JP3081478B2 - Low voltage lighting circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a self-excited oscillation type low voltage lighting circuit, and more particularly to a low voltage lighting circuit capable of reliably protecting circuit components when a load is short-circuited.

[0002]

2. Description of the Related Art FIG. 2 is a circuit diagram of a main part of a self-oscillation type low voltage lighting circuit which has been frequently used. In the figure, R, R4 and R5 are resistors, respectively, T11 is an oscillating transformer whose primary winding is L1 and whose primary windings are L2 and L3,
Reference numeral 12 denotes an output transformer whose primary winding is L5 and whose secondary winding is L6. Q1 and Q2 are oscillation transistors, respectively.
3 and Q6 are trigger elements, respectively, and Q5 is a thyristor.

A transistor Q1 and a resistor R5 and a transistor Q2 and a resistor R are connected between power supply terminals + and-.
Are connected. One terminal of the primary winding L1 of the oscillation transformer T11 is connected to a connection point D between the resistor R5 and the transistor Q2, and the other terminal is connected to the output transformer T12.
Of the primary winding L5. Further, one terminal of the secondary winding L2 of the oscillation transformer T11 is connected to the base of the transistor Q2, and the other terminal is connected to the ground G. One terminal of the secondary winding L3 is connected to the base of the transistor Q1, and the other terminal is connected to the connection point D. A series circuit of a resistor R4 and a trigger element Q6 is connected to the base of the transistor Q2. Thus, a self-excited oscillation type low voltage lighting circuit is formed.

On the other hand, between the base of the transistor Q2 and the ground G, an anode is used as a base and a cathode is used as a ground G.
Is connected to the thyristor Q5, and the thyristor Q5
Is connected to the other terminal of the trigger element Q3 having one terminal connected to the connection point between the emitter of the transistor Q2 and the resistor R. Note that the trigger element Q3 and the thyristor Q5 form protection means in the event of a short circuit on the load side. When an abnormality such as a filament short circuit occurs in the lamp L of the load connected to the secondary winding L6 of the output transformer T12, this protection means protects each circuit component from destruction due to overvoltage or overcurrent. To work.

That is, the current flowing through the transistor Q2 is equal to the overcurrent detection resistor R connected in series with the transistor Q2.
And is applied to the trigger element Q3. Then, when an abnormality such as a load-side short circuit occurs, the current flowing through the transistor Q2 increases compared to the normal state on the load side, so that the voltage across the resistor R exceeds a predetermined voltage value.
Then, the trigger element Q3 operates to generate a pulse signal. When the pulse signal of the trigger element Q3 is applied to the gate of the thyristor Q5, the thyristor Q5 is turned on, and the base potential of the transistor Q2 is forcibly set to be lower than the emitter potential. As a result, the transistors Q2 and Q1 stop oscillating, so that no overvoltage or overcurrent is applied to each circuit component, and the circuit component is protected from destruction.

The secondary winding L2 of the oscillation transformer T11
The winding direction and the number of turns of L3 and L3 are set in advance so as to be a base potential that disables transistor Q2 when the load is short-circuited.

[0007]

As described above, in the conventional circuit, in the event of an abnormality on the load side, the two active elements, the trigger element Q3 and the thyristor Q5, are operated to function so that the oscillation transistor Q2 is turned off. Means protected circuit components. However, in the protection means configured as described above, the resistor R for overcurrent detection itself has a variation in resistance value, so that the oscillation waveform is likely to be distorted. In order to ensure that the protection means functions when the load side is abnormal, it is necessary to increase the constant of the resistor R. However, since the main current also flows through the resistor R, increasing the constant of the resistor R There was a problem that heat loss at R became large. For this reason, it is necessary to select the resistance value of the resistor R to a balanced value, but the operation for this is extremely complicated.

An object of the present invention is to provide a low-voltage lighting circuit which solves the above-mentioned difficulties and provides a highly reliable protection means with simple means.

[0009]

A self-excited oscillation type low voltage lighting circuit which converts a commercial power supply supplied by turning on a power switch SW to a high frequency power supply and supplies the high frequency power to a load L.
An oscillation transformer T11 provided with a secondary winding L1 and secondary windings L2, L3, L4, and an output transformer T12 provided with a secondary winding L6 connecting the primary winding L5 and the load L;
Capacitor C2 between output terminals + and-of full-wave rectifier DB
A series circuit of C3, a series circuit of resistors R1, R2 and R3,
A series circuit including an oscillating transistor Q1 and a resistor R5 and an oscillating transistor Q2 and a resistor R6;
1 and D2, and a capacitor C4 is connected in parallel with the resistor R3.
2, C3 connection point and resistor R1, R2 connection point B
To the terminal H of the primary winding L5 of the oscillation transformer T12, the connection point C of the diodes D1 and D2 and the resistor R5
The connection point D of the transistor Q2 is connected to the terminal E of the primary winding L1 and the terminal J of the secondary winding L3 of the oscillation transformer T11, and the terminal R of the secondary winding L3 is connected to the base of the transistor Q1. The terminal P of the winding L2 is connected to the base of the transistor Q2, the terminal O of the secondary winding L2 and the terminal N of the secondary winding L4 are respectively connected to the ground G, and a resistor is connected between the terminal T2 and the gate. The terminal T1 of the bidirectional thyristor Q4 connected to R7 is connected to the base of the transistor Q2, the terminal T2 is connected to the terminal M of the secondary winding L4, and the series circuit of the resistor R4 and the trigger element Q3 is connected to the resistor 3 and the capacitor C4. Of the oscillation transformer T11 when the load side is short-circuited.
The thyristor Q4 is turned on by the voltage induced between the next windings L4 and L2 to stop the transistors Q1 and Q2 from oscillating and to charge the capacitor C3 with the resistors R2 and R4.
Is applied to the trigger element Q3 via the trigger element Q3.
Is turned on, and the transistor Q2 is kept in the oscillation stop state.

[0010]

When the load is short-circuited, a large induced voltage generated between the secondary windings L2 and L4 causes the bidirectional thyristor Q4 of the switching element to conduct, and the base potential of the oscillation transistor Q2 is forcibly set to be lower than the emitter potential. As a result, the oscillation transistors Q2 and Q1 enter an oscillation stop state. Further, by setting the base potential of the transistor Q2 low, the trigger element Q3 becomes conductive without generating a trigger signal even if a high charging voltage charged in the capacitor C3 is supplied to the trigger element Q3.
The oscillation stop state of the transistor Q2 is maintained.

On the other hand, when the power switch SW is turned on again after removing the abnormal state, the small charging voltage charged in the capacitor C4 is applied to the trigger element Q3 via the resistor R4.
And the trigger element Q3 generates a trigger signal. Here, the transistor Q2 to which the trigger signal generated by the trigger element Q3 has been applied to the base is again oscillated.

[0012]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing an embodiment of the present invention. In the figure, a series circuit of capacitors C2 and C3, a series circuit of resistors R1, R2 and R3, and an oscillation transistor Q are provided between output terminals + and-of a full-wave rectifier DB.
1 and a resistor R5, and an oscillation transistor Q2 and a resistor R
6 and a series circuit of diodes D1 and D2 are connected in parallel. Diodes D1, D
2 is connected to a connection point D of a resistor R5 and an oscillation transistor Q2, and a capacitor C4 is connected to the resistor R3 in parallel. A connection point A between the capacitors C2 and C3 and a connection point B between the resistors R1 and R2 are connected. The diodes D1 and D2 are protection elements for the oscillation transistors Q1 and Q2, respectively.

T11 and T12 are an oscillation transformer and an output transformer, respectively, and the primary winding L of the output transformer T12.
The terminal H of No. 5 is connected to the connection point B, and the load L is connected in series to the secondary winding L6. Also, the oscillation transformer T1
The terminal E of the primary winding L1 is connected to the connection point D, and the terminal F is connected to the terminal I of the primary winding L5 of the output transformer T12.

On the other hand, the secondary winding L is connected to the oscillation transformer T11.
2, L3, L4, the terminal P of the secondary winding L2 is at the base of the transistor Q2, and the terminal O is at the ground G.
Connected to each other. The terminal N of the secondary winding L4 is connected to the ground G, and the terminal M is connected to the terminal T2 of the bidirectional thyristor Q4.
The resistor R7 is connected between the gates, and the terminal T1 of the thyristor Q4 is connected to the base of the transistor Q2. The terminal R of the secondary winding L3 is connected to the base of the transistor Q1, and the terminal J is connected to the connection point D. Further, a series circuit of the resistor R4 and the trigger element Q3 is connected between a connection point Q between the resistor R3 and the capacitor C4 and the base of the transistor Q2.

The secondary winding L of the oscillation transformer T11
2, the number of turns and the winding direction of L4 are set in advance so that the induced voltage at the time of load-side short circuit becomes a gate voltage for making the bidirectional thyristor Q4 conductive. The black circles indicate the winding start sides of the secondary windings L2 and L4.

In the low voltage lighting circuit thus configured, when the power switch SW is turned on, the commercial power AC supplied from the outside is supplied to the full-wave rectifier via the filter circuit including the capacitor C1 and the choke coil CH1. Provided to DB. Then, DC power is supplied to the load side. If an abnormality such as a short circuit occurs on the load side, the oscillation of the transistor Q2 is controlled by the bidirectional thyristor Q4 constituting the protection means of the present invention which will be specifically described below. The protection means functions to stop the operation, and no overvoltage or overcurrent is applied to each circuit component, and each element is protected from destruction.

That is, when the load side is short-circuited, the output transformer T
Since a large current flows through the twelve primary windings L5, a large current also flows through the primary winding L1 of the oscillation transformer T11. As a result, each secondary winding L of the oscillation transformer T11
A large voltage is induced in each of L2, L3 and L4.
Here, the voltage induced between the secondary windings L4 and L2 is applied to the gate of the thyristor Q4.
When the voltage value between the two exceeds a predetermined value, the thyristor Q4 conducts, and the base potential of the transistor Q2 is forcibly set to the inoperable potential of the transistor Q2. As a result, the oscillation transistor Q2 stops oscillating.

When the oscillation of the transistor Q2 stops, the electric charge charged in the capacitor C3 is discharged while being applied to the trigger element Q3 via the resistors R2 and R4. However, since the charging voltage of the capacitor C3 is set to be large in advance, the trigger element Q3 becomes conductive without outputting a trigger signal. Therefore,
A trigger signal necessary for oscillating the transistor Q2 is not generated from the trigger element Q3.
2 holds the oscillation stop state.

On the other hand, to make the transistor Q2 oscillate again, simply removing the cause of the abnormality on the load side and then turning on the power switch SW again can be easily performed. In this case, since the charging voltage of the capacitor C4 set to be small in advance is applied to the trigger element Q3 via the resistor R4, the trigger element Q3 outputs a trigger signal to make the transistor Q2 oscillate again. .

[0020]

According to the present invention, even when an abnormality such as a short circuit occurs on the load side, the oscillation of the oscillation transistor can be reliably stopped by simple means, and the oscillation stop state can be maintained. Thus, it is possible to easily return to the oscillation state simply by removing the cause of the abnormality. As a result, circuit components can be protected from destruction due to overvoltage or overcurrent, and a low-voltage lighting circuit with excellent reliability can be obtained. Further, complicated operations such as selection of the constant of the resistor are not required, and an inexpensive low-voltage lighting circuit can be obtained. The practical effect is great.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention.

FIG. 2 is a circuit diagram showing a conventional example.

[Explanation of symbols]

L Load SW Power switch C1, C2, C3, C4 Capacitor CH1 Choke coil D1, D2 Diode R, R1, R2, R3, R4, R5, R6, R7 Resistor Q1, Q2 Oscillation transistor Q3, Q6 Trigger element Q4 Bidirectional Thyristor Q5 Thyristor T11 Oscillation transformer T12 Output transformer L1, L5 Primary winding L2, L3, L4, L6 Secondary winding DB Full-wave rectifier circuit +,-Output terminal of full-wave rectifier circuit A, B, C, D, Q Connection point G Ground H, I Primary winding terminal of output transformer E, F Primary winding terminal of oscillation transformer J, M, N, O, P, R Secondary winding terminal of oscillation transformer

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-97279 (JP, A) JP-A-62-163293 (JP, A) JP-A-5-184160 (JP, A) 128400 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) H05B 41/24 H02M 7/48 H02M 7/5383 H05B 41/232 H05B 41/282

Claims (1)

(57) [Claims] A self-oscillation type low voltage lighting circuit for converting a commercial power supply supplied by turning on a power switch to a high frequency power supply and supplying the high frequency power to a load.
Oscillation transformer T11 provided with secondary windings L2, L3, L4
And an output transformer T12 provided with a secondary winding L6 connecting the primary winding L5 and the load L.
A series circuit of capacitors C2 and C3, a series circuit of resistors R1, R2 and R3, a series circuit of an oscillating transistor Q1 and a resistor R5, and a series circuit of an oscillating transistor Q2 and a resistor R6, a diode D1 , D2, a capacitor C4 is connected in parallel with the resistor R3, and a connection point A between the capacitors C2 and C3 and a connection point B between the resistors R1 and R2 are connected to the primary winding of the oscillation transformer T12. L5, the connection point C of the diodes D1 and D2 and the connection point D of the resistor R5 and the transistor Q2 to the terminal E of the primary winding L1 and the terminal J of the secondary winding L3 of the oscillation transformer T11. The terminal R of the secondary winding L3 is connected to the base of the transistor Q1, and the terminal P of the secondary winding L2 is connected to the base of the transistor Q2. Terminal O, 2 winding L4 of the terminal N to connect to the ground G, respectively, and terminals T2, terminal T of the bidirectional thyristor Q4 connected a resistor R7 between the gates of
1 is connected to the base of the transistor Q2, the terminal T2 is connected to the terminal M of the secondary winding L4, and a series circuit of the resistor R4 and the trigger element Q3 is connected between the connection point Q of the resistor 3 and the capacitor C4 and the base of the transistor Q2. When the load side is short-circuited, the secondary windings L4 and L4 of the oscillation transformer T11 are connected.
The thyristor Q4 is turned on by the voltage induced between the two to stop the oscillation of the transistors Q1 and Q2, and the charging voltage of the capacitor C3 is applied to the trigger element Q3 via the resistors R2 and R4 to turn on the trigger element Q3. ,
A low-voltage lighting circuit characterized in that the transistor Q2 is held in an oscillation stop state.