The following DC Power supply circuit is a linear power supply (using transformer). The voltage output of 13.8V power supply is highly regulated, can be adjusted in the moderate range, at up to 20A continuous current. This power supply is suitable for use for amateur radio equipment. DC Power supply is easily constructed and suitable for heavy duty because it is very efficient, small and lightweight.

In the DC power supply presented here, the pass transistors are located in the negative rail and connected in common-emitter configuration rather than as emitter-followers. Thanks to this, the regulator’s minimum voltage drop is extremely low, only about 0.1V for the transistors plus 0.5V for the equalizing resistors.

The other advantage is that the collectors are directly connected to the negative pole of the power supply’s output, which in most applications is grounded. That means that no insulation is required between the transistors and the grounded power supply cabinet! This eases the cooling very considerably. Thanks to the low regulator drop, a low cost 25V filter capacitor can be used.

Some Notes of DC Power Supply Circuit

• Use a transformer for the primary voltage you need. The 3A fuse is for 220 or 240V primaries. If you use something in the neighborhood of 110V, use a 6A fuse.
• The rather high transformer rating of 35A accounts for the losses that occur due to the capacitive input filter. If your transformer is rated for capacitive input, then a 25A value is enough.
• Of course you can make up C1 by placing several smaller capacitors in parallel. Likewise, the 0.1 Ohm, 5 Watt resistors can be made up by several in parallel, for example by 5 resistors of 0.5 Ohm, 1 Watt each.
• The LM336Z-5.0 voltage reference IC should not be replaced by a zener diode. Zeners are not nearly as stable. A different voltage reference IC can of course be used, if R2 and R3 are modified for the different voltage.
• D1 and Q2 through Q6 need heatsinking. Only Q2 needs insulation. D1 dissipates up to 60W, Q2 up to 25W, while the pass transistors dissipate up to 30W each in normal use, but may reach a level of 130W during short circuit! Take this into account when choosing the heat sink!
• R5 exists only to make sure that the transistors can actually be driven off. The 741 is not a single-supply operational amplifier, so it cannot drive its output very low. If a true single-supply opamp is used, then R5 becomes unnecessary.
  

This electronic project stereo amp is based on the STK415-090-E class H audio power amplifier hybrid IC that features a built-in power supply switching circuit.
This STK415-090-E class H audio power amplifier provides high efficiency audio power amplification by controlling (switching) the supply voltage supplied to the power devices according to the detected level of the input audio signal.
STK415-090-E class H audio power amplifier is pin to pin compatible with STK416-100 stereo amp .
This electronic project stereo amp will provide an 50 + 50 watts output power with 0.8 % THD , but it can provide more power , up to 80 watts with 10% THD .
STK415-090-E class H audio power amplifier supports output loads from 4 up to 8 ohms and require an input DC voltage from 27 up to 60 volts .
For 8 ohms load , voltage required by this stereo amp project are : +/- 27V for VL and +/-37V for VH .

This 2x50 watt stereo amp project must be designed so that (|VH|-|VL|) is always less than 40V when switching the power supply with the load connected. Set up the VL power supply with an offset voltage at power supply switching (VL-VO) of about 8V as an initial target.
To prevent over heating damage thermal design must be implemented and a thermoplastic adhesive resin must be used for this hybrid IC .
A value of 2.34.C/W, satisfies all required thermal resistance of the heat sink .
Electronic parts required for this 2x50 watt stereo amp electronic project are : R01, R02 1.5k ; R03, R04 100 /1W , R05, R06 56k ; R08, R09 4.7 /1W ; R11, R12 4.7, R14,R15 560 ; R18, R19 56k ; R21, R22 1k ; R24, R26 0.22 10%, 5W ; C01, C02 100.F/100V ; C03, C04 100.F/50V ; C05, C06 100.F/ 100V ; C07, C08 3pF; C10, C11 0.1.F; C13, C14 22.F/10V ; C16, C17 2.2.F/50V ; C19, C20 470pF ; C22, C23 100pF ; D01, D02 15V ; D03, D04 3A/60V ; L01, L02 3.H .

A very simple continuity tester electronic project can be designed using the LM3909 LED flasher integrated circuit .

This continuity tester project , require few external electronic parts and can be used for testing continuity of coils and cables .
This continuity tester project must be powered from a 1.5 volt DC power supply , you can use a 1.5 volts battery cell .

Given is a pretty generic High-End Power Amplifier. Circuit Schematic quite similar to the one that ghosts around the block as "The G0ldm0uth" Amplifier over at DIYA, but with bipolar tripple emitter follower output and not mosfets, output runs at a fair bit of bias current, around 1 Amp in total and uses three complementary pairs of 30MHz (nominal) output transistors.

High-End Power Amplifier Circuit

However effective a domestic alarm system may be, it’s invariably better if it never goes off, and the best way to ensure this is to make potential burglars think the premises are occupied. Indeed, unless you own old masters or objects of great value likely to attract ‘professional’ burglars, it has to be acknowledged that the majority of burglaries are committed by ‘petty’ thieves who are going to be looking more than anything else for simplicity and will prefer to break into homes whose occupants are away.

Rather than simply not going on holiday – which is also one solution to the problem (!) – we’re going to suggest building this intelligent presence simulator which ought to put potential burglars off, even if your home is subjected to close scrutiny. Like all its counterparts, the proposed circuit turns one or more lights on and off when the ambient light falls, but while many devices are content to generate fixed timings, this one works using randomly variable durations.

Circuit diagram:

So while other devices are very soon caught out simply by daily observation (often from a car) because of their too-perfect regularity, this one is much more credible due to the fact that its operating times are irregular. The circuit is very simple, as we have employed a microcontroller – a ‘little’ 12C508 from Microchip, which is more than adequate for such an application. It is mains powered and uses rudimentary voltage regulation by a zener diode.

A relay is used to control the light(s); though this is less elegant than a triac solution, it does avoid any interference from the mains reaching the microcontroller, for example, during thunderstorms. We mustn’t forget this project needs to work very reliably during our absence, whatever happens. The ambient light level is measured by a conventional LDR (light dependent resistor), and the lighting switching threshold is adjustable via P1 to suit the characteristics and positioning of the LDR.

Note that input GP4 of the PIC12C508 is not analogue, but its logic switching threshold is very suitable for this kind of use. The LED connected to GP1 indicates the circuit’s operating mode, selected by grounding or not of GP2 or GP3 via override switch S1. So there are three possible states: permanently off, permanently on, and automatic mode, which is the one normally used. Given the software programmed into the 12C508 (‘firmware’) and the need to generate very long delays so as to arrive at lighting times or an hour or more, it has been necessary to make the MCU operate at a vastly reduced clock frequency.

PCB Layout:

In that case, a crystal-controlled clock is no longer suitable, so the R-C network R5/C3 is used instead. For sure, such a clock source is less stable than a crystal, but then in an application like this, that may well be what we’re after as a degree of randomness is a design target instead of a disadvantage. Our suggested PCB shown here takes all the components for this project except of course for S1, S2, and the LDR, which will need to be positioned on the front panel of the case in order to sense the ambient light intensity.

The PCB has been designed for a Finder relay capable of switching 10 A, which ought to prove adequate for lighting your home, unless you live in a replica of the Palace of Versailles. The program to be loaded into the 12C508 is available for free download from the Elektor website as file number 080231-11.zip or from the author’s own website: www.tavernier-c.com. On completion of the solder work the circuit should work immediately and can be checked by switching to manual mode.

The relay should be released in the ‘off’ position and energized in the ‘on’ position. Then all that remains is to adjust the day/night threshold by adjusting potentiometer P1. To do this, you can either use a lot of patience, or else use a voltmeter – digital or analogue, but the latter will need to be electronic so as to be high impedance – connected between GP4 and ground. When the light level below which you want the lighting to be allowed to come on is reached, adjust P1 to read approximately 1.4 V on the voltmeter.

If this value cannot be achieved, owing to the characteristics of your LDR, reduce or increase R8 if necessary to achieve it (LDRs are known to have rather wide production tolerances). Equipped with this inexpensive accessory, your home of course hasn’t become an impregnable fortress, but at least it ought to appear less attractive to burglars than houses that are plunged into darkness for long periods of time, especially in the middle of summer. (www.tavernier-c.com)

COMPONENTS LIST
Resistors
R1 = 1k 500mW
R2 = 4k7
R3 = 560R
R4,R6 = 10k
R5 = 7k5
R 7 = LDR
R8 = 470k to 1 M
P1 = 470k potentiometer
Capacitors
C1 = 470µF 25V
C2 = 10µF 25V
C3 = 1nF5
C4 = 10nF
Semiconductors
D1,D2 = 1N4004
D3 = diode zener 4V7 400 mW
LED1 = LED, red
D4 = 1N4148
T1 = BC547
IC1 = PIC12C508, programmed, see Downloads
Miscellaneous
RE1 = relay, 10A contact
S1 = 1-pole 3-way rotary switch
F1 = fuse 100 mA
TR1 = Mains transformer 2x9 V, 1.2 -3 VA
4 PCB terminal blocks, 5 mm lead pitch
5 solder pins 

A Transcutaneous Electrical Nerve Stimulation (TENS) device is, put bluntly, a machine for giving electric shocks. The author was prescribed such a device on loan by his orthopaedic specialist. The unit has a large number of programmes, of which he used only one. Measuring the signals at the output of the device in this mode revealed damped oscillations at a frequency of approximately 2.5 kHz, with a repetition rate of approximately 100 Hz.

Running Light circuit uses a CMOS 555 timer