Showing posts with label current. Show all posts
Showing posts with label current. Show all posts
Wednesday, November 20, 2013
Low Current Relay
Low current relay
This low current relay circuit is designed to be used in battery operated electronic devices. Its operating current is in micro amperes (µA). This is done by using a bistable relay and adding some components to force the relay to behave like a monostable relay.
A bistable relay stays at its last state when the power is turned off but consume at least 50mA trigger current. A monostable relay switches back to its original state when the power is turned off.
How does the low current relay works?
When the power is turned ON, the C1 charges via D1 and the relay coil and this current activates the relay. D1 ensures that the base of T1 is always more positive than its emitter and because of this T1 and T2 are always blocked.
Once the power is turned OFF, the emitter of T1 is coupled to the charge voltage at the positive pole of C1. Its base and the relay coil on the other hand are coupled to the negative pole of C1 and now T1 and T2 conduct, C1 can discharge through T2 and relay. The current flows to the relay coil but in reverse order so is activated to its other state.
It has the advantage of consuming little current, around 150 µA. For a reliable operation, select the relay’s operating voltage as 2/3 to 3/4 of the main power supply. For example is using a 12V power supply select a 9V relay.
Transistors replacements:
T1 = 2SA499 = BC557, BC558
T2 = 2SC734 = BC547, BC548
Low current relay switch
source:http://electroschematics.com/6546/low-current-relay/
This low current relay circuit is designed to be used in battery operated electronic devices. Its operating current is in micro amperes (µA). This is done by using a bistable relay and adding some components to force the relay to behave like a monostable relay.
A bistable relay stays at its last state when the power is turned off but consume at least 50mA trigger current. A monostable relay switches back to its original state when the power is turned off.
How does the low current relay works?
When the power is turned ON, the C1 charges via D1 and the relay coil and this current activates the relay. D1 ensures that the base of T1 is always more positive than its emitter and because of this T1 and T2 are always blocked.
Once the power is turned OFF, the emitter of T1 is coupled to the charge voltage at the positive pole of C1. Its base and the relay coil on the other hand are coupled to the negative pole of C1 and now T1 and T2 conduct, C1 can discharge through T2 and relay. The current flows to the relay coil but in reverse order so is activated to its other state.
It has the advantage of consuming little current, around 150 µA. For a reliable operation, select the relay’s operating voltage as 2/3 to 3/4 of the main power supply. For example is using a 12V power supply select a 9V relay.
Transistors replacements:
T1 = 2SA499 = BC557, BC558
T2 = 2SC734 = BC547, BC548
Low current relay switch
source:http://electroschematics.com/6546/low-current-relay/
Tuesday, October 29, 2013
FPF270X Over Current Protection
Using the FPF270X adjustable over-current protection IC can be designed a very simple adjustable current-limiting electronic project .FPF270X provide full protection to systems and loads from excess current conditions.Minimum current limit is adjustable from 0.4A to 2.0A.The input voltage range is 2.8V to 36V. Loads can be activated or deactivated with a low-voltage logic compatible ON pin. Fault conditions can be monitored using the error flag pin and/or the power-good pin.
All devices clamp the load current so that it cannot exceed an externally programmed current level. An over temperature feature provides further device protection in case of excessive levels of power dissipation.
FPF2700 responds to an overload condition that lasts longer than a fixed blanking period by turning off the load, followed by a retry after the auto-restart time.The FPF270X has an adjustable 0.4A to 2.0A minimum current limit set through an external resistor, RSET, connected between ISET and GND.A 4.7 F to 100 F ceramic capacitor is adequate for CIN in most cases. Larger CIN values may be required in high-voltage or high-current applications.
A 0.1 F to 1 F capacitor, COUT, should be placed between the OUT and GND pins. This capacitor helps prevent parasitic board inductances from forcing the output voltage below ground when the switch turns off.
During a hard short condition on the output while operating at greater than 24V VIN, a large instantaneous inrush current is delivered to the shorted output. A capacitor must be placed at the OUTPUT pin, acting as a current source to support the instantaneous current draw (Table 2).
For more details about how to design a protection circuit using FPF270X IC please consult the manufacturer datasheet.
All devices clamp the load current so that it cannot exceed an externally programmed current level. An over temperature feature provides further device protection in case of excessive levels of power dissipation.
FPF2700 responds to an overload condition that lasts longer than a fixed blanking period by turning off the load, followed by a retry after the auto-restart time.The FPF270X has an adjustable 0.4A to 2.0A minimum current limit set through an external resistor, RSET, connected between ISET and GND.A 4.7 F to 100 F ceramic capacitor is adequate for CIN in most cases. Larger CIN values may be required in high-voltage or high-current applications.
A 0.1 F to 1 F capacitor, COUT, should be placed between the OUT and GND pins. This capacitor helps prevent parasitic board inductances from forcing the output voltage below ground when the switch turns off.
During a hard short condition on the output while operating at greater than 24V VIN, a large instantaneous inrush current is delivered to the shorted output. A capacitor must be placed at the OUTPUT pin, acting as a current source to support the instantaneous current draw (Table 2).
For more details about how to design a protection circuit using FPF270X IC please consult the manufacturer datasheet.
Monday, October 7, 2013
LED Torch using NSI45090JDT4G Constant Current Regulator
A very simple LED torch can be designed using the NSI45090JDT4G adjustable constant current regulator (CCR) designed by ON Semiconductor ,using extreme few external components. NSI45090JDT4G device is designed to provide a cost effective solution for regulating current in LEDs. This Constant current regulator is based on patent-pending Self-Biased Transistor (SBT) technology and regulates current over a wide voltage range. It is designed with a negative temperature coefficient to protect LEDs from thermal runaway at extreme voltages and currents.
LED Torch Circuit Diagram
The Radj pin allows Ireg(SS) to be adjusted to higher currents by attaching a resistor between Radj (Pin 3) and the Cathode (Pin 4). The Radj pin can also be left open (No Connect) if no adjustment is required.The maximum current that can be adjusted using this chip is around 160 mA , and the maximum input voltage is around 45 volts The D1 from the circuit shown here is used for reverse battery protection .
Bellow you can see how simple is to design a circuit using this chip ( all data shown bellow are for this schematic ) .
LED’s = ((Vin − QX VF − D1 VF)/LED VF)
Example: Vin = 12 Vdc, QX VF = 3.5 Vdc, D1VF = 0.7 V
LED VF = 2.2 Vdc @ 30 mA
(12 Vdc − 4.2 Vdc)/2.2 Vdc = 3 LEDs in series.
LED Torch Circuit Diagram
The Radj pin allows Ireg(SS) to be adjusted to higher currents by attaching a resistor between Radj (Pin 3) and the Cathode (Pin 4). The Radj pin can also be left open (No Connect) if no adjustment is required.The maximum current that can be adjusted using this chip is around 160 mA , and the maximum input voltage is around 45 volts The D1 from the circuit shown here is used for reverse battery protection .
Bellow you can see how simple is to design a circuit using this chip ( all data shown bellow are for this schematic ) .
LED’s = ((Vin − QX VF − D1 VF)/LED VF)
Example: Vin = 12 Vdc, QX VF = 3.5 Vdc, D1VF = 0.7 V
LED VF = 2.2 Vdc @ 30 mA
(12 Vdc − 4.2 Vdc)/2.2 Vdc = 3 LEDs in series.
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