JPS5932211Y2 - Intermittent control DC stabilized power supply circuit - Google Patents

Description

[Detailed Description of the Invention] This invention relates to an intermittent control DC stabilized power supply circuit having an output limiting circuit.

FIG. 1 shows the countries in which this type of conventional intermittent control DC stabilized power supply circuit is constructed, and numeral 1 in the figure indicates an unstable DC power supply.

This unstable DC power supply 1 is connected to a load 4 via a control switch repeater 2 and a smoothing circuit 3, and an output voltage appearing on the load 4 is detected by an output detection circuit 5, and the detected value and a reference voltage are The error is amplified by the error amplifier 6 and sends an error signal to the pulse modulation and drive circuit γ.

With this, the pulse modulation and drive circuit γ sends a signal with a pulse width corresponding to the error signal to the control switch element 2 to drive the control switch element 2, and the control switch element 2 outputs an output voltage that is applied to the load 4. control so that it remains constant.

When the switching repetition frequency of the control switch element 2 is constant, the ratio of conduction and non-conduction is changed, that is, pulse width modulation is used, and a smoothing choke is inserted between the control switch element 2 and the load 4, the unstable DC power supply 1 At the voltage Vin and the output voltage Vout, the conduction ratio τ of Vou is τ-, and a constant voltage is obtained by controlling τXVin to be constant in.

Since such an intermittent controlled DC stabilized power supply circuit uses the control switch element 2 as an active element, there is little loss for stabilizing the output, and the range of output variation is wide.

That is, in the above case, while τ is from zero to 1, the output is variable from zero volts to Vin.

Since it is possible to obtain any output voltage from zero to Vin with low loss, the commercial AC power is generally rectified and smoothed without going through a power transformer to obtain the voltage of the unstable DC power supply 1. In many cases, it is necessary to obtain an arbitrary output voltage.

However, there is an upper limit to the voltage applied to the load 4, and it is necessary to pay close attention to the adjustment so as not to exceed the allowable load voltage.

Also, no matter how careful you are, there is no way to prevent the output from increasing due to an abnormality such as a short-circuit between the collector or emitter of the error amplifier transistor, and the high output may destroy the load 4 or leave stress on it. It often happened.

In response to this, attempts were made to insert a varistor between the output and ground, but this resulted in the stabilizing power supply circuit itself being destroyed by the overcurrent.

In this way, while the conventional intermittent control DC stabilized power supply circuit has the ability to easily vary the output, it is also difficult to adjust.
There was a drawback that the output could change too widely due to abnormal operation.

This idea was made in order to eliminate the above-mentioned drawbacks of the conventional method.By adding a new output voltage limiting circuit, the upper limit of the output voltage can be determined, and the pulse modulation can be stabilized at this output voltage. As if performing the ``Hakukyaku'',
An intermittent control DC stabilized power supply that eliminates situations where the output voltage increases significantly due to a short circuit in the error amplifier transistor, and eliminates load destruction and residual stress without putting a burden on the power supply circuit. It provides a circuit.

Next, an embodiment of the intermittent control DC stabilized power supply circuit of this invention will be explained based on the drawings. FIG. 2 is a circuit diagram showing one embodiment, and in this FIG. are described with the same reference numerals. An unstable DC power supply 1 is connected to a load 4 via a torpedo switch element 2 and a smoothing circuit 3, and is configured to supply a constant voltage to the load 4. , this point is similar to the case of FIG.

The output voltage supplied to the load 4 is detected by a detection circuit 5, and as is clear from FIG. The output terminal 8 is connected to one end of the load 4, that is, between the output side of the smoothing circuit 3 and one end of the load 4.

The connection point between the resistor 9 and the variable resistor 10 is the transistor 1.
Connected to 10 base.

This transistor 11 constitutes the main part of the error amplifier 6, and its emitter is connected to the output terminal 8 through a resistor 12.
and is grounded via a constant voltage diode 13.

The collector of the transistor 11 is connected via a resistor 14 to the base of a transistor 210 of the pulse modulation and drive circuit T, to which a capacitor 29 is connected (.
reactor.

The capacitor 29 is a constant frequency sawtooth wave compensating capacitor for pulse width modulation.

On the other hand, reference numeral 15 is an output voltage limiting circuit, which is a newly added circuit based on this invention, in which output voltage detection resistors 16 and 17 are connected in series between the output terminal 8 and the ground, and both output voltages are The connection point between the detection resistor 16 and 1γ is connected to the base of the control transistor 190 via the switch voltage regulator diode 18.

The emitter of the transistor is grounded, and the collector is connected to resistor 2.
0 to the base of the transistor 210 of the pulse modulation and drive circuit I.

The above-mentioned pulse modulation and drive circuit 1 mainly consists of transistors 21 and 22 to constitute a simulator circuit, and the emitters of the transistors 21 and 22 are directly connected.
The emitter of transistor 22 is grounded via resistor 23.

The collector of the transistor 21 is connected to the output terminal 8 via a resistor 24, and a resistor 25 is connected between this collector and the base of the transistor 220.
A resistor 26 is connected between the base and ground.

The transistor 22 operates as a driving transistor, and its collector is connected to the output terminal 8 via the primary winding of the driving transformer 2γ.

Both ends of the secondary winding of the drive transformer 2γ are connected to a terminal 28, and the output of the pulse modulation and drive circuit γ is induced at the terminal 28, and this output is sent to the control switch element 2. It is designed to drive.

In this case, the drive transformer 2γ is connected to a polarity that makes the control switch element 2 conductive during pulse modulation and when the transistor 21 of the drive circuit 1 is conductive.

Next, the operation of the intermittent control DC stabilized power supply circuit of this invention constructed as described above will be explained.

First, in the detection circuit 5, the output voltage is divided by the resistor 9 and the variable resistor 10, and the divided voltage is applied to the base of the transistor 110 of the error amplifier 6.
and the connection point voltage of the constant voltage diode 13, and the error voltage is passed through the resistor 14 to the pulse modulation and drive circuit γ.
is applied to the base of transistor 210.

A constant frequency sawtooth signal is also introduced to the base of the transistor 210 through the capacitor 9, and the transistor 21 repeats the ON operation each time the sawtooth signal is introduced.

Then, when the transistor 21 is conductive, the driving transformer 2
7 is energized to make the control switch element 2 conductive.

In this state, if the above error voltage is applied to the base of the transistor 210 from the output side of the error amplifier 6 in a direction in which the base DC potential increases, depending on the error voltage,
Appears on load 4 and the output voltage increases.

That is, as the value of the variable resistor 10 is decreased, the conduction ratio of the transistor 21 increases, the width of the pulse applied to the driving transformer 2γ is modulated, and the output voltage supplied to the load 4 increases.

This also results in an abnormal operation such as a short circuit between the collector and emitter of the transistor 11.

Conversely, if the error voltage is applied in the direction in which the DC potential at the base of the transistor 210 decreases, the transistor 210
The conduction ratio of the control switch element 2 decreases, and the output voltage supplied to the load 4 decreases.

On the other hand, in the output voltage limiting circuit 15, the voltage detection resistor 16
, 17 exceeds the constant voltage value of the constant voltage diode 18, that is, when the output voltage exceeds a predetermined voltage, the transistor 19 becomes conductive, and the output side of the error amplifier 6 performs pulse modulation and drive. The error voltage appearing at the base of transistor 210 of circuit 6 will be connected to ground via resistor 20 and transistor 19.

As a result, the width of the pulse that controls the pulse width modulation by the transistor 21 and energizes the first driving transformer 2γ becomes smaller, and therefore the conduction ratio of the control switch element 2 becomes smaller, and the output that is supplied to the load 4 becomes smaller. The voltage is maintained at a constant value determined by the resistor 9, the variable resistor 10, and the constant voltage diode 13.

Also, by increasing the value of the variable resistor 10, the output voltage can be returned to the variable range.

In addition, the output voltage detection point during steady operation and the output type.

Although the detection points of the voltage limiting circuit 15 are the same, if precision is not required for output limiting, the applied voltage may be detected at a different point in the load circuit. However, similar results can be obtained using pulse repetition frequency modulation.

Further, although the above embodiments have been described mainly on the assumption that a smoothing choke for intermittent power is connected in series with the load, the same effect can be obtained when a smoothing choke is used as the transformer primary winding.

As described above, according to this invention, by newly adding an output voltage limiting circuit to the conventional intermittent control DC stabilization circuit, when the output voltage exceeds a predetermined value, the error voltage that is the output of the error amplifier is bypassed. Since pulse width modulation is regulated in this way, it is possible to prevent the output voltage from increasing significantly by abnormally adjusting the output regulator of the intermittent control DC stabilized power supply circuit or by shorting the transistor of the error amplifier. It is possible to eliminate such situations, and eliminate load destruction and residual stress without applying a negative phase to the intermittent control DC stabilizing circuit.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional intermittent control DC stabilizing power supply circuit, and FIG. 2 is a circuit diagram showing an embodiment of the intermittent control DC stabilization power supply circuit of the present invention. 1... Unstable DC power supply, 2... Control switch element,
3...Smoothing circuit, 4...Load, 5...Detection circuit, 6
...Error amplifier, γ...Pulse modulation and drive circuit, 15...Output voltage limiting circuit, 11, 19, 21, 2
2...Transistor, 13.18... Constant voltage diode, 2γ... Drive transformer. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Scope of utility model registration request] An error amplifier that amplifies and outputs the error between the output voltage output to the load and the reference voltage.The DC error voltage from this error amplifier and a predetermined repetition frequency signal are input, and the pulse width is modulated according to this error voltage. a control switching element that receives the voltage of the unstable DC power source and is driven by the output of the pulse width modulation and drive circuit to supply a constant output voltage to the load, and performs a switching action; Detects the above output voltage, sets a predetermined upper limit value for this output voltage, and when the upper limit value is reached, conducts to bypass the above error voltage.It is equipped with an output voltage limiting circuit, and when this output voltage limiting circuit conducts, outputs at the above upper limit value. An intermittent control DC stabilized power supply circuit in which the pulse modulation and drive circuit controls pulse modulation so that the voltage is stabilized.