Simple battery voltage detector

Source: 2020 - 04 - 11 and clicks: simple battery voltage detector people often encounter a lot of battery equipment, when the battery voltage drops to a certain threshold, it should give instructions, remind people to replace batteries or quick charge. On the phone's screen, for example, have a like a battery symbol, the battery voltage at any time, can timely reminder to recharge. But no such and many devices, such as radio and rechargeable haircut. In fact this battery voltage detector can self-control, here are 5 circuit: figure 1 shows a composed of a transistor circuit, can be used to detect the 3 v to 15 v battery power supply equipment. Q1 and Q2 is composed of two levels of inverting amplifier, they adjust VRl, make circuit with preset threshold ( Such as 9 v battery) Light LED, and it is set to 8. 2 v to warn ( The leadership ignition) 。 The two-stage inverter amplifier is basically linear, battery LED lights in 8. 2 - 8. Between 0 v, but the brightness is different The current flowing through the LED in 3 ma - Between 15 ma) , indicating that the discrete component of circuit is not ideal. Model is used in Q1 and Q2 drawings BC547, but changed to 9014. Figure 2 is designed to detect circuit of 9 v battery. It is the main component of silicon controlled rectifier ( 可控硅) 。 The whole circuit is essentially a bridge circuit structure. ZDl voltage fixed voltage regulator in 8. 2v。 When the 9 v battery voltage is normal, B will be higher than 8. 2 v, namely SCRl control voltage is higher than the cathode, thyristor will be triggered, so the LED light up immediately. When the battery voltage drop to eight. 2 v, thyristor to stop working, LED out, indicates that the battery in a state of undervoltage. Figure 3 is designed to detect 1. 25 v nickel cadmium battery circuit. Nickel cadmium battery powered by solar batteries. It's cloudy, battery charging current fell, the battery voltage is lower than 1. 25V。 Then trigger LM3909, LED lights, nickel cadmium battery in a state of undervoltage. Note: LM3909 of the low voltage power supply unit. Figure 4 is an integrated circuit consisting of 8211, can detect 5 v to 25 v battery, regulate VRl make circuit in the preset threshold of fixing the leds, shown in figure 1. For example, in the test of 9 v battery, the LED should be set to 8. 2 v lamps ( Warning) 。 Because the circuit is composed of integrated blocks, so the effect is very good, of course. As shown in figure 5, the internal structure of integrated block 8211 is mainly composed of 1. The 15 v power supply of reference and a comparator. When the battery voltage is lower than a certain value, the inversion circuit and LED lighting. In addition, due to the integrated block 8211 working voltage range is very wide, therefore requires a constant current power supply as the power supply system. At the same time, in order to make the LED brightness constant, constant current power supply is needed. Therefore, in the integrated block set inside the constant current source circuit.