Saturday, April 10

CDS (Cadmium Sulfide) Light detector Circuit

This kit works as a "light" detector which energizes a miniature relay when the CDS (Cadmium Sulfide) photo resistor detects bright light. The relay is de-energized in subdued light. A trim pot is provided for adjusting the sensitivity of the detector.

Video Amplifier

Part List :

R1= 15Kohm+15Kohm R12= 100ohm trimmer C3=4.7pF ceramic
R2-3-4= 10Kohm R13-15= 47ohm IC1= LH0032
R5.....9= 1Kohm R14= 10Kohm S1= 1X2 mini switch
R10= 820ohm C1= 10uF 63V MKT S2= 1X6 sel.
R11= 1Mohm C2-4= 100nF 63V J1-2= BNC connector

Video signal emphasis Circuit

With this circuit we can amplification selectively the high signal of picture frequencies [Video] with result bigger clarity than this. The circuit should be placed between a Video unit and the reception Scart or the plug Video input of television receiver. The designing is simple, it�s based in three only transistor. The first stage of Q1 function as isolator - adapter of input impedance. The second stage round the Q2 in common base connection which the gain is determined by the TR2. The TR1, R6 and C3 determine the frequency response. The third stage round the Q3 works as output buffer and 75-ohm line driver. The TR2 should be regulated in a place where the circuit output voltage, to be 1Vp-p, in 75 ohm load. The circuit functions with 12Volts - 50mA well stabilized. [Elektor 7/8 92

Pat List :
R1=82ohm R10=2.2Kohm C8=100nF 100V MKT
R2=5.6Kohm R12=180ohm TR1=250ohm trimmer
R3-9-11=2.7Kohm R13=68ohm TR2=500ohm trimmer
R4=330ohm C1-4-5=100uF 16V D1=1N4148
R5=220ohm C2=2200uF 16V Q1-2-3=BC547

R6=470ohm C3=470pF ceramic J1-2=Female RCA jack
R7=270ohm C6=470uF 16V J3=2pin connector 2.54mm step
R8=12Kohm C7=220uF 16V

Wednesday, April 7

IC LM350. t oBattery Charger

The schematic diagram can be used for charging the 12V lead acid batteries.

The circuit is designed as a constant voltage source with a negative temperature coefficient. The transistor Q1 (BD 140) is used as the temperature sensor. The transistor Q2 is used to prevent the battery from discharging through R1 when the mains power is not available. The circuit is designed based on the voltage regulator IC LM350. The output voltage of the charger can be adjusted between 13-15 V by varying the POT R6.

The LM350 will try to keep the voltage drop between its input pin and the output pin at a constant value of 1.25V. So there will be a constant current flow through the resistor R1. Q1 act here as a temperature sensor with the help of components R6/R3/R4 which more or less control the base current of Q1. As the emitter/base connection of transitor Q1, just like any other semiconductor, contains a temperature coefficient of -2mV/°C, the output voltage will also show a negative temperature coefficient. That one is only a factor of 4 larger, because of the variation of the emitter/basis of Q1 multiplied by the division factor of P1/R3/R4. This results in approximately -8mV/°C. The LED will glow whenever the mains power is available.

Simple Nicad Battery Circuit

This simple and low cost battery 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.

Monday, April 5

0-15 VDC Power Supply

This circuit of power supply, are very simple in the manufacture, the finding of his materials , is very easy and cost, small. The output voltage is stabilised and is regulated in the region from 0V until + 15V dc, with biggest provided current 1 A. The regulation becomes with the R2. The Q1 of is classic power transistor and it needs it is placed in heatsink, one and heating when it works continuously in the region of biggest current. The type of transformer is standard in the market.

Components ;
R1= 56ohm 2W Q1= 2N3055
R2= 330ohm Lin. pot. T1=220V@18V 1.5A
C1= 2200uF 35V
C2= 100uF 35V D1= 18V 1.5W zener
C3= 10uF 25V
C4= 220uF 25V
C5= 100nF 100V
GR1= 4 X 1N4007

Electronic Fuse Circuit

The power supply, with electronic stabilisation - mainly those of laboratories - it should they are protected from over current that emanates from short-circuits, erroneous association or damage of repaired appliance. The circuit offers effective protection in power supply with output voltage through to 45V DC. Transistor Q3 of is type in all cases BC148, while the types of Q1-2, as well as R1-2, depend from the biggest intensity of current, according to the table. The entry is connected in the exit power supply. Under regular conditions of work, the Q2 turn on, completely via the R1-Q1 and functions in the saturation. The output voltage is 2V roughly lower than the voltage of supply. If grow the dip of voltage, in the R2 at 0.7V. because short-circuit, then conduct the Q3 and the voltage between the collector and his emitter is 0.3V. the Q1-2, however is driver only when his voltage between the base of Q1 and emitter of Q2 is 1.4V at least. But in case of overcharge, this voltage is 0.7V+0.3V=1V, with result the circuit is regulated automatically in the predetermined biggest intensity. The transistors that I give in the table can be replaced with corresponding, it is enough they suit their characteristics.

Imax (A)	R1 (Ω)	R2 (Ω)	Q1	Q2	Q3
5	100	0.12	2Ν1613	2N3055	BC148
0.5	1000	1	BC107	2N1613	BC148
0.1	4700	4.7	BC107	2N1613	BC148

BROEDHIEN