Showing posts with label for. Show all posts
Showing posts with label for. Show all posts
Thursday, December 26, 2013
LDR Based 12V White LED Driver for up to 30 LEDs
While we have now published quite a few LED driver circuits, to date we have not published a design to drive a bunch of high-brightness white LEDs. Such a circuit is now quite desirable as the price of white LEDs has fallen and you can have a handful for not a lot of dollars. However, white LEDs do present a problem because they need a higher drive voltage than monochromatic types such as red, green, orange etc.
Instead of around 1.8V to 2V or thereabouts, they normally require more than 3V to produce their rated brightness. In fact, if you are driving a bunch of them you need to drive them all at constant current otherwise their individual brightness tends to vary markedly. However, if you only have a 12V supply available, you can only put two or maybe three LEDs in series together with a constant current source and this leads to poor efficiency.
The approach in this circuit is to boost the 12V supply to something around 21V and this means that we can have groups of five LEDs, each in series with their own current source transistors. The result is a single PC board with the drive circuitry and 30 white LEDs. It can be used for lighting in caravans and recreational vehicles, emergency lighting or whatever application you can think of. Current drain is around 190mA at 12V.
Now let’s have a look at the circuit of Fig.1. It uses just one IC (a 4093 quad NAND Schmitt trigger gate package), a few transistors and diodes, 30 white LEDs and not much else. So where is the familiar boost converter circuit? Answer: there isn’t one or least not one with an inductor switched by a Mosfet. Instead, there is a charge pump inverter, comprising IC1c, transistors Q2 & Q3, Schottky diodes D1 & D2 and a few capacitors. It works as follows:
IC1c is connected as an inverter oscillator and its running frequency of about 30kHz is determined mainly by the 6.8kΩ resistor between pins 8 & 10 together with the 4.7nF capacitor at pin 8. This produces a rectangular waveform (not quite square but pretty close) at pin 10 to drive complementary switching transistors Q2 & Q3.
The waveform at their commoned emitters drives a diode pump consisting of two 100μF capacitors and Schottky diodes D1 & D2. The waveform generated by the circuit can be seen in the scope photo of Fig.2.
Oscillator IC1c is controlled by an RS (Reset/Set) flipflop comprising the two NAND gates IC1a & IC1b and this is controlled by pushbutton switches S1 and S2. Normally, this has its pin 4 low and pins 1 & 6 are pulled high via 470kΩ resistors. Momentarily closing S1 (ON) pulls pin 6 low, causing the flipflop to change state so that pin 4 now goes high to enable IC1c which now oscillates at 30kHz.
The 30kHz waveform produced by transistors Q2 & Q3 drives the diode pump referred to earlier and this develops about 21V to drive the LED columns. Each column of five white LEDs is driven by its own current source transistor which has a 33Ω emitter resistor. The bases of all six current source transistors (Q4-Q9) are driven from pin 4 of IC1b via a 6.8kΩ resistor and clamped to a maximum of +1.2V by diodes D3 & D4.
Subtract the 0.6V between the base and emitter of each transistor and you are left with 0.6V across each 33Ω resistor, thus setting the LED drive current to 18mA. Switching the circuit off is accomplished by pushing the OFF switch, S2. This momentarily pulls pin 1 low to toggle the RS flipflop, thus causing pin 4 to go low. This disables IC1c, Q2 & Q3 and also turns off the current source transistors.
Note that there is an interesting wrinkle to this drive circuit, because there is no On/Off switch. This means that the current source transistors must be turned off otherwise they would continue to draw current from the 12V supply even when the circuit is nominally off. The current path may not be obvious but it is via the boost circuit’s diodes, D1 & D2.
As well as using the pushbutton switches S1 & S2 to turn the circuit on and off, there is also a facility to automatically turn the circuit on and off depending on ambient light levels. Links L1 & L2 can be used to provide Auto On and Auto Off respectively and these features can be used separately or together.
An LDR (light dependent resistor) is used to monitor the ambient light level. When light falls upon it, it pulls the base of Q1 low, causing pins 12 & 11 of IC1d to go low and its pin 11 to go high. When darkness falls (or the room lights go out), the process is reversed. Depending on whether you have one or both links connected, you can use the pushbuttons to turn the circuit on and off and have it turn on and/off automatically as well.
Q1 also drives a red high brightness LED (LED1) at very low current, via a 470kΩ resistor. This is a bit of a gimmick but it does have the benefit of showing that this part of the circuit is working, if you have to trouble-shoot it.
Pins 1 & 2, 5 & 6 and 8 & 9 of IC1 on the circuit are all swapped. The PC board overlay diagram is correct.
Continue Reading[..]
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| 30 White LEDs Driver Circuit Diagram |
Instead of around 1.8V to 2V or thereabouts, they normally require more than 3V to produce their rated brightness. In fact, if you are driving a bunch of them you need to drive them all at constant current otherwise their individual brightness tends to vary markedly. However, if you only have a 12V supply available, you can only put two or maybe three LEDs in series together with a constant current source and this leads to poor efficiency.
The approach in this circuit is to boost the 12V supply to something around 21V and this means that we can have groups of five LEDs, each in series with their own current source transistors. The result is a single PC board with the drive circuitry and 30 white LEDs. It can be used for lighting in caravans and recreational vehicles, emergency lighting or whatever application you can think of. Current drain is around 190mA at 12V.
Circuit description
Now let’s have a look at the circuit of Fig.1. It uses just one IC (a 4093 quad NAND Schmitt trigger gate package), a few transistors and diodes, 30 white LEDs and not much else. So where is the familiar boost converter circuit? Answer: there isn’t one or least not one with an inductor switched by a Mosfet. Instead, there is a charge pump inverter, comprising IC1c, transistors Q2 & Q3, Schottky diodes D1 & D2 and a few capacitors. It works as follows:
IC1c is connected as an inverter oscillator and its running frequency of about 30kHz is determined mainly by the 6.8kΩ resistor between pins 8 & 10 together with the 4.7nF capacitor at pin 8. This produces a rectangular waveform (not quite square but pretty close) at pin 10 to drive complementary switching transistors Q2 & Q3.
The waveform at their commoned emitters drives a diode pump consisting of two 100μF capacitors and Schottky diodes D1 & D2. The waveform generated by the circuit can be seen in the scope photo of Fig.2.
RS flipflop
Oscillator IC1c is controlled by an RS (Reset/Set) flipflop comprising the two NAND gates IC1a & IC1b and this is controlled by pushbutton switches S1 and S2. Normally, this has its pin 4 low and pins 1 & 6 are pulled high via 470kΩ resistors. Momentarily closing S1 (ON) pulls pin 6 low, causing the flipflop to change state so that pin 4 now goes high to enable IC1c which now oscillates at 30kHz.
The 30kHz waveform produced by transistors Q2 & Q3 drives the diode pump referred to earlier and this develops about 21V to drive the LED columns. Each column of five white LEDs is driven by its own current source transistor which has a 33Ω emitter resistor. The bases of all six current source transistors (Q4-Q9) are driven from pin 4 of IC1b via a 6.8kΩ resistor and clamped to a maximum of +1.2V by diodes D3 & D4.
Subtract the 0.6V between the base and emitter of each transistor and you are left with 0.6V across each 33Ω resistor, thus setting the LED drive current to 18mA. Switching the circuit off is accomplished by pushing the OFF switch, S2. This momentarily pulls pin 1 low to toggle the RS flipflop, thus causing pin 4 to go low. This disables IC1c, Q2 & Q3 and also turns off the current source transistors.
Note that there is an interesting wrinkle to this drive circuit, because there is no On/Off switch. This means that the current source transistors must be turned off otherwise they would continue to draw current from the 12V supply even when the circuit is nominally off. The current path may not be obvious but it is via the boost circuit’s diodes, D1 & D2.
Auto on/off
As well as using the pushbutton switches S1 & S2 to turn the circuit on and off, there is also a facility to automatically turn the circuit on and off depending on ambient light levels. Links L1 & L2 can be used to provide Auto On and Auto Off respectively and these features can be used separately or together.
An LDR (light dependent resistor) is used to monitor the ambient light level. When light falls upon it, it pulls the base of Q1 low, causing pins 12 & 11 of IC1d to go low and its pin 11 to go high. When darkness falls (or the room lights go out), the process is reversed. Depending on whether you have one or both links connected, you can use the pushbuttons to turn the circuit on and off and have it turn on and/off automatically as well.
Q1 also drives a red high brightness LED (LED1) at very low current, via a 470kΩ resistor. This is a bit of a gimmick but it does have the benefit of showing that this part of the circuit is working, if you have to trouble-shoot it.
Note:
Pins 1 & 2, 5 & 6 and 8 & 9 of IC1 on the circuit are all swapped. The PC board overlay diagram is correct.
Sunday, December 22, 2013
Preregulator for Power Supply Circuit Diagram
This SCR pre-regulator keeps the filter capacitor Vc, in a variable output power supply, a few volts above the output voltage V0. The benefits include: less heat dissipated by the pass transistor and therefore small heatsink, cooler operation and higher efficiency, especially at low output voltages. Ql, Rl, R2, Dl and D2 form a constant current source for zener Zl, so that the contribution to the output current is always a few mA (2-3 mA). The Darlington pair Q2, Q3 keeps the SCR off.
Preregulator for Power Supply Circuit Diagram
The voltage Vc decreases until Vc = V0 = V at which point the Darlington pair fires the SCR, charging the filter capacitor to a higher voltage VC1 in less than half the period of the input voltage. The component values, shown are for a 0 - 250-V, 3-A power supply.
Preregulator for Power Supply Circuit Diagram
The voltage Vc decreases until Vc = V0 = V at which point the Darlington pair fires the SCR, charging the filter capacitor to a higher voltage VC1 in less than half the period of the input voltage. The component values, shown are for a 0 - 250-V, 3-A power supply.
Tuesday, December 17, 2013
Protection For Telephone Line Circuit
A long time ago when telephones were so simple almost nothing could go amiss from an electrical point of view, Telecom operators installed surge protection on all telephone lines exposed to storm risks. Paradoxically, now that we are hooking up delicate and expensive equipment such as telephones filled with electronics, fax machines, (A)DSL modems, etc., this protection has disappeared.
However, if you have the good fortune to live in the countryside in a building served by overhead telephone lines, there’s an obvious risk of very high voltages being induced on the lines during thunderstorms. While we have lost count today of all of the modems, fax machines and other telephones that have been destroyed by a ‘bolt of lightning’, surprisingly you only have to invest a few pounds to get a remarkably efficient protection device like the one we are proposing here.
During a storm, often with lightning striking near a telephone line, the line carries transient voltages up to several thousands of volts. Contrary to the HV section of television sets or electrical fences, on which practically no current is running, in the case of lighting striking current surges of thousand of amps are not uncommon. To protect oneself from such destructive pulses, traditional components are not powerful or fast enough.
As you can see on our drawing, a (gas-filled) spark gap should be used. Such a component contains three electrodes, insulated from each other, in an airtight cylinder filled with rare gas. As long as the voltage present between the electrodes is below a certain threshold, the spark gap remains perfectly passive and presents an impedance of several hundreds of MW. On the other hand, when the voltage rises above this threshold, the gas is very rapidly ionized and the spark-gap suddenly becomes a full conductor to the point of being able to absorb colossal currents without being destroyed.
Protection Circuit Diagram For Telephone Line :
The one we are using here, whose size is of the same magnitude as an ordinary one watt resistor, can absorb a standardized 5,000 amps pulse lasting 8/20 ms! Since we are utilizing a three-electrode spark gap, the voltage between the two wires of the line or between any wire and ground, cannot exceed the sparking voltage, which is about 250 volts here. Such protection could theoretically suffice but we preferred to add a second security device made with a VDR (GeMOV or SiOV depending on the manufacturer), which also limits the voltage between line wires to a maximum of 250 volts.
Even if this value seems high to you, we should remember that all of the authorized telephone equipment, carrying the CE mark must be able to withstand it without damage. This is not always the case however with some low-end devices made in China, but that’s an entirely different problem. Since pulses generated by lightning are very brief, the ground connection of our assembly must be as low-inductance as possible.
It must therefore be short, and composed of heavy-duty wire (1.5 mm2 c.s.a. is the minimum). If not, the coil, composed of the ground connection, blocks the high frequency signal that constitutes the pulse and reduces the assembly’s effectiveness to nothing. Finally, please note that this device obviously has no effect on the low frequency signals of telephones and fax machines and it does not disturb (A)DSL signals either.
Author: Christian Tavernier - Copyright: Elektor Electronics Magazine
Friday, April 12, 2013
Solid State Switch For Dc Operated Gadgets
This solid state DC change generally is assembled using just three transistors and some passive components. It can be utilized to change on one system whereas swaping off the 2d machine with non permanent operation of swap. To reverse the operation, you just need to momentarily depress every other switch.
The circuit functions over 6V-15V DC provide voltage. It makes use of certain remarks from transistor T2 to transistor T1 to keep this transistor pair in latched state (on/ off), whereas the state of the 0.33 transistor stage is the complement of transistor T2’s habitsion state.
Initially when change S3 is closed, both transistors T1 and T2 are off, as no ahead bias is available to those, whereas the bottom of transistor T3 is successfully floored by means of resistors R8 and R6 (shunted by way of the burden of the primary machine). As a consequence, transistor T3 is ahead biased and machine 2 gets the provide. This is indicated by using glowing of LED2.
Circuit diagram :
Solid-State Switch For Dc-Operated Gadgets Circuit Diagram
When change S1 is momentarily depressed, T1 will get the base pressure and it floors the bottom of transistor T2 by implys of resistor R4. Hence transistor T2 (pnp) additionally habitss. The sure voltage available at the collector of transistor T2 is fed back to the bottom of transistor T1 by way of resistor R3. Hence a latch is formed and transistor T2 (as additionally transistor T1) proceeds to behavior, which prompts system 1 and LED1 glows.
Conduction of transistor T2 lead tos its collector to be pulled towards certain rail. Since the collector of T2 is connected to the bottom of pnp transistor T3, it result ins transistor T3 to bring to an end, swaping off the supply to device 2) in addition to extinguishing LED2. This standing is maintained except swap S2 is momentarily pressed. Depression of switch S2 successfully floors the base of transistor T1, which reduces off and therefore just about opens the bottom-emitter circuit of transistor T2 and thus reducing it off. This is the same situation as used to be bought originally. This situation can be reversed with the help of momentarily urgent swap S1 as defined earlier.
EFY lab note. During checking out, it was once no longericed that for right kind operation of the circuit, system 1 should draw a current of more than a hundred mA (i.e. the resistance of gadget 1 have to be lower than 220 ohms) to maintain the latched ‘on’ state. But this stipulation isn't acceptable for machine 2. A maximum present of 275 mA may be drawn by means of any machine.
Author : Praveen Shanker
Saturday, April 6, 2013
Lambda Probe Readout For Carburettor Tuning
A lambda probe (or oxygen sensor) can be found on the exhaust system of most cars running on unleaded fuel. Having reached its normal operating temperature (of about 600 degrees Celsius!) the lambda probe supplies an output voltage proportional to the amount of residual oxygen measured in the exhaust gas.
This information is indicative of, among others, the air/fuel ratio supplied by the carburetor(s) and hence the combustion efficiency. In modern car (and motorcycle) engines, this information is used to (electronically) adjust engine parameters like ignition timing and fuel injection. The indicator described here is intended for permanent installation on a motorcycle of which the air/fuel ratio needed to be watched, with the obvious aim engine power tuning after fitting a different set of carburetors. Apart from this obvious technical use the unit’s bright LEDs will no doubt attract the attention of curious motorcyclists.
At the local junkyard a single-wire lambda probe may be salvaged from a wrecked car. Once a suitable nut has been found, the probe can screwed into the exhaust pipe of the motorcycle, at about 30 cm from the cylinders. Since we’re talking of welding and drilling in an expensive (chrome-plated) exhaust pipe, you may find that actually fitting the probe is best left to specialists! The starting point for the design of a suitable electronic indicator is that in the noble art of carburetor tuning an air/fuel ratio of 14.7 to 1 is generally considered ‘perfect’, the range covering 16.2 to 1 (‘lean’) to 11.7 to 1 (‘rich’). The perfect ratio typically corresponds to a probe output voltage of 0.45 V.
Referring to the circuit diagram, that is the input level at which 5 of the 10 LEDs will light, including the green one, D5. If one of the red LEDs lights, the mixture is definitely too rich. Note that in general it is better to have a mixture that is a little to rich than one that’s on the lean side, hence a yellow LED lights between the green LED and the first red one. Also note that the engine needs to be at its normal operating temperature before a meaningful indication is obtained.
Author : P. G oossens
Wednesday, April 3, 2013
Oil Temperature Gauge for 125 cc Scooter
Lots of Far-Eastern scooters are fitted with GY6 engines. These already elderly units are sturdy and economical, but if you want to “push” the power a bit (so called ‘Racing’ kits, better handling of the advance, etc.), you soon find yourself faced with the problem of the engine temperature, and it becomes essential to f it a heat sink (of ten wrongly referred to as a ‘radiator’) on the oil circuit. Even so, in these circumstances, it’s more than reassuring for the user to have a constant clear indication of the oil temperature. Here are the specifications we set for the temperature gauge we wanted to build:
Oil Temperature Gauge Circuit Diagram :
- no moving parts (so not meter movement), as scooters vibrate a lot!;
- as cheap as possible (around £12);
- robust measuring transducer (avoid NTC thermistors and other ‘exotic’ sensors);
- temperature range 50–140 °C. (122 – 291 °F);
- audible and visual warning in case of dangerous temperature;
- compact;
- waterproof.
Let’s start by the sensor. This is a type-K thermocouple, as regularly used by multimeter manufacturers. Readily available and fairly cheap, these are robust and have excellent linearity over the measurement range we’re interested in here. The range extends from 2 mV to 5.7 mV for ten measurement points. The positive output from the thermocouple is applied to the non-inverting input of IC3.A, wired as a non-inverting amplifier. Its gain of 221 is determined by R1 and R2. IC3 is an LM358, chosen for its favourable characteristics when run from a single-rail supply. IC3.B is wired as a follower, just to avoid leaving it powered with its pins floating.
IC3.B output is connected to pin 5 of IC1, an LM3914. This very common IC is an LED display driver. We can choose ‘point’ or ‘bar’ mode operation, according to how pin 9 is connected. Connected as here to the + rail, the display will be in ‘bar’ mode. Pin 8, connected to ground, sets the full scale to 1.25 V. R3 sets the average LED current. Pin 4, via the potential divider R7/R8+R9, sets the offset to 0.35 V. Using R8 and R9 in series like this avoids the need for precision resistors.
As per the LM3914 application sheet , R4-R5-R6 and C5 will make the whole display flash as soon as D10 lights (130 °C = 226 °F). Simultaneously, via R10 and T1, the (active) sounder will warn the user of overheating. Capacitor C6 avoids undesirable variations in the reference voltage in ‘flashing’ mode. IC2 is a conventional 7808 regulator and C1– C4 filter the supply rails. Do not leave these out! D1 protects the circuit against reverse polarity.
The author has designed two PCBs to be fit-ted as a ‘sandwich’ (CAD file downloadable from [1]). In the download you’ll also find a document with a few photos of the project. You’ll note the ultimate weapon in on-board electronics: hot-melt glue. Better than epoxy (undoable!) and quite effective against vibration.
Author : Georges Treels - Copyright : Elektor
Source : http://www.ecircuitslab.com/2012/08/oil-temperature-gauge-for-125-cc-scooter.html
Friday, March 29, 2013
Simple RF Detector For 2M
This simple
circuit helps you sniff out RF radiation leaking from your transmitter,
improper joints, a broken cable or equipment with poor RF shielding.
The tester is designed for the 2-m amateur radio band (144-146 MHz in
Europe). The instrument has a 4-step LED readout and an audible alarm
for high radiation voltages. The RF signal is picked up by an antenna
and made to resonate by C1-L1. After rectifying by diode D1, the signal
is fed to a two-transistor high-gain Darlington amplifier, T2-T3.
Assuming
that a 10-inch telescopic antenna is used, the RF level scale set up
for the LEDs is as follows: When all LEDs light, the (optional) UM66
sound/melody generator chip (IC1) is also actuated and supplies an
audible alarm. By changing the values of zener diodes D2, D4, D6 and D8,
the step size and span of the instrument may be changed as required.
For operation in other ham or PMR bands, simply change the resonant
network C1-L1. As an example, a 5-watt handheld transceiver fitted with a
half-wave telescopic antenna (G=3.5dBd), will produce an ERP
(effective radiated power) of almost 10 watts and an e.m.f. of more
than 8 volts close to your head.
Inductor
L1 consists of 2.5 turns of 20SWG (approx. 1mm dia) enameled copper
wire. The inside diameter is about 7mm and no core is used. The
associated trimmer capacitor C1 is tuned for the highest number of LEDs
to light at a relatively low fieldstrength put up by a 2-m transceiver
transmitting at 145 MHz. The tester is powered by a 9-V battery and
draws about 15mA when all LEDs are on. It should be enclosed in a metal
case.
circuit helps you sniff out RF radiation leaking from your transmitter,
improper joints, a broken cable or equipment with poor RF shielding.
The tester is designed for the 2-m amateur radio band (144-146 MHz in
Europe). The instrument has a 4-step LED readout and an audible alarm
for high radiation voltages. The RF signal is picked up by an antenna
and made to resonate by C1-L1. After rectifying by diode D1, the signal
is fed to a two-transistor high-gain Darlington amplifier, T2-T3.
Assuming
that a 10-inch telescopic antenna is used, the RF level scale set up
for the LEDs is as follows: When all LEDs light, the (optional) UM66
sound/melody generator chip (IC1) is also actuated and supplies an
audible alarm. By changing the values of zener diodes D2, D4, D6 and D8,
the step size and span of the instrument may be changed as required.
For operation in other ham or PMR bands, simply change the resonant
network C1-L1. As an example, a 5-watt handheld transceiver fitted with a
half-wave telescopic antenna (G=3.5dBd), will produce an ERP
(effective radiated power) of almost 10 watts and an e.m.f. of more
than 8 volts close to your head.
Inductor
L1 consists of 2.5 turns of 20SWG (approx. 1mm dia) enameled copper
wire. The inside diameter is about 7mm and no core is used. The
associated trimmer capacitor C1 is tuned for the highest number of LEDs
to light at a relatively low fieldstrength put up by a 2-m transceiver
transmitting at 145 MHz. The tester is powered by a 9-V battery and
draws about 15mA when all LEDs are on. It should be enclosed in a metal
case.
Saturday, March 23, 2013
Wiring Circuit For Guitar Amplifier
The aim of this design was to reproduce a Combo amplifier of the type very common in the sixties and the seventies of the past century. It is well suited as a guitar amplifier but it will do a good job with any kind of electronic musical instrument or microphone. 5W power output was a common feature of these widespread devices due to the general adoption of a class A single-tube output stage (see the Vox AC-4 model). Furthermore, nowadays we can do without the old-fashioned Vib-Trem feature frequently included in those designs. The present circuit can deliver 10W of output power when driving an 8 Ohm load, or about 18W @ 4 Ohm. It also features a two-FET preamplifier, two inputs with different sensitivity, a treble-cut control and an optional switch allowing overdrive or powerful treble-enhancement.
Parts:P1______________4K7 Linear Potentiometer
P2_____________10K Log. Potentiometer
R1,R2__________68K 1/4W Resistors
R3____________220K 1/4W Resistor
R4,R6,R11_______4K7 1/4W Resistors
R5_____________27K 1/4W Resistor
R7______________1K 1/4W Resistor
R8______________3K3 1/2W Resistor
R9______________2K 1/2W Trimmer Cermet
R10___________470R 1/4W Resistor
R12_____________1K5 1/4W Resistor
R13___________470K 1/4W Resistor
R14____________33K 1/4W Resistor
C1____________100pF 63V Ceramic Capacitor
C2____________100nF 63V Polyester Capacitor
C3____________470µF 35V Electrolytic Capacitor
C4____________220nF 63V Polyester Capacitor (Optional, see Notes)
C5_____________47µF 25V Electrolytic Capacitor (Optional, see Notes)
C6______________1µF 63V Polyester Capacitor
C7,C8,C9,C10___47µF 25V Electrolytic Capacitors
C11____________47pF 63V Ceramic Capacitor
C12__________1000µF 35V Electrolytic Capacitor
C13__________2200µF 35V Electrolytic Capacitor
D1_____________5mm. Red LED
D2,D3________1N4004 400V 1A Diodes
Q1,Q2________2N3819 General-purpose N-Channel FETs
Q3____________BC182 50V 200mA NPN Transistor
Q4____________BD135 45V 1.5A NPN Transistor (See Notes)
Q5____________BDX53A 60V 8A NPN Darlington Transistor
Q6____________BDX54A 60V 8A PNP Darlington Transistor
J1,J2________6.3mm. Mono Jack sockets
SW1____________1 pole 3 ways rotary switch (Optional, see Notes)
SW2____________SPST Mains switch
F1_____________1.6A Fuse with socket
T1_____________220V Primary, 48V Center-tapped Secondary 20 to 30VA Mains transformer
PL1____________Male Mains plug
SPKR___________One or more speakers wired in series or in parallel, Total resulting impedance: 8 or 4 Ohm, Minimum power handling: 20W
Notes:
- SW1 and related capacitors C4 & C5 are optional.
- When SW1 slider is connected to C5 the overdrive feature is enabled.
- When SW1 slider is connected to C4 the treble-enhancer is enabled.
- C4 value can be varied from 100nF to 470nF to suit your treble-enhancement preferences.
- In all cases where Darlington transistors are used as the output devices it is essential that the sensing transistor (Q4) should be in as close thermal contact with the output transistors as possible. Therefore a TO126-case transistor type was chosen for easy bolting on the heatsink, very close to the output pair.
- To set quiescent current, remove temporarily the Fuse F1 and insert the probes of an Avo-meter in the two leads of the fuse holder.
- Set the volume control to the minimum and Trimmer R9 to its minimum resistance.
- Power-on the circuit and adjust R9 to read a current drawing of about 25 to 30mA.
- Wait about 15 minutes, watch if the current is varying and readjust if necessary.
Sensitivity:
30mV input for 10W output
Frequency response:
40 to 20KHz -1dB
Total harmonic distortion @ 1KHz and 10KHz, 8 Ohm load:
below 0.05% @ 1W, 0.08% @ 3.5W, 0.15% at the onset of clipping (about 10W).
Wednesday, March 20, 2013
Automatic Switch For Voltage Converters
New applications for DC voltage converters, such as the ‘workhorse’ LT1070, arise every day. These converters can be adapted to nearly every imaginable ratio of input and output voltages. However, all of these circuits and devices have the same shortcoming, which is that they lack an on/off switch. Especially when they are used as a source of 6-V / 12-V power for a car radio, this is highly impractical. The circuit described here adds automatic load detection to the converter. For use in a car, the additional circuitry must be small and fit into a compact enclosure together with the converter. Since the battery voltage and ambient temperature vary over wide ranges, a simple form of load detection must be used. Besides this, the voltage drop across the load sensing circuitry must naturally be as small as possible. This can be achieved by using ‘ultra-modern’ SiGe technology.
The 6 V from the battery and the 12 V from the converter are combined in the MB R2545 dual diode. Consequently, a voltage of at least 6 V is always applied to the radio (for memory retention). If the radio is switched on, it draws a current from the 6-V battery, which may be around 100 mA.This current produces a voltage across R1. If this voltage is 75 mV or greater, the AC128 germanium transistor starts conducting and charges electrolytic capacitor C1, which is connected to the gate of the BUZ10. The MOSFET energises RE1 and thus connects the supply voltage to the converter. As a result, 12-V power is connected to the radio. The resulting increased current causes the voltage drop across R1 to increase, which is undesirable, so a 10-A Schottky diode is connected in parallel. The total voltage drop is thus approximately 0.6 V. The RC network connected to the BUZ10 ensures that the transistor always remains switched on for at least several seconds, to prevent the circuit from ‘chattering’ with varying current consumption.
Circuit diagram :
Automatic Switch For Voltage Converters
If the load is switched off, the AC128 cuts off, the electrolytic capacitor discharges and the relay again disconnects the voltage converter. The residual current consumption is so small that the circuit can also be connected ahead of the ignition switch. The Schottky diodes need only be rated for the necessary voltages and currents, and above all, they should have the lowest possible saturation voltage. The exact type is not critical. Two separate diodes can also be used. A small heat sink for the MBR diode won’t hurt, but this is normally not essential. Practically any type of PNP germanium transistor that is still available or on hand can be used (AC125, AC126 and AC128 work perfectly).
It may be necessary to modify the value of R1. In combination with the germanium transistor, R1 determines which level of current will be ignored (for memory retention) and which level of current will cause the converter to be switched on. With the component values shown in Figure 1, this level is between 10 mA and 25 mA. It is recommended to measure the quiescent current (at 6 V) and switch-on current of the load and then simulate the switching process using dummy load resistors. When selecting the 6-V relay, ensure that its contacts have an adequate current rating. The actual value can be significantly greater than the nominal output current. With a load of 5 A at 12 V and a converter efficiency of 70 percent, the current through the relay contacts rises to 14.3 A.
Author: C. Wolff - Copyright: Elektor Electronics
Source : www.extremecircuits.net
Tuesday, March 19, 2013
Intercom Circuit for Factories
Intercom Circuit for Factories
Here I have given a intercom circuit This circuit is most suitable for factories.Because These units have high quality.Only 2 wires are required to connect the units together.
Note
# Be careful when you work with 230v
Saturday, March 9, 2013
Discussing Clock Signals for Inverter Circuit
Please read the previous post for continuation...
Hi Swagatam, the 4069 square wave circuit I was using originally has 2 Clock signals . The first signal comes out of Pin# 2 of the 4069 goes to 10K resistor then to base of TR1. Part of that signal is diverted back into Pin# 3 and inverted out through Pin# 4 and out the other resistor and to base of TR2. Please correct me if Im wrong.
Hi Swagatam, the 4069 square wave circuit I was using originally has 2 Clock signals . The first signal comes out of Pin# 2 of the 4069 goes to 10K resistor then to base of TR1. Part of that signal is diverted back into Pin# 3 and inverted out through Pin# 4 and out the other resistor and to base of TR2. Please correct me if Im wrong.
I only used the clock signal coming out of Pin# 2 to TR1. I did not use the inverted half coming out of Pin# 4 to TR2.
I connected Pin# 3 to ground and Pin# 4 N/C, and I did not use TR2.
Is this OK??????
Sincerely Ali
Hi Aliman,
The two gates are required to create a push-pull effect and make both the windings saturate alternately. Only due to this function we are able to get complete AC cycles at the output, so, its better that we follow the original design only.
Best Regards.
Best Regards.
Sorry for the confusion on my part.
So let me get this right, I should use the complete 4069 circuit as per the Schematic I sent you. Ok ,so where the Clock signal comes out of TR1s collector and TR2s collector, do I connect those two points to the Clock Input connection on your circuit ?
Thanks for your patience Swagatam
Sincerely Ali
Hi Swagatam, so I should combine the outputs of TR1 & TR2 and connect them to the Clock Input connection on your circuit ?? Is that correct??
P.S. I told you I was a beginner,lol...
Sincerely Ali
Hi Swagatam, my confusion lies in the final connection between the 4069 circuit and your PWM circuit. Here is a diagram of both circuits, how do I connect the two outputs from TR1 & TR2 to the Clock Input in your circuit ?
Sincerely Ali
Hi Ali,
Please do the connections as per the following steps:
We dont need the gate of IC 4069 with the pin 3 and 4, so take it out of the scene, but remember to connect pin 3 to ground, just as pin 5 and pin 9.
The clock output from pin 2 of IC 4069 now gets disconnected from the transistor bases and goes to the clock input of our 4017 ICs.
Finally the diode outputs from the two ICs 4017 now gets connected to the two transistor bases respectively.
Thats it.... your modified PWM circuit is ready.
Thanks and Regards.
Continued HERE,
We dont need the gate of IC 4069 with the pin 3 and 4, so take it out of the scene, but remember to connect pin 3 to ground, just as pin 5 and pin 9.
The clock output from pin 2 of IC 4069 now gets disconnected from the transistor bases and goes to the clock input of our 4017 ICs.
Finally the diode outputs from the two ICs 4017 now gets connected to the two transistor bases respectively.
Thats it.... your modified PWM circuit is ready.
Thanks and Regards.
Continued HERE,
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