JPS60180473A - Self-excited converter type dc power source circuit - Google Patents

Abstract

PURPOSE:To eliminate the necessity of separately providing a current monitor circuit by performing a role of monitoring the current by a switching element switching control circuit when a load shortcircuit occurs at the secondary side of a transformer. CONSTITUTION:When a terminal voltage of a resistor 66 of a switching element switching control circuit 6 rises and arrives at the sum of the voltage between the base and the emitter of a transistor 62, a positive going voltage of a diode 63 and a breakdown voltage of a diode 65, the transistor 62 starts conducting, thereby reducing the potential of the gate of a FET3 toward a negative direction. Thus, the FET3 stops conducting. The polarity of the voltage of the tertiary winding 23 of a transformer is inverted simultaneously upon stopping of conducting of the FET3, a reverse bias is applied to the FET3, thereby continuing the conduction stopping state of the FET3.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a self-excited converter type direct current source circuit. The circuit according to the present invention uses a power supply voltage, for example, 5V, for operating an IC in a power supply circuit using, for example, a -48V in-house power supply in a switchboard or the like.

It is used when obtaining 12V etc.

Technical Background, Prior Art and Problems In general, in switchboards etc., for example, +5■ or +1
A 2V DC power supply is obtained, but this power supply circuit includes an IC, and a power supply is required to operate this IC.

For example, when converting a voltage of -48V to a low-voltage DC voltage using a DC/DC converter, there is a problem that an abnormal current occurs, but as a countermeasure against this abnormal current, conventionally a monitoring circuit has been installed separately. This is used to monitor the current or voltage and prevent the occurrence of abnormal currents.

However, in this conventional type, a monitoring circuit must be provided separately, and power loss occurs in the monitoring circuit, which is not advantageous.

Object of the Invention The object of the present invention is to provide a switching element switching control circuit that controls opening and closing of an FET switching element connected in series to the primary winding of a transformer in a self-excited converter type DC power supply circuit. Based on the idea of providing a current transformer connected in series and a transistor that sets the upper limit value of the secondary current of this current transformer, the switching element opening/closing control circuit itself performs a current monitoring function while performing DC/DC conversion. An object of the present invention is to obtain a self-excited converter type DC power supply circuit which operates properly.

Structure of the Invention The present invention includes a current transformer whose primary winding is connected in series with a power source, a transistor that sets the upper limit value of the secondary current of the current transformer, and an FE whose conduction is stopped when the transistor is conductive.
A T switching element, a transformer primary winding connected in series with the FET switching element to the power supply, and a transformer secondary winding wound in a polarity opposite to the transformer primary winding. A self-excited converter type DC power supply circuit is provided.

Embodiment of the Invention A self-excited converter type DC power supply circuit as an embodiment of the present invention is shown in FIG. The device shown in FIG.
．． Second winding 22. and with a third winding 23, N
Channel type FgT3° resistor 41. Resistance 42. Capacitor 43. Switching element opening/closing control circuit6. Diode 51. Capacitor 52. and output terminals 53 and 54.

The switching element opening/closing control circuit 6 has, for example, a turns ratio of 1:
10 current transformers (current transformers) 61. ) Rangistaro 2
．． Diode 63, 65, 67° and resistor 64.66
has. Third winding 23 of transformer 2. Resistance 42. The circuit consisting of the capacitor 43 and the capacitor 43 operates as a positive feedback drive circuit. In addition, in the transformer and current transformer shown in Figure 1,
May be that those with black dots on the same side are of the same polarity, and those with black dots on opposite sides are of opposite polarity.

The operation of the FIG. 1 apparatus is described below. First, upon startup, a voltage is applied from the power supply 1 to the gate of the FET 3 through the resistor 41, and the FET 3 becomes conductive. FET
3 starts to conduct, a current B611) starts to flow through the primary winding 611 of the current transformer 61, and a current I (612
) begins to flow. This current increases linearly until transistor 62 begins to conduct, and then drops to zero.

Accordingly, the voltage V (66) between the terminals of the resistor 66 also increases linearly and has a decreasing waveform, similar to the current I (611) of the primary winding 611 of the current transformer 61.

A voltage V(3, GS) consisting of a positive rectangular waveform and a negative iR waveform is applied between the gate and source of the FET3. Due to this FET gate-source voltage,
A positive feedback drive is provided through the third winding 23 of the transformer 2.

The voltage V (66) between the terminals of the resistor 66 increases, and the voltage V (62, BE) between the pace emitter of the transistor 62, the forward voltage vF of the diode 63, and the breakdown of the diode 65 becomes the sum of the voltage v2, VS. When the transistor 62 reaches
begins to conduct and pulls down the potential 1 of the gate of FET3 in the negative direction. This causes pFET3 to stop conducting.

At the same time as FET 3 stops conducting, the polarity of the voltage in the third winding 23 of the transformer is reversed, applying a reverse bias to the FET, and
Continue the non-conduction state of T3. Accordingly, the circuit of FIG. 1 operates on the secondary side of the flyback transformer, and during the period when FET 3 is in a non-conducting state, the voltage V(22), 'ili current I(22) is applied to the secondary side of the transformer 2. ).

In this way, the energy stored in the transformer 2 is released to the secondary side of the transformer, but as a result of this energy release, when the voltage of the third winding 23 of the transformer decreases, the energy is released again. The voltage of power supply 1 is applied to the gate of FET 3 through resistor 41, FET 3 starts conducting, and the series of operations described above is performed again.

The voltage or current waveform in each part of the circuit in Figure 1 is
As shown in the figure. In FIG. 2, (1) the voltage V(21) that appears in the first winding 21 of the transformer 2, and (2) the current I(21) that flows in the primary winding 611 of the current transformer 61.
611), (3) Voltage between terminals of resistor 66 V(66), (4), F
ET3 (7) Gate-source voltage V (3, GS), (
5) Current I(22) flowing through the second winding 22 of the transformer 2,
(6) Voltage V(2
2), each waveform of is shown.

The circuit in FIG. 1 performs current detection control using a current transformer 61, and when a load short circuit or the like occurs on the secondary side of the transformer 2, the switching element switching control circuit 6 plays the role of current monitoring. Therefore, no overcurrent flows through the FET 3. Furthermore, the circuit shown in FIG. 1 does not require a separate current monitoring circuit to prevent current abnormalities, as is the case in the past, and the switching element opening/closing control circuit itself performs the current monitoring function.

Effects of the Invention According to the present invention, in a self-excited converter type DC power supply circuit, the current monitoring function by the switching element opening/closing control circuit itself is exhibited, and the DC/DC conversion operation is properly performed.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a self-excited converter type DC power supply circuit as an embodiment of the present invention, and FIG. 2 is a diagram showing voltage or current waveforms at various parts of the circuit shown in FIG. DESCRIPTION OF SYMBOLS 1...DC power supply, 2...Transformer, 21...1st winding, 22...2nd winding, 23...3rd winding, 3...
・FET. 41.42...Resistance, 43...Kanogushita, 51
...Diode, 52... Cano motherboard, 53,5
4... Output terminal, 6... Switching element opening/closing control circuit, 61... Current transformer, 611... Primary winding, 6
12... Secondary winding, 62... Transistor, 63
...Diode, 64...Resistor, 65...Diode, 66...Resistor, 67...Diode.

Claims (1)

[Claims] 2 of the current transformer whose primary winding is connected in series with the power supply
A transistor that sets the upper limit value of the next current; a FET switching element that is stopped from conducting when the transistor is turned on;
A self-exciting converter comprising a transformer primary winding connected in series with the FET switching element to a power source, and a transformer secondary winding wound in a polarity opposite to the transformer primary winding. Type DC power supply circuit.