Showing posts with label Simplest. Show all posts
Showing posts with label Simplest. Show all posts
Sunday, 26 March 2017
Simplest Transformerless LED Drivers
In this post we learn regarding three interesting transformerless power supply circuits for illuminating LEDs from mains that uses minimum number of components
Circuit 1
A capacitor must be having a rating of more than 200V and should be having dialectic of metallize polyester or poly poplin.
A resistor 1K is employed to limit the in rush current the resistor should be having the wattage value of more than 1Watt.
A diode is connected in anti-parallel to the LED. This diode limits the reverse voltage across the LED. The diode also provides the path for the negative half cycle as the LED is connected to a AC power source.
This particular circuit behaves like a constant current source of 15 to 20mA depending on LED voltage bias and supply line stability with a nominal 60Hz power supply frequency. The circuit 2 is an improvisation over circuit 1 and it enables to glow two LED’s at a time. This gives a color benefit also.
Putting two switches to the series part of individual LEDs can enable the viewer to have three colors.
In this transformerless circuit using the above formula the current can be manipulated by changing the capacitor value. Power LEDs can also be driven directly from AC power source.
Circuit2
The third circuit employs a zener diode of 5.6 V/1W. The zener diode serves dual purpose. Firstly it acts as a bias of the negative half of circuit like the diodes employed in circuit 1 and 2. Secondly, it acts as a voltage regulator for the LED driver circuit.
This circuit provides 5 Volts steady output with a 30mA current pumping facility. The 1000uF capacitor acts as a ripple suppressor and it allows a moderate ripple of 6% that is 300mV in this case. Employing the third circuit the use can expect better life of the LED. The current limiting capacitor used is 1.5uF at 200Volts.
The capacitor supplies the current to the driver as well it biases the zener to remain active during operation.
Please note that while using any LED it's datasheet should be studied beforehand. In general natural white LEDs, cool white LEDs, warm white LEDs all have a nominal bias voltage of 3.5V DC. But the activation starts at 2 to 2.4V DC.
The highest efficiency of the LED is achieved at 3.5V DC. Optimization of power supply is the highest priority in any LED driver circuit.
Circuit 3
If a constant voltage supply is provided it is to be notes that the power supply must have minimum ripple content.
The peak of the ripple shall also effect the performance of the LED so far as the junction temperature of the wafer is concerned. However a constant current source is a safest power supply alternative for a LED. A constant current source can achieved in many ways.
A variable power supply that is regulated by a current loop is the general trend. A capacitor in series is obviously the most economic constant current source so far as AC power supply is concerned.
Any fluctuation in the input power might result into the change in the current value,for this purpose,a regulator like 5.6 V zener is a safe practice.
While connecting the LED to the regulator circuit the power capacity of the regulator is to be kept in the mind along with the power requirement of the specific LED.
Tuesday, 17 January 2017
Simplest Single Phase Preventor Circuit for Three Phase Motor Potection
For a 3-phase induction motor,Lit is necessary that all the three phases of supply are present while it is on load.
When any one of the fuses goes out, or a phase is missing, the motor will continue to run with two phases only, but it will start drawing a huge current for the same load. This high current may ruin the motor, unless switched off immediately. A single phase preventor circuit avoids such a mishap. With this circuit the motor will not run, unless all the three phases are present. In a 3-phase supply, the voltages are 120 degrees apart from each other. Thus the addition of three phases gives zero voltage. lf any one of the phase goes, voltage present at the summing point equals half the line voltage. ‘ In this circuit, the three phases (R, Y, B) are connected to line neutral, which in turn is connected to the ground of the circuit. When all three phases are present, voltage at point D is zero. So potential at pin 3 of 1C 741 is also zero, but voltage at pin 2 is nearly 4V. Here 741 is used as a comparator and the voltage at pin 6 is zero. Hence the relay cannot operate. When a phase goes out, voltage at point D goes up to about halt the line voltage. This voltage is divided by 150k and 50k resistors. The voltage at pin 3 is about 8V when 50k potentiometer is properly adjusted. The voltage at pin 6 is about 12V. This base voltage can drive the relay into operating condition. So, the relay would operate when any of the phases goes out. This relay, when used in the control circuit of the 3-phase motor, or with a circuit breaker, would switch the power oft on operation.
When any one of the fuses goes out, or a phase is missing, the motor will continue to run with two phases only, but it will start drawing a huge current for the same load. This high current may ruin the motor, unless switched off immediately. A single phase preventor circuit avoids such a mishap. With this circuit the motor will not run, unless all the three phases are present. In a 3-phase supply, the voltages are 120 degrees apart from each other. Thus the addition of three phases gives zero voltage. lf any one of the phase goes, voltage present at the summing point equals half the line voltage. ‘ In this circuit, the three phases (R, Y, B) are connected to line neutral, which in turn is connected to the ground of the circuit. When all three phases are present, voltage at point D is zero. So potential at pin 3 of 1C 741 is also zero, but voltage at pin 2 is nearly 4V. Here 741 is used as a comparator and the voltage at pin 6 is zero. Hence the relay cannot operate. When a phase goes out, voltage at point D goes up to about halt the line voltage. This voltage is divided by 150k and 50k resistors. The voltage at pin 3 is about 8V when 50k potentiometer is properly adjusted. The voltage at pin 6 is about 12V. This base voltage can drive the relay into operating condition. So, the relay would operate when any of the phases goes out. This relay, when used in the control circuit of the 3-phase motor, or with a circuit breaker, would switch the power oft on operation.
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