Let's take a look at what this circuit does and help analyze it.

灞波儿奔

Let's take a look at what this circuit does and help analyze it. [Copy link]

 

As shown in the circuit below, after pressing TEST, how do T3, T2, and T1 work?

How does the IC2 voltage regulator chip power the MCU? What happens if you release the TEST?

Please help me analyze what this circuit does

maychang

This circuit involves a single-chip microcomputer, so it must be analyzed together with the program executed by the single-chip microcomputer. If we just look at the circuit, we can only guess.

maychang

"How does the IC2 voltage regulator chip provide power to the MCU?"

IC2 is obviously an ordinary three-terminal regulator. IC2 supplies power to the microcontroller, and T3 must be turned on. If T3 is turned off, IC2 cannot supply power to the microcontroller anyway. The condition for T3 to be turned on is that its base is pulled down. There are two ways: one is that T1 is turned on, and the base of T3 is pulled down through the LED. The other is that the Test button is pressed, and the base of T3 is pulled down through the emitter junction of T2.

When IC2 does not supply power to the microcontroller, the microcontroller IO2 obviously cannot be at a high level, so T1 cannot be turned on. The Test button is not pressed, so it is impossible to pull down the base of T3 through the emitter junction of T2. Therefore, IC2 cannot supply power to the microcontroller.

maychang

Assuming that the Test button is pressed when IC2 is not supplying power to the microcontroller, the base of T3 will be pulled down through the Test button and the emitter junction of T2. Then T3 is turned on and IC2 starts supplying power to the microcontroller.

If the IO2 pin is at a low level after the microcontroller is powered, T3 will be turned off after the Test button is released, and IC2 will stop supplying power to the microcontroller. In order for IC2 to continue to supply power to the microcontroller after the Test button is released, the microcontroller must set the IO2 pin to a high level in the initialization routine after power-on reset (not shown in the microcontroller reset circuit diagram). If IO2 is at a high level, T1 is turned on, and even if the Test button is released, T1 will still pull the base of T3 down, so IC2 continues to supply power to the microcontroller, and the microcontroller can work normally and execute various programs after initialization.

maychang

What does this circuit do?

In this circuit, the microcontroller can turn off its own power supply. After the microcontroller executes the program it should execute, as long as the IO2 pin is set to a low level, T1 will be turned off. At this time, the Test button is disconnected (released), so after T1 is turned off, T3 will be turned off by R10 because the base is no longer pulled low, IC2 loses power, no longer supplies power to the microcontroller, and the microcontroller will no longer continue to work.

maychang

The IO1 pin is used to detect whether the Test button is released. If the Test button is released, T2 is turned off due to no base current, and the IO1 pin should be high. If the Test button is not released, the IO1 pin is low because T2 is turned on.

maychang

Therefore, the function of this circuit is: when the Test button is pressed once, the microcontroller executes a series of programs and then turns off its own power supply. Until the Test button is pressed again, the microcontroller executes again.

Since I don't know the microcontroller program, the above are all guesses.

chunyang

This is a single-button soft start/shutdown circuit. Working principle: Assume that the MCU system is in a power-off state. When the switch is pressed, the emitter junction of T2 provides a base current loop for T3, T3 is turned on, IC2 is powered on, the MCU system starts working and makes IO2 output a high level to turn on T1, so that even if the switch is released, the conduction of T3 can be maintained. When the switch is pressed again, T2 turns on and gives IO1 a signal, and then the software controls IO2 to output a low level to turn off T1, so that the system is naturally powered off after the switch is released.

Fred_1977

This is a simple soft on/off hardware circuit. The purpose is to disconnect the battery power supply after shutdown, so that the system circuit does not consume battery current after shutdown. Make the battery work longer.

tagetage

The 8th and 9th floors have said everything I want to say. This is the final answer.

Fred_1977

The working principle is as follows: 1. When the button is pressed, IC2 will be turned on and output VCC voltage. 2. After VCC supplies power to MCU, it detects whether IO1 is at a low level. If it is at a low level, it means that a button is pressed. Whether the button is pressed to turn on or off, MCU determines it by the holding time of the button. For example, if a short press is to turn on, then MCU's IO2 outputs a high level. At this time, when the button is released, the battery power supply path is fully opened; if it is pressed for a long time to turn off, MCU's IO2 outputs a low level. When the button is released, the battery power supply path is closed, thereby realizing the shutdown function.

se7ens

Fred_1977 posted on 2021-12-22 18:23 The working principle is as follows: 1. When the button is pressed, IC2 will be turned on and output VCC voltage. 2. After VCC supplies power to the MCU, it detects whether IO1 is at a low level, such as...

Makes sense, it takes a long time to boot up, so you should set long press to boot up

After powering on, detect IO1 is low and pull IO2 high to power the system.

When shutting down, detect IO1 as low and turn off IO2 to power off the system.

The whole operation is similar to the power on and off action of a mobile phone.

灞波儿奔

maychang posted on 2021-12-22 11:46 Assuming that the Test button is pressed when IC2 is not supplying power to the microcontroller, the base of T3 will be pulled down through the Test button and the emitter junction of T2. Then T3 is turned on, and IC2 starts to supply power to the microcontroller...

Thanks for your reply, thank you

灞波儿奔

chunyang posted on 2021-12-22 17:29 This is a single-key soft start/shutdown circuit. Working principle: Assume that the MCU system is in a power-free state. When the switch is pressed, the emitter junction of T2 provides base current to T3...

Thanks for the analysis, I understand a little bit

灞波儿奔

se7ens posted on 2021-12-24 11:04 It makes sense. The boot time is relatively long. You should set the long press to detect IO1 as low after booting, and pull IO2 high to power the system to shut down...

Thanks for the analysis

灞波儿奔

Fred_1977 posted on 2021-12-22 18:23 The working principle is as follows: 1. When the button is pressed, IC2 will be turned on and output VCC voltage. 2. After VCC supplies power to the MCU, it detects whether IO1 is at a low level, such as...

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