Stablised Power Supply for Prototyping

Stablised Power Supply for Prototyping

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This stabalised power supply circuit may be directly connected to 230V AC mains to derive output voltages of 3V to 12V DC for connection to the prototyping board.

230V AC mains input is down-converted to 15V AC by step-down transformer X1, whose secondary winding can support a current of 2 amperes. A bridge rectifier converts the AC to pulsating DC with a peak voltage level of 21V (15x1.4142). LED1 lights up to indicate the availability of output from the rectifier. Resistor R1 (2.2-kilo-ohm) limits the current through LED1 to a safe value below 10 mA. The output from the bridge rectifier is smoothed by 470µF capacitor C1. Capacitor C2 bypasses high-frequency ripple.
An adjustable, LM317T series 3-terminal, positive-voltage regulator is used at the output of the rectifier section for regulation. It is capable of supplying in excess of 1.5A over 1.2V to 37V output voltage range. However, here it has been used to supply discrete voltages in steps of 3V, 5V, 6V, 9V and 12V with the help of 5-way rotary switch S2, which brings in different resistor values between Adj pin of the regulator and ground, while R2 (between Adj pin and output pin) is a fixed resistor of 220 ohms. The output voltage (Vo) is given by the relation:



where ‘Rx’ is the resistance connected between Adj pin of the regulator and ground.

In 12V position (‘off’ position of the switch), the value of Rx is R3+R4=1900 ohms, while in various other positions it is the series equivalent of 1900 ohms in shunt with another resistance selected by the rotary switch. The table shows the equivalent series resistance in various positions of the rotary switch.

Fig. 1: Adjustable power supply

Note: X1 rating in the circuit diagram is wrongly printed. That is, 15V-0-15V should be read as 0-15V.

Discrete resistor (with 1% tolerance) switching is preferred to employment of a variable resistor because the wiper contact becomes erratic after some use and the tolerance (variation with temperature) of a variable resistor is also much higher.

The LM317T regulator is to be fitted with a heat-sink between the regulator and PCB to provide the best heat transfer. Note that the higher the load current or the lower the voltage across the load, the higher will be the heat dissipation at the regulator. Assuming that you adjust the output to 3V and the load draws a current of 1.5A, there is a voltage drop of approximately 10 volts across IC1. The power dissipation at IC1 is 10×1.5=15 watts. To dissipate this heat, you must use a heat-sink of 4×10cm size or so. A 3mm aluminium plate of the mentioned size screwed to the regulator will work efficiently. A minimum voltage differential of 3 to 4V between the input and output voltages is essential for proper regulation.

Fig. 2: Pin configuration of LM317

Switch S1, transformer X1, LED1, fuse F1 and rotary switch S2 are preferably mounted suitably in a metallic box. The heat-sink (aluminium sheet) is to be inserted flat between regulator and the PCB and secured using a nut and bolt after applying some heat-sink paste on the metal portion of LM317T. Use a rotary switch mounted on the box and extend the connections from the PCB to the rotary switch position with common connection going to the pole of the rotary switch. As LM317T has built-in short-circuit protection, no fuse at its output is necessary. The circuit should be wired using a proper PCB.

Cat and Dog Repellent Circuit Diagram

august 23, 2012 by team elprocus 

The electronic dog repellent circuit diagram below is a high output ultrasonic transmitter which is primarily intended to act as a dog and cat repellent. The ultrasonic dog repellant uses a standard 555 timer IC1 set up as an oscillator using a single RC network to give a 40 kHz square wave with equal mark/space ratio. This frequency is above the hearing threshold for humans but is known to be irritating frequency for dog and cats.

Since the maximum current that a 555 timer can supply is 200mA an amplifier stage was required so a high-power H-bridge network was devised, formed by 4 transistors TR1 to TR4. A second timer IC2 forms a buffer amplifier that feeds one input of the H-bridge driver, with an inverted waveform to that of IC1 output being fed to the opposite input of the H-bridge which can be seen at A & B in an oscilloscope.

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With this cool cat/dog repeller circuit you could chase the cats  off  from any where you want. In fact, I designed this circuit to chase my cat from my computer table. Most of the animals like cats respond violently to ultrasonic sound and in fact it’s the best way to chase them off. This principle is employed in this circuit.

The circuit here is nothing but an astable multivibrator wired around NE555 (IC1). The cat repellent circuit produces an ultrasonic sound in the range 15-20Khz. The NE 555 is enough to drive a small piezo buzzer and no amplification stages are needed. The POT R2 can be used to adjust the frequency of sound.

Cat Repeller Circuit diagram with Parts list. 

Notes.

• The circuit can be powered from a 9V battery or the power can be tapped from your computer SMPS.
• The circuit can be assembled  on a general purpose PCB.

Authors view. 

I do not guarantee the full effectiveness of the circuit.You have try a lot of frequency settings to make your cat feel discomfort at last. More over the cat may get accustomed to the sound after some time. For me the circuit was only a partial success  and now my cat feels nothing even if the speaker is placed in it’s ear.You try your luck. Best of luck.

Inverter Hack From UPS

PC Temperature Controller

Here is a simple temperature controller that turns your personnel computer (PC) off when the temperature of the PC increases beyond the optimal temperature value. Some of the larger integrated circuits become quite hot and if the temperature inside the PC becomes too high, these devices may not be able to dissipate heat fast enough. This, in turn, could lead to failure of devices and eventually of the PC.

Let us assume that the maximum working temperature of your PC is 55°C. So for safe working of your PC, this temperature controller uses a temperature sensor (LM35) and a comparator (CA3140) which disconnect the PC from the power supply whenever the temperature of your PC rises above 55°C. This threshold value is user-adjustable and can be set anywhere between 0°C and 100°C.

Fig. 1: Temperature controller circuit

Fig. 1 shows the circuit of the PC temperature controller, while Fig. 2 shows pin configurations of the components used. The circuit works off 9V DC, which is derived from main power as follows: Mains power supply is rectified by a bridge rectifier comprising diodes D1 through D4, divided by a resistor network comprising R1 and R2, and stabilised by zener diode ZD1. Capacitor C1 filters the ripples.

Using preset VR1 you can set the reference voltage. The reference voltage at non-inverting pin 3 of the comparator is set such that the temperature of the PC is 55°C. When the temperature of the PC is below 55°C, the voltage at the inverting input (pin 2) of IC2 is lower than the voltage at the non-inverting input (pin 3). At this stage, the comparator output at pin 6 of IC2 is high. This high output triggers triac 1 (BT136), providing mains power to operate the PC.

Fig. 2: Pin configurations of components

When the temperature of the PC increases above 55°C, the inverting input (pin 2) of IC2 also goes above the non-inverting input (reference voltage) at pin 3 and hence the comparator output goes low. This stops triggering of triac 1 (BT136) preventing mains power supply from reaching the PC.

Thus this arrangement provides mains voltage to the PC at temperature of up to 55°C and stops when the temperature goes above 55°C.

Assemble the circuit on any general-purpose PCB in the form of a PC expansion card, so you can use it as an add-on card to any PC. Plug it in, switch-on the supply and use your computer with safety temperature device.

Power Pulser

The idea behind this multipurpose power pulser is very simple. As shown in the circuit (Fig. 1), it uses a low-frequency oscillator to drive a voltage regulator. Timer chip LM555 (IC1) is wired as an astable multivibrator. Components R1 and R2, VR1 and C1 produce the free-running frequency. You can adjust it to some extent by varying potentiometer VR1. The output of IC1 at pin 3 controls the switching on/off of adjustable voltage regulator LM317T (IC2) through npn transistor SL100B (T1).

Fig. 1: Power pulser circuit

You can use input power supply of 5V-18V, 1.5A and adjust the output to 1.25V-15V, 1.5A. This pulsed output can be used for incandescent lamps, DC motors, electromagnetic relays and LEDs.

After selecting the desired load, power up the unit with switch S1 in ‘on’ condition. Now connect a digital multimeter across the output terminal (pin 2) of IC2 and set the required output voltage using potmeter VR2. The frequency of IC1 can be set through VR1, provided switch S1 is ‘on.’ Note that with 18V DC input, the maximum output voltage is approximately 15V only. The frequency of the astable multivibrator can be selected by using values of components R1, VR1, R2 and C1 according to your requirement.

Fig. 2: Pin configuration of regulator lm317

Fig. 3: Proposed cabinet

Assemble the circuit on any general-purpose PCB and enclose in a cabinet as shown in Fig. 3. Connect switch S1 and LED1 on the side of the cabinet. Fix potmeters VR1 and VR2 at the bottom of the front side. Also fix the input and output terminals on the front side of the cabinet. Using external wires, connect the power supply to the input terminal and the load to the output terminal.

Sunset Lamp

LDR-based automatic lights flicker due to the change in light intensity at dawn and dusk. So compact fluorescent lamps (CFLs) are unsuitable in such circuits as flickering may damage the electronic circuits within these lamps. The circuit described here can solve the problem and switch on the lamp instantly when the light intensity decreases below a preset level.

The circuit uses popular timer IC NE555 (IC1) as a Schmitt trigger to give the bistable action. The set and reset functions of the comparators within the NE555 are used to give the instantaneous action. The upper threshold comparator of IC1 trips at 2/3Vcc, while the lower trigger comparator trips at 1/3Vcc. The inputs of both the threshold comparator and the trigger comparator of NE555 (pins 6 and 2) are tied together and connected to the voltage divider formed by LDR1 and VR1. The voltage across LDR1 depends on the light intensity.

In daylight, LDR1 has low resistance and the input voltage to the threshold comparator goes above 2/3Vcc and its output becomes zero, which resets the internal flip-flop of IC1. But the input to the trigger comparator is still more than 1/3Vcc, which keeps output pin 3 of IC1 low. Triac BT136 connected to output pin 3 of IC1 remains quiescent due to insufficient value of current for firing it. Thus lamp L1 remains ‘off’ during daytime.
At sunset, the resistance of LDR1 increases, and the voltage at the input of the threshold comparator decreases below 2/3Vcc and that of the trigger comparator goes below 1/3Vcc. As a result, the outputs of threshold and trigger comparators go high, which sets the flip-flop. This changes output pin 3 of IC1 from low to high. Triac1 gets the necessary gate current through resistor R2 and fires. Thus it completes the power supply to the lamp through Triac1. LED1 glows to indicate the high output state of IC1.

Power supply to the circuit is directly derived from the mains through capacitor C4. This capacitor delivers current in the circuit. Diodes D1 and D2 rectify the AC from capacitor C4 and capacitor C3 provides the necessary smoothing. Zener diode ZD1 provides rectified 15V DC for the circuit. Bleeder resistor R4 removes the stored voltage of the capacitor when the circuit is unplugged.

Assemble the circuit on any general-purpose PCB and enclose in a plug-in type adaptor box. Connect the live and neutral points to the pins of the adaptor box. Provide in the box 5mm holes for LDR1 and LED1. Plug the unit at a place where daylight is sufficient to inhibit the circuit operation during daytime. Light from the lamp should not fall on LDR1 at night.

Caution. The circuit carries 230V AC and most of its points are at mains lethal potential. So do not touch any point in the circuit when it is powered and adjust the preset only with a plastic or insulated screwdriver.

Crystal AM Transmitter

Here is the circuit of a medium-power AM transmitter that delivers 100-150 mW of radio frequency (RF) power.

At the heart of the circuit is a crystal oscillator. A 10MHz crystal is used to generate highly stable carrier frequency. Audio signal from the condenser mic is amplified by the amplifier built around transistors T1, T2 and T3. The amplified audio signal modulates the RF carrier generated by the crystal oscillator built around transistor T4. Here modulation is done via the power supply line. The amplitude-modulated (AM) signal is obtained at the collector of oscillator transistor T4.

Fig. 1: Circuit of crystal AM transmitter

Fig. 2: Oscillator coil

Fig. 3: Modulation transformer

By using matching dipole antenna and co-axial cable, the range of signal transmission can be increased. For maximum range, use a sensitive radio with external wire antenna.

The circuit works off a 9V-12V battery. For oscillator coil L1, wind 14 turns of 30SWG wire round an 8mm diameter radio oscillator coil former with a ferrite bead (see Fig. 2). For modulation transformer X1, you can use the audio output transformer of your old transistor radio set. Alternatively, you can make it from E/I section transformer lamination with inner winding having 40 turns of 26SWG wire and the outer winding having 200 turns of 30SWG as shown in Fig 3.

Assemble the circuit on a general-purpose PCB and enclose in a suitable cabinet.