0-50V 2A Bench power supply

An 0-50v bench power supply can be made using electronic diagram below which is designed using LM10 op amp and 2n3055 transistors.

50V Bench Power Supply Circuit Diagram:

0-50V 2A Bench power supply

This LM10 2n3055 50v bench power supply allows an output voltage regulation in a range between 0 and 50 volts and the output current can be limited to a maximum of 2A. Output voltage increases linearly with the amount of resistance potentiometer P1, while the current can be adjusted linear using potentiometer P3. Potentiometer P2 serves to regulate maximum output current (maximum value is 2A).

Transformerless 5 Volt DC Power Supply

An increasing number of appliances draw a very small current from the power supply. If you need to design a mains-powered device, you could generally choose between a linear and a switch-mode power supply. However, what if the appliance’s total power consumption is very small? Transformer-based power supplies are bulky, while the switchers are generally made to provide greater current output, with a significant increase in complexity, problems involving PCB layout and, inherently, reduced reliability.

Is it possible to create a simple, minimum part-count mains (230 VAC primary) power supply, without transformers or coils, capable of delivering about 100mA at, say, 5 V? A general approach could be to employ a highly inefficient stabilizer that would rectify AC and, utilizing a zener diode to provide a 5.1 V output, dissipate all the excess from 5.1 V to (230×√2) volts in a resistor. Even if the load would require only about 10mA, the loss would be approximately 3 watts, so a significant heat dissipation would occur even for such a small power consumption.

Transformerless 5 Volt DC Power Supply Circuit Diagram:

Power Supply Circuit Diagram
At 100mA, the useless dissipation would go over 30 W, making this scheme completely unacceptable. Power conversion efficiency is not a major consideration here; instead, the basic problem is how to reduce heavy dissipation and protect the components from burning out. The circuit shown here is one of the simplest ways to achieve the above goals in practice. A JVR varistor is used for over-voltage/surge protection. Voltage divider R1-R2 follows the rectified 230 V and, when it is high enough, T1 turns on and T3 cannot conduct.

When the rectified voltage drops, T1 turns off and T3 starts to conduct current into the reservoir capacitor C1. The interception point (the moment when T1 turns off) is set by P1 (usually set to about 3k3), which controls the total output current capacity of the power supply: reducing P1 makes T1 react later, stopping T3 later, so more current is supplied, but with increased heat dissipation. Components T2, R3 and C2 form a typical ‘soft start’ circuit to reduce current spikes — this is necessary in order to limit C1’s charging current when the power supply is initially turned on. At a given setting of P1, the output current through R5 is constant.

Thus, load R4 takes as much current as it requires, while the rest goes through a zener diode, D5. Knowing the maximum current drawn by the load allows adjusting P1 to such a value as to provide a total current through R5 just 5 to 6mA over the maximum required by the load. In this way, unnecessary dissipation is much reduced, with zener stabilization function preserved. Zener diode D5 also protects C1 from over voltages, thus enabling te use of low-cost 16 V electrolytics. The current flow through R5 and D5, even when the load is disconnected, prevents T3’s gate-source voltage from rising too much and causing damage to device. In addition, T1 need not be a high-voltage transistor, but its current gain should exceed 120 (e.g. BC546B, or even BC547C can be used).


Temperature Sensor Circuit using 1N4148 diode

There are components that have special characteristics, one of them is the 1N4148 diode, it is a diode High-speed, and its switching speed is 4th, its voltage is 100 V and current of 450 mA. It besides a diode 1N4148 is used as the temperature sensor, that due to its characteristics that cause it to change its resistance with temperature change. Of course it does not compare to a sensor like the LM38, but for some circuits of low precision, which just need to know if an element is hot or cold it is very useful.

Temperature Sensor using 1N4148 diode Circuit Diagram:

Temperature Sensor Circuit Diagram

The scheme above is a circuit that measures the temperature in a simple manner using a multimeter. It uses 1N4148 diode, and VR1 and VR2 must be adjusted with a thermometer, and is more precise measurement. On the scale of the multimeter can be compared to the scale of degree Celsius with Volt.

Temperature sensor with diode 1N4148:

Temperature sensor with diode 1N4148

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Door Opening Alarm with Sound Alert

Door Opening Alarm with Sound Alert

The door opening alarm circuit or “Front Office Visitor Alert” is used for alerting you when a customer is at your office/shop. It will produce a beep sound when each new customer or visitor is entering, and will automatically switch OFF after few seconds.

Door Opening Alert Circuit Diagram:

Alarm with Sound Alert

In this circuit timer IC NE555 is used as monostable mode. Initially when the door is closed; reed switch (normally open type) near the magnet is closed. When the door is opened by someone, the reed switch near the magnet is open and the base of Transistor Q1 goes low through the 10k Resistor R2, and so Transistor Q1 is ON. At this time trigger pin 2 of the IC1 go low, it triggers the monostable built around IC NE555. Once triggered, output pin 3 of IC1 goes high, and both Buzzer and LED are turned on.

At this time the Capacitor C1 starts charging through the Transistor Q1. After few seconds the Buzzer and LED will automatically switched OFF. When the door is closed the T ransistor base become high, Transistor Q1 goes OFF and the Capacitor C1 starts discharging through the Resistor R4 is connected parallel with the capacitor C1. You can change the time period of IC1 by changing the values of resistor R5 and capacitor C2.

Assemble the circuit on a general-purpose PCB, enclose in a suitable cabinet and the magnet is fixed on the door frame and the reed switch is fixed on the door, near the magnet. The circuit can be powered from a 6V battery or from mains by using a 6V power adaptor.


Amplifier Using BEL1895 I.C

Here is a very simple and easy to use audio amplifier using I.C BEL(Bharat electronics limited)1895 , a very common IC. This circuit can run on 3V to 6v, making it easy to use in pocket amplifier. Cost is under 25/-

Amplifier Using BEL1895 I.C:


Parts list:

  • BEL1895 I.C (DIP8),
  • C1 = 470uF/10V,
  • C2 = 1000uF/16V,
  • C3 = 220uF/10V,
  • C4 = 100uF/10V,
  • C5 = 4.7uF/10V,
  • C6 = 47pF,
  • C7,C8 = 1uF,
  • R1 = 47Ohm,
  • R2 = 470Ohm,
  • R3 = 100K,
  • R4 = 1Ohm,
  • R5 = 10K V/C,
  • speaker, etc…
  • Total cost is around 20-30 rupeess(INR) or 0.6USD.
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