Showing posts with label off. Show all posts
Showing posts with label off. Show all posts
Wednesday, October 9, 2013
Auto Power Off
We are surrounded by battery operated equipment of all kinds, and this array is growing still. Manufacturers and designers lean over backwards to make sure that their equipment draws a small current and can thus be operated by a battery. This has its flip side, too. because even if the equipment in question draws only a small current, when it is not switched off, the battery is flat after a few days or weeks. The circuit presented here can prevent this happening. It may be added to all kinds of equipment operating from a 9 V battery and switches this off automatically one minute after a preset time has elapsed. The peak switching current is 20 mA, which is more than enough for most applications.
The switch is formed by a p-n-p darlington, T1, which is actuated by push-button switch S1. The very high amplification of the darlington enables it to be kept on fairly long with the aid of a relatively small-value capacitor, C1 (= 100 µF). Resistor R3 limits the charging current of C1 to ensure a long life of S1. Resistors R1 and R2, in conjunction with C1, determine the switch-on time. When this time has elapsed, R1 ensures that T1 is switched off. Since the darlington can handle a UBE of –10 V, a polarity protection diode is not needed.
Continue Read...
The switch is formed by a p-n-p darlington, T1, which is actuated by push-button switch S1. The very high amplification of the darlington enables it to be kept on fairly long with the aid of a relatively small-value capacitor, C1 (= 100 µF). Resistor R3 limits the charging current of C1 to ensure a long life of S1. Resistors R1 and R2, in conjunction with C1, determine the switch-on time. When this time has elapsed, R1 ensures that T1 is switched off. Since the darlington can handle a UBE of –10 V, a polarity protection diode is not needed.
Tuesday, April 9, 2013
LED Bar Off Indicator
The simple indicator presented in this article may be combined, in principle, with any circuit that contains an LED bar display driven by a Type LM3914 IC. It ensures that an LED will light when all LEDs driven by the LM3914 are out. This prevents one drawing the erroneous conclusion that, since all the LEDs are out, the circuit is switched off. The circuit then continues to draw current, which, especially if it is battery powered, costs unnecessary money, apart from other considerations. The LED in the monitor draws a current of only 1 mA. When the LEDs forming the bar, D1–D10 are all out, there is no potential difference across R3, so that T1 is off and T2 is on.
This results in T3, in conjunction with R5 and the internal reference voltage of IC1, to form a current source that causes a constant current to flow through D11 so that the diode lights. When on of diodes D1–D10 lights, a potential difference ensues across R3, which causes T1 to come on. This results in T2 being switched off so that there is no collector current through T3. Consequently, there is no feedback at the emitter of T3, so that the current through R2 rises appreciably. The current through R2 determines the current through the LEDs in the bar. Therefore, when T3 is enabled, the current through R2, and thus the total current in the circuit, is reduced considerably.
Continue Read...
This results in T3, in conjunction with R5 and the internal reference voltage of IC1, to form a current source that causes a constant current to flow through D11 so that the diode lights. When on of diodes D1–D10 lights, a potential difference ensues across R3, which causes T1 to come on. This results in T2 being switched off so that there is no collector current through T3. Consequently, there is no feedback at the emitter of T3, so that the current through R2 rises appreciably. The current through R2 determines the current through the LEDs in the bar. Therefore, when T3 is enabled, the current through R2, and thus the total current in the circuit, is reduced considerably.
Monday, April 8, 2013
High And Low Voltage Cut Off Circuit
This is a design for protection voltage. This circuit is called as high and low voltage cut off. The circuit is using time delay for cut off the voltage. This is a low cost and reliable circuit for protecting such equipments from damages. This is the figure of the circuit.
Whenever the power line is switched on it gets connected to the appliance only after a delay of a fixed time. If there is hi/low fluctuations beyond sets limits the appliance get disconnected. The system tries to connect the power back after the specific time delay, the delay being counted from the time of disconnection. If the power down time (time for which the voltage is beyond limits) is less than the delay time, the power resumes after the delay: If it is equal or more, then the power resumes directly. This circuit is using op-amp 741 and 555 IC for control the operation.
The complete circuit is consisting of various stages. They are: - Dual rail power supply, Reference voltage source, Voltage comparators for hi/low cut offs, Time delay stage and Relay driver stage. Under normal operating conditions i.e. when the input voltage is between maximum and minimum limit the output from the both the comparators are low. The transistor Q1 is OFF and the relay is in de-energized (pole connected to N/C pin) state and the output is obtained. When the input voltage is below or above the limits set by the pre-sets R8 or R9, the output of the Op-Amps goes either low or high and diodes D1 or D2 would be forward biased depending on the situation. Transistor Q1 switches ON and the flow of current from collector to emitter energizes the relay and the output is cutoff.
Whenever the power line is switched on it gets connected to the appliance only after a delay of a fixed time. If there is hi/low fluctuations beyond sets limits the appliance get disconnected. The system tries to connect the power back after the specific time delay, the delay being counted from the time of disconnection. If the power down time (time for which the voltage is beyond limits) is less than the delay time, the power resumes after the delay: If it is equal or more, then the power resumes directly. This circuit is using op-amp 741 and 555 IC for control the operation.
The complete circuit is consisting of various stages. They are: - Dual rail power supply, Reference voltage source, Voltage comparators for hi/low cut offs, Time delay stage and Relay driver stage. Under normal operating conditions i.e. when the input voltage is between maximum and minimum limit the output from the both the comparators are low. The transistor Q1 is OFF and the relay is in de-energized (pole connected to N/C pin) state and the output is obtained. When the input voltage is below or above the limits set by the pre-sets R8 or R9, the output of the Op-Amps goes either low or high and diodes D1 or D2 would be forward biased depending on the situation. Transistor Q1 switches ON and the flow of current from collector to emitter energizes the relay and the output is cutoff.
Subscribe to:
Posts (Atom)