JPH04128432U - Power-on reset circuit - Google Patents

Abstract

(57) [Summary] (with modifications) [Purpose] To stably generate a reset signal with a pulse width of a certain time when the power is turned on, and to use it in circuits that require miniaturization such as microprocessors. [Structure] It has a circuit whose output voltage changes as a function of time after power-on, and a threshold circuit IC that compares the output voltage with a predetermined threshold and outputs the comparison result as a reset signal. and the emitter are inserted between the power supply terminal and the ground point via the capacitor C, and the resistor R is inserted between the base and the power supply terminal. A diode-connected transistor Q2 connected in parallel between the base and the emitter makes the temporal change in the potential of the transistor Q1 constant. A diode D inserted between the connection point between the capacitor C and the transistor Q1 and the ground speeds up the discharge of the capacitor C and allows the circuit to operate stably even when the power is turned on again.

Description

[Detailed explanation of the idea]

0001

【Technical field】

This invention is designed to set a certain state when the power is turned on, such as in a microprocessor circuit. In circuits that require This relates to a power-on reset circuit that generates a reset signal.

0002

[Background technology]

Conventionally, such a power-on reset circuit has been constructed of a circuit as shown in FIG. In the figure, E is the second terminal of the DC power supply, R is the resistor, C is the capacitor, IC is the threshold circuit, CPU is the microprocessor, RESET is the reset terminal of the microprocessor, and V _i is the input of the threshold circuit. It is voltage. Further, G is the first terminal of the DC power supply.

The operation of such a power-on reset circuit is as follows. The input voltage V _i of the threshold circuit is

[Math 1] This curve is shown in FIG. T is the time until the threshold is reached. In FIG. 1, a threshold circuit IC generates a reset signal with a width T until V _i reaches a threshold value.

[0004] In a power-on reset circuit that utilizes such an RC transient phenomenon, where the slope of the V _i curve is large, the voltage change rate is large, so the threshold circuit I C operates stably, but the time width is I can't take it long enough. On the other hand, if T is set to be sufficiently long, the rate of voltage change will be small in the vicinity, and the threshold circuit will not operate stably. In order to make the time width T sufficiently long and to ensure stable operation, the product of the resistance value and the capacitance of the capacitor must be made large. However, when the resistance value is increased, the final value of V _i increases due to leakage current of the IC circuit, etc., and the time width T is limited. Therefore, in general, the capacitance C of the capacitor is increased, but in this case, the physical volume of the capacitor becomes large, making it difficult to implement the circuit.

[0005]

[Problems to be devised]

In order to eliminate these drawbacks, the present invention uses a transistor circuit and makes the change in V _i linear. One of its features is that it is a circuit in which the output voltage changes as a function of time after power is turned on. , a threshold circuit that compares the output voltage of the circuit with a predetermined threshold value and outputs the comparison result as a reset signal, and provides a reset signal with a predetermined time width when the power is turned on. , a configuration in which the collector and emitter of the transistor are inserted between the power supply terminal and the ground point via a capacitor, a resistor inserted between the base and the power supply terminal of the transistor, and a configuration in which the collector and emitter of the transistor are inserted in the same direction as the polarity of the base and emitter. a first diode connected in parallel between the base and the emitter; and another diode connected in opposite polarity with respect to the normal operating voltage of the transistor between the connection point of the capacitor and the transistor and the ground point. and is in a power-on reset circuit such that the output of the transistor is connected to the input of the threshold circuit.

[0006]

[Structure and operation of the device]

Figure 3 is a reference diagram for explaining the present invention, where R is a resistor, C is a capacitor, D is a diode, Q1 is a transistor, IC is a threshold circuit, E is the second terminal of a DC power supply, and G is a DC The first terminal of the power supply, CPU, is the microprocessor, RESET is the reset terminal of the microprocessor, and V _i is the input voltage of the threshold circuit.

The operation of the power-on reset circuit configured with the connections shown in FIG. 3 is as follows. When a DC voltage E is applied, a current flows through the diode D through the resistor R. As a result, the base of the transistor Q1 has a potential equal to the voltage drop across the diode, and a constant voltage is maintained between the base and emitter of the transistor, so that a constant current I _C flows through the collector of the transistor Q1. Therefore, the collector potential V _i of transistor Q1 is

[Math 2] becomes. This straight line is shown in FIG. T is the time until the threshold of the threshold circuit is reached. In this circuit, since the current I _C flowing through the capacitor is constant, the rate of change of V _i changes linearly from the power supply voltage E until the transistor Q1 is saturated. Also, since this current value is determined by the base-emitter voltage of the transistor, it is determined by the value of the resistor R connected between the base and the power supply and the voltage drop of the diode, but the value of R is determined by the change in V _i Does not affect range.

As explained above, in the reference example shown in FIG. 3, since V _i changes linearly, the rate of change of V _i is constant no matter where the threshold value is set. Therefore, the threshold circuit operates stably no matter where the threshold value is set within the variation range of _Vi . Furthermore, since the slope of the straight line can be changed by the resistance value and does not narrow the variation range of V _i , it is possible to obtain a sufficiently long pulse width by decreasing the capacitor value and increasing the resistance. can. Moreover, since the dimensions of the resistor have no direct relationship to the resistance value, by adopting such a circuit configuration, a power-on reset circuit with a large time width, stability, and small mounting area can be realized. Although the reference example uses an NPN type transistor, a similar circuit can be constructed using a PNP type.

[0009] Figure 5 shows a transistor base collector instead of diode D in the reference example shown in Figure 3. This is a transistor with a so-called diode connection connected to a transistor. In this case, the operation is similar to that of the first embodiment. In this case, further pair Q1 and Q2. By using an IC with a The advantage is that the current flowing through the first transistor Q1 is equal to the current flowing through the first transistor Q1. Ru.

0010 FIG. 6 shows the current between the emitter and collector of the transistor Q1 according to the embodiment of the present invention. flows from the emitter to the collector (the normal operating voltage of the transistor A diode is inserted in the opposite polarity. insert this diode By doing this, the charge on capacitor C can be quickly discharged when the power is turned off. The path will be set. Therefore, even if the power is turned on again, the circuit will not operate for a long time. This is equivalent to turning the power off and then turning it on, and the circuit operates stably. here The inserted diode becomes reverse biased when the power is turned on, so it has no effect on the operation of the circuit. It has no effect and the charge on capacitor C is cut off only when the power is cut off. It plays the role of bypassing the transistor Q1 and allowing the flow to flow.

[0011]

[Effect of the idea]

As explained above, in this invention, just by increasing the resistance value, a large time width can be achieved. The circuit can be made smaller because it can stably generate reset pulses. Wear. Therefore, it is necessary to set the initial state of the microprocessor, etc., and it is necessary to set the initial state of the microprocessor. Can be used in required circuits.

[Brief explanation of drawings]

FIG. 1 is a conventional power-on reset circuit.

FIG. 2 is a characteristic diagram of the input voltage of the threshold circuit.

FIG. 3 is a reference diagram for explaining the present invention.

FIG. 4 is a characteristic diagram of the input voltage of the threshold circuit.

FIG. 5 is another reference diagram for explaining the present invention.

FIG. 6 is a circuit diagram showing an embodiment of the present invention.

[Explanation of symbols]

E Second terminal of DC power supply C Capacitor R Resistor CPU Microprocessor IC Threshold circuit G First terminal of DC power supply RESET Microprocessor reset terminal V _i Input voltage of the threshold circuit T V _i is the threshold of the threshold circuit Q1 First transistor D Diode Q2 Second transistor

Claims (2)

[Scope of utility model registration request] 1. A power supply system comprising: a circuit whose output voltage changes as a function of time after power is turned on; and a threshold circuit that compares the output voltage of the circuit with a predetermined threshold value and outputs the comparison result as a reset signal; A power-on reset circuit that provides a reset signal with a predetermined time width when turned on includes a bipolar transistor, a configuration in which the collector and emitter of the transistor are inserted between a power supply terminal and a ground point via a capacitor, and a base and a base of the transistor. A resistor inserted between the power supply terminals and a first resistor connected in parallel between the base and emitter in the same direction as the polarity of the base and emitter.
and another diode connected between the connection point of the capacitor and the transistor and the ground point with a polarity opposite to the normal operating voltage of the transistor, and the output of the transistor is connected to the input of the threshold circuit. A power-on reset circuit characterized in that the power-on reset circuit is connected. 2. The power-on reset circuit according to claim 1, wherein said diode is provided by a characteristic between the collector and emitter of a transistor whose collector and base are connected.