JPS5879431A - Overcurrent protecting circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to a unilateral 7-word converter having a drive transformer for primary and secondary separation using a constant current source power supply. ◎ Regarding the overcurrent protection circuit to be used (2) Conventional technology and problems One rectangular forward type core with a drive transformer for primary and secondary separation using a conventional constant voltage R source P overcurrent is detected using a transformer, etc., and the conduction width of the secondary switching transistor and eventually the main switching transistor is changed to prevent overcurrent.0 Votes1Figure shows a conventional converter circuit that detects overcurrent using a resistor. Figure 11g2 shows pull 1 of a converter circuit that detects overcurrent using a conventional current transformer.
A diagram is shown.

In the figure, Tt is the main transformer, 7x is the drive transformer, Tr is the main switching transistor, 'J:'r* is the double switching transistor, E is the DC power supply, and is constant 1! fIt
source, 1 expanded sawtooth voltage generator, 2 comparator, 3 expanded output voltage detector, 4 and 5 overcurrent detector, 6! 11 Juji, V
r@f, , Vrefl is standard (pressure, R4 to R8 is resistance m
Dj to Da are diodes, C is a capacitor, L is a coil, and Ta is a current source.

In operation, the output DC voltage is divided by resistors Rs and R+, and the output voltage detector 3 divides the divided voltage and standard voltage V.
refl, and changes the slice level of the sawtooth wave from the sawtooth wave voltage generator 1 in the comparator 2 depending on the magnitude of the output voltage to control the conduction of the switching current of the re-switching transistor Tr. an e-return switching transistor TR, which is controlled so that the output voltage is constant.
The main switching transistor Trt is turned on and off during the same conduction through the drive transformer T by turning on and off of the DC power supply E, and the main switching transistor T
For overcurrent detection, the voltage across the resistor R1 is input to the overcurrent detector 4, The output is input to the comparator 2, and when the output current becomes an overcurrent, the comparator 2 changes the slice level of the sawtooth wave of the sawtooth wave voltage generator 1 and returns switching 2.
During the conduction of the switching current of the transistor Try,
The conduction period of the switching current of the main switching transistor Tr1 is narrowed through the drive transformer T to prevent overcurrent. However, in this case, there is a drawback that it is not possible to protect against an overcurrent inside the resistor R6 due to damage to the layer structure of the winding of the main transformer T, short circuit of the diode D#, etc.

In Figure 2, the main transformer T+ is shown in the current transformer Ts.
The current flowing through K is detected, and the rectifier circuit 6 converts it into a DC voltage. The overcurrent detector 5 amplifies the differential pressure between the standard voltage Vref and adds it to the comparator 2. When an overcurrent occurs, it is compared! ! At iF2, the slice level of the sawtooth wave of the sawtooth voltage generator 1 is changed to narrow the conduction period of the switching current of the switching transistor Tr8, and the switching current of the main switching transistor Tr is passed through the drive transformer T. The conduction area is narrowed to prevent overcurrent. However, in this case, there is a drawback that the p-device which requires a current source T is large and expensive.

(3) Purpose of the Invention The purpose of the present invention is to eliminate the above-mentioned drawbacks by providing a small and inexpensive converter equipped with an overcurrent protection circuit that can prevent overcurrent caused by short circuits of internal S components. .

(4) Structure of the Invention In order to achieve the above object, the present invention provides an emitter circuit of a main switching transistor in a unilateral forward converter having a driving transformer for primary and secondary separation using a constant current source power source. A resistor is inserted into the drive transformer, a winding is added to the core winding, the voltage induced in the core winding is rectified into a DC voltage, and the main switching transistor is turned on and off via the drive transformer. Transistors are connected in parallel, and the above DC voltage controls the DC current flowing through the two transistors to the mosquito drive transformer.If an overcurrent occurs, the DC current saturates the drive transformer. It is characterized by narrowing the conduction period of the switching current of the main switching transistor to prevent overcurrent.

(5) Embodiment of the Invention Below, one embodiment of the present invention will be explained according to the drawings. B-H curve showing the relationship, Figure 5. Drive transformer T! ′ is saturated,
These are the operating characteristics in the case of non-saturation.

Components with the same functions as those in Figure 1 are indicated by the same symbols. OT, / is a drive transformer, TrS is a transistor, D is a diode, C1 is a capacitor, R, , Rs are resistors, N
a, Na -Na is the winding of the drive transformer T, VN
, , VNlVy, u volume 11iNx l N, -N
The difference from FIG. 1 in this circuit showing the voltage across both ends of s is that a resistor R1 is connected to the emitter of the main switching transistor TrI.
The point provided with and the driving force T! 'Ic winding N, is added and the diode D-capacitor rectifies this voltage and converts it to DC? C, is provided, and this voltage is divided by resistors R @ and R, and DC is applied to the winding N1 of the drive transformer T and / through the newly installed transistor TrllC and the transistor Tr■, and in case of overcurrent, the drive transformer T ! ′ becomes saturated.

Therefore, the general operation is the same as that described in Section 1 and FIG. 2. As the output commutation increases, the voltage drop across the resistor R1 increases.Since the current connected to the winding Nl of the constant current source El and the drive transformer T is a constant current, the voltage across the winding N increases. vN increases, and therefore the voltage vN across the winding Nl increases.This causes the transistor T
The DC voltage applied to the base of r increases, and the collector current increases. This collector current is the drive transformer T, /
Direct current is flowing through the winding Nl. This DC current is B-H in ^4 diagram! If it is a straight line part of the shrine, DC・rL#L is 1
Although the change in magnetic flux density is in the range of /a for the magnetic field λ in Fig. 5 p, which is unexpected, as the collector current of the transistor r increases, The saturation point of the B-H curve as shown in Figure 4A of the imperial order is reached. In this case, as shown in Fig. 5, the magnetic flux density>return switching transistor T
During the conduction of the switching current of the main switching transistor Tr, a narrow overcurrent is prevented.In this case, the voltage across the line resistance R1 Since the overcurrent is detected by the main transformer T, it is also possible to protect against internal overcurrent caused by the layer seat of the winding of the main transformer T, short circuit of the diode D1, etc. Also, the winding N1
is the drive transformer fil, / is wound around the Atamata diode D
, the resistor R., and the R1 transistor Trs are also small and inexpensive, so that the overcurrent protection circuit can be constructed small and inexpensively.

(6) Effects of the Invention As described above in detail, the present invention has the advantage of being able to prevent overcurrents due to short circuits in internal components and realizing a tJh type converter having an inexpensive overcurrent protection circuit.

[Brief explanation of drawings]

Figure 1 is a block diagram of a conventional converter circuit that detects overcurrent using a resistor, Figure 2 is a block diagram of a conventional converter circuit that detects overcurrent using a current transformer, and Figure 3 is an embodiment of the present invention. Figure 4 is a block diagram of a converter with an overcurrent protection circuit, and Figure 4 shows the relationship between magnetic field and magnetic flux density.
-) (Curve, Figure 5 shows the operating characteristics when the drive transformer T, / is saturated and non-infantile. In the figure, T is the main transformer, T, , T,' are the drive transformer, and Trl is the main switch. Trl is a switching transistor, Trm is a transistor, E
is a direct N, power supply, E is a constant current source, 1 is a sawtooth voltage generator, 2 is a comparator, 3 is an output voltage detector, 4.5 is an overcurrent detector, 6 is a rectifier circuit, vrCfI, Vref is the standard voltage, Rs''-Ryu resistance, D, ~D. is the diode sc+c1 is the capacitor, L is the coil, T
1 is a current transformer. P1 figure 72 figure Pzu figure 1!

Claims (1)

[Claims] In a one-sided forward type Humbatterer with a drive transformer for primary and secondary separation using a constant current source power supply, a resistor is inserted in the main switching transistor circuit and a winding is added to the drive transformer. A transistor is connected in parallel to a switching transistor which rectifies the voltage induced by the core 5illK into a DC voltage and turns the main switching transistor on and off via the drive transformer, and the DC voltage causes the transistor to turn on and off. An overcurrent protection circuit characterized in that it controls a direct current flowing through a cough drive transformer Kfi.