JPS645966Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to a power supply circuit, and more particularly to a power supply circuit having main and auxiliary power supplies and capable of being backed up.

Background of the Invention As electronic devices have become more sophisticated in recent years, the number of devices that include built-in memory for calculation processing, storage of setting conditions, etc. is rapidly increasing. Many of these memories are volatile, and when the power is turned off, the stored contents are lost in a short time. On the other hand, for oscilloscopes, especially plug-in oscilloscopes, it is common to turn off the main power when moving to a measurement location or replacing a plug-in unit. The previous memory contents are then lost and the measurement or operating procedure has to be repeated again.

To avoid this, an auxiliary power source (e.g. battery)
By incorporating it or connecting it externally, you can switch to an auxiliary power supply when the main power supply is cut off.
A backup-capable power supply circuit was devised to protect loads such as memory. However, since such auxiliary power supplies are used temporarily when needed, their voltages are not constantly monitored, and if the output voltage is excessive, it may permanently destroy the load such as memory that should be protected. There is a possibility that This permanent destruction
This inflicts more damage on electronic devices than the loss of stored contents in memory.

Purpose of the invention Therefore, the purpose of the invention is to temporarily switch to an auxiliary power source to back up the memory section of an electronic device that normally operates on the main power supply, and to back up the memory section of an electronic device that normally operates on the main power supply. An object of the present invention is to provide a power supply circuit equipped with an automatic protection function that prevents switching when a transient overvoltage is applied from a power supply.

Summary of the invention The present invention provides first and second switch means that enable the output of the main power supply and the auxiliary power supply to be supplied to the load, respectively, and selectively operates these switch means according to the output voltage of the main power supply. overvoltage protection means for controlling conduction of the second switch means when the voltage of the auxiliary power supply is not a predetermined value;
This power supply circuit is provided with a transient voltage protection means that prevents conduction of the second switch means when a transient excessive voltage that rises sharply is applied from the auxiliary power supply.

Embodiment FIG. 1 shows one preferred embodiment of a power supply circuit according to the present invention. Main and auxiliary power supply is input terminal 10
and 11, respectively. A first switching transistor 12 is connected in series between input terminal 10 and output terminal 20, with its emitter connected to terminal 10 and its collector connected to terminal 20. Similarly, the second switching transistor 13 connects the terminals 11 and 2 via the first protection circuit 14.
It is inserted between 0. The bases of these switching transistors 12, 13 are connected via resistors 17, 18, respectively, to the respective collectors of a pair of emitter-coupled transistors 15, 16 forming the comparator. The emitters of these transistors 15 and 16 are grounded via a resistor 19. Capacitor 21 is connected between the base of transistor 15 and the collector of transistor 16. The collectors of the transistors 12 and 13 are connected to the resistor 22.
connected to the base of transistor 16 via
It is grounded via bypass capacitors 23 and 24. The base of transistor 16 is grounded through a pair of series diodes 25 and 26.

The control circuit 27 has emitter follower transistors 28, 29, thereby controlling the transistor 1
Drives the base of 5. The control voltage is at the control terminal 30
added to. The emitter of transistor 28 is grounded through series resistors 31 and 32, their common connection point is connected to the base of transistor 29, and the emitter of transistor 29 is coupled to the base of transistor 15. Collectors of transistors 28 and 29 are connected to first terminal 10. The second protection circuit 33 has a transistor 34 whose collector-emitter junctions are connected to both ends of the diodes 25 and 26, and the base of the transistor 34 is grounded via resistors 35 and 36. Zener diode 37 is connected between the output point of first protection circuit 14 and the connection point of resistors 35 and 36. 1st
The protection circuit 14 includes a fast-melting fuse 38, a diode 39, a low resistance resistor 40, and a zener diode 1.
It has 4 series circuits. In addition, the transistor 75
and a transient voltage protection circuit 76 composed of related resistors 72, 73 and capacitor 74.
is connected between the emitter and base of the second switching transistor 13.

The operation of the above power supply circuit is as follows. When the main power supply is normal, the voltage at the control terminal 30 is high, turning on the transistors 28 and 29. This turns transistor 15 on and transistor 16 off. Switching transistor 12 is conductive through which the main power applied to terminal 10 is supplied to output terminal 20. This output voltage is
A base bias of transistor 16 of approximately +1.2 volts is applied across diodes 25, 26, while the base voltage of transistor 15 is at terminal 30.
and the control voltage applied to resistors 31 and 32 to be higher than +1.2 volts. Transistors 16 and 13 therefore remain non-conducting even when external or built-in auxiliary power supply is applied to terminal 11.

However, if the main power supply is interrupted or insufficient, the control voltage to terminal 30 will drop, turning transistor 15 off and transistor 16 on. The charge accumulated in the capacitor 21 during the non-conducting period of the transistor 13 increases the speed of the switching operation of the transistors 15 and 16 of the comparator.
Used for up. The collector current of transistor 16 maintains switching transistor 13 conductive and transfers power from the auxiliary power supply connected to terminal 11 to output terminal 20. It is therefore noteworthy that the switching from the main power source to the auxiliary power source occurs smoothly with minimal delay time.

The first protection circuit 14 has two different purposes. Diode 39 protects the circuit when the auxiliary power supply is connected with reverse polarity. SCR 41 and fuse 38 protect the circuit from overvoltage. When the auxiliary supply voltage exceeds a certain value (e.g. 15 volts) determined by Zener diode 44, SCR4
1 is turned on, causing a large current to flow through the low resistance resistor 40, and quickly blowing out the fuse 38. The second protection circuit 33 is an overvoltage protection circuit used to turn off the switching transistor 13 when the auxiliary power supply voltage exceeds the withstand voltage value (for example, about 7 volts) of the load connected to the output terminal 20. .
Transistor 34 turns on when the auxiliary supply voltage exceeds the zener voltage of zener diode 37, turning transistors 16 and 13 off. The load is thus isolated from the auxiliary power supply. Even if the auxiliary power supply voltage drops back to the predetermined range, power will not be restored until the main power supply is restored. This means that once transistor 34 is turned on, both transistors 15 and 1
6 remains non-conducting.

Transient voltage protection circuit 76 including transistor 75
insulates output terminal 20 from the rapid voltage rise applied to terminal 11. The transistor 75 is
Although normally held off by resistor 72, if a rapidly rising voltage is applied to terminal 11, voltage dividers 72, 73 and capacitor 74 momentarily turn on transistor 75, turning transistor 13 off. It is forced to turn off momentarily, thereby preventing spike voltage from reaching the output terminal 20. Without this protection circuit, a rapid voltage transient at terminal 11 would pass through resistor 18, capacitor 21, transistor 15 and resistor 19 to first protection circuit 14.
turns on transistor 13 before it responds,
There is a risk of creating a spike voltage at the output terminal 20.

FIG. 2 is a block diagram of a digital memory oscilloscope using the power supply circuit according to the present invention. The analog input signal to be observed is input to the input terminal 50.
Vertical preamplifier 54, switch circuit 5
6 and a vertical main amplifier 58 to the vertical deflection plate of the CRT 52. The same input signal is also applied to a sampling and digitizing circuit 60 which sequentially converts the instantaneous values of the input signal into a digital representation and stores it in a digital memory 62, such as random access memory (RAM). The stored data is sequentially read out at any desired time and applied to the CRT 52 via a switch circuit 56 and a vertical main amplifier 58. The time axis signal is generated by the timing circuit 64 in synchronization with the input signal or sampling signal in order to drive the horizontal deflection plate of the CRT 52 via the horizontal amplifier 66.

The power supply circuit 68 includes a main power supply 65 and an auxiliary power supply 67. The former supplies operating voltage to the circuit block including the memory 62 through the power line 69;
The latter is connected only to memory 62 via power line 70. A control line 71 from the main power supply 65 to the auxiliary power supply 67 provides a control signal to the comparator shown in FIG. 1 and previously described.

When the switch 56 is in the up position, the input signal is input to the CRT 52 like a normal oscilloscope.
will be displayed. At the same time, the input signal is transferred to the memory 6
To observe the data stored in 2, it is sufficient to move the switch 56 to the down position. The data in memory 62 can be retained for a desired period of time for further analysis or as a reference. However, it is often desired to cut off the main power while retaining the data stored in the memory 62. For example, when replacing a plug-in unit in a plug-in oscilloscope, it is common to turn off the power.
Power supply circuit 68 is useful for this purpose. The main power supply 65 receives power from an AC power supply (not shown in FIG. 2) and supplies operating power to each circuit including the digital memory 62 through a power line 69. if,
When the main power supply 65 stops, the control signal is transferred to the control line 71.
The signal is sent to the auxiliary power source 67 via the auxiliary power source 67. Auxiliary power supply 67
supplies power only to memory 62 via power line 70 to maintain its stored data.

Although only the preferred embodiments have been described above, it goes without saying that various modifications can be made without departing from the gist of the present invention.

Effects of the invention As explained above, according to the invention, as long as the main power supply supplies a predetermined voltage, the load is driven by the main power supply, and when the voltage drops below the predetermined value, it is immediately switched to the auxiliary power supply for backup. It is suitable for use in a plug-in oscilloscope having a semiconductor memory. Furthermore, when switching, if the auxiliary power supply voltage exceeds the withstand voltage value of the load such as the memory, switching of the auxiliary power supply is prevented, so that the load such as the memory can be protected from destruction. Furthermore, even if a transient excessive voltage is applied from the auxiliary power source, the transient voltage can be cut off, so that the load circuit can be completely protected.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a preferred embodiment of the present invention;
FIG. 2 is a block diagram of a digital memory oscilloscope using the present invention. 10...Main power input terminal, 11...Auxiliary power input terminal, 12...First electronic switch means, 13...
...Second electronic switch means, 15, 16...Switch control means, 33...Overvoltage protection means, 76...
Transient voltage protection measures.

Claims (1)

[Claims for Utility Model Registration] First and second electronic switch means that enable the output of the main power source and the auxiliary power source to be supplied to the load, respectively; conducts the electronic switch means and cuts off the second electronic switch means, and when the output voltage of the main power source falls below the first predetermined value, the first
switch control means that cuts off the electronic switch means and conducts the second electronic switch means; and overvoltage protection means that cuts off the second electronic switch means when the voltage from the auxiliary power source exceeds a second predetermined value. A series circuit of a resistor and a capacitor connected between the auxiliary power source and the reference potential source detects a transient overvoltage from the auxiliary power source, and shuts off the second electronic switch means in response to the detection. A power supply circuit comprising a transient voltage protection means.