Time delay circuit for use in a reset circuit

1. Technical Field

The present disclosure relates to a time delay circuit for use in a reset circuit.

2. Description of the Related Art

In electronic systems, a reset function is widely used to clear pending errors or events. When chips have a run error, a time delay is needed for the chips to reset. Therefore, a time delay circuit is employed in a reset circuit to provide the time delay. Current time delay circuits are typically an integrated chip, such as a power source comparison chip, which is costly.

What is needed, therefore, is a time delay circuit for use in reset circuit, which can overcome the above-described problem.

Many aspects of the present time delay circuit use should be better understood with reference to the accompanying drawing. The components in the drawing are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the time delay circuit. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

The FIGURE is a schematic view of a time delay circuit use in a reset circuit in accordance with an exemplary embodiment.

Embodiments of the present time delay circuit use will now be described in detail with reference to the drawing.

Referring to FIG. 1 , one embodiment of a time delay circuit 10 used in a reset circuit 12 for providing a time delay to reset an integrated circuit 600 . According to an exemplary embodiment, the time delay circuit 10 includes a first circuit 100 , a second circuit 200 , an AND gate 300 , and a control signal input 400 .

The first circuit 100 includes a first resistor R 1 and a first capacitor C 1 . The second circuit 200 includes a second resistor R 2 and a second capacitor C 2 . The AND gate 300 includes a first input 310 , a second input 320 , and output 330 .

The first resistor R 1 includes an input coupled to a power source 20 , and an output. The first capacitor C 1 includes an input coupled to the output of the first resistor R 1 and an output coupled to the ground. The input of the first capacitor C 1 is coupled to the power source 20 by the first resistor R 1 . In this embodiment, the first resistor R 1 is about 100K ohms, and the first capacitor C 1 is 1 microfarad.

The second resistor R 2 includes an input coupled to the power source 20 and an output. The second capacitor C 2 includes an input coupled to the output of the second resistor R 2 , and an output coupled to the ground. In this embodiment, the resistance value of the first resistor R 1 is equal to that of the second resistor R 2 . The capacitance value of the first capacitor C 1 is equal to that of the second capacitor C 2 . It should be noted that the resistance value of the first resistor R 1 , the second resistor R 2 , and the capacitance value of the first capacitor C 1 and the second capacitor C 2 are not limited by this embodiment, but can be configured depending on requirements. In other alternative embodiments, the resistance value of the first resistor R 1 is greater than that of the second resistor R 2 , and the capacitance value of the first capacitor C 1 is greater than that of the second capacitor C 2 .

The AND gate 300 includes a first input 310 , a second input 320 and an output 330 . The first input 310 is coupled to the input of the first capacitor C 1 . The second input 320 is coupled to the input of the second capacitor C 2 . The output 330 of the AND gate 300 is coupled to the integrated circuit 600 that needs to be reset. The integrated circuit 600 can be a main board chip or a power supply chip, for example.

The control signal input 400 is coupled to the output of the second resistor R 2 and configured for providing a LOW level control signal such as about 0V, to the junction of the second resistor R 2 and the second capacitor C 2 . In this embodiment, the control signal input 400 is coupled to a watchdog chip (not shown). The watchdog chip is configured for detecting running errors of the integrated circuit 600 . If the watchdog chip detects that the integrated circuit 600 has a run error, the watchdog chip sends a reset signal, i.e., a LOW level signal, to the control signal input 400 . As a result, the second input 320 receives a LOW level signal too, and therefore the AND gate 300 outputs a LOW level signal to reset the integrated circuit 600 coupled thereto.

In this embodiment, the time delay circuit 10 further includes a switch 500 configured for manually resetting the integrated circuit 600 . A first end of the switch 500 is coupled to the junction of the first resistor R 1 and the first capacitor C 1 , and a second end is grounded. The switch 500 is a depress type switch.

In operation, initially, the power source 20 provides a HIGH level signal, e.g., about 3.3 volts in one embodiment, to the first capacitor C 1 via first resistor R 1 , and the second capacitor C 2 via the second resistor R 2 . Accordingly, both the capacitors C 1 , C 2 begin to charge to about the HIGH volt level. After charging of the capacitors C 1 , C 2 to about the HIGH volt level, the first and second inputs 310 , 320 of the AND gate 300 receive the HIGH level signal. As a result, the output 330 of the AND gate 300 also changes to the HIGH level signal from the original LOW level signal, and output the HIGH level signal to the integrated circuit 600 . The integrated circuit 600 boots up. However, the boot-up is time delayed by the time delay circuit 10 . According to charging formula of a RC circuit: T=RC, where T is the charging time, i.e., the time delay, R is the resistance value of the resistor of the RC circuit, and C is the capacitance value of the capacitor of the RC circuit. That is, the integrated circuit 600 have time T to boot up. It should be noted that the charging time of the first capacitor C 1 and the second capacitor C 2 can be set according to the resistance value of the resistors R 1 , R 2 , and the capacity value of the capacitors C 1 , C 2 . In this embodiment, charging times of the first capacitor C 1 and the second capacitor C 2 are greater than a rest time of the integrated circuit 600 .

When any chip of the integrated circuit 600 has a run error, the watchdog chip detects the run error and sends a reset signal, i.e., the LOW level signal, to the control signal input 400 . As a consequence, the output 330 outputs the LOW level signal to the chip to power off the integrated circuit 600 . Then, the second capacitor C 2 discharges and recharges, providing a time delay of about 2T 1 , where T 1 =R 2 C 2 , for the integrated circuit 600 power on again. That is, the integrated circuit 600 has a time delay time of about 2T 1 to reboot.

In other alternative embodiments, if the integrated circuit 600 is to be manually reset, the switch 500 can be actuated. After actuation, the first capacitor C 1 is grounded. The first input 310 receives a LOW level signal. As a result, the output 330 of the AND gate 300 also outputs a LOW level signal to the integrated circuit 600 . Meantime, the first capacitor C 1 discharges and recharges. This process also provides 2T 2 , where T 2 =R 1 C 1 , for the integrated circuit 600 to reboot.

The time delay circuit 10 is capable of providing a time delay for the integrated circuit 600 to reboot, and therefore can be adopted in a variety of devices. Despite of its great commercial value, all components thereof are inexpensive. Therefore, this time delay circuit 10 should be more desired by commercial practice.

It will be understood that the above particular embodiments and methods are shown and described by way of illustration only. The principles and the features of the present invention may be employed in various and numerous embodiment thereof without departing from the scope of the invention as claimed. The above-described embodiments illustrate the scope of the invention but do not restrict the scope of the invention.