Simple DC to AC Inverter

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This DC to AC inverter circuit work based on unstable multi vibrator does. In this circuit, IC CD4047 is chosen as a heart of unstable multi vibrator, because this IC type gives a complementary output that has opposite phase to another ( pin 10 and 11 as seen in Figure 1), and has 50 % duty cycle that satisfy to generate a pulse for inverter.

In order to increase the current out of multi

vibrator so enough to generate a higher AC power too, then we must use MOSFET IRFZ44. IRFZ44 gives out high current to drive a step-up transformer, so AC power is available at the high voltage side of transformer.

This circuit is called as simple DC to AC inverter because of the output haven't a sinusoidal signal

yet, so there are many harmonic signal at the output. To suppress this signal we must use a filter such as a capacitor C. Because of this simplicity this circuit is suitable only for lighting demand. To build a sinusoidal DC to AC inverter, we can use a PWM signal for driving a step-up transformer, such as at page of DC to AC inverter using AT89C2051.

SG3525 DC Converter 12V to +35V,-35V

The selected switching topology is called a "push-pull" converter, because the transformer has a double primary (or a "centre-tapped" one, if your prefer). The centre tap is permanently connected to the car battery (via an LC filter to avoid creating peaks in the battery lines, which could affect other electronic equipment in the car). The two ends of the primary are connected to a pair of paralleled MOSFETs each that tie them to ground in each conduction cycle (Vgs of the corresponding MOSFET high).

These MOSFETs should be fast, able to withstand high currents (in excess of 30A each if possible) and have the lowest possible Rds(on). The proposed On-Semiconductor�s MTP75N06 can withstand 75Amp and has a Rds(on) below 10 milliohm. This is important, because the lower this resistance is, the less power they are going to dissipate when switching with a square waveform. Another alternatives are MTP60N06, or the more popular BUZ11 and IRF540.

Although the schematics show a previous bipolar push-pull stage, you can also connect the gate resistor directly to the output of the controlling IC, leaving out the transistors, as the SG3525 is capable to drive up to 500 mA (theoretically), more than enough to switch the MOSFETs fast.

Read More
http://sound.westhost.com/project89.htm

5V power supply with overvoltage protection.

Description.

For circuits using TTL ICs the supply voltage is a great concern and a slight increase in supply from the rated 5V may damage the IC. Using fuses alone does not solve the problem because a fuse may take several milliseconds to blow off and that’s enough time for the IC to get damaged.

In this circuit a crowbar scheme is used in which a triac short circuits the power supply and burns the fuse. The burning time of the fuse is not a concern because the power supply is already shorted by the triac and the output voltage will be zero. When the output voltage exceeds 5.6 volts the zener diode D2 conducts and switches ON the triac T1.Now T1 acts as a closed switch, shorting the circuit. The output voltage drops to zero and fuse gets burned off. Since the switching of triac takes place within few micro seconds there will be no damage to the TTL ICs or any other such voltage sensitive components in the load circuit.

Circuit diagram with Parts list.

Notes.

• Assemble the circuit on a general purpose PCB.
• If 1A Bridge is not available, make one using four 1N4007 diodes.
• The trip voltage can be varied by varying the values of D2 and R2.
• All capacitors must be rated at least 25V.
• The transformer T1 can be a 230 V AC primary, 12v secondary, 2A step-down transformer.

Automatic Battery Charger

The following automatic battery-charger design is created with a circuit that could qualify as the simplest window comparator ever built around a single transistor. It starts charging when the battery voltage drops beyond a preset value, and it stops when an upper preset voltage is attained.

With the help of a precise variable voltage supply, the upper and lower voltage levels were set. The normally connected (NC) lead of the relay isn't joined to the 15-V dc supply, which blocks this voltage from passing to the battery leads. This will accurately set the upper and lower levels. But the charging supply of 15 V dc was connected to the circuit.

First, the variable supply is fixed at 13.3 V dc—the voltage of a fully charged battery—and linked to the battery point of the circuit. The slider of VR1 is turned to the extreme end on the side that's attached to the positive terminal of the battery. VR2's slider should be turned toward the end that's connected to VR1. The transistor turns on, shunting VR1. Then the slider of VR1 is turned toward the other extreme, which is the end connected to VR2.

The test supply voltage is now set to 11.8 V dc, which is the voltage of a drained battery. VR2 is then adjusted so that it just turns off the transistor again. The test voltage is raised to 13.3 V dc again, and VR1 is adjusted so that the transistor turns on. With the upper and lower levels set, the NC point is connected to the circuit (15-V dc charging voltage). Now the battery charger is set and ready to go.

Reference:

http://electronicdesign.com/Articles/Index.cfm?AD=1&ArticleID=1823

Off Line-UPS Offers (100 -5000 Watts)

With increased dependency on electric power for various domestic, commercial purposes and the seemingly declining capacity of power utilities in many countries, the need for additional backup power sources is on the rise. Various modules are already available to address these different needs. However, most modules are too expensive, too bulky, or too rigid in their power capacity, capability, and flexibility.

The circuit described here is an off-line uninterruptible power supply. It has an expandable power stage design that can be easily modified for use with power ranges from as low as 100 W to as high as 5000 W with forced cooling.

The design is based on the LM3524D, a popular industrial-grade, pulse-width-modulation (PWM) controller. This device is fully self-contained and has all of the necessary logic built-in to ensure a compact and cost-effective product. The controller offers:

• Complementary power drive output stage with 180° out-of-phase switching.
• Stable oscillator with shutdown capability and noise suppression.
• Current-sense and voltage-sense circuitry.
• Dead time between the two complementary switching stages to prevent cross conduction and subsequent core saturation.
• Low voltage cutoff.

The on-chip oscillator frequency is controlled by the RC pair R2 and C1, and the required frequency is calculated as f_OSC = 1/(R2 × C1). Depending on the country, f_OSC = 50 Hz or 60 Hz. The low-power drive stage, containing transistors Q1 and Q2, is driven by the outputs at pin 12 and 13 of the controller; out-of-phase switching is handled by its own internal logic.

The final switching stage is comprised of transistors Q5 and Q6 wired across the main step-up transformer. These transistors are switched on in tandem to drive current through the two halves of the primary winding of transformer T2, independently.

Power diodes D2 and D3 are included to protect the power-stage transistors against reverse currents. Switching pulses from the drive transistors are transferred to the power stage via transistors Q3 and Q4, which serve as current amplifiers.

Resistor R10 is used to feed back the current to the current-sense monitor via pin 5. The current-sense logic monitors this feedback and triggers shutoff in event of either overload or power-stage failure.

The value of R10 is calculated as I_MAX = 200 mV/R10, where I_MAX is proportional to the power rating of the load, and 200 mV is the minimum required potential drop across R10 to trigger a shutdown by the current-sense logic.

The transformer T1 is connected to the standard mains supply and the rectified dc is fed to the shutdown pin (pin 10). This pin serves to turn off the LM3524 during the presence of the standard mains supply. If the mains supply fails, the bias on the shutdown pin is removed, thus starting the oscillator and hence the drive stages.

The power stages and transformer T2 must be appropriately rated for the required output power. The power transistors (Q3, Q4, Q5, and Q6) can be paralleled with similar devices for increased power-handling capacity. In addition, forced cooling can be used to achieve an even higher output power rating. However, for low- or medium-output power ratings, these transistors must be mounted on a large heat sink. Transformer T2 is a standard 12 V: 0:12 V to 230-240 V step-up winding, while T1 is a small 230-V to 12-V step-down transformer rated for 50 mA on the secondary windings. Additional filter and shaping circuitry can be added on the secondary winding of T2 to obtain a near sine-wave output. The RC network comprising R3 and C2 is included for compensation.

13.8V 40A Switching Power Supply By LM3524,LM324

This article was originally published (in a slightly modified form) in the QST magazine, December 1998 and January 1999, and in the Radio Amateur's Handbook, 1999. Visit the American Radio Relay League for information on these publications, and a world of ham radio related things!

Design decisions

There are several different topologies for switchers in common use, and the first decision a designer must take is which of them to consider. Among the factors affecting the decision are the power level, the number of outputs needed, the range of input voltage to be accepted, the desired tradeoff between complexity, quality and cost, and many more. For this power supply I decided to use the half bridge forward converter design. This topology connects the power transformer to a bridge formed by two power transistors and two capacitors. It is reasonably simple, puts relatively low stress on the power transistors, and makes efficient use of the transformer's magnetic capabilities.The second basic decision is which switching frequency to use. The present trend is to use ever higher frequencies. But by doing so it becomes more difficult to filter out the RF noise inevitably generated by the switching. So I decided to stay at a low switching frequency of only 25 kHz for the full cycle, which due to the frequency doubling effect of the rectifiers results in 50 kHz on the output filter.

For the main switching elements, bipolar transistors or MOSFETs can be used. Bipolars have lower conduction losses, while MOSFETs switch faster. As in this design I wanted to keep the RF noise at an absolute minimum, very fast switching was not desired, so I used bipolar transistors. But these tend to become too slow if the driving is heavier than necessary. So, if the transistors have to switch at varying current levels, the drive to them must also be varied. This is called proportional driving, and is used in this project.

The half bridge converter is best controlled by pulse width modulation. There are several ICs available for this exact purpose. I chose the 3524, which is very simple to use and easy to find. Any 3524 will do the job. It can be an LM3524, SG3524, etc.

This basically ends the big decisions. From now on, designing the circuit is a matter of calculating proper values for everything.

More Source :
http://ludens.cl/Electron/PS40/PS40.html

High Current Regulated Supply By LM317

The high current regulator below uses an additional winding or a separate transformer to supply power for the LM317 regulator so that the pass transistors can operate closer to saturation and improve efficiency. For good efficiency the voltage at the collectors of the two parallel 2N3055 pass transistors should be close to the output voltage. The LM317 requires a couple extra volts on the input side, plus the emitter/base drop of the 3055s, plus whatever is lost across the (0.1 ohm) equalizing resistors (1volt at 10 amps), so a separate transformer and rectifier/filter circuit is used that is a few volts higher than the output voltage.

The LM317 will provide over 1 amp of current to drive the bases of the pass transistors and assuming a gain of 10 the combination should deliver 15 amps or more. The LM317 always operates with a voltage difference of 1.2 between the output terminal and adjustment terminal and requires a minimum load of 10mA, so a 75 ohm resistor was chosen which will draw (1.2/75 = 16mA). This same current flows through the emitter resistor of the 2N3904 which produces about a 1 volt drop across the 62 ohm resistor and 1.7 volts at the base. The output voltage is set with the voltage divider (1K/560) so that 1.7 volts is applied to the 3904 base when the output is 5 volts. For 13 volt operation, the 1K resistor could be adjusted to around 3.6K. The regulator has no output short circuit protection so the output probably should be fused.

600 Volt Power Supply For QRO

Amateur Radio Transmitters using valves such as 807 or1625 works well with a plate voltage between 600V to 700 Volts.The circuit described here is a full wave voltage doubler. The output voltage is twice the input voltage. For 230V AC input the output will be nearly 600 Volts.

Resister R1 is used to limit the initial high voltage and high currents. Capacitor C1, C2, C3 together with coils L1 and L2 form input line filter. The capacitors C4 and C5 protects diodes from high voltage transients on the AC line as well as reduces inter carrier hum modulation of the R.F picked up by the mains. Capacitors C6 and C7 provides enough filtering for the output DC Voltage.

C1, C2, C3 - 0.1 mf 630V
C4, C5 - 0.01 mf 630V
C6, C7 - 100 mf 450V
R1 - 10E 5W Wire Wound
R2, R3 - 220KE 2Watts
D1, D2 - BY127
D3, D4 - BY127
L1, L2 - 12 Turns 18 SWG
Wound over 4 Cm
long Ferrite Rode.

Variable Regulated Powersupply(1.2 to 30V @ 1.5 Amps)

Parts List
BR1 = Bridge Rectifier, 100V - 3A
C1 = 2200 ìF, 63V
IC1 = LM317, adjustable regulator
C2 = 0.1 ìF
V = Meter, 30V,
Ri = 85 ohm
C3 = 1 ìF, 40V
TR1 = Transformer, 25V, 2A Plug = 3-wire plug & cord
R1 = 1K8, 5%
S1 = On-Off toggle switch
R2 = 220 ohm, 5%
D1 = 1N4001
R3 = 27K, 5%
Fuse = 110V, 500mA, slow-blow
P1 = 5K, potentiometer FuseHolder, wire, solder, case, knob for P1
P2 = 10K, 10-turn trim-pot Red & Black Banana Jacks

Couple Notes:

This is a simple, but low-ripple powersupply, and an excellent project if you're starting out in electronics. It will suit your needs for most of your bench testing and prototypeapplications. The output is adjustable from 1.2 volts to about 30 volts. Maximum current is about 1.5 amps which is also sufficient for most of your tinkering. It is relatively easy to build and can be pretty cheap if you have some or all the required parts. A printed circuit board is not included and I'm not planning on adding one since the whole thing can easily be build on perforated or vero board. Or buy one of Radio Shack/Tandy's experimenters boards (#276-150). Suit yourself. The meter and thetransformer are the money suckers, but if you can scrounge them up from somewhere it will reduce the cost significantly. BR1 is a full-wave bridge rectifier. The two '~' denotes 'AC' and are connected to the 25vac output coming from the transformer. IC1 is a 3-pin, TO-220 model. Be sure to put a cooling rib on IC1, at it's max 1.5 A current it quickly becomes very hot...

Most of the parts can be obtained from your local Radio Shack or Tandy store. The physical size of the power supply case depends largely on the size of the meter &: transformer. But almost anything will do, even wood. Go wild.

Circuit Description:

The 110V-AC coming from the powercord is fed to the transformer TR1 via the on-off switch and the 500mA fuse. The 30vac output (approximately) from the transformer is presented to the BR1, the bridge-rectifier, and here rectified from AC (Alternating Current) to DC (Direct Current). If you don't want to spend the money for a Bridge Rectifier, you can easily use four general purpose 1N4004 diodes. The pulsating DC output is filtered via the 2200ìF capacitor (to make itmore manageable for the regulator) and fed to 'IN'-put of the adjustable LM317 regulator (IC1). The output of this regulator is your adjustable voltage of 1.2 to 30 volts varied via the 'Adj' pin and the 5K potmeter P1. The large value ofC1 makes for a good, low ripple output voltage.

Why exactly 1.2V and not 0-volt? Very basic, the job of the regulator is two-fold; first, it compares the output voltage toan internal reference and controls the output voltage so that it remains constant, and second, it provides a method for adjusting the output voltage to the level you want by using a potentiometers. Internally the regulator uses a zener diode to provide a fixed reference voltage of 1.2 volt across the external resistor R2. (This resistor is usually around 240 ohms, but220 ohms will work fine without any problems). Because of this the voltage at the output can never decrease below 1.2volts, but as the potentiometer (P1) increases in resistance the voltage across it, due to current from the regulator plus current from R2, its voltage increases. This increases the output voltage.

D1 is a general purpose 1N4001 diode, used as a feedback blocker. It steers any current that might be coming from the device under power around the regulator to prevent the regulator from being damaged. Such reverse currents usually occur when devices are powered down.The 'ON' Led will be lit via the 18K resistor R1. The current through the led will be between 12 - 20mA @ 2V depending on the type and color Led you are using. C2 is a 0.1ìF (100nF) decoupler capacitor to filter out the transient noise which can be induced into the supply by stray magnetic fields. Under normal conditions this capacitor is only required if the regulator is far away from the filter cap, but I added it anyway. C3 improves transient response. This means that while the

regulator may perform perfectly at DC and at low frequencies, (regulating the voltage regardless of the load current), at higher frequencies it may be less effective. Adding this 1 ìF capacitor should improve the response at those frequencies.

R3 and the trimmer pot (P2) allows you to 'zero' your meter to a set voltage. The meter is a 30Volt type with an internal resistance of 85 ohms. I you have or obtained a meter with a different Ri (internal resistance) you will have to adjust R3 to keep the current of meter to 1mA. Just another note in regards this meter, use the reading as a guideline. The reading may or may not be off by about 0.75volts at full scale, meaning if your meter indicates 30 volts it may be in reality almost 31volts or 29 volts. If you need a more precise voltage, then use your multimeter.

Construction:

Because of the few components you can use a small case but use whatever you have available.I used a power cord from a computer and cut the computer end off. All computer power cords are three-prong. The ground wire, which is connected to the middle pin of the power plug is connected to the chassis. The color of the ground-wire is either green or green/yellow. It is there for your protection if the 110vac accidentally comes in contact with the supply housing (case). BE CAREFUL always to disconnect the powerplug when you working inside the chassis. If you choose to use an in-line, or clip-type fuseholder be sure to isolate it with heat shrink or something to minimize accidental touching.

I use perf-board (or Vero board) as a circuit board. This stuff is widely available and comes relatively cheap. It is either made of some sort of fiber material or Phenolic or Bakelite pcb. They all work great. Some Phenolic boards come with copper tracks already on them which will make soldering the project together easier. I mounted the LM317(T) regulator on a heatsink. If you use a metal/aluminum case you can mount it right to the metal case, insulated with the mica insulator and the nylon washer around the mounting screw. Note that the metal tab of theLM317 is connected internally to the 'Output' pin. So it has to be insulated when mounting directly to the case. Use heat sink compound (comes in transparent or white color) on the metal tab and mica insulator to maximize proper heat transfer between LM317 and case/ or heatsink.

Drill the holes for the banana jacks, on/off switch, and LED and make the cut-out for the meter. It is best to mount everything in such a way that you are able to trouble-shoot your circuit board with ease if needed. One more note about the on-off switch S1, this switch has 110VAC power to it. After soldering, insulate the bare spots with a bit of silicon gel. Works great and prevents electrical shock through accidental touching.

If all is well, and you are finished assembling and soldering everything, check all connections. Check capacitors C1 & C3 for proper polarity (especially for C1, polarity reversal may cause explosion). Hookup a multimeter to the power supply output jacks. Set the meter for DC volts. Switch on S1 (led will light, no smoke or sparks?) and watch the meter movement. Adjust the potentiometer until it reads on your multimeter 15Volts. Adjust trimpot P2 until the meter also reads 15volts. When done, note any discrepancies between your multimeter and the power supply meter at full scale (max output). Maybe there is none, maybe there is a little, but you will be aware of it. Good luck and have fun building!

Final Note:

You can add two silicon diodes (in series) to the output of the LM317 to drop the final 1.2V, giving the full 0-30V range. I built a similar supply using the LM317, to supply a wafer coating spinner motor. The 1.2V kept the motor spinning at over100rpm, which was unacceptable to the researcher, who needed to ramp the motor speed from 0-8krpm.

555 DC-AC Inverter

Parts List:
R1 = 10K
R2 = 100K
R3 = 100 ohm
R4 = 50K potmeter, Linear
C1,C2 = 0.1uF
C3 = 0.01uF
C4 = 2700uF
Q1 = TIP41A, NPN, or equivalent
Q2 = TIP42A, PNP, or equivalent
L1 = 1uH
T1 = Filament transformer, your choice

This DC-to-AC inverter schematic produces an AC output at line frequency and voltage. The 555 is configured as a low-frequency oscillator, tunable over the frequency range of 50 to 60 Hz by Frequency potentiometer R4.

The 555 feeds its output (amplified by Q1 and Q2) to the input of transformer T1, a reverse-connected filament transformer with the necessary step-up turns ratio. Capacitor C4 and coil L1 filter the input to T1, assuring that it is effectively a sine wave. Adjust the value of T1 to your voltage.

The output (in watts) is up to you by selecting different components.

Input voltage is anywhere from +5V to +15Volt DC, adjust the 2700uF cap's working voltage accordingly. Replacement types for Q1 are: TIP41B, TIP41C, NTE196, ECG196, etc. Replacement types for Q2 are: TIP42B, TIP42C, NTE197, ECG197, etc. Don't be afraid to use another type of similar specs, it's only a transistor... ;-)

12V to 16V DC/DC Converter with LM2577

The circuit is a boost step-up regulator based around an LM2577-ADJ voltage regulator chip and a few other discrete components. Resistors R1 and R2 set the regulated output voltage.

A switch inside the voltage regulator closes between pins 4 and 3, causing current to flow through the inductor to ground. When the switch is released a few microseconds later, a back-EMF 'kick' is produced by the inductor, resulting in a positive pulse with respect to the input voltage. This pulse charges the output capacitor via the schottky diode, which tends towards an equilibrium voltage.

The switch continues to oscillate, the diode preventing the switch from shorting the output capacitor during the 'on' phase. The output voltage is monitored via the voltage divider R1/R2, causing the duty cycle of the switch oscillator to be continuously regulated in order to maintain a constant output voltage under varying loads.

Simple 40W inverter

Description

This is the schematic of a simple 40W , 12 to 220 V inverter.You don’t believe, this is simple and cheap and working for me for last 4 years.The heart of the circuit is a CD 4047 IC which is wired as an astable multi vibrator here.Resistance and Capacitance at pin 1&2 determines the out put frequency.Here it is set to 60Hz.Due to this a two 180 degree out of phase ,120 Hz , 50% dutycycle waveforms will appear at pin 10 & 11.These waves are amplified by the complementary symmetry amplifier made of transistors BC 337 & TIP 3055 to drive the out put transformer.Don’t get feared of the technical terms, just wire it on a all purpose PCB.It is simple and will work.Don’t worry about the transformer windings ,buy a 220-110-0 primary,12-0-12 secondary , <50w>

Circuit Diagram:

Tips :

First wire to oscillator part only.Then check out put Pin 10 &11 of CD4047 to obtain the required wave forms ( two 120Hz ,180 degree out of phase,50% duty cycle waves.

Then connect transistors ,transformer and load (25 W bulb for test).See it working!.

500W Mos-Fet Power Inverter from 12V to 110V/220V

500W Mos-Fet Power Inverter from 12V to 110V/220V

This circuit will provide a very stable "Square Wave" Output Voltage. Frequency of operation is determined by a pot and is normally set to 60 Hz. Various "off the shelf" transformers can be used. Or Custom wind your own FOR BEST RESULTS. Additional MosFets can be paralleled for higher power. It is recommended to Have a "Fuse" in the Power Line and to always have a "Load connected", while power is being applied. The Fuse should be rated at 32 volts and should be aproximately 10 Amps per 100 watts of output. The Power leads must be heavy enough wire to handle this High Current Draw!

Appropriate Heat Sinks Should be used on the RFP50N06 Fets. These Fets are rated at 50 Amps and 60 Volts. ** Other types of Mosfets can be substituted if you wish. The LT1013 offers better drive that the LM358, but its your choice. The Power transformer must be capable of handling the chosen wattage output. Also, Appropriate Heat Sinks are Necessary on the Mos-Fets. Using a rebuilt Microwave transformer as shown below, it should handle about 500 watts Maximum. It requires about 18 turn Center-Tapped on the primary. To handle 500 watts would require using a 5 AWG wire. Pretty Heavy Stuff, but so is the current draw at that power.

12V to +/- 30V DC to DC Converter

This is a DC to DC converter for car power amplifier. 12V input generates +30V and -30V output for preamp or power amplifiers. Circuit uses SG3525 IC, Mosfets and switching power supply.

Inverter 100W by IC 4047 + 2N3055

This circuit Inverter input 12V (battery 12V) to out 220V 50HZ, Easy circuit because less component to use. It use IC 4047 (oscillator 50HZ) and Power Transistor 2N3055 x 2 ,OUTPUT Power 100W.

Circuit Inverter 100W by IC 4047 + 2N3055

PCB Inverter 100W by IC 4047 + 2N3055

Temperature Controlled NICD Charger

Introduction

This circuit is for a temperature controlled constant current battery charger. It works with NICD, NIMH, and other rechargeable cells. The circuit works on the principle that most rechargeable batteries show an increase in temperature when the cells becomes fully charged. Overcharging is one of the main causes of short cell life, hot cells pop their internal seals and vent out electrolyte. As cells dry out, they lose capacity.

Theory

The transformer, bridge rectifier, and 1000uF capacitor provide around 22 Volts of DC power to run the rest of the circuit. The 7812 regulator drops this to 12V to run the 311 comparator and 4011 nand gates.

The start switch is pressed to start the charging cycle. This causes the two 4011 nand gates, which are wired as an r-s flip-flop, to go into the charging mode. The Red LED is lit, and the VMOS FET current switch is turned on. Charging current runs though the battery pack. If the battery starts out warmer than the reference temperature, the circuit will not switch into charging mode. Let the pack cool down. When the battery pack reaches a full state of charge, the differential temperature sensor causes the flip-flop to switch off, turning off the VMOS current switch, and lighting the Green LED.

The 7805 voltage regulator is wired as a constant current regulator. This provides a safe maximum charge current for a number of different cell types. The 500 ohm resistor across the VMOS FET sets the trickle charge current which flows through the battery pack after the bulk charging is finished.

The 1N5818 diode prevents the pack from discharging if the AC power is turned off.

The resistor, diode, and capacitor around the start switch cause the circuit to auto-start when power is first applied.

The differential temperature sensor circuit works by presenting two voltages to the input of the 311 comparator. The comparator output switches on or off depending on which input is at a higher voltage than the other. As the thermistors warm up, their resistance drops, lowering the associated comparator input. Since there are two sensors, the room temperature can vary and the circuit will only react to the difference in temperature between the sensors.

Construction

Parts placement is non critical with the exception of the thermistors which should be epoxied to separate aluminum plates and connected back to the main circuitry via a cable with two wires and a shield. The 7805 regulator should be mounted on a heat sink. The current setting resistor may be a high power potentiometer, switch selectable resistors as shown in the schematic, or a single fixed resistor if you only need one current setting.

Be sure to thermally separate the battery and sensors from the other electronics so the heat from the circuitry doesn't affect the sensors. In my prototype, I glued the both thermistors to separate aluminum sheets, approximately 2" X 2" and set the battery sensor on top of the pack being charged, usually with a weight on top. It is important to make sure the batteries have a decent thermal contact to the sensor.

Alignment

Allow the two temperature sensor plates to reach the same temperature, place a volt meter across the 311 chip's + and - inputs (pins 2 and 3). Adjust the sensor balance trimmer for a reading of -0.02 volts on the meter. Press the reset button and make sure the "charging" LED lights. Warm the battery temperature plate up with your hand and observe that the "done" light comes on.

Use

* Connect a rechargeable battery pack to the charger "+" and "-" connectors. The pack may need to cool down to the ambient temperature before charging.

* Place the "battery temperature" sensor under the battery pack and hold it in place with a rubber band or a heavy object.

* Place the "reference temperature" sensor in a location that is not too close to the charger, the battery, or any other source of heat.

* Press the "reset" button, observe that the "charging" light lights. Note: if the battery was recently discharged at a high rate, or it was moved from a warmer place, it may be warmer than the ambient temperature sensor and the circuit won't go into charging mode. Let the battery cool down to ambient temperature, or temporarily warm up the reference sensor if you are in a hurry.

* Note that some cells in a series string will always be first to get warm. After several cycles it would be a good idea to leave the pack on the charger for a few hours to trickle charge the lower cells up to a full state of charge. This process is called "equalizing" the pack. It is also possible to press the start button again, the weak cells will get more charge for a while, then the full cells will warm up and turn of the current.

Parts

The Thermistors and most of the other parts in this circuit may be obtained from DigiKey (1-800-DIGI-KEY). Also see: http://www.digikey.com/ I have no connection to DigiKey other than being a satisfied customer.

Discharging NiCd Packs

Many people discharge their NICD packs to prevent the memory effect. Memory effect is a controversial topic, the reader may want to research it on their own. Discharging is, in the least, fairly harmless if it is done correctly. Discharging may also be beneficial for equalizing the charge level in a group of cells. It may prevent the situation where a partially charged cell reaches full charge before more fully discharged cells in a series string.

A good way to kill NiCd cells is to put a reverse voltage on them. If you incorrectly discharge your NiCd packs as a string, the weak cells will go to zero volts and will then go negative as the stronger cells continue discharging, thus damaging the reversed cells. Over-discharging to a negative voltage is supposed to cause conductive dendrite growth within the cell, that causes the cells to self-discharge.

If want to discharge your cells, it is best to discharge them individually, the cells should not be drawn down to zero volts. An easy way to accomplish this goal is to put a silicon diode in series with a resistor for each cell, this sets the minimum battery voltage to about 0.7 Volts. For multi-cell packs, a discharger can be built with a multi-cell battery holder and resistors and diodes for each cell.

A typical discharge current is C/5 where C is the amp hour capacity of the cell. For a 500ma AA NiCd a 1N4001 or similar 1A diode in series with 5 ohm 1/2W resistor should give a C/5 (100ma) discharge rate assuming a 1.2V cell, and an 0.7V final resting voltage.

Afterthought

This circuit has been working quite nicely for several years now, I have recharged many NICD and NIMH packs repeatedly with no problems. The 1K thermistors may exhibit a small amount of self heating, which may result in less sensitivity to battery temperature changes. Changing to 5K thermistors would greatly reduce the effect. The balance pot should be changed to 2K and the resistors on either end of the balance pot should be changed to 3.9K.

Batteries charger & PSU - ideal for digital cameras

This circuit was created for digital cameras. It's known the digital cameras have considerable power consumption. For example my camera Minolta E223 requires approximately 800 mA. In practice a mains power supply or high capacity NiMH accumulators (batteries) can satisfy this demand.

This circuit consists of two parts, charger and adapter. The transformer, rectifier bridge and buffer condensator are common. Adapter is quite simply its main part is an adjustable voltage regulator LM 317 according to usual setting. Output is a suitable for camera jack plug. Voltage can be adjusted in range 2-9 V.

In the charger circuit a 7805 fixed voltage regulator works as current generator assured constant current during charging. This charging current can be adjusted with the 100 /1W potentiometer in range about 50-300 mA indicated by a small current measuring instrument. From one to four batteries can be charged simultaneously. The switch must be set according to number of batteries, and charging current of batteries given by manufacturer must be adjusted. This circuit doesn't measure charging time and charging condition of batteries. Manufacturers give charging time, usually 14-16 h. I solved this problem with a simply, cheap mechanical mains timer. I think its accuracy is sufficient.

Nicad Battery Charger

Notes:

This simple charger uses a single transistor as a constant current source. The voltage across the pair of 1N4148 diodes biases the base of the BD140 medium power transistor. The base - emitter voltage of the transistor and the forward voltage drop across the diodes are relatively stable. The charging current is approximately 15mA or 45mA with the switch closed. This suits most 1.5V and 9V rechargeable batteries. The transformer should have a secondary rating of 12V ac at 0.5amp, the primary should be 220/240volts for Europe or 120volts ac for North America.

WARNING: Take care with this circuit. Use a voltmeter to observe correct polarity. Nicads can explode if short circuited or connected with the wrong polarity.

High and Low Voltage Cutout with delay and Music

Voltage variations and power cuts adversely affect various equip- ment such as TVs, VCRs, music systems and refrigerators. This simple circuit will protect the costly equipment from high as well as low voltages and the voltage surges (when power resumes). It also gives a melodious tune when mains power resumes. When mains voltage is normal, the DC voltage at the cathode of zener diode D4 is less then 5.6V. As a result transistor T1 is in ‘off’ state. The DC voltage at the cathode of zener diode D5 is greater than 5.6V and as a result transistor T2 is in ‘on’ state. Consequently, relay RL1 gets energised, which is indicated by lighting up of green LED. Under high mains voltage condition, transistor T1 switches to ‘on’ state because the voltage at cathode of zener diode D4 becomes greater than 5.6V. Consequently, transistor T2 switches to ‘off’ state, making the relay to de-energise Under low mains voltage condition, transistor T1 switches to ‘off’ state and as a result transistor T2 also switches to ‘off’ state, making the relay to de-energise.

Timer IC 555 in the circuit is configured to operate in a monostable mode. The pulse width is about 10 seconds with the timing component values used in the circuit. When the power resumes after a break, pin 2 of IC 555 goes low briefly and this triggers it. Its output makes music IC UM66 to operate through transistor T3. Simultaneously, transistor T1 also gets forward biased as the monostable IC1 output is connected to its base via diode D8 and resistor R7. As a result, transistor T1 conducts and biases transistor T2 to cut off. Thus relay RL1 remains de-energised for the duration of mono pulse and the load is protected against the voltage surges.

To adjust presets VR1 and VR2, you may use a manually variable auto-transformer. Set the output of auto-transformer to 270V AC and connect it to the primary of transformer X1. Adjust preset VR1 such that relay RL1 just de-energises. Next set the output of auto-transformer to 170V AC. Now adjust preset VR2 such that relay RL1 again de-energises. Volume control VR3 may be adjusted for the desired output volume of the tune generated by IC UM66.

Over / Under Voltage Cut-Out

This over/under voltage cut-out will save your costly electrical and electronic appliances from the adverse effects of very high and very low mains voltages. The circuit features auto reset and utilises easily available components. It makes use of the comparators available inside 555 timer ICs. Supply is tapped from different points of the power supply circuit for relay and control circuit operation to achieve reliability. The circuit utilises comparator 2 for control while comparator 1 output (connected to reset pin R) is kept low by shorting pins 5 and 6 of 555 IC. The positive input pin of comparator 2 is at 1/3rd of Vcc voltage .

Thus as long as negative input pin 2 is less positive than 1/3 Vcc, comparator 2 output is high and the internal flip-flop is set, i.e. its Q output (pin 3) is high. At the same time pin 7 is in high impedance state and LED connected to pin 7 is therefore off. The output (at pin 3) reverses (goes low) when pin 2 is taken more positive than 1/3 Vcc. At the same time pin 7 goes low (as Q ouptput* of internal flip- flop is high) and the LED connected to pin 7 is lit. Both timers (IC1 and IC2) are configured to function in the same fashion. Preset VR1 is adjusted for under voltage (say 160 volts) cut-out by observing that LED1 just lights up when mains voltage is slightly greater than 160V AC. At this setting the output at pin 3 of IC1 is low and transistor T1 is in cut-off state. As a result RESET* pin 4 of IC2 is held high since it is connected to Vcc via 100 kilo-ohm resistor R4. Preset VR2 is adjusted for over voltage (say 270V AC) cut-out by observing that LED2 just extinguishes when the mains voltage is slightly less than 270V AC.

With RESET* pin 4 of IC2 high, the output pin 3 is also high. As a result transistor T2 conducts and energises relay RL1, connecting load to power supply via its N/O contacts. This is the situation as long as mains voltage is greater than 160V AC but less than 270V AC. When mains voltage goes beyond 270V AC, it causes output pin 3 of IC2 to go low and cut-off transistor T2 and de-energise relay RL1, in spite of RESET* pin 4 still being high. When mains voltage goes below 160V AC, IC1’s pin 3 goes high and LED1 is extinguished. The high output at pin 3 results in conduction of transistor T1. As a result collector of transistor T1 as also RESET* pin 4 of IC2 are pulled low. Thus output of IC2 goes low and transistor T2 does not conduct. As a result relay RL1 is de-energised, which causes load to be disconnected from the supply. When mains voltage again goes beyond 160V AC (but less than 270V AC) the relay again energises to connect the load to power supply.