CN202172305U - Power supply circuit of remote meter reading terminal - Google Patents

Abstract

The utility model discloses a power supply circuit of a remote meter reading terminal, which comprises a rechargeable battery, an electronic switch of a battery charging circuit, an electronic switch of a battery power supply circuit, and a CPU. Both of the two electronic switches are connected to the battery. The electronic switch of the battery charging circuit is connected to the power supply and is controlled by the CPU on/off for charging the battery. The battery provides backup power for the main system through the electronic switch of the battery power supply circuit. The CPU has an AD converter , and the AD converter is connected with the battery for detecting the battery voltage, and the electronic switch of the battery power supply circuit is also connected with a wake-up circuit, and the wake-up circuit can open the battery power supply circuit so that the battery supplies power to the main system. The utility model can wake up the terminal to work again after the mains power failure, and will not cause the battery to be over-discharged to damage the life of the battery. When the mains power is normal, the battery will be charged without overcharging to cause damage to the battery.

Description

Power circuit of remote meter reading terminal

technical field

The utility model relates to a power supply circuit of a remote meter reading terminal.

Background technique

The existing technical solution is that the terminal is equipped with a backup battery (battery voltage 4.8VDC) and a power failure detection circuit and a battery charging circuit. When the high level drives the switch of the power supply channel of the battery to be in the off state, the battery cannot supply power to the system at this time; the battery charging circuit keeps charging the battery. After the mains power failure of the terminal, when the power-failure detection circuit inside the terminal detects that the 5VDC power supply of the system has dropped below 4.2VDC, the power-failure detection circuit outputs a low level at this time, and the low level immediately drives the battery to supply power. The channel switch is in the ON state, and the backup battery can supply power to the terminal at this time, providing time for the terminal to save and upload some terminal data. The terminal does not stop working until the power of the backup battery is exhausted.

There are following disadvantages in the prior art:

1. The terminal is in a city power failure and the backup battery is exhausted. If the staff needs to query the internal data or parameters of the terminal at this time, it cannot be realized at this time;

2. When the terminal is powered by the backup battery in the mains power failure, there is no mechanism to detect the voltage of the battery, causing the battery to supply power to the outside until the power is exhausted, which will affect the life of the battery in the long run;

3. The terminal keeps charging the backup battery when the mains power is normal. At this time, there is no mechanism to detect the voltage of the battery, which keeps the battery in a charging state for a long time. In severe cases, the battery may be damaged.

Utility model content

The purpose of the utility model is to provide a power supply circuit of a remote meter reading terminal which can ensure the power supply of the backup battery and improve the service life of the battery when the mains power is cut off.

The power supply circuit of the remote meter reading terminal provided by the utility model includes a rechargeable battery, an electronic switch of the battery charging circuit, an electronic switch of the battery power supply circuit, and a CPU, and the two electronic switches are connected to the battery. The electronic switch of the battery charging circuit is connected to the power supply and is controlled by the CPU on/off for charging the battery. The battery provides backup power for the main system through the electronic switch of the battery power supply circuit. The CPU has an AD converter , and the AD converter is connected with the battery for detecting the battery voltage, and the electronic switch of the battery power supply circuit is also connected with a wake-up circuit, and the wake-up circuit can open the battery power supply circuit so that the battery supplies power to the main system.

The wake-up circuit is a logical OR wake-up circuit, and the wake-up circuit has two trigger circuits, one of which can be used, one is a button trigger circuit, and the other is an infrared trigger circuit. The infrared trigger circuit is mainly composed of an infrared receiving tube, an ultra-low power consumption comparator, an RC integration circuit and an RC differential circuit. The button trigger circuit is mainly composed of a button (K11) and a transistor (V29).

The advantages of the utility model mainly contain the following points:

1. After the mains power failure, the terminal can wake up the terminal to work again, so that data and parameters can be queried;

2. When the terminal is powered off by the mains and the backup battery is powered, it will not cause the battery to be over-discharged and damage the life of the battery;

3. The terminal charges the battery when the mains power is normal, which will not lead to battery damage due to overcharging.

Description of drawings

Fig. 1 is the schematic diagram of the utility model.

Fig. 2 is a wake-up circuit diagram of the utility model.

FIG. 3 is the key trigger circuit of FIG. 2 .

Fig. 4 is the infrared trigger circuit of Fig. 2.

Detailed ways

Fig. 1 reflects the power circuit framework of the remote meter reading terminal of the present invention. It can be seen from the figure that when the mains power supply is normal, the 5VDC converted from the mains is converted into 4.7VDC through a diode to supply power to the communication unit, and the 4.7VDC is converted into 3.3VDC through an LDO to supply power to the entire system. When the mains power supply is normal, the AD converter inside the CPU continuously samples the voltage of the backup battery. According to the sampled voltage value, you can know whether the current backup battery is fully charged (determined by the selected battery), if not fully charged , then the CPU controls the electronic switch to open the charging circuit to charge the backup battery. The charging here is intermittent, because the voltage of the battery needs to be sampled during the charging process. Otherwise, the sampled voltage is not the real voltage of the battery, but the voltage of the charging circuit power supply. When the CPU detects that the battery is fully charged, it turns off the power supply of the rechargeable battery circuit to prevent the battery from being damaged due to overcharging. When the external mains power fails, when the power failure detection circuit detects that the 5VDC power supply of the main circuit is lower than 4.2VDC, the output logic is reversed, thereby driving the electronic switch to open the battery power supply circuit, and the battery supplies power to the system. The power event notifies the CPU to let the CPU know that it is powered by the battery at this time. When the battery is powered, the CPU finishes processing the events that need to be processed (according to customer needs), and then the CPU controls the electronic switch to turn off and cut off the battery power supply. At this time, the entire terminal system stops working, and the only working circuit is directly powered by the battery. wake-up circuit. At this time, when the mains power is still in a power outage, if the staff needs to restart the terminal to query the data or parameters inside the terminal, at this time the staff can wake up the terminal by long pressing the down button on the terminal (trigger the electronic switch to turn on the battery power supply) or send a wake-up signal (38K square wave signal) through the infrared handheld to wake up the terminal. After the staff inquires the required data, stop operating the terminal, and the terminal will automatically turn off the battery power supply circuit after one minute, so that the terminal will stop working again.

Figure 2 reflects the detailed wake-up circuit. In the figure, KEY_D is the button wake-up signal, ir-WAKE is the infrared wake-up signal, and BATT_CTRL is the CPU control signal. They are usually at low level and high level is valid. V55 is a power-down detection chip. When the system 5VDC power supply is normal, the output is high level, and the transistor V57 is cut off, so the B input signal of D14 is low level. R29 R184 C61 form a voltage divider circuit, which is input to the AD converter of the CPU to detect the battery voltage.

Battery switching process: When the mains power supply is normal, the system 5VDC is normal, the CPU is running normally, and the CPU sets the control signal BATT_CTRL to high level. At this time, the A input pin of the AND gate D14 is high level. When the output is high level, the transistor V57 is cut off, so the B input signal of the AND gate D14 is low level. The two input signals A and B of D14 are input at low level, so V66 is off, and V50 is also off, so the signal V4P7_CTRL is low, so V46 is off, and V47 is on at this time, but because V46 is cut off, so the gate of V51 cannot form a loop to the ground, and it is still in a high level state, so V51 is in a cut-off state, so the battery cannot supply power to the system at this time. When the mains power fails, the 5VDC drops slowly at this time, and when it is lower than 4.2VDC, the power detection chip V45 outputs a low level to drive the triode V57 to conduct, and the B input of the AND gate D14 is at a high level. When 5VDC is lower than 4.2VDC, the 3.3V system of the system is still normal at this time, so the CPU is running normally, so the BATT_CTRL signal controlled by the CPU is already at a high level at this moment. In this way, the A and B inputs of the AND gate D14 are both high level, so the output is also high level, and the high level of the output drives the transistor V56 to conduct, so that the base of the transistor V50 is very low, causing V50 to conduct, so that The signal V4P7_CTRL is at a high level, and the high level drives V46 to conduct, because V47 is always in the conduction state, so the gate of the MOS transistor V51 is pulled to a low level, so that V51 is conducted, and at this time, the power provided by the battery is turned on. The power supply is provided to the system, which ensures that the terminal will not stop working immediately when the power fails. When the battery power supply is working, the CPU completes the processing of the data that needs to be saved or uploaded, and automatically sets the control signal BATT_CTRL to low level, thereby turning off the battery power supply circuit, and the terminal stops working.

Wake-up process: At this time, the mains power is in a power failure state, and the system 5VDC has no voltage. The power detection chip V45 outputs a low level to drive the transistor V57 to conduct, and the B input of the AND gate D14 is a high level. This means that the CPU stops working State, of course, the signal BATT_CTRL is low at this time, at this time, the key wake-up signal KEY_D and the infrared wake-up signal ir-WAKE, any one of which is implemented (the state becomes high), then the A input signal of D14 will be changed to high level. Then the A and B input terminals of D14 are both at high level, so the output is also at high level after the phase AND, and the output high level drives the transistor V56 to conduct, so that the base of the transistor V50 is at a low level, causing V50 to conduct , so that the signal V4P7_CTRL is at a high level, and the high level drives V46 to conduct, because V47 is always in the conduction state, so the gate of the MOS transistor V51 is pulled to a low level, so that V51 is conducted. At this time, the The power provided by the battery is supplied to the system to make the terminal work again. After the terminal works again, if there is no interface operation on the terminal, the CPU will automatically set the control signal BATT_CTRL to low level, thereby turning off the battery power supply circuit, and the terminal stops working.

It is worth mentioning that the RC delay circuit composed of R156 C92 and the RC delay circuit composed of R157 C177, why there is such a delay circuit? That's because our terminal CPU uses a Linux system, and it takes a certain amount of time to start the system, especially when the CPU starts to control its own I/O state (BATT_CTRL signal), and our wake-up signal is not always Imposed, only for a period of time. The wake-up signal is applied until the CPU starts to control the BATT_CTRL signal to be at a high level, so that the battery can keep supplying power. The button wake-up signal is not a big problem, it can be realized by pressing and holding for a few seconds, but the infrared wake-up signal does not work. As mentioned above, the infrared wake-up signal is actually a 38KHz square wave signal. The high level of this signal is not long enough for the terminal to start and wait for the CPU to start to control the BATT_CTRL signal to be high. At this time, an RC composed of R156 and C92 is needed. Delay circuit, the function of this delay circuit is to keep a certain delay time when the infrared wake-up signal is triggered for the first time to enable the battery to supply power to the outside when the infrared wake-up signal is activated and the CPU controls the BATT_CTRL signal to a high level. , so that the infrared wake-up can be woken up normally.

It is precisely because of the RC delay circuit composed of R156 C92 that when the terminal has no external power supply, the battery is installed on the terminal at this time, then the base of the V50 cannot If the signal V4P7_CTRL becomes high level and is still in the conduction state in time, the signal V4P7_CTRL will become high level to drive V46 to conduct. It will be in the conduction state, then the gate of V51 will directly form a loop to the ground and then conduct, so that the battery supplies power to the outside. This situation is not allowed. Therefore, the RC delay circuit composed of R157 and C177 is here to prevent such a situation from happening. Its delay time is longer than that of the RC delay circuit composed of R156 and C92. The condition of the power supply.

Figure 3 reflects the key-press wake-up trigger circuit. When the key K11 is not pressed, the triode V29 is in the cut-off state, and the key wake-up signal KEY_D is low level, because the electronic switch of the battery power circuit needs a high level to be turned on, so the terminal cannot be woken up when the key is operated. When the button is pressed, the triode V29 is turned on, and the signal KEY_D is at a high level, so the electronic switch driving the battery power supply circuit is turned on to wake up the terminal.

Figure 4 reflects the infrared wake-up trigger circuit. In the figure, LED2 is an infrared receiving tube, and D4 is an ultra-low power comparator. When there is no infrared signal, LED2 is in the cut-off state. At this time, the voltage of the negative input terminal of comparator D4 is the divided voltage composed of R5 and R30, which is equal to V3P3_A*1/21, and the positive input terminal of D4 is cut off because of LED2. The voltage is 0. The negative input terminal voltage of the comparator D4 is greater than the positive input voltage, so the output of D4 is low level. Because the electronic switch of the battery power supply circuit needs a high level to turn on, it cannot wake up the terminal when there is no infrared signal. In the figure, C30 R44 R41 C28 constitutes an RC integral circuit and an RC differential circuit. According to f=1/2*pi*RC, the cut-off frequency of the signal can be determined. Because the terminal infrared communication uses 38kHz carrier communication, the value of RC we choose should take 38kHz as the center frequency, which can shield the interference of other signals. When there is an infrared 38kHz carrier signal input, LED2 will be turned on continuously under the action of this signal. In this way, this signal is coupled to the positive input terminal of D4 through the integration and differential circuit mentioned above, so that the voltage of the positive input terminal is greater than the voltage of the negative input terminal, so that D4 continuously outputs a square wave signal to drive the motor. The electronic switch of the power supply circuit is turned on and off continuously.

When the mains power failure terminal stops working, if the staff want to inquire some parameters or data inside the terminal at this time, they can press and hold the button K11 to make the button trigger circuit trigger the wake-up circuit and then wake up the terminal; or through the infrared handheld Turn on the infrared trigger circuit, thereby triggering the wake-up circuit and waking up the start-up terminal.

Claims (4)

1. the power circuit of a long-distance transcribe terminal; The electronic switch, the electronic switch in powered battery loop, the CPU that comprise chargeable battery, battery charge loop; Said two electronic switches all are connected with said battery, and wherein the electronic switch in battery charge loop is connected with power supply and by its ON/OFF of CPU control, is used for the charging of battery; Said battery is that main system provides back-up source through the electronic switch in powered battery loop; It is characterized in that said CPU has AD converter, and this AD converter is connected with said battery, is used to detect cell voltage; The electronic switch in said powered battery loop has also connected a wake-up circuit, and this wake-up circuit can be opened the powered battery loop, and to make battery be main system power supply.

2. the power circuit of long-distance transcribe terminal according to claim 1; It is characterized in that said wake-up circuit is the wake-up circuit of a logic OR, this wake-up circuit has the two-way circuits for triggering, can select one of which and use; One the tunnel is the button circuits for triggering, and another road is infrared circuits for triggering.

3. the power circuit of long-distance transcribe terminal according to claim 2 is characterized in that said infrared circuits for triggering mainly by infrared receiving tube, and ultra-low power consumption comparer and RC integrating circuit and RC differential circuit are formed.

4. the power circuit of long-distance transcribe terminal according to claim 2 is characterized in that said button circuits for triggering mainly are made up of button (K11) and triode (V29).

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