Voltage Inverter Circuit

This simple and inexpensive circuit can produce a dual (positive and negative) voltage from a single supply input. It is therefore extremely useful for powering opamp and other circuits that require a dual voltage from a single battery. The circuit will operate at an input voltage from around 5V to 20V and produce a output from +-2.5V to +-10V.

Schematic-

Parts List-
R1 - 1 - 1M Linear Pot
C1,C2 - 2 - 15uf 25V Electrolytic Capacitor
U1 - 1 - LM380 Audio Amp Chip
MISC - 1 - Heatsink For U1, Binding Posts (For Input/Output), Wire, Board

Notes -
1) U1 dissipates around 1W and will therefore require a heatsink.

2) R1 is used to equalize the outputs. The first time you use the circuit, it should be set to mid range and then adjusted with the aid of a voltmeter. Measure each output while adjusting. The circuit is calibrated when both outputs read the same voltage (either positive or negative).

Read More

6V to 12V Converter Circuit

This inverter circuit can provide up to 800mA of 12V power from a 6V supply. For example, you could run 12V car accessories in a 6V (British?) car. The circuit is simple, about 75% efficient and quite useful. By changing just a few components, you can also modify it for different voltages.

Schematic-

Parts List-
R1, R4 - 2 - 2.2K 1/4W Resistor
R2, R3 - 2 - 4.7K 1/4W Resistor
R5 - 1 - 1K 1/4W Resistor
R6 - 1 - 1.5K 1/4W Resistor
R7 - 1 - 33K 1/4W Resistor
R8 - 1 - 10K 1/4W Resistor
C1,C2 - 2 - 0.1uF Ceramic Disc Capacitor
C3 - 1 - 470uF 25V Electrolytic Capcitor
D1 - 1 - 1N914 Diode
D2 - 1 - 1N4004 Diode
D3 - 1 - 12V 400mW Zener Diode
Q1, Q2, Q4 - 3 - BC547 NPN Transistor
Q3 - 1 - BD679 NPN Transistor
L1 - 1 - See Notes
MISC - 1 - Heatsink For Q3, Binding Posts (For Input/Output), Wire, Board

Notes-
1. L1 is a custom inductor wound with about 80 turns of 0.5mm magnet wire around a toroidal core with a 40mm outside diameter.

2. Different values of D3 can be used to get different output voltages from about 0.6V to around 30V. Note that at higher voltages the circuit might not perform as well and may not produce as much current. You may also need to use a larger C3 for higher voltages and/or higher currents.

3. You can use a larger value for C3 to provide better filtering.

4. The circuit will require about 2A from the 6V supply to provide the full 800mA at 12V.

Read More

Voltage Inverter

This simple circuit is a good solution to the powering a dual supply op amp from a single battery problem. The circuit simply takes a positive voltage and inverts it. It uses only one 555 timer and a few other passive components, so it doesn't add much in the way of size and cost to a project.

Schematic-

Parts List-
R1 - 1 - 24K 1/4 Watt Resistor
R2 - 1 - 56K 1/4 Watt Resistor
C1 - 1 - 3300pF 25V Ceramic Capacitor
C2 - 1 - 47uF 25V Electrolytic Capacitor
C3 - 1 - 10uF 25V Electrolytic Capacitor
C4 - 1 - 100uF 25V Electrolytic Capacitor
D1, D2 - 2 - 1N4148 Silicon Diode
U1 - 1 - 555 Timer
MISC - 1 - Wire, Board

Read More

12V to 120V Inverter Circuit

Parts -
C1, C2 - 2 - 68 uf, 25 V Tantalum Capacitor
R1, R2 - 2 - 10 Ohm, 5 Watt Resistor
R3, R4 - 2 - 180 Ohm, 1 Watt Resistor
D1, D2 - 2 - HEP 154 Silicon Diode
Q1, Q2 - 2 - 2N3055 NPN Transistor (see "Notes")
T1 - 1 - 24V, Center Tapped Transformer (see "Notes")
MISC - 1 - Wire, Case, Receptical (For Output)

Notes
1. Q1 and Q2, as well as T1, determine how much wattage the inverter can supply. With Q1,Q2=2N3055 and T1= 15 A, the inverter can supply about 300 watts. Larger transformers and more powerful transistors can be substituted for T1, Q1 and Q2 for more power.

2. The easiest and least expensive way to get a large T1 is to re-wind an old microwave transformer. These transformers are rated at about 1KW and are perfect. Go to a local TV repair shop and dig through the dumpster until you get the largest microwave you can find. The bigger the microwave the bigger transformer. Remove the transformer, being careful not to touch the large high voltage capacitor that might still be charged. If you want, you can test the transformer, but they are usually still good. Now, remove the old 2000 V secondary, being careful not to damage the primary. Leave the primary in tact. Now, wind on 12 turns of wire, twist a loop (center tap), and wind on 12 more turns. The guage of the wire will depend on how much current you plan to have the transformer supply. Enamel covered magnet wire works great for this. Now secure the windings with tape. Thats all there is to it. Remember to use high current transistors for Q1 and Q2. The 2N3055's in the parts list can only handle 15 amps each.

3. Remember, when operating at high wattages, this circuit draws huge amounts of current. Don't let your battery go dead :-).

4. Since this project produces 120 VAC, you must include a fuse and build the project in a case.

5. You must use tantalum capacitors for C1 and C2. Regular electrolytics will overheat and explode. And yes, 68uF is the correct value. There are no substitutions.

6. This circuit can be tricky to get going. Differences in transformers, transistors, parts substitutions or anything else not on this page may cause it to not function.

7. If you want to make 220/240 VAC instead of 120 VAC, you need a transformer with a 220/240 primary (used as the secondary in this circuit as the transformer is backwards) instead of the 120V unit specified here. The rest of the circuit stays the same. But it takes twice the current at 12V to produce 240V as it does 120V.

Read More

40W Fluorescent Lamp Inverter

Parts-
R1- 180 Ohm 1W Resistor
R2- 47 Ohm 1/4W Resistor
R3- 2.2 Ohm 1W Resistor (only needed once)
C1, C2- 100uF 16V Electrolytic Capacitor
C3- 100nF Ceramic Disc Capacitor
Q1- TIP 3055 or 2N3055 or equivalent
L1- See "Notes"
T1- See "Notes"
MISC- Wire, Case, Board, Heatsink For Q1, heatshrink, AM antenna rod for coil

Notes-
1) Wind L1/T1. You will need an AM antenna rod that is about 60mm (2.5 inches) long to wind T1/L1 on. T1/L1 are wound on the same core. Shrink a layer of heatshrink over the core to insulate it. Leave 50mm of wire at each end of the coils.
Primary: Wind 60 turns of 1mm diameter enamelled copper wire on the first layer and put a layer of heatshrink over it.
Feedback: Wind 13 turns of 0.4mm enamelled copper wire on the core and then heatshrink over that.
Secondary: This coil has 450 turns of 0.4mm enamelled copper wire in three layers. Wind one layer and then heatshrink over it. Do the same for the next two.

2) Calibrate/test the circuit. To calibrate/set up the circuit connect the 2.2 Ohm 1W resistor (R3) in series with the positive supply. Connect a 40W fluorescent tube to the high voltage ends of the transformer. Momentarily connect power. If the tube doesn't light immediately reverse the connections of L1. If the tube still doesn't work, check all connections. When you get the tube to light remove the 2.2 ohm resistor and the circuit is ready for use. You will not need R3 again.

3) This circuit is designed for 220V lamps. It will work with 120V units just fine, but will shorten the life of the tube.

Read More