make 1.5V to 5V !

In many cases can be very handy to be able to convert 1.5V to 5V. Then you can power microcontroller or LED from a single AA or AAA battery. It is simple to do this as there are special IC’s as MAXIM MAX1674 or MAX7176. This is step-up DC-DC converter that can convert voltages from 0.7V to any in range from 2V to 5.5V. MAX1676 have already preset pins for 3.3V and 5V, that makes easer integration in 3.3 and 5V circuits. IC can dissipate up to 444mW.

Bellow is a circuit that converts 1.5V to 5V.

Lets say wee need to get maximum output current 300mA, then wee need to put some efforts. Because output power is 5V·0.3A=1.5W. Lets say efficiency is 100% then the power drawn from battery will be 1.5W too. At 1.5V voltage this will be 1A current. Not all batteries can drive such currents. Other important part is inductor. For this wee need inductor with high current saturation which usually leads to increase of size.

• If current is over 300mA, then inductor inductance 47uH;

• If current is over 120mA, then inductor inductance 22uH;

• If current is over 70mA, then inductor inductance 10uH;

You will find recommended inductors in datasheet.

In this case if FB pin of MAX1614 is connected to ground, then output voltage is equal to 5V. If FB would be connected to OUT pin then output voltage would be 3.3V. If put voltage between OUT and ground, then we can control output voltage in range from 3.3V to 5V.

Biggest real efficiency of ic is at 120mA – 94%.

Manufacturer recommends to design PCB with sort and thick traces. Inductor should have minimal resistance.

Original source: www.radiokot.ru

Triangle and Squarewave Generator

Here is a simple triangle/squarewave generator using a common 1458 dual op-amp that can be used from very low frequencies to about 10 Khz. The time interval for one half cycle is about R*C and the outputs will supply about 10 milliamps of current. Triangle amplitude can be altered by adjusting the 47K resistor, and waveform offset can be removed by adding a capacitor in series with the output.

Source : http://ourworld.compuserve.com/homepages/Bill_Bowden/

Telephone Audio Interface

Audio from a telephone line can be obtained using a transformer and capacitor to isolate the line from external equipment. A non-polarized capacitor is placed in series with the transformer line connection to prevent DC current from flowing in the transformer winding which may prevent the line from returning to the on-hook state. The capacitor should have a voltage rating above the peak ring voltage of 90 volts plus the on-hook voltage of 48 volts, or 138 volts total. This was measured locally and may vary with location, a 400 volt or more rating is recommended. Audio level from the transformer is about 100 millivolts which can be connected to a high impedance amplifier or tape recorder input. The 3 transistor amplifier shown above can also be used. For overvoltage protection, two diodes are connected across the transformer secondary to limit the audio signal to 700 millivolts peak during the ringing signal. The diodes can be most any silicon type (1N400X / 1N4148 / 1N914 or other). The 620 ohm resistor serves to reduce loading of the line if the output is connected to a very low impedance.

source : http://ourworld.compuserve.com/homepages/Bill_Bowden/

Light-sensitive Alarm

The circuit detects a sudden shadow falling on the light-sensor and sounds the bleeper when this happens. The circuit will not respond to gradual changes in brightness to avoid false alarms. The bleeper sounds for only a short time to prevent the battery running flat. Normal lighting can be used, but the circuit will work best if a beam of light is arranged to fall on the light-sensor. Breaking this beam will then cause the bleeper to sound. The light sensor is an LDR (light-dependant resistor), this has a low resistance in bright light and a high resistance in dim light.

- The light-sensitivity of the circuit can be adjusted by varying the 100k preset.
- The length of bleep can be varied from 0.5 to 10 seconds using the 1M preset.

Using the 7555 low-power timer ensures that the circuit draws very little current (about 0.5mA) except for the short times when the bleeper is sounding (this uses about 7mA). If the circuit is switched on continuously an alkaline PP3 9V battery should last about a month, but for longer life (about 6 months) you can use a pack of 6 AA alkaline batteries.

source : http://www.free-electronic-circuits.com

FM Transmitter Circuit

This circuit is a simple two transistor (2N2222) FM transmitter. No license is required for this transmitter according to FCC regulations regarding wireless microphones. If powered by a 9 volt battery and used with an antenna no longer than 12 inches, the transmitter will be within the FCC limits. The microphone is amplified by Q1. Q2, C5, and L1 form an oscillator that operates in the 80 to 130 MHz range. The oscillator is voltage controlled, so it is modulated by the audio signal that is applied to the base of Q2. R6 limits the input to the RF section, and it's value can be adjusted as necessary to limit the volume of the input. L1 and C6 can be made with wire and a pencil. The inductor (L1) is made by winding two pieces of 24 gauge insulated wire, laid side by side, around a pencil six times. Remove the coil you have formed and unscrew the two coils apart from each other. One of these coils (the better looking of the two) will be used in the tank circuit, and the other can be used in the next one you build. The antenna (24 gauge wire) should be soldered to the coil you made, about 2 turns up from the bottom, on the transistor side, and should be 8-12 inches long. To make C6, take a 4 inch piece of 24 gauge insulated wire, bend it over double and, beginning 1/2" from the open end, twist the wire as if you were forming a rope. When you have about 1" of twisted wire, stop and cut the looped end off, leaving about 1/2" of twisted wire (this forms the capacitor) and 1/2" of untwisted wire for leads.

source : http://www.free-electronic-circuits.com

VU meter circuit for LM3915

This circuit uses just one IC and a very few number of external components. It displays the audio level in terms of 10 LEDs. The input voltage can vary from 12V to 20V, but suggested voltage is 12V. The LM3915 is a monolithic integrated circuit that senses analog voltage levels and drives ten LEDs providing a logarithmic 3 dB/step analog display. LED current drive is regulated and programmable, eliminating the need for current limiting resistors. The IC contains an adjustable voltage reference and an accurate ten-step voltage divider. The high-impedance input buffer accepts signals down to ground and up to within 1.5V of the positive supply. Further, it needs no protection against inputs of ฑ35V. The input buffer drives 10 individual comparators referenced to the precision divider. Accuracy is typically better than 1 dB.

source : http://www.free-electronic-circuits.com

Simple but reliable car battery tester

author: Jonathan Filippi

This circuit uses the popular and easy to find LM3914 IC. This IC is very simple to drive, needs no voltage regulators (it has a built in voltage regulator) and can be powered from almost every source.

This circuit is very easy to explain:

When the test button is pressed, the Car battery voltage is feed into a high impedance voltage divider. His purpose is to divide 12V to 1,25V (or lower values to lower values). This solution is better than letting the internal voltage regulator set the 12V sample voltage to be feed into the internal voltage divider simply because it cannot regulate 12V when the voltage drops lower (linear regulators only step down). Simply wiring with no adjust, the regulator provides stable 1,25V which is fed into the precision internal resistor cascade to generate sample voltages for the internal comparators. Anyway the default setting let you to measure voltages between 8 and 12V but you can measure even from 0V to 12V setting the offset trimmer to 0 (but i think that under 9 volt your car would not start). There is a smoothing capacitor (4700uF 16V) it is used to adsorb EMF noise produced from the ignition coil if you are measuring the battery during the engine working. Diesel engines would not need it, but i'm not sure. If you like more a point graph rather than a bar graph simply disconnect pin 9 on the IC (MODE) from power. The calculations are simple (default)

For the first comparator the voltage is : 0,833 V corresponding to 8 V
* * * * * voltage is : 0,875 V corresponding to 8,4 V
...
..
for the last comparator the voltage is : 1,25 V corresponding to 12 V

Have fun, learn and don't let you car battery discharge... ;-)

From: http://www.electronics-lab.com/

Nite Rider Lights

As a keen cyclist I am always looking for ways to be seen at night. I wanted something that was a novelty and would catch the motorists eye. So looking around at my fellow cyclists rear lights, I came up with the idea of 'NITE-RIDER'. NINE extra bright LED's running from left to right and right to left continuously. It could be constructed with red LEDs for use on the rear of the bike or white LED's for an extra eye catcher on the front of the bike.

All IC's are CMOS devices so that a 9V PP3 battery can be used, and the current drawn is very low so that it will last as long as possible.


The circuit comprises of ...

1 555 timer IC4.
1 4027 flip flop IC1.
2 4017 Decade Counter IC2 and IC3.
3 4071 OR gate IC5, IC6 and IC7.
1 470 Ohm resistor 1/4 watt R3.
2 10K resistors 1/4 watt R1 and R2.
1 6.8UF Capasitor 16V C1.
9 Super brght LED's 1 to 9.
1 9V PP3 Battery.
1 single pole switch SW1.
1 Box.

How The Circuit Works.

IC4, C1, R1 and R2 are used for the clock pulse which is fed to both the counters IC2 and IC3 Pin 14.

IC1 is a Flip Flop and is used as a switch to enable ether IC2 or IC3 at pin 13.

IC7a detects when ether IC2 or IC3 has reached Q9 of the counter pin 11.

IC5, IC6 and IC7a protects the outputs of the counters IC2 and IC3 using OR gates which is then fed to the Anodes of the
LED's 1 to 9.

From : http://www.electronics-lab.com/

Automotive 12V to +-20V converter (for audio amplifier)

Automotive 12V to +-20V converter (for audio amplifier)
author: Jonathan Filippi - www.cool-science.tk



The limitation of car supply voltage (12V) forces to convert the voltages to higher in order to power audio amplifiers.

In fact the max audio power x speaker (with 4 ohm impedance) using 12V is (Vsupply+ - Vsupply-)^2/(8*impedance) 12^2/32 = 4.5Watts per channel, that is laughable...

For powering correctly an amplifier the best is to use a symmetric supply with a high voltage differential. for example +20 - -20 = 40Volts
in fact
40^2/32 = 50 Watts per channel that is respectable.

This supply is intended for two channels with 50W max each (of course it depends on the amplifier used). Though it can be easily scaled up or the voltages changed to obtain different values.



click on image for higher resolution schematic



Overview - How it works

It is a classic push-pull design , taking care to obtain best symmetry (to avoid flux walking). Keep in mind that this circuit will adsorb many amperes (around 10A) so take care to reinforce power tracks with lots of solder and use heavy wires from the battery or the voltage will drop too much at the input.

The transformer must be designed to reduce skin effect, it can be done using several insulated magnet wire single wires soldered together but conducting separately. The regulation is done both by the transformer turn ratio and varying the duty cycle. In my case i used 5+5 , 10+10 turns obtaining a step up ratio of 2 (12->24) and downregulating the voltage to 20 via duty cycle dynamic adjust performed by the PWM controller TL494.

The step-up ratio has to be a little higher to overcome diode losses, winding resistance and so on and input voltage drop due to wire resistance from battery to converter.



Transformer design

The transformer must be of correct size in order to carry the power needed, on the net there are many charts showing the power in function of frequency and core size for a given topology. My transformer size is 33.5 mm lenght, 30.0 height and 13mm width with a cross section area of 1,25cm^2, good for powers around 150W at 50khz.

The windings , especially the primary must be heavy gauged, but instead of using a single wire it is better to use
multiple wires in parallel each insulated from the other except at the ends. This will reduce resistance increase due to skin effect. The primary and secondary windings are centertapped, this means that you have to wind 5 turns, centertap and 5 windings again. The same goes for the secondary, 10 turns, centertap and 10 turns again.

The important thing is that the transformer MUST not have air gaps or the leakage inductance will throw spikes on the switches overheating them and giving a voltage higher than expected by turn ratio prediction, so if your voltage output (at fully duty cycle) is higher than Vin*N2/N1 - Vdrop diode, your transformer has gap (of course permit me saying you that you are BLIND if you miss it), and this is accompanied with a drastical efficiency reduction. Use non-gapped E cores or toroids (ferrite).



Output diodes, capacitors and filter inductor

For rectification i preferred to use shottky diodes since they have low forward voltage drop, and are incredibly fast.
I used the cheap 1N5822, the best alternative for low voltage converters (3A for current capability).

The output capacitors are 4700uF 25V, not very big, since at high frequency the voltage ripple is most due to internal cap ESR fortunately general purpose lytics have enough low esr for a small ripple (some tens of millivolts). Also at high duty cycle they are feed almost with pure DC, giving small ripple. The filter inductor on the secondary centertap furter increases the ripple and helps the regulation in asymmetrical transients


Power switch and driving

I used d2pak 70V 80A 0.004 ohms ultrafets (Fairchind semiconductor), very expensive and hard to find. In principle any fet will work, but the lower the on-resistance, the lower the on-state conduction losses, the lower the heat produced on the fets, the higher efficiency and smaller the heatsinks needed. With this fets i am able to run the fets with small heatsinks and without fan at full rated power (100W) with an efficiency of 82% and perceptible heating and with small heating at 120W (some degrees) (the core starts to saturate and the efficiency is a bit lower, around 75%)

Try to use the lowest resistance mosfet you can put your dirty hand :-) on or the efficiency will be lower than rated and you will need even a small fan. The fet driver i used is the TPS2811P, from Texas instruments, rated for 2A peak and 200ns. Is important that the gate drive is optimized for minimal inductance or the switching losses will be higher and you risk noise coupling from other sources. Personally i think that twisted pair wires (gate and ground/source) are the best to keep the inductance small. Place the gate drive resistor near the Mosfet, not near the IC.

Controller

I used the trusty TL494 PWM controller with frequency set at around 40-60 Khz adjustable with a potentiometer. I also implemented the soft start (to reduce powerup transients). The adjust potentiometer (feedback) must be set to obtain the desired voltage. The output signals is designed with two pull-up resistors on the collector of the PWM chip output transistor pulling them to ground each cycle alternatively. This signal is sent to the dual inverting MOSFET driver (TPS2811P) obtaining the correct waveform.


Power and filtering

How i said before the power tracks must be heavy gauged or you will scarify regulation (since it depends of transformer step up ratio and input voltage) and efficiency too. Don't forget to place a 10A (or 15A) fuse on the input because the car batteries can supply very high currents in case of shorts and this will save you face from a mosfet explosion in case of failture or short, remember to place a fuse also on the battery side to increase the safety (accidental shorts->fire, battery explosion, firemen, police and lawyers around). Input filtering is important, use at least 20000uF 16V in capacitors, a filter inductor would be useful too (heavygauged) but i decided to leave it..

Final considerations

This supply given me up to 85% efficiency (sometimes even 90% at some loads) with an input of 12V because i observed all these tricks to keep it functional and efficient. An o-scope would be useful, to watch the ripple and gate signals (watching for overshoots), but if you follow these guidelines you will avoid these problems.

The cross regulation is good but keep in mind that only the positive output is fully regulated, and the negative only follows it. Place a small load between the negative rail and ground (a 3mm led with a 4.7Kohm resistor) to avoid the negative rail getting lower then -20V. If the load is asymmetric you can have two cases:

-More load on positive rail-> no problems, the negative rail can go lower than -20V, but it is not a real issue for an audio amplifier.
-More load on negative rail-> voltage drop on negative rail (to ground) especially if the load is only on the negative rail.

Fortunately audio amplifiers are quite symmetrical as a load, and the output filter inductor/capacitors helps to maintain the regulation good during asymmetrical transients (Basses)


ATTENTION

Keep in mind that THIS IS NOT A PROJECT FOR A BEGINNER, IT CAN BE VERY DANGEROUS IN CASE OF PROBLEMS, NEVER BRIDGE, BYPASS OR AVOID FUSES THESE WILL SAVE YOUR BACK FROM FIRE RISK.


FOR FIRST TESTING USE A SMALL 12V power supply and use resistors as load monitoring switches heat and current consumption (and output) and try to determine efficiency, if it is higher then 70-75% you are set, it is enough. Adjust the frequency for best compromise between power and switching losses, skin effect and hysteresis losses


Bill Of Materials
=================
Design: 12V to 20V 100W DC-DC conv
Doc. no.: 1
Revision: 3
Author: Jonathan Filippi
Created: 29/04/05
Modified: 18/05/05

Parts List
--- --------- -----
Resistors
---------
2 R1,R2 = 10
4 R3,R4,R6,R7 = 1k
1 R5 = 22k
1 R8 = 4.7k
1 R9 = 100k

Capacitors
----------
2 C1,C2 = 10000uF
2 C3,C6 = 47u
1 C4 = 10u
3 C5,C7,C14 = 100n
2 C8,C9 = 4700u
1 C12 = 1n
1 C13 = 2.2u

Integrated Circuits
-------------------
1 U1 = TL494
1 U2 = TPS2811P

Transistors
-----------
2 Q1,Q2 = FDB045AN

Diodes
------
4 D1-D4 = 1N5822
1 D5 = 1N4148

Miscellaneous
-------------
1 FU1 = 10A
1 L1 = 10u
1 L2 = FERRITE BEAD
1 RV1 = 2.2k
1 RV2 = 24k
1 T1 = TRAN-3P3S

From http://www.electronics-lab.com/

Electronic car ignition

Description:
This scheme is for 4 cylinder motor. This will make your car spent less fuel, be a little bit faster and you won�t have to frequently open your distributor cap to change the contact buttons thus wasting less money.

T1/T2 create one monostable multivibrator in which C2 and R5 determine the length of impulse which is 1,5 msec. Next in line are T3 and then T4 which is Darlington transistor specially developed for electronic ignition which is used as a switch to turn on/off primary coil. Impulses from switch P turn on monostable multivibrator T1/T2. You need to un-connect capacitor that is in distributor cap because it is not needed anymore. While switch P is closed T1 is in off state but T2 is in on state, also T3 and T4 which enables current to flow trough primary coil. When switch P is opened, T1 gets in on state for a moment causing C2 to charge over R6 which makes T2 go to off state because of voltage drop on R6. When T2 is off also T3 and T4 are off and current that was flowing trough primary coil is stopped. Because T2 is in off state, voltage on R8 is increased which is passed trough R5 on T1 base which is still in on state and C2 is still charging. After 1,5 msec. C2 value reaches the level where T2 goes to on state again and T1 goes to off state. Now T2, T3 and T4 are in on state, again, and current flows trough primary coil again. R2 and D1 are used to neutralize the effect of impulses caused from «jumping» of switch P which could turn on monostable multivibrator when it shouldn't.

Zener diodes Z5 and Z6 are together with R10 limit overcharged voltage impulses that are caused by self induction of primary coil which could damage T4. They should be connected as close as possible to T4.
D7 protects device from wrong polarity.

Coil should have ratio of 1:80 or 1:100 with external resistor Rv which is used for better cooling. Total resisting value (Rp) of primary coil and Rv resistor shouldn't be under 1,6 ohm's so current trough T4 wouldn�t be bigger than 10A.
Depending on Rp, R9 have different values:

120Ω/2W for Rp tot > 2,2Ω
100Ω/2W for 1,8Ω <>Parts:
D1-D4 = 1N4148
D5-D6 = BZX85C � 180 (replicable with all equivalent types with power of 1,3W)
D7 = 1N4001
R1 = 470 - 1W
R2 = 22k
R3 = 2,2k
R4 = 1k
R5 = 4,7k
R6 = 39k
R7 � R10 = 100
R8 = 680
C1 � C2 = 47nF (ceramic)
C3 = 0,22uF 400V (ceramic)
C4 = 100uF (electrolytic)
T1 � T2 = BC327 (BC327-25, BC327-40)
T3 = BC237B (BC547B, BC547C)
T4 = BUX37 (BU323, BU920, BU921, BU922, BUV37B (u TOP3), BUW29, BUW81, MJ10012, MJ10013, MJ10014, TIP662, TIP665, 2SD683)

12 Volt to 220 Volt Inverter 500W

This is circuit Inverter 12VDC to 220V 50Hz 500W.
It easy to make and Low cost.

measurements temperature by diode 1N4148

measurements temperature by diode 1N4148

temperature by diode 1N4148 and ic 741.
easy to make and use.
Out to Voltmeter.
*** Low cost too !