Troubleshooting and repairing Switch Mode Power Supplies

The Basics Of 555 Timer IC

The presence of thousands of integrated circuits in the world today That is IC With them we can make it easier to build the circuit There is a use of the most widely used chip When called the Chip 555 This video I will introduce this chip is how it works And how to achieve different functions by the addition of external components let’s start Translation, timeline, proofreading: Schrodinger bunny paper Translated By BlackieVan First, let us look at the 555 chip internal functional diagram Between 1 and 8 feet series connection of three 5 Kohm resistor Chip not only its name And because the power connection pin No.

1,8 Three resistors also constitute a voltage divider No. 2 is the trigger pin end A comparator connected to the interior of the inverting input terminal And comparator inverting input terminal Portion is connected to a voltage divider of 1 / 3Vcc of And the output of the comparator is connected to a set terminal of the flip-flop internal 3 is an output terminal pin A drive circuit connected to the internal It is then connected to the output terminal of the flip-flop 4 is a reset terminal pin Internal triggers are directly connected to the reset terminal By grounding pin No. 4 Flip-flop can be reset immediately inside Therefore, under normal circumstances, have received 4 feet Vcc 5 is a control terminal pin It is not only connected to a second inverting input of comparator Also connected to that end of the voltage divider 2 / 3Vcc of You can change the reference voltage of the comparator through a voltage to the input pins It may be directly 10nF capacitor to a stable reference voltage This usage is very common circuit 555 Translator’s Note: is yù zhí, not fá zhí pin 6 is the threshold terminal Inverting input terminal and the second trigger its internal connections The output of the comparator to a reset terminal of the flip-flop Finally, the foot 7 is a discharge end Internal directly connected to the collector of a transistor The transistor emitter is connected to ground A base connected to the output of the flip-flop This composition of the whole circuit group 555 In order to better understand it Let’s look at a few chestnuts circuit Let’s look at a specific monostable multivibrator program At the beginning of the capacitors are not charged Therefore, the potential of the feet 6,7 are 0V Pin No.

6 of the second comparator with the inverting input terminal voltage of 0V is Since the low voltage than the inverting input terminal of the inverting input terminal Comparator output is low so no change We need to do is press the button No. 2 feet This button is the No. 2 feet to the ground In this case the first comparator inverting input terminal It will be higher than the inverting input voltage The comparator outputs a high level Since the output directly to the set terminal of flip-flop Open inverted output of flip-flop At the same time open up the chip output And the closure of the transistor Now is no longer the No. 7 pin capacitance to ground the This capacitor will begin to charge through resistor Once the voltage across the capacitor to reach 2 / 3Vcc The second comparator inverting input terminal It will be higher than the inverting input voltage Then the comparator outputs a high level Will be reset flip-flop The off chip output And open triode It took immediately let go of electrical capacitance Then returned to the initial state This program is called the one-shot Because only low-level output is stable Temporary high output is The length of time depends on the resistance and capacitance product of This is the more common usage Do notice a delay off the lights or something similar The next is a flip-flop Chestnut Just like the name says as Generating two stable output states High and low Translator’s Note: In actual use, will add to the stability of the keys on the pull-down resistor without any resistance and capacitance circuit element Using only 2 feet do assert pins Translator’s Note: I can do is shut down by 6 feet, but closed and use a high level reset pin No.

4 Translator’s Note: I can do is shut down by 6 feet, but to use a high level close to that of course is to make use of reset In this case one of the pin to ground Inside the trigger turns on or off This creates two kinds of stable state Very suitable key switch to control the LED switch Finally, a chestnut is astable multivibrator It can generate a substantially square wave oscillator circuit High and low and adjustable time You can even adjust the frequency The capacitor is charged through resistor Chestnut Lane 1 and 2 2 is discharged only by the resistor So high time depends on the values ​​of the resistors 1 and 2 And low time depends only on the resistance 2 In order to improve this problem we often see, there are two diode circuit In order to make the charging current only through R1 And a discharge current after only R2 Unfortunately, this program can not produce good fixed frequency pwm signal In order to achieve this We charge and discharge resistor to the output That is, the chip 3 feet So since the charge and discharge in the same loop It can be adjusted to produce a square wave of 50% duty ratio of the frequency However, this is not actually Problems with NE555 itself It is used as an internal transistor used to switch Low-level voltage close to 0V While the high level voltage is about 4.6V At a time when the supply voltage is 5V This has resulted in the charge and discharge of asymmetrical The solution is to use a CMOS 555 chip Such as TLC555 This version allows the high voltage power supply voltage is very close Because they are using a MOSFET output section This can easily hit 50% duty cycle But more than that It also has a smaller current consumption You can achieve higher frequencies And may operate at a lower voltage But down compared to its current output capacity is much lower than the TTL version In order to adjust the duty cycle Alternatively we just put into two diodes and resistors Potentiometer Such adjustment may be separated and discharging current Finally able to produce beautiful perfect fixed-frequency PWM signal the It can be used to control the power circuits With the above said, you should understand the principles-based chip 555 I hope you like this video Do not forget to point Like Comment Share the coin to me Keeping innovation We see you next time!

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