JPH0134269Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a relay control circuit for a protective relay that protects an amplifier circuit, a speaker, etc. from transient operations during power-on and power-off in audio equipment, for example.

Normally, in audio equipment such as stereo playback equipment, a relay contact is inserted between the output terminal of the amplifier circuit and the speaker, and this relay contact turns on after a predetermined time when the power is turned on, and instantly when the power is turned off. By turning off the amplifier circuit, the generation of unpleasant sounds is prevented, and the amplifier circuit and the speaker are protected.

For example, FIG. 1 is a circuit diagram showing the configuration of a relay control circuit of this type of protection relay. In this figure, 1 is a power transformer, and when commercial AC power (AC100V) is supplied to the primary winding 1a of this power transformer 1, the output of its first secondary winding 1b is converted into a bridge type rectifier. A main power supply circuit 4 consisting of a circuit 2 and a smoothing capacitor 3 converts it into a DC voltage +Vc and outputs it, and the output of the second secondary winding 1c is connected to a diode 5 and a smoothing capacitor 6. It is converted into a DC voltage +V ₁ and output by a relay control power supply circuit 7 consisting of the following. Also, resistor 8 (value R ₁ ) and capacitor 9 (value C ₁ ) are a time constant circuit that determines the delay time when the power is turned on. When the power is turned on and a voltage +Vc is generated, this voltage +Vc causes the resistor 8 to
Capacitor 9 is charged via
When the voltage +V 2 at the connection point between the capacitor 9 and the resistor ₈ exceeds a predetermined value after a predetermined time corresponding to C ₁ and R ₁ has elapsed, the NPN transistor 10 becomes conductive. And this transistor 1
0 conducts, relay winding 1 of protective relay 11
1a is driven and the relay contact 11b is closed, thereby connecting the output terminal of the amplifier circuit 12 and the speaker 13.
are connected. In this case, the voltage +V ₁ is set to be higher than the voltage +V ₂ in the steady state, so that the diode 14 is turned off. On the other hand, when the power is cut off, the charge stored in the capacitor 6 is discharged through the resistor 15 (value R ₂ ), so the voltage +V ₁ immediately decreases, thereby making the diode 14 conductive. As a result, the charge stored in the capacitor 9 is discharged sequentially through the diode 14 and the resistor 15, so that the voltage _V2 also immediately decreases following the voltage + _V1 , and the transistor 10 is turned off. However,
When the power is cut off, the relay contact 11b is turned off within an extremely short time corresponding to the time constants C ₁ and R ₂ .

By the way, in the conventional relay control circuit shown in FIG. 1, in order to shorten the delay time from when the power is cut off to when the relay contact 11b is turned off, it is necessary to reduce the value _R2 . this value
If R ₂ is made small, the loss in the power supply circuit 7 will increase, and in this case, in order to maintain the smoothing function of the capacitor 6, the capacitance of the capacitor 6 must be made as large as the capacitance of the capacitor 9. must be set. Therefore, in such conventional circuits, there is a problem in that there is a limit to the reduction of the delay time when the power is cut off. In addition, in this relay control circuit, if diode 5 is destroyed, there is a risk that reverse voltage will be applied not only to capacitor 6 but also to capacitor 9, so for safety reasons, both capacitors 6 and 9 should be non-polar. There was also the problem that the circuit had to be made expensive.

In view of the above circumstances, this invention was developed in a relay control circuit for a protective relay that protects circuits, etc. from transient operations when the power is turned on and when the power is turned off.It is possible to operate the protective relay immediately when the power is turned off, and it is inexpensive. The purpose of the relay protection circuit was to provide a relay protection circuit that could be configured in a number of ways, including a current control element configured to conduct immediately when the power is turned off, and a capacitor that determines the delay time when the power is turned on. The present invention is characterized in that the electric charge is discharged through the current control element.

Hereinafter, one embodiment of the relay control circuit according to this invention will be described in detail with reference to the drawings.

FIG. 2 is a circuit diagram showing the configuration of an embodiment of this invention, and in this figure, parts corresponding to those in FIG. 1 are given the same reference numerals.

In FIG. 2, the positive output terminal 2a of the bridge rectifier circuit 2 is grounded via a smoothing capacitor 3, and is also connected to an NPN transistor 17 (value R ₃ , second resistance element) via a resistor 16 (value R 3 , second resistance element). resistor 8 (value R ₁ , fourth resistive element) and capacitor 9
(value C ₁ , capacitive element), and is connected to the NPN transistor 10 (second current control element) via the relay winding 11a of the protective relay 11.
connected to the collector. Further, the negative side output terminal 2b of the bridge type rectifier circuit 2 is grounded,
A diode 18 for absorbing back electromotive force is connected in parallel to the relay winding 11a. In this case, the series circuit of the resistor 8 and capacitor 9 constitutes a time constant circuit 19 in this invention. On the other hand, the secondary winding 1 of the power transformer 1
One end of the secondary winding 1c is connected to the cathode of the rectifying diode 5, and the other end of the secondary winding 1c is grounded.
The anode of the diode 5 is grounded via a smoothing capacitor 6 (value C ₂ ), is grounded via a resistor 15 (value R ₂ , first resistance element), and is grounded via a resistor 20 (value R _{4 )} . , a third resistance element) to the base of the transistor 17. In this case, the series circuit of the resistor 16 and the resistor 20 is the bias circuit 21 in this invention.
It consists of Further, the emitter of the transistor 17 is grounded, and the collector of the transistor 17 is connected to the resistor 8 via a resistor 22 (value R ₅ ).
and the connection point P between the capacitor 9 and the capacitor 9.
Further, this connection point P is grounded through a resistor 23 and a resistor 24 in order, and the connection point between these resistors 23 and 24 is connected to the base of the transistor 10, and the emitter of the transistor 10 is grounded. Note that the resistance values R ₃ and R ₄ are both set to relatively large values.

In the above configuration, AC100V is applied to the primary winding 1a.
is supplied (i.e., when the power is turned on),
The positive side power supply voltage +Vc of the main power supply and the negative power supply voltage _-V1 for relay control each reach a predetermined voltage within a short time. Here, the resistance values R ₃ and R ₄ are set so that when these voltages +Vc and -V ₁ reach respective predetermined voltages, the voltage at the base of the transistor 17 becomes a slightly negative voltage. 17 remains off, resulting in a voltage +
Charging of the capacitor 9 via the resistor 8 is started by Vc. Then, when a predetermined time determined by the time constants C ₁ and R ₁ has elapsed and the voltage +V ₂ at the connection point P reaches a predetermined voltage, the transistor 10 is turned on, thereby driving the relay 11 . Therefore, in this embodiment, the output terminal of the amplifier 12 and the speaker 13 are connected after a certain period of time determined by the time constant C ₁ ·R ₁ after the power is turned on.

Next, when the power supply is cut off, the charge stored in the capacitor 6 is immediately discharged via the resistor 15, and the voltage _-V1 becomes the ground potential. On the other hand, since the charge stored in the capacitor 3 is only gradually discharged, the voltage at the base of the transistor 17 becomes a positive voltage, so that the transistor 17 immediately becomes conductive. As a result, the electric charge stored in the capacitor 9 is immediately discharged through the resistor 22 and the transistor 17 in sequence, and as a result, the voltage +V ₂ decreases and the transistor 10
turns off. In this case, since the capacitance C ₂ of capacitor 6 is originally a small value, the value of resistor 15 is
If R ₂ is set to a small value to the extent that the smoothing function of the capacitor 6 is not impaired, the time it takes for the voltage -V ₁ to reach the ground potential can be made to an extremely small value. Further, the value R ₅ of the resistor 22 may be set to a small value such that the transistor 17 is not destroyed by the discharge current, and therefore the time for discharging the charge of the capacitor 9 can be set to an extremely small value.

According to this embodiment, the time from when the power is cut off until the relay contact 11b turns off is
It can be significantly shortened compared to conventional relay control circuits. Furthermore, according to this embodiment, the capacitance C ₂ of the capacitor 6 can be set to a small value, so even if the capacitor 6 is made non-polar, it is inexpensive, and the capacitor 9 is connected to the AC voltage. An inexpensive polar type may be used since there is no fear that the voltage will be applied.

As is clear from the above explanation, the relay control circuit according to this invention is provided with a current control element configured to be turned on immediately when the power is turned off, and the electric charge of the capacitor that determines the delay time when the power is turned on is Since it is configured to discharge through the control element, it is possible to significantly shorten the delay time when the power is turned off compared to conventional relay control circuits, and it is also useful as a capacitor that determines the delay time when the power is turned on. The advantage is that polar capacitors can be used and the circuit can be constructed at low cost.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of the configuration of a conventional relay control circuit, and FIG. 2 is a circuit diagram showing the configuration of an embodiment of the relay control circuit according to this invention. 1... Power transformer, 4... First power supply circuit (main power supply circuit), 7... Second power supply circuit (relay control power supply circuit), 8... Fourth resistance element (resistance), 9... Capacitive element (capacitor), 10...
...Second current control element (NPN transistor), 1
1...Protection relay, 11a...Relay winding, 15
...First resistance element (resistance), 16...Second resistance element (resistance), 17...First current control element (NPN transistor), 19...Time constant circuit, 2
0... Third resistance element (resistance), 21... Bias circuit.

Claims (1)

[Scope of utility model registration request] A first power supply circuit that rectifies and smoothes AC input and outputs the same, a second power supply circuit whose polarity is different from that of the first power supply circuit, and between the output terminal of the second power supply circuit and the ground point. the inserted first resistance element, the output terminal of the first power supply circuit, and the second
has a second and third resistive element inserted in series with the output terminal of the power supply circuit, and controls the first current using the voltage at the connection point of the second and third resistive elements. a bias circuit for controlling on/off of the element, and a fourth resistance element and a capacitance element inserted in series between the output terminal of the first power supply circuit and a ground point; A time constant circuit is provided in which the charge of the capacitive element is discharged when the control element becomes conductive, and a relay winding and a second current control element are provided between the output terminal of the first power source and the ground point. are inserted in series, and the second current control element is controlled to be turned on and off by the voltage across the capacitive element.