JPS5914823Y2 - voltage converter - Google Patents

Description

[Detailed explanation of the idea] As a voltage converter, there is one shown in FIG.

In the figure, reference numeral 1 designates a first power supply circuit, in which a capacitor 4 is connected to a DC power supply 2 via a diode 3, and the negative side of the power supply 2 is grounded.

5 is a second power supply circuit, which is configured such that a capacitor 8 is connected to a DC power supply 6 via a diode 7, and the positive side of the power supply 6 is grounded.

Power supplies 2 and 6 have the same voltage value Eo.

9 is a low-pass filter, which includes a coil 10 and a capacitor 11.
Consisting of

A transistor 12 is connected between the first power supply circuit 1 and the low-pass filter 9, and a transistor 13 is connected between the second power supply circuit 5 and the low-pass filter 9.

Transistors 12 and 13 constitute a switch circuit.

Further, a diode 14 is connected between the power supply circuit 1 and the low-pass filter 9, and a diode 14 is connected between the power supply circuit 5 and the low-pass filter 9.
A diode 15 is connected between the two.

16 is an output end. Transistors 12 and 13 are driven by the rectangular wave signal, and in the period of "0", transistor 12 is on and transistor 13 is off, and the "1"
'', the drive is controlled so that the transistor 12 is turned off and the transistor 13 is turned on, whereby a converted DC voltage is obtained at the output terminal 16.

The duty ratio of the rectangular wave signal is controlled in accordance with this output DC voltage, thereby stabilizing the output DC voltage.

However, in this conventional device, if the duty ratio of the rectangular wave signal that drives the switch circuit continues to be large or small for a certain period of time, there is a risk that the transistors 12 and 13 forming the switch circuit will be destroyed.

Looking at the output short-circuit current, Figures 2 and 3
As shown on the left side of the figure, the duty ratio of the rectangular wave signal SA is
When the ratio is negative, a current of 11 is applied to the coil 1.0 from the power supply circuit 1 through the transistor 12 in the "0" section.
flows, and in the section of "1", first, the current 11 causes the coil 1 to
Due to the energy stored at 0, a current i2 flows from the power supply circuit 5 to the coil 10 through the diode 15, and then a current i3 flows from the coil 10 to the power supply circuit 5 through the transistor 3, and in the next "0" section, the current i
3, the energy stored in the coil 10 causes a current i4 to flow from the coil 10 to the power supply circuit 1 through the diode 14, and then a current 11 flows from the power supply circuit 1 to the coil 10 through the transistor 2, and this state is repeated.

The currents 11 and i4 are such that the former reduces the polarity voltage of the capacitor 4 in the power supply circuit 1, whereas the latter increases this voltage, so the terminal voltage of the capacitor 4 EA does not change, and the voltage value E of power supply 2.

can be suppressed to

The same applies to the currents i3 and 12, and the terminal voltage EB of the capacitor 8 does not change and is suppressed to the voltage value Eo of the power supply 6.

However, as shown on the right side of FIG.
When the duty ratio of A becomes smaller than a certain time, the value of current 11 increases, so only this current 11 and current 12 based on this current 11 flow, and in the power supply circuit 5, the diagram of capacitor 8 The current i3 in the direction of decreasing the polarity voltage no longer flows.

Therefore, the terminal voltage EB of the capacitor 8 increases.

Conversely, as shown on the right side of FIG. 3, when the duty ratio of the rectangular wave signal SA becomes larger than a certain time ±, the value of current i3 becomes high, so that this current i3 and the current based on this current i3 Only i4 now flows, and current 11 in the direction of reducing the voltage of the polarity of capacitor 4 in the figure no longer flows in power supply circuit 1.

Therefore, the terminal voltage EA of the capacitor 4 increases.

In this way, when the tenity ratio of the square wave signal SA continues to be large or small for a certain period of time, the voltage of the first or second power supply circuit 1 or 5, that is, the terminal voltage EA or EB of the capacitor 4 or 8 increases. becomes significantly large, and a voltage exceeding the maximum collector voltage Vc8 or the maximum emitter voltage vEB is applied to the transistors 2 to 13 constituting the switch circuit, which may destroy these transistors 2 to 13.

This invention eliminates these drawbacks.

In this invention, the diodes 14 and 15 are not connected between the power supply circuits 1 and 5 and the coil 10 of the low-pass filter 9 as in the conventional device shown in FIG. Another coil 17 is transformer-coupled to the coil 10 of the filter 9, a first diode 18 is connected between the first power supply circuit 1 and the coil 17, and the connection between the second power supply circuit 5 and the coil 17 is A second diode 19 is connected between them.

Here, the polarity of the coupling between the coils 10 and 17 and the polarity of the diodes 18 and 19 are determined by the energy stored in the coil 10 due to the current 11 flowing from the power supply circuit 1 to the coil 10 through the transistor 12. Current 1/2 flows in the same power supply circuit 1, and energy stored in the coil 10 due to the current i3 flowing from the coil 10 to the power supply circuit 5 through the transistor 13 causes a current 1 to flow from the same power supply circuit 5 to the coil 17 through the diode 19. Make the polarity such that /4 flows.

In this way, since the coils 10 and 17 have a transformer coupling configuration with opposite polarities, the capacitor 4 of the power supply circuit 1
When the current 11 flows in the direction of decreasing the voltage with the polarity shown in the figure, 1/2 of the current flows in the direction of increasing this voltage, and the current i3 in the direction of decreasing the voltage of the polarity shown in the figure of the capacitor 8 of the power supply circuit 5 flows. Flowing, 1/4 of the current flows in the direction of increasing this voltage, so the terminal voltages EA and EB of capacitors 4 and 8 match the tenacity ratio of the rectangular wave signal that drives the switch circuit. Regardless, it is always held constant and suppressed to the voltage value Eo of the power supplies 2 and 6.

Therefore, even if the rectangular wave signal has a high or low duty ratio for a certain period of time, there is no risk of the transistors 12 and 13 constituting the switch circuit being destroyed.

FIG. 5 shows a specific example of this invention, in which the base of the transistor 12 and the collector of the transistor 13 are connected, and the coil 10 of the low-pass filter 9 and the transistor 1
A diode 29 is connected between the collectors of the switching transistors 12 and 13, and overcurrent protection circuits 21 and 25 are provided for the switching transistors 12 and 13, respectively.

The overcurrent protection circuits 21.25 each include an overcurrent detection resistor 22.26 and a protection transistor 23.2.
It consists of 4.27.28.

Note that a rectangular wave signal generation source 30 is connected to the base side of the transistor 13.

In the “0” section of the rectangular wave signal SA, the transistor 13
is turned off, and therefore transistor 12 is turned on, allowing current 11 to flow through transistor 12. Conversely, in the period of "1" of signal SA, transistor 13 is turned on, and therefore transistor 12 is turned off. As a result, current i3 begins to flow through diode 29 and transistor 13.

Then, as shown on the right side of FIG. 2, the duty ratio of the square wave signal SA becomes smaller and the current 11 becomes larger. When this reaches a certain constant value o, the transistor 1
In the protection circuit 21 on the 2 side, transistors 24 and 2
3 is turned on, the base and emitter of the transistor 12 are short-circuited, and the transistor 12 is turned off.

Since the transistors 24 and 23 form a positive feedback loop, the on state of the transistors 24 and 23 is maintained until the next time the signal SA becomes "1" and the transistor 13 is turned on.

Therefore, the current 11 is a constant value I. will not exceed.

As shown on the right side of FIG. 3, the tenacity ratio of the rectangular wave signal SA increases, and the current i3 becomes thicker, and reaches a certain constant value I.

When the voltage reaches , the protection circuit 25 on the transistor 13 side operates in the same manner as described above.

Therefore, the current i3 is also a constant value I. will not exceed.

In this way, when an overcurrent is detected, the protection circuit 21.2
5, the transistors 12.13 are immediately cut off and do not operate in the active region, so that the safe operation area of the transistors 12.13 can be widened.

[Brief explanation of drawings]

Fig. 1 is a connection diagram of the conventional device, Figs. 2 and 3 are waveform diagrams for explaining the same, Fig. 4 is a connection diagram of the device according to this invention, and Fig. 5 is a specific example of the device according to this invention. FIG. 1 and 5 are first and second power supply circuits, 9 is a low-pass filter, 10 is its coil, 12 and 13 are switching transistors, 17 is another coil, 1ε and 19 are first and second diodes. , 16 is an output end.

Claims (1)

[Scope of utility model registration request] a first power supply circuit that provides a positive DC voltage with respect to the reference potential point; a second power supply circuit that provides a negative DC voltage with respect to the reference potential point; a first capacitor connected via a diode, a second capacitor connected to the second power supply circuit via a second diode, and a low-pass filter including a coil and a third capacitor; A first switching element connected between the first diode and the low-pass filter, a second switching element connected between the second diode and the low-pass filter, and the coil of the low-pass filter. a third diode connected between the first diode and the other coil;
a fourth diode connected between the second diode and the another coil, the first and second switching elements are controlled so that when one is on, the other is off; A voltage conversion device designed to