JPH01318544A - Dc-dc converter - Google Patents

Abstract

PURPOSE:To prevent a transformer against saturation by reducing the duty of a driving pulse of a switching transistor in starting the power supply and by extending the OFF-time for switching. CONSTITUTION:A DC/DC converter is composed of a DC power source 10, a transformer 20, a switching transistor(Tr) 30 and a DC smoothing circuit 40 to feed the current to a load 50. An overcurrent monitoring circuit 70 inputs the output of a current transformer 21 provided to the primary winding Np of the transformer 20 and monitors the current. In putting the power supply to work, when the overcurrent is detected, a pulse width control is performed in synchronization with the output clock of a PG 63 with a control circuit 60. On the other hand, until the overcurrent is detected by the overcurrent monitoring circuit 70, H-level signals are outputted, which are then inputted into an FF85. A clock output through 1/2 frequency demultiplying circuit 80 is also inputted and the pulses of reduced duty is outputted from an AND circuit 90. The output of this AND circuit 90 is added to the Tr 30, so that constant output voltage is supplied to the load 50.

Description

[Detailed Description of the Invention] [Summary] Regarding DC/DC converters used in various devices, it is an object of the present invention to provide a DC/DC converter that prevents saturation of the transformer at the time of power supply startup and enables miniaturization of the transformer. A transformer with a primary winding and a secondary winding, in which one end of the primary winding and the other end of the primary winding are connected to a DC power supply via a switch circuit, and a transformer with a secondary winding of the transformer. connected to both ends of the winding,
It has a rectifier and smoothing circuit that rectifies and smoothes the input signal, and a pulse generator that outputs a clock pulse with a predetermined pulse width and duty.The switch circuit is controlled on/off depending on the output state of the rectifier and smoother. In a DC/DCC/type transformer equipped with a control circuit that outputs a control signal to , overcurrent monitoring means that inputs the current transformer output and monitors the current flowing through the primary/secondary windings, and a clock pulse of the output of the pulse generator in the control circuit that is connected to the overcurrent monitoring means and is in the control circuit when the power supply is started. launch means that divides the frequency to a predetermined frequency and outputs a predetermined value when an overcurrent is detected in the overcurrent monitoring means; and a launch means that is connected to the outputs of the control circuit and the latch means, is input, and a gate means for calculating the logical product of the two and outputting the result.

[Industrial application field]

The present invention relates to improvements in DC/DCC/type controllers used in various devices.

At this time, there is a demand for a DC/DCC/type converter that prevents the saturation of the transformer during power-up and allows the transformer to be made smaller.

[Conventional technology]

FIG. 4 is a block diagram of a circuit configuration of a conventional example.

In FIG. 4, if the voltage across the load 5 is Eo, then
The voltage at the midpoint f of the resistor R is Eo/2. This voltage is applied to one input terminal of a known operational amplifier (hereinafter referred to as an operational amplifier) 6-1 in the control circuit 6. A reference voltage Vref set to 172, which is the voltage value to be output to the load 5, is applied to the other input terminal, and the voltage difference between Eo/2 and Vref is determined. This is a voltage/pulse width conversion circuit (hereinafter referred to as PW).
In addition to one input terminal of an operational amplifier 6-2 (hereinafter referred to as PG), an output pulse of a pulse generator (hereinafter referred to as PG) 6-3 with a constant pulse width and duty is applied to the other input terminal of the operational amplifier 6-2. The pulse width is changed according to the output voltage of 1, and the output pulse is applied to the base of the switching transistor (hereinafter referred to as Sw Tr) 30. For example, when the output voltage of the load 5 is larger than the desired value, the pulse width of the output pulse is controlled to be smaller in the PWH, and when the output voltage of the load 5 is smaller than the desired value, the pulse width is controlled to be increased. do.

In this way, a constant output voltage was supplied to the load.

[Problem to be solved by the invention]

However, in the above circuit, since the output voltage supplied to the load is small when the power supply is started, the pulse width of the pulse applied to the base of the 5sTr is wide (the width of the pulse applied to the primary winding Np and the secondary winding of the transformer 2 is large). An overcurrent may flow through the line Ns, saturating the transformer, and damaging parts such as the Sw Tr.

In order to avoid this, the transformer must be made larger, but this poses the problem of hindering the miniaturization of the power supply.

Therefore, it is an object of the present invention to provide a DC/DCC system that prevents the saturation of the transformer at the time of power supply startup and enables the miniaturization of the transformer.
/Equation-ta.

[Failure to solve the problem]

The above problem is solved by the circuit configuration shown in FIG.

That is, in FIG. 1, it has a primary winding Np and a secondary winding Ns, and one end of the primary winding and the other end of the primary winding are connected to a DC power supply 100 via a switch circuit 300. It has a transformer 200, a rectifier and smoothing circuit 400 connected to both ends of the secondary winding of the transformer, which rectifies and smoothes an input signal, and a pulse generator which outputs a clock pulse having a predetermined pulse width and duty. , and a control circuit 600 that outputs a control signal to turn on/off the switch circuit depending on the output state of the rectifier and smoothing circuit, and 210 is the primary/secondary winding of the transformer. This is a current transformer that is installed in the primary and secondary windings and amplifies the current flowing through the primary and secondary windings.

Reference numeral 700 denotes overcurrent monitoring means for inputting the current transformer output and monitoring the current flowing through the primary/secondary windings.

800 is connected to the overcurrent monitoring means, and when the power supply is started, the clock pulse of the output of the pulse generator in the control circuit is divided into a predetermined frequency and outputted, and when the overcurrent monitoring means detects an overcurrent, the clock pulse is outputted at a predetermined frequency. This is a latch means that outputs.

Gate means 900 is connected to the outputs of the control circuit and the launch means, inputs the outputs of the control circuit and the latch means, calculates the logical product of both, and outputs the result. 210.700 above
, 800 and 900 are added.

[For production]

In FIG. 1, a current transformer 210 causes a transformer 2 to
Pick up the current flowing through the primary/secondary windings of 00. The overcurrent monitoring means 700 receives the current transformer output and monitors the current flowing through the primary/secondary windings of the transformer.

The launch means 800 divides the clock pulse output from the pulse generator in the control circuit into a predetermined frequency and outputs the divided clock pulse when the power is started. Further, when the overcurrent monitoring means detects an overcurrent, the launch means 800 outputs a predetermined value. Then, the gate means 900 inputs the outputs of the control circuit and the launch means, calculates the logical product of both, and outputs the result.

As a result, the launch means 800 outputs a frequency-divided clock pulse from the time the power is turned on until the overcurrent is detected, and this clock pulse is output from the gate means 900. This also prevents saturation of the transformer when the power is turned on.

〔Example〕

FIG. 2 is a circuit configuration block diagram of an embodiment of the present invention.

FIG. 3 is a time chart explaining the operation of the embodiment.

The same reference numerals indicate the same objects throughout the figures.

In FIG. 2, an overcurrent monitoring circuit 70 inputs the output of a current transformer 21 provided in the primary winding of a transformer 20, and
Monitor the current flowing through the primary winding. In the normal case where no overcurrent is detected, an "H" level signal is output, and when an overcurrent is detected, an "L" level signal is output.

Now, if we consider the case when the power is turned on, the current flowing through the primary winding Np gradually increases as shown in Figure 3 (■).
The overcurrent is detected when the detection level is reached. Then, the control circuit 60 performs pulse width control in synchronization with the output clock of the PG 63, but since the output voltage supplied to the load is small until it reaches the detection level, the maximum allowable pulse width is Outputs a voltage of width.

On the other hand, until an overcurrent is detected in the overcurrent monitoring circuit 70, an "H" level signal is output as shown in FIG.

On the other hand, an output obtained by dividing the output clock of the PG 63 by 172 in a known 172 frequency divider circuit 80 composed of FFs (not shown) is applied to the D input terminal of the FF 85. and F
When the F85 receives an "H" level signal, it directly outputs the 172-divided clock output from the 172-divided circuit 80 from the C terminal.

The outputs of the above FF 85 and the control circuit 60 are combined into an AND circuit 90.
By adding this to , the AND circuit 90 outputs a pulse with a reduced duty as shown in FIG.

Next, when the overcurrent monitoring circuit 70 detects an overcurrent, the third
The control circuit 60 outputs the “L” level signal shown in Fig.
Add to the C terminal of PWM62 and FF85 inside. As a result, the control circuit 60 reduces the pulse width of the output pulse as shown in FIG. 3, as in the conventional example. Also, F
In the F85, when an "L" level is applied to the C terminal, the Q output maintains the "H" level as shown in FIG.

By adding these outputs to the AND circuit 90, the AN
From the D circuit 90, an output voltage with a small pulse width as shown in FIG. 3 is obtained. The output of this AND circuit 90 is
w A constant output voltage is supplied to the load 50 in addition to the base of the Tr 30.

In this way, when the power is turned on, the duty of the drive pulse of the Sw Tr is reduced to lengthen the switching off time, thereby preventing saturation of the transformer.

〔Effect of the invention〕

As described above, according to the present invention, saturation of the transformer at startup can be prevented and the size of the transformer can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a principle diagram of the present invention, Fig. 2 is a circuit configuration block diagram of an embodiment of the present invention, Fig. 3 is a time chart explaining the operation of the embodiment, and Fig. 4 is a circuit configuration block diagram of a conventional example. It is. In the figure, 210 is a current transformer, 700 is overcurrent monitoring means, and 80 is
0 indicates a latch means, and 900 indicates a gate means. life? Look up↑ Goemi (Shinaga)

Claims (1)

[Claims] It has a primary winding (Np) and a secondary winding (Ns), one end of the primary winding, and the other end of the primary winding via a switch circuit (300). a transformer (200) connected to a DC power supply (100), and a rectifier and smoothing circuit (400) connected to both ends of the secondary winding of the transformer to rectify and smooth the input signal.
) and a control circuit ( 600) and D
In a C/DC converter, a current transformer (21
0), overcurrent monitoring means (700) for inputting the output of the current transformer and monitoring the current flowing through the primary/secondary windings; a latch means (800) that divides the clock pulse of the output of the pulse generator within the circuit to a predetermined frequency and outputs the divided clock pulse, and outputs a predetermined value when an overcurrent is detected in the overcurrent monitoring means; A DC/DC converter further comprising gate means (900) connected to the output of the latch means, inputting the outputs of the control circuit and the latch means, calculating the logical product of both, and outputting the result.