Loudspeaker Protector Monitors Current

This circuit uses a 0.1O 1W resistor connected in series with the output of a power amplifier. When the amplifier is delivering 100W into an 8O load, the resistor will be dissipating 1.25W. The resulting temperature rise is sensed by a thermistor which is thermally bonded to the resistor. The thermistor is connected in series with a resistor string which is monitored by the non-inverting (+) inputs of four comparators in an LM339 quad comparator. All of the comparator inverting inputs are connected to an adjustable threshold voltage provided by trimpot VR1. As the thermistor heats up, its resistance increases, raising the voltage along the resistor ladder.

Circuit diagram:

Loudspeaker Protector Circuit Diagram

When the voltage on the non-inverting input of each comparator exceeds the voltage at its inverting input, the output switches high and illuminates the relevant LED. NOR gate latches are connected to the outputs of the third and fourth comparators. When the third comparator switches high, the first latch is set, turning on Q1 and relay 1. This switches in an attenuation network (resistors RA & RB) to reduce the power level. However, if the power level is still excessive, comparator 4 will switch, setting its latch and turning on Q2 and relay 2.

This disconnects the loudspeaker load. The thermistor then needs to cool down before normal operation will be restored. The values of R1-R4 depend on the thermistor used. For example, if a thermistor with a resistance of 1.5kO at 25°C is used, then R1 could be around 1.5kO and R2, R3 and R4 would each be 100O (depending the temperature coefficient of the thermistor). The setup procedure involves connecting a sinewave oscillator to the input of the power amplifier and using a dummy load for the output. Set the power level desired and adjust trimpot VR1 to light LED1. Then increase the power to check that the other LEDs light at satisfactory levels.

 

 

 

Source by : Streampowers

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Lead Acid Battery Protector

The circuit described right here can be used to  ensure  that  a  12 V  sealed  lead  acid  (SLA)  gel battery isn’t discharged too deeply. The  predominant part of the circuit is a bistable relay,  which is pushed by using the output of an op amp. 

Circuit diagram :

Lead Acid Battery Protector Circuit Diagram

The battery voltage is first diminished by way of D1, R1,  P1 and R2, and then repeatedly compared  with a reference voltage set up with the support of diode D2.  When the battery discharges too much and  its terminal voltage drops beneath the level  set by using P1, the output of the opamp becomes  High, which causes the relay to toggle. This  in turn isolates the weight from the battery. The  battery will additionally be reconnected by manner of S1 once the  battery has been changed or recharged. 

The relay used in the prototype is a 5 V bistable type made through Omron (G6AK-234P-ST-US  5 VDC). The two windings of the relay each  have a resistance of 139 Ω (for the RAL-D 5  W-K made with the aid of Fujitsu that is 167 Ω). When the  battery voltage starts to develop into too low and  the relay is being reset the present consumption of the circuit is ready 45 mA. Shortly  after the burden has been disconnected, when the battery voltage upward throughsts above the reference  voltage once more, the reset coil will no longer be  powered and the current consumption drops  back to about 2.5 mA. 

The vary of P1 has deliberately been kept  small. With a reference voltage of 5.6 V (D2)  and a voltage drop of 0.64 V throughout D1, the circuit reacts within a voltage span of eleven.5 V and  11.8 V. This vary is clearly depending on the zener diode used and the tolerance. 

For a larger span you can use a larger value  for P1 without any problems. With the potentiometer at its mid setting the circuit switches  at about 11.6 V.

 

 

Author : Jürgen Stannieder

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