JPS61199466A - Temperature compensation system for switching power source - Google Patents

Abstract

PURPOSE:To compensate the variation in the environmental temperature by controlling the duty ratio of a drive pulse constant in response to the temperature change of a storage time of a switching element. CONSTITUTION:A DC voltage is converted by a switching element to pulse, rectified and smoothed to obtain the prescribed output voltage. Thus, the output voltage and a reference voltage are compared by a comparator 9 to obtain an error voltage, which is applied to a comparator 10. The output of a CR oscillator 7 for deciding the oscillating frequency by external resistor 7-1 and a capacitor 7-2 is converted to a triangular wave by a triangular wave generator 8 and applied to the comparator 10. A drive pulse varied in the width corresponding to the error voltage is obtained from the output of the comparator 10. In this case, a posistor having a temperature change corresponding to the temperature change of the storage time of a switching element is used as the resistor 7-1. Thus, even if the environmental temperature varies, the duty can be maintained constant.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in the temperature compensation method of a switching power supply used in electronic equipment requiring a stabilized DC power supply.

Series regulators, shunt regulators, switching regulators, etc. are used to obtain DC constant voltage power supplies, but switching regulators (hereinafter referred to as switching power supplies) are smaller and smaller than other methods.
It is widely used because it is lightweight and has a high conversion efficiency of 75 to 80%.

In recent years, it has also been used as a power supply to convert DC input voltage, which fluctuates by 200 to 400V, into a constant DC output voltage. It becomes difficult to obtain an output voltage of

Therefore, there is a need for a temperature compensation system for switching power supplies that can provide a constant output voltage even when the ambient temperature changes.

[Conventional technology]

In general, switching power supplies use either a forward method or a bridge method when converting input DC voltage into pulses.

FIG. 3 shows a block diagram of a switching power supply using a forward type, and FIG. 4 shows an operation diagram of FIG. 3.

□ In Fig. 3, the input commercial AC voltage is rectified and smoothed by the rectifier/smoothing section and converted into a DC voltage. This DC voltage is converted into a pulse by a transistor 2-2 performing a switching operation in a DC/pulse converter 2, and then converted into a pulse by a transistor 2-1. The DC output voltage is sent to the outside via the rectifier/smoothing section 3.

On the other hand, a part of the DC output voltage is compared with a reference voltage in the control circuit 4-1, and an error voltage is taken out and added to this error voltage. Therefore, transistor 2 is set so that the error voltage becomes 0.
-1 switching operation is controlled.

Here, the voltage of the transformer 2-1 changes as shown in FIG. That is, when the transistor 2-2 is on (time To
Since energy is stored in the transformer 2-1 during the time (time Toff) and all of the stored energy must be released when the transformer is turned off (time Toff), Ton≦%·T must be satisfied. Note that T does not indicate the period.

Therefore, if it is possible to control Ton close to O-%.T, the control range will be expanded and a constant DC output voltage can be obtained even for DC input voltages that have large fluctuations.

FIG. 5 shows a block diagram of a conventional example of a bridge type switching power supply, and FIG. 6 shows an operation diagram of FIG. 5.

In FIG. 5, transistors 6-1 and 6-4 are turned on at the same time, and @ current flows as shown by the dotted line. At this time, transistors 6-2 and 6-3 are off.

Next, transistors 6-2 and 6-3 are turned on at the same time, and a current flows as shown by the dash-dotted line, but transistor rows 1 and 6-4 are turned off (see FIG. 6).

Therefore, alternating current flows through the transformer 2-1, which is rectified and
Send it to the smoothing section 3.

After that, the operation is the same as in the forward method.

Here, the rest period Td is the transistor 6-1 as described later.
This period is necessary to prevent the destruction of 6-4, and the shorter this period is, the more constant the DC output voltage can be with respect to the DC input voltage that has large fluctuations.

That is, in either method, the closer the duty D=Ton/T is to %, the wider the control range becomes.

[Problem that the invention seeks to solve]

Here, the collector current of the transistor is such that the base current is 0.
It continues for the storage time Ts tg even if it becomes. Moreover, since this time changes in response to changes in ambient temperature, Ton changes in response to ambient temperature. However, the period T
is set to be independent of the ambient temperature, so D
The value of varies depending on the ambient temperature.

Now, if D>%, in the case of the forward method, the energy stored in the transformer 2-1 is stored again before it is completely released, so this accumulates and causes an excessive current in the transistor 2-2. current and destroys this transistor.

In the case of the bridge method, since the rest time Td disappears and both transistors 6-1.6-2 and 6-3.6-4 are turned on, a large short-circuit current flows and these transistors are destroyed.

Therefore, it is necessary to make the storage time Ts 05% including the temperature change of Ts tg.

It becomes difficult to bring n close to %·T and Td close to 0, resulting in the problem that it is difficult to keep the output voltage constant against a DC input voltage that fluctuates greatly.

[Means to Solve Problem C] The above problem can be solved by using a book that controls the period of the drive pulse so that the duty cycle of the drive pulse remains constant in response to temperature changes during the storage time of the switching element. This problem is solved by the temperature compensation method for switching power supplies of the invention.

[Function] According to the present invention, the period of the switching operation is changed in accordance with the temperature change of the storage time of the switching element. In other words, D considering changes in ambient temperature is (To
n −1−ΔTon ) /T.

Here, Ton is, for example, the time during which the collector current of the switching transistor flows when the ambient temperature is 20°C.
ΔTon is the time corresponding to the change in storage time Tstg caused by the ambient temperature changing from 20°C, and T is the period.

Now, if ΔTon is larger than O, there is a possibility that the value of D is larger than the value at 20° C. and exceeds 50%, so T is changed by ΔT in accordance with ΔTon. Thereby, D can be kept almost constant regardless of temperature.

Therefore, the DC output voltage can be kept constant even if the ambient temperature changes.

〔Example〕

The present invention will be specifically explained below with reference to illustrated examples. The same reference numerals indicate the same objects throughout the drawings.

The above period T is determined by the oscillation frequency of, for example, a CR oscillator included in the control 1ff1 circuit 4-1. Therefore, this oscillation frequency was controlled in accordance with the storage time.

FIG. 1 shows a block diagram of an embodiment of the present invention, and FIG. 2 shows an operation waveform diagram of FIG. 1.

The portion shown in FIG. 1 is included in the control section 4 shown in FIG.

In the figure, external resistor 7-1 and capacitor 7-
The output of the CP oscillator 7, whose oscillation frequency is determined by the value of
Added to O.

On the other hand, a part of the DC output voltage of the switching power supply is compared with a reference voltage by a comparator 9 to obtain an error voltage, which is also applied to a comparator 10.

Therefore, a drive pulse whose width changes in accordance with the error voltage is obtained at the output of the comparator 10 (Fig. 2-2).

■Reference).

Now, for example, by using a POSISTOR that has the same temperature change as the change in ΔTon as the resistor 7-1, the period of the triangular wave can be changed as shown by the dotted line in response to the change in ambient temperature.
Pulse cycle 2! It is possible to change IIT to T+ΔT.

As a result, we were able to keep D at a constant value even if the ambient temperature changed (see Figure 2-■).

〔Effect of the invention〕

As explained in detail above, it compensates for changes in ambient temperature and ζ
Since the value of D can always be kept close to 2, there is an effect that the DC output voltage can be made more constant even with the DC input voltage having large fluctuations.

[Brief explanation of drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG. 2 is a block diagram of an embodiment of the present invention.
Figure 3 is a block diagram of a conventional switching power supply; Figure 4 is a block diagram of a conventional example of a switching power supply;
The figure shows the operation diagram of Figure 3, Figure 5 is a block diagram of another conventional example of a switching power supply, and Figure 6 is the operation diagram of Figure 5. In the figure, 7 is a CR oscillator, 8 is a triangular wave generator, 9 .10 indicates a comparator.

Claims (1)

[Claims] a DC/pulse converter that converts input DC voltage into pulses using a switching element; a rectifier/smoothing unit that rectifies and smoothes the output of the DC/pulse converter to convert it into DC voltage; and a DC/smoother A switching power supply comprising a control unit that generates a drive pulse with a width corresponding to an error voltage obtained by comparing a part of the output of the output with a reference voltage and applies it to the switching element. A temperature compensation system for a switching power supply, characterized in that the period T of the drive pulse is controlled so that the duty ratio of the drive pulse becomes constant in response to temperature changes over time.