistor but its much more stable, efficient, and higher current output (around 5A or even higher). The converter output voltage is given by the approximate equation:
Vout/Vin = (1-D); D is the Duty Cycle of 555 IC output.
See 555 timer calculator for more info about output frequency, duty cycle and combinations of resistors and capacitor.

schematic diagram

Part List:
R1 - 2 kilo ohms 1/4W
R2 - 5 kilo ohms 1/4W
R3 - 1.2 kilo ohms 1/4W
R4 - 27 ohms 1W (optional and can be removed)
C1, C2 - 100 nano-Farad capacitor
C3 - 2200uF electrolytic capacitor rated 16V
Q1 - IRF9530 or any similar P-channel Mosfet (10A current min)
D1 - SR506 or any diode rated 6A min (SCHOTTKY preferable)
L1 - 1mH Inductor minimum 6A current rating
555 - LM555 IC

555 pins

P-Channel Mosfet

When the converter is unloaded, its output is usually high but it drops to 5V when loaded. If you want to make your converter  more stable  (5V output loaded or unloaded), try to add the regulator circuit across its output pins.

regulator circuit

Regulator part list:
Dz - 1N4732A or 4.7V zener diode minimum 1W
R1 - 56 ohms 1W
Q - TIP41C, 2N3055 or similar NPN transistor

4 12V to 10V buck converter using 555 timer IC

This  buck converter is driven by 555 timer IC and converts 12V dc from a battery to 10V dc. The 555 IC  (operated in astable mode ) generates pulses of voltages of 83.3% duty cycle. This pulses turns the transitor on and off and drives the inductor L (buck converter circuit), and as a result generates 10V dc output. For this configuration,

Ra =240K

Rb =4.7K

C =10nF

Q = TIP41C or any of the same specs

Cout = 2200uF (higher the better)

You can add 1N4740A zener diode for output stability.

1 12V to 9V buck converter using 555 timer IC

converter schematic

This  buck converter is driven by 555 timer IC and converts 12V dc from a battery to 9V dc. The 555 IC  (operated in astable mode ) generates pulses of voltages of 75% duty cycle. This pulses turns the transistor on and off and drives the inductor L (buck converter circuit), and as a result generates 9V dc output. For this configuration,

Ra =27K

Rb =10K

C =10nF

L = 20 turns of #22AWG in antenna bar

Q = TIP41C or any of the same specs

Cout = 2200uF (higher the better)

You can add 1N4739A zener diode at the output side for better regulation.

3 12V to 6V buck converter using 555 timer IC

This  buck converter is driven by 555 timer IC and converts 12V dc from a battery to 6V dc. The 555 IC  (operated in astable mode ) generates pulses of voltages of 50% duty cycle. This pulses turns the transistor on and off and drives the inductor L (buck converter circuit), and as a result generates 6V dc output. For this configuration,

Ra =18K

Rb =18K

C =10nF

Q = TIP41C or any of the same specs

Cout = 2200uF (higher the better)

L= 40 turns #22AWG magnetic wire on antenna bar

For better regulation, you can add zener diode (1N5233B) across  the output.

converter schematic

8 12V to 5V buck converter using 555 timer IC

converter schematic

This  buck converter is driven by 555 timer IC and converts 12V dc from a battery to 5V dc. The 555 IC  (operated in astable mode ) generates pulses of voltages of 42% duty cycle. This pulses turns the transistor on and off and drives the inductor L (buck converter circuit), and as a result generates 5V dc output. For this configuration,

Ra =20K

Rb =27K

C =1nF

Q = TIP41C or any of the same specs

Cout = 2200uF (higher the better)