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CAMCORDER_BATTERY_PROTECTOR

2016-05-11 12:58  
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CAMCORDER_BATTERY_PROTECTOR
Many camcorder enthusiasts use their spare battery for powering video lights. Many such lights give no indication when the battery has gone flat. This can be avoided by the use of this protection circuit. When it gets switched on, the potential across C1 is zero, so that T2 is cut off, the relay is inactive, and the indicator lamp lights. As long as the battery voltage remains above a certain level, T1 is on and holds the base of T2 at earth potential. In this state, only a small current is drawn. When the battery voltage is no longer higher than the sum of the zener voltage, the potential set by divider R2-P1, and the drop across the base-emitter junction of T1, this transistor is cut off, whereupon C 1 is charged via R2. When the potential across C1 has risen to a value high enough for T2 to be switched on, the relay is energized, and its contact disconnects the lamp from the battery. Because the current drain (≤70 rnA) is then determined almost entirely by the relay, it is essential to remove, or disconnect, the battery from the light unit. The switch-off voltage level, set with P1, should be about 1 V per battery cell.