JP2842941B2 - Pre-regulated output variable power supply - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pre-regulation type variable output power supply.

[Conventional technology]

 FIG. 4 shows a conventional example.

In FIG. 4, 1 is a pre-regulator, 2 is a dropper element (transistor) which is a main part of a dropper type regulator section, and 2 'is a collector
A detector for detecting the emitter voltage _VCE , 3 is a load, 4 is a load current detector, 5 is a reference power supply, and 6 is a comparator.

In this kind of conventional pre-regulated output variable power supply, V _CE is detected by a detector 2 ′ for high efficiency and high stability, and the voltage V _CE applied to the dropper element (transistor) 2 becomes constant. Output Vs of pre-regulator 1
Had control.

The above conventional example will be described with reference to the specific circuit of FIG. 5 and the characteristics of FIG.

Pre-regulator PWM switching regulator 1
Is a variable pulse width generator 1a (corresponding to the _VCE detector 2 'in FIG. 4), a capacitor 1b, a switching element (transistor) 1c, a transformer 1d, a rectifier diode 1e, a choke coil 1
f, 1g of smoothing capacitor.

As is well known, when the control voltage _VCE fluctuates, for example, when the control voltage _VCE increases, the output pulse width of the variable pulse width generator 1a becomes narrow, and the switching element (transistor) 1c
ON time becomes shorter (shorter). Then, the output pulse width on the secondary side of the transformer 1d also becomes narrow, and the output voltage Vs smoothed by the choke coil 1f and the smoothing capacitor 1g becomes low. Conversely, when the control voltage V _CE decreases, the output pulse width of the variable pulse width generator 1a increases, and the switching element 1c
Of the transformer 1d also increases, the output pulse width on the secondary side of the transformer 1d increases, and the output voltage _VCE increases.

The dropper regulator comprises a load current detector 4, a reference voltage source 5, a comparator 6, and a dropper element 2.

As is well known, when the load power supply Io changes,
For example, when it becomes larger, the + input terminal voltage of the comparator 6 becomes lower and is compared with the reference voltage source 5. Then the comparator 6
Output voltage becomes low, and the emitter current of the dropper element 2 becomes small. Since the emitter current becomes the load current Io, the load current Io is reduced to suppress the fluctuation.

Conversely, when the load current decreases, the emitter current increases via the comparator 6, and the load current Io increases, thereby suppressing the fluctuation. The constant current control is performed by the operation of the dropper regulator described above.

Here, paying attention to the pre-regulator 1, since the output voltage Vs of the pre-regulator 1 is controlled so that the voltage V _CE applied to the dropper element 2 is constant, Vs is equal to the load 3
Voltage is always V _CE voltage higher than Vo according to, i.e., the minimum output voltage Vs (min) is higher by V _CE than Vo (min), the output variable width Vs (wide) is the same as Vo (wide).

This is Vs = 5V-51V under the operating conditions of FIG. 5, switching frequency fs = 100 KHz, maximum pulse width Pw = 4 μs
Then, the pulse width Pw is equivalent to 0.39 μs to 4 μs, and it is difficult to realize a narrow pulse width.

As one of the solutions, an operation changeover switch 1h for continuously changing the output frequency fs of the variable pulse width generator 1a according to the input voltage Vi and an element 1 for determining the output frequency are provided.
In some cases, a variable resistor 1i whose resistance changes according to the input voltage Vi (V _CE ) is provided.

That is, as shown in FIG. 6, while the input voltage Vi is low, the operation changeover switch 1h is turned off, and the normal PWM (pulse width modulation) operation is performed. Turn on the operation changeover switch 1h to perform PWM (pulse width modulation) + FM (frequency modulation) operation. further
When Vi becomes high and the pulse width Pw exceeds the minimum limit, the operation shifts to the FM operation and the control for stabilizing Vs is continued, so that a wide output variable width Vs (wide) is secured.

However, the prior art described above uses PWM operation and FM operation as shown in FIG.
The operation point at which the operation is started is discontinuous, which causes problems such as a change in output impedance or a change in output ripple. A peripheral circuit for automatically switching the operation changeover switch 1h is also required.

[Problems to be solved by the invention]

In addition, the above-mentioned prior art has a minimum output of the pre-regulator 1.
No consideration is given to Vs (min) and output variable width Vs (wide), and there is a problem that the minimum output V (min) is small and the output variable width Vs (wide) needs to be widened. Was.

 An object of the present invention is to solve the above problems.

[Means for solving the problem]

The present invention is configured as follows to achieve the above object. The reference numerals of the components are the same as those of the embodiment shown in FIG.

The present invention relates to a pre-regulated output variable power supply including a pre-regulator 1 and a dropper-type regulator. Constant current control means for controlling the current flowing through the pre-regulator 1 so that the power loss PD of the dropper element 2 becomes constant in parallel with the constant current control.
And constant power control means for controlling the output of

In the example of FIG. 1, the constant current control means is constituted by the load current detector 4 and the comparator 6, and the constant power control means is constituted by the power loss detector 7 and the pre-regulator 1.

[Action]

According to the above configuration, constant current control is constantly performed on the load, and constant power control is performed on the dropper element 2 of the dropper type regulator unit. Among them, for the constant power control, the power loss PD of the dropper element 2 is detected and fed back to the pre-regulator 1 so that the power loss PD of the dropper element 2 becomes constant regardless of the constant current output Io. Output Vs of regulator 1
Control. Thereby, the output of pre-regulator 1
Vs rather than method for feedback control of the voltage V _CE applied to the dropper element 2, raising the final output Vs (min), it can be made to be narrower output variable width Vs (wide).

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

FIG. 1 is a circuit diagram showing one embodiment of the present invention, and FIG.
FIG. 3 is a circuit diagram showing the circuit of the first embodiment more specifically. In the figure, the same reference numerals as those in the conventional example shown in FIGS. 4 and 6 denote the same or common elements.

Conventional example differs from the embodiment and Figure 4 is used instead of PD detector 7 to V _CE detector 2 ', pre-regulator 1 is controlled to Vs so that power dissipation PD is constant.

When the load current Io changes due to a change in the load 3 or the like, the current is detected by the current detector 4, and the voltage reference source 5 and the comparator 6
And the current flowing through the dropper element 2 so as to cancel the change (fluctuation) of the output current Io at the output.
Constant current control of _IE .

Here, the power loss PD (PD = V _CE × I _E ) is detected based on the voltage V _CE applied to the dropper element 2 and the flowing current _IE , and the detected power loss PD is fed back to the pre-regulator 1.
The output Vs is controlled so that PD becomes constant.

 The above example will be described with reference to FIG.

The pre-regulator 1 is a PWM switching regulator and includes a variable pulse width generator 1a, a capacitor 1b, a switching element 1c, a transformer 1d, a rectifier diode 1e, a choke coil 1f, and a smoothing capacitor 1g.

As is well known, when the control voltage V (V∝V _CE ) fluctuates, for example, when it rises, the variable pulse width generator 1a
, The output pulse width Pw becomes narrow, and the on-time of the switching element 1c also becomes narrow. Then, the output pulse width on the secondary side of the transformer 1d becomes narrow, and the output voltage Vs smoothed by the choke coil 1f and the smoothing capacitor 1g becomes low.

Conversely, when the control voltage V decreases, the output voltage Vs
Will be higher.

The dropper regulator comprises a load current detector 4, a reference voltage source 5, a comparator 6, and a dropper element 2. As is well known, when the load current Io fluctuates, for example, when it increases, the + input terminal voltage of the comparator 6 decreases and is compared with the reference voltage source 5. Then, the output voltage of the comparator 6 decreases, and the emitter current of the dropper element 2 decreases. Since the emitter current becomes the load current Io, the load current Io is reduced to suppress the fluctuation. Conversely, when the load current decreases, the emitter current increases by the same operation, and the load current Io increases to suppress the fluctuation.

In this embodiment, by controlling the output voltage Vs of the pre-regulator 1 so that the power loss PD of the dropper element 2 is constant, Vs is a voltage higher by Vo than the value obtained by dividing PD by Io, that is, PD is Even if Io is small, Vs does not need to be so low because it is constant.

This is Vs = 30.4V-51V under the operating conditions of FIG. 3 [FIG. 2 shows the relationship between the output voltage Vo and the pre-regulator output voltage Vs when the power loss PD is controlled to be constant. The relationship is expressed in comparison with the conventional _VCE constant control method, and the solid line of the characteristic imaginary line is in the range of the output variable width Vs (wide)], the switching frequency fs = 100 KHz, and the maximum pulse width Pw.
= 4 μs, this corresponds to a pulse width Pw = 2.38 μs to 4 μs, and the minimum pulse width and the pulse change width may be narrower than in the case where V _{CE is} constant. Therefore, realization is easy. Here, the power loss PD of the dropper element 2 is always constant. Even if the control is performed so that _VCE is constant, the dropper element 2 is designed so that heat dissipation does not pose a problem at the time of the maximum power loss PD (max). Therefore, the result is equivalent, and it can be said that there is no waste.

〔The invention's effect〕

According to the present invention, as shown in FIG.
(Min) and the output variable width Vo (wide), the minimum output voltage Vs (min) of the pre-regulator 1 is high, and the output variable width Vs (wide) can be set narrow. Can be loose.

Therefore, the pre-regulator 1 can perform only the PWM operation. As a result, the peripheral circuit for performing the combined operation of the conventional PWM operation and the FM operation is unnecessary, and there is no discontinuity in the transition portion between the PWM operation and the FM operation. In addition, there is an effect that a stable circuit operation can be performed.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram of one embodiment of the present invention, FIG. 2 is a characteristic diagram of the conventional example and the present invention, FIG. 3 is an electric circuit diagram that embodies the above embodiment, and FIG. FIG. 5 is a specific electric circuit diagram of the above conventional example, and FIG. 6 is a characteristic diagram of the conventional example of FIG. DESCRIPTION OF SYMBOLS 1 ... Preregulator (switching regulator), 2 ... Dropper element, 3 ... Load, 4 ... Load current detector, 5 ... Reference voltage source, 6 ... Comparator, 7 ...
Dropper element power loss detector.

Claims (1)

(57) [Claims] 1. A pre-regulated output variable power supply having a pre-regulator and a dropper-type regulator, wherein a load current is detected, and when the load current fluctuates, the current flows to a dropper element of the dropper-type regulator so as to cancel the fluctuation. Constant current control means for controlling current; and constant power control means for controlling the output of the pre-regulator so that the power loss of the dropper element becomes constant in parallel with the constant current control. Pre-regulated output variable power supply.