JPH0320974B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power supply circuit useful for electronic devices driven by an AC power supply having an arithmetic control unit, and in particular to a power supply circuit that can maintain a constant voltage on the secondary side for a long time when the primary AC input is suddenly cut off. The purpose is to hold.

FIG. 1 shows an example of a conventional electronic device having an arithmetic control section. In the figure, 1 is a power supply circuit of the power supply section, 2 is an arithmetic control section, 3 is an input/output section, 4 is a power failure detection circuit of the power supply section, a is an alternating current (AC) primary input, and b and b' are A direct current (DC) output, c is a power failure interrupt signal, and d is a control signal, and control of the input/output section 3 and numerical calculation processing are performed by the arithmetic control section 2. It is necessary to protect the computed data and maintain the input/output devices in case of interruptions in the AC power supply, including power outages during computation processing.

Therefore, when the AC primary input a is suddenly cut off,
The power failure detection circuit 4 detects this and generates a power failure interrupt signal c. In response to this, the calculation control unit 2 performs so-called power failure processing such as protection of calculation data and maintenance of the input/output device 3. It is configured. However, the power outage process can only be performed within the time period after the power outage interrupt is detected while the power supply voltage from the power supply circuit 1 to the arithmetic control unit 2 is maintained within its normal operating range. There was a problem with not having enough time.

The present invention aims to provide a power supply circuit in which the above drawbacks are eliminated by a simple additional circuit, and one embodiment thereof will be described below with reference to FIGS. 2 and 3. In Figure 2, T is a transformer with one set of AC primary inputs (V _AC ) and two sets of AC secondary outputs V _AC1 ,
V _AC2 . RC1 and RC2 are rectifiers, C ₁ ~
_C3 is a capacitor, _R1 to _R6 are resistors, TR1 to TR4
is a transistor, ZD ₁ to _{ZD 2} are constant voltage elements, V ₁ is the first smoothed output voltage as the output of the rectifier RC2,
V ₂ is the constant voltage output, V ₃ is the voltage of the second smoothed output,
GND is the ground terminal, rectifier RC1 and capacitor _C1
A first smoothing circuit is constructed by the rectifier RC2 and a smoothing circuit by the capacitor _C2 .

In the above configuration, the secondary output of the power transformer T becomes two types of DC voltages, the first and second smoothed outputs (voltages) V ₁ and V ₂ through the rectifier and smoothing circuit, of which the first smoothed output V ₁ supplies a constant voltage output V ₂ to the above-mentioned arithmetic control section 2 through the series stability control transistor TR2. ZD ₂ is constant voltage
It is a constant voltage element for obtaining _V2 , and _R6 is a resistor for supplying base current to the transistor TR2.

The detection circuit A is composed of a constant voltage element ZD ₁ , transistors TR3, TR4, and resistors R ₃ , R ₄ , R ₅ .
Detects when the voltage of the first smoothed output V ₁ becomes equal to or lower than its reference voltage V ₄ (see Figure 3 below),
This makes the transistor TR4 conductive, and at this time, the collector current of the transistor TR4 acts as the base current of the transistor TR1, making the transistor TR1 conductive.

Next, the operation of this embodiment will be explained. Figure 3 shows AC
This is a timing diagram showing the voltage change when the primary input (V _AC ) is cut off, where () is the AC primary input, () is the power failure interrupt signal I _PF , () is the smoothed output, and () is the constant voltage V ₂ , () indicates the smoothed output _V3 . When the AC primary input (V _AC ) is interrupted at timing A, the power supply section generates a power failure interrupt signal (I _pf ) (the generation circuit is not shown), and the first smoothed output V ₁ is used for smoothing. Discharge begins with a time constant determined by the capacitor C ₂ and the load resistance. When the first smoothed output V ₁ reaches the reference voltage V ₄ , the aforementioned detection circuit A turns on the transistor TR 1 , and the charge stored in the capacitor C ₁ is transferred through the transistor TR 1 and the current limiting resistor R ₂ . , are supplied to the first smoothing circuit. That is, according to the above configuration, in addition to the discharge charge of the capacitor C ₂ , the discharge charge of the capacitor C ₁ can also be used as power to maintain the constant voltage V ₂ after the AC primary input (V _AC ) is cut off. The holding time can be changed from _T1 when only capacitor _C1 is used, to T3, which is the effect of capacitor _C2 , which is the sum _{of T2} . In Figure 3, broken lines B and C indicate the first smoothed output V ₁ and constant voltage output in the conventional configuration.
This shows how V ₂ decreases.

Generally, the accumulated charge Q of a capacitor is given by the product of the capacitance C and the charging voltage V.
By increasing the capacity of C ₂ and increasing its charging voltage, the amount of accumulated charge and discharged charge can be increased, and it is possible to lengthen the retention time T ₁ .

However, increasing the capacitance of the capacitor C ₂ requires a large space, and also slows down the rise of the first smoothed output V ₁ and constant voltage output V ₂ when the AC primary input (V _AC ) is energized. There is a problem with the starting timing of the control unit. Also, capacitor
Increasing the charging voltage of _C2 increases the emitter-collector voltage of the series control transistor TR2, which is a problem in terms of heat dissipation and also causes a large amount of power loss.

However, according to the above configuration, even if the capacitance of the capacitor _C1 is not so large, if the charging voltage is increased, a sufficiently large charge can be stored, and the heat generated by the transistor TR1 and the resistor _R2 can be reduced. This is not a major problem because it only occurs momentarily when the AC primary input (V _AC ) is interrupted.

Furthermore, in the case of many electronic devices, a smoothing circuit and a smoothing output that are already available as a power supply circuit of an input/output section can be used as the first smoothing circuit.

As explained above, according to the present invention, by simply adding a simple circuit, a large effect can be produced as a power supply circuit for processing a power outage when the primary AC input is cut off.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an arithmetic and control device using a conventional power supply circuit, FIG. 2 is a wiring diagram showing the configuration of a power supply circuit in an embodiment of the present invention, and FIG.
The figure is a timing chart for explaining its operation. RC1, RC2... Rectifier, C ₁ to C ₂ ... Capacitor, TR1 to TR4... Transistor, R ₁ to _{R 6} ...
...Resistance, ZD ₁ , ZD ₂ ... Constant voltage element.

Claims (1)

[Claims] 1. First and second smoothing circuits each consisting of a rectifier and a capacitor that transform and take out and input the AC input voltage, a constant voltage control circuit for making the output of the second smoothing circuit a constant voltage, and the above-mentioned a detection circuit that detects a drop in the output voltage of the second smoothing circuit when the AC input voltage is interrupted; and applying means for converting the charge in the capacitor of the circuit into a current and applying it to the output of the second smoothing circuit via a resistor, the input voltage of the first smoothing circuit being higher than that of the second smoothing circuit. A power supply circuit characterized by: