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In the digital circuit design, it is sometimes necessary to delay a signal for a period of time and another signal. The typical delay circuit is a string guide, and the delay time is the sum of the delay of each guide.
As we all know, when it comes to time delay, many people will think of using software pieces to achieve, such as timers and so on. Today we will talk about the way to achieve timing with hardware, although not so accurate, some occasions are still used. Today we will introduce six kinds of delay circuit working principles.
The circuit consists of CD4060 as the timer's time base circuit. The timing time base pulse generated by the circuit is divided by the internal frequency divider and then the time base signal is output. The timing control time is obtained by dividing the frequency through the external frequency divider circuit.
Precise long delay circuit
After power-on, the time base oscillator is oscillating out of the time base signal. The count division is started as the IC2 of the divider. When counting to 10, Q4 outputs a high level. The high level is inverted by D1 to a low level so that VT is cut off and the relay is released to cut off the power supply to the controlled circuit.
At the same time, the low level of D1 output is inverted to the high level by D2 and then added to the CP terminal of IC2, so that the high-level output of the output terminal is maintained.
After the circuit is energized to reset IC1 and IC2, the four outputs of IC2 are low. The low level of Q4 output is inverted to a high level by D1, which makes VT conductive through R4, and the relay is energized to absorb. This working state is on for power on and off for timing.
The RC delay circuit is shown in the figure, the delay time of the circuit can be adjusted by the size of R or C. Due to the simplicity of the delay circuit, there is a disadvantage of short delay time and low accuracy. For occasions that require long and accurate delay, the time relay should be selected as well.
RC delay circuit
In automatic control, sometimes the relay delay circuit is often employed in the appropriate time in the predetermined period of time in automatic control. A few relay delay circuits are given.
The circuit shown in Fig. (A) is a cantoco-suction circuit. When the circuit is turned on and off, the charge and discharge of the RC is used to achieve the latency and release, which is mainly used in the need for short delay. Sometimes the relay is slowly released according to the needs of the control, and the circuit shown in Fig. (B) can be employed at this time when the relay is slowly released.
When the power is just turned on, since the contact KK一l is a normally open state, the RC delay circuit does not generate a delay in the time of the suction. And when relay K is activated, its contact Kk-1, closes, allowing the release of relay kk to proceed slowly. Simply calculate the time delay generated by the RC delay circuit, such as R = 470K, C = 0.15uf time constant directly with R * C.
When the button SB is pressed, the 12V power supply is charged through the resistor RT to the capacitor CT, so that the potential of the pin 6 continues to increase. When the potential of pin 6 rises to the potential of pin 5, the circuit reset is ended.
555 simple long delay circuit
Since a diode Vd1 on the pin 5 string makes the pin 5 potential rise, it has a longer period of time than the general pickup (suspended or through small capacitance ground).
The IC1 555-time base circuit is connected as a self-excited multi-tuned oscillator with an adjustable duty cycle. When button SB is pressed, a 12V DC voltage is applied to the circuit. Since the voltage of capacitor C6 cannot change abruptly, IC2 circuit pin 2 is low and the IC2 circuit is in a set state. The contacts K-1 and K-2 are closed, and the K-1 contact is closed to form a self-locking state, and the K-2 contact is connected to the power device to control the power device.
Long-delay circuit consisting of two 555 time-based circuits
At the same time, IC1 555 time-based circuit begins to form oscillation, so 3 pin is alternately output high and low. When the 3 pin outputs a high level, the capacitor C3 is charged by the diode VD3.
When pin 3 is output low, diode VD3 is cut off and C3 is not charged. Therefore, C3 is only charged when pin 3 is high. The charging time of capacitor C3 is long.
When the potential of capacitor C3 rises to 2/3VDD, the IC2 555 time base circuit resets. Pin 3 outputs a low level, relay K is de-energized, and contacts K-1 and K-2 are disconnected, returning to the initial state and ready for the next timing.
In normal state, the IC output stays low, and this state is stable. When the negative pulse is input to the inverting terminal via C1, the potential of the inverting terminal is lower than the potential of the in-phase terminal, and the output flips from low to high, and this state is unstable.
Monostable delay circuit with a single op-amp
This high level is divided by R1 and R2 and then added to the in-phase terminal of IC, so that the potential of the in-phase terminal is higher than that of the inverted terminal, thus keeping the high-level output. At the same time, this high level is charged by R3 and C2, and when the voltage on C2 is charged to make the potential of the inverting terminal higher than the potential of the in-phase terminal, its output flips to a low level again.
At this time, the same phase end potential is about zero, while the voltage on the C2 is discharged to the output terminal via VD1 so that the circuit accelerates to restore the initial state.
After the circuit is stable, the inverted end potential is still higher than the same phase end potential, which is maintained at a low level of the output.
The delay time T of the circuit depends not only on R3, C2, but also depends on the voltage ratio of R1 and R2.
Therefore, the adjustment delay is very convenient, which can be adjusted to C2 and R3 for delaying, and adjustable R2 for fine (bit pressure ratio to 1/2 ~ 2/3, the delay accuracy is high).
However, the state is random at power-on, and there are two ways to have the only output state after the circuit is powered on.
One is to add R4 to the circuit so that, at power-up, the power supply voltage can be set low by adding R4 and C1 to the inverted side because the voltage on C1 cannot change suddenly.
Second, one diode VD2 and a switch S are connected between the same phase end and the ground (as shown by the dashed line).
However, as mentioned above, it takes time T for the output to go low, and in practice, it is often necessary to reset the circuit immediately upon power-up.
To this end, the S can be turned on, when the output is high, then C2 is charged to 0.7V to reset the circuit, greatly shorten the time of the circuit on the circuit. After the reset, the s is broken, the circuit can work normally.
The delay section consists of BG1 and BG2 compounded with capacitor C to form a Mille integral circuit. The terminal voltage of C is zero before the power is turned on. After the power is turned on, BG3 and BG4 conduct, and relay J is activated, while capacitor C is charged. The charging current is looped through R2, C, and R. The potential at point A rises, causing the potential at point b to fall. The fall in potential at point b limits the rise in potential at point a.
Transistor delay circuit
The result of mutual compensation of the potential at points a and b makes the rise of the potential at point a very small and the charging current close to seemingly constant.
When the potential at point b rises to about 10V, BG3 and BG4 close to cut-off, relay J is released and the delay process ends. Press the button AN, capacitor C quickly discharged by D1, relay J suction, start the next delay process.
The delay circuit is often used, and the RC circuit is a relatively simple circuit. Of course, different delay times can be achieved by changing the parameters of each component of the circuit.
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