JPH06334886A - Voltage resonance type switching circuit - Google Patents

Abstract

PURPOSE:To reduce the loss of a switching transistor(TR) by providing a diode having almost the same time of reverse recovery as an ON operation time of the switching TR between a collector and an emitter of the switching TR in the polarity opposite to that of the power supply voltage. CONSTITUTION:Since a voltage across a diode 1b takes a low voltage for a time, at least trr1 in a reverse recovery time trr of the diode 1b, a collector- emitter voltage of a TR 1a for on-time is specified by the low voltage across the diode 1b and reaches a small voltage. Since the impedance of the diode 1b increases gradually from zero for a time trr2, the on-current flowing in the inside of the TR 1a gradually increases and only the on-current of the TR 1a remains finally and a collector current is stopped when the gate is turned off. That is, lots of current during the ON-time of the TR 1a flows from the diode 1b and since the collector-emitter flowing time is short, then the loss is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage resonance type switching circuit used for passing a sawtooth current through a deflection coil of a horizontal deflection circuit of a CRT display, for example.

[0002]

2. Description of the Related Art Conventionally, bipolar transistors having a low collector-emitter saturation loss have been used as switching transistors in conventional voltage resonance type switching circuits. Further, a diode having a small loss is used as a diode connected in parallel with the switching transistor in order to suppress the loss, but the reverse recovery time thereof has not been taken into consideration.

[0003]

In such a conventional voltage resonance type switching circuit, since the bipolar transistor is a current control type element, it is necessary to flow a sufficiently large current between the base and the emitter during the on-time and turn-off time. There is a large power consumption,
There is also a problem that it becomes difficult to design peripheral circuits such as a drive transformer as the switching frequency becomes higher.

In particular, when the voltage resonance type switching circuit is applied to drive a deflection coil of a horizontal deflection circuit of a television, as the horizontal deflection frequency becomes higher, even if the storage time is improved, the switching speed of the bipolar transistor is not improved. There is also a problem that it becomes a limit and switching loss increases.

Under these circumstances, MOS gate type transistors, which are faster than bipolar transistors and easy to drive, are being used. However, MO
Although the S-gate transistor is high-speed, the on-resistance between the drain and the source becomes higher as the demand for higher withstand voltage of the switching transistor increases, which increases loss and causes thermal runaway depending on operating conditions. there were.

The present invention has been made to solve such a problem, and an object thereof is to provide a voltage resonance type switching circuit in which the loss of the switching transistor is reduced.

[0007]

SUMMARY OF THE INVENTION In a voltage resonance type switching circuit of the present invention, a diode having a reverse recovery time which is substantially the same as the ON operation time of a switching transistor is used, and a collector (drain) and an emitter (source) of the switching transistor are provided. It is characterized in that it is provided in parallel with a polarity opposite to the power supply voltage. This diode can also utilize an internal diode parasitic on the switching transistor.

Further, current detecting means for detecting the current of the diode when the switching transistor is off, and operation stopping means for stopping the switching operation of the switching transistor when the current of the diode is detected by the current detecting means. It is characterized by having and.

[0009]

With this configuration, the electric charge stored in the diode during the ON operation time of the switching transistor flows as a reverse recovery current, and the apparent (between) collector (drain) and emitter (source) of the switching transistor appears. The resistance is reduced to reduce the loss during ON operation.

Further, when the reverse recovery time of the diode becomes longer than the on-time of the switching transistor, the switching operation is stopped by the current detecting means and the operation stopping means to prevent the abnormal operation.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a configuration of a first embodiment in which a voltage resonance type switching circuit of the present invention is applied to a horizontal deflection output circuit.

In FIG. 1, the horizontal deflection output circuit 1 includes an IGBT (Insulat) in the horizontal deflection output transistor 1a.
ed Gate Bipolar Transistor) and is composed of a diode 1b connected between the collector and emitter of the transistor 1a, a deflection coil 1c, and a tuning capacitor 1d connected in parallel with the deflection coil 1c.

The transistor 1a of the horizontal deflection output circuit 1 is driven by the switching control signal output from the horizontal drive circuit 2 via its gate.

Further, this embodiment is based on the horizontal deflection output circuit 1
The phase comparison circuit 3 controls the horizontal drive circuit 2 by comparing the phase of the output current of the transistor 1a and the switching control signal of the output of the horizontal drive circuit.

The phase comparison circuit 3 rectifies the detection coil 3a wound around the collector power supply line for detecting the current flowing in the collector of the transistor 1a or the diode 1b, and the detection voltage induced in the detection coil 3a to rectify the direct current. Switching control of the diode 3b for converting into a voltage, the capacitor 3c, the DC voltage converted detection voltage is compared with the reference voltage 3d, and the detection output is sent out if it is larger than the reference voltage 3d, and the horizontal drive circuit 2. An inverter 3f that takes in a signal output into the phase comparison circuit 3 and an AND circuit 3g that logically compares the detection output of the comparator 3e and the output of the inverter 3f. The logical judgment result of the AND circuit 3g is sent to the horizontal drive circuit 2, The horizontal drive circuit 2 is controlled by the judgment output.

The operation of the embodiment having such a configuration will be described with reference to FIG. FIG. 1A is an explanatory diagram of the reverse recovery time of the diode 1b of the horizontal deflection output circuit 1 and the current flowing in the diode 1b at that time, and FIG. 1B is the collector current of the transistor 1a, the current of the diode 1b and the collector current. 6 shows a voltage waveform between emitters.

Before explaining the operation of the embodiment, the reverse recovery time of the diode 1b, which is the basis of the idea of the present invention, will be explained with reference to FIG. 2 (a). Generally, diode 1b
When the applied voltage is reversed after applying a forward current to the diode, the diode 1b at this point is considered to be a kind of capacitor,
The reverse recovery current Irr flows in the opposite direction to the time until the stored charge amount is discharged. That time is the reverse recovery time trr.

Of the time, the time trr1 from when the current Irr starts flowing in the opposite direction to when it reaches the peak value Irrp is the time when the load is the inductive load of the deflection coil 1c.
It increases linearly with the slope determined by the load inductance and the power supply voltage Vcc. Therefore, it can be considered that the impedance of the diode 1c is close to zero during this period, and therefore the voltage across the diode 1c has a low value.

The impedance of the diode 1b changes from zero to infinity during the time trr2 until the current decreases from the peak value Irrp to zero. In a circuit in which such a diode 1b is connected between the collector and the emitter of the transistor 1a, as shown in FIG.
During the period from 1 to t2, the transistor 1a is turned on, and the load current is the inductance of the deflection coil 1c and the power supply voltage Vcc.
It increases linearly with the slope determined by.

At T2, the transistor 1a is turned off, and the next period from t2 to t4 is a retrace period, and a resonance voltage due to the deflection coil 1c shown by the broken line in the figure is generated between the collector and the emitter. Further, during the next period of t4 to t5, the diode 1b becomes conductive due to the resonance voltage and the forward current I
f flows.

At t5, the forward current of the diode 1b becomes zero, and the transistor 1a is turned on during the period from t5 to t6 thereafter. During this period, the reverse recovery of the diode 1b is performed, the reverse recovery current Irr flows, and the transistor 1
The apparent impedance of a shows a value close to zero.

In this embodiment, the reverse recovery time trr of the diode 1b is set to more than 90% of the on-time and less than the on-time, which is almost the same as the on-time of the transistor 1a.

As described above, the reverse recovery time trr of the diode 1b is set to be approximately the same as the on-time of the transistor 1a, so that the saturation voltage between the collector and the emitter of the transistor 1a during this on-time is reversed recovery time trr of the diode 1b. Can be replaced with the voltage at.

As described above, the voltage across the diode 1b takes a low value at least during the reverse recovery time trr of the diode 1b, so that the collector-emitter voltage during the on-time of the transistor 1a is low across the diode 1b. It is a small value specified by the voltage.

After that, during the period of trr2, the impedance of the diode 1b gradually increases from zero, so that the on-current flowing inside the transistor 1a gradually increases.
Eventually, only the ON current of the transistor 1a will be reached,
The collector current stops when the gate is turned off.

As described above, most of the current flows through the diode 1b during the on-time of the transistor 1a, and the time during which the current flows between the collector and the emitter is short, so that the loss during the on-time of the transistor 1a can be reduced.

However, the reverse recovery time trr of the diode 1b
Is longer than the on-time of the transistor 1a, even if the transistor 1a is turned off, a current flows from the diode 1b and a predetermined circuit operation cannot be obtained.

Therefore, the "L" signal of the switching control signal of the horizontal drive circuit 2 at the time when the transistor 1a is turned off is inverted via the inverter 3f of the phase comparison circuit 3 and input to the AND circuit 3g as the "H" signal. At the same time, the detection coil 3a detects the presence / absence of a current flowing through the diode 1b. If the current from the diode 1b is detected at this time, the comparator 3e outputs an "H" signal and sends it to the AND circuit 3g. .

The AND circuit 3 includes an inverter 3f and a comparator 3
Since both signals sent from e are "H", it is judged to be abnormal, and the logical output "H" signal is sent to the horizontal drive circuit 2 to stop the switching operation.

FIG. 3 shows a horizontal deflection output circuit of the second embodiment. In this embodiment, the horizontal deflection output transistor 1a has M
This is an example using an OSFET. Generally MOSFE
A diode De is equivalently incorporated between the drain and source of T. In this example,
In the manufacturing process of the MOSFET 1a, the reverse recovery time trr of the internal diode De parasitic between the sources is adjusted to be the same as the ON time of the MOSFET 1a.

With this structure, the loss in the on-time of the MOSFET 1a can be reduced as described in the first embodiment. When the reverse recovery time of the diode De is longer than the on-time of the MOSFET 1a,
Similarly to the first embodiment, the circuit current is detected by the detection coil 3a to stop the switching operation.

According to this embodiment, the parasitic diode De can be used without externally attaching a diode between the drain and source, and the number of parts can be reduced.
FIG. 4 shows a horizontal deflection output circuit of the third embodiment. In this embodiment, the horizontal deflection output transistor 1a has a SENSE F
It is an example using ET.

This embodiment utilizes the reverse recovery time of the diode De parasitic between the drain and the source as in the second embodiment, and as shown in the figure, the resistor R connected to the monitor terminal is used. Monitor the source current via
The detected "H" signal is sent to the phase comparison circuit 3, and if the reverse recovery time trr of the diode De is longer than the ON time of the SENSE FET 1a, the horizontal deflection operation is stopped as in the first and second embodiments. To do.

According to this embodiment, the detecting coil 3a in the first and second embodiments is not required, and the external diode is not required as in the second embodiment, so that the circuit is simplified. To be done.

The present invention is not limited to the above-mentioned embodiment, but can be modified and carried out within the scope of the invention. In each of the above-described embodiments, when the reverse recovery time of the diode is longer than the on-time of the switching transistor, the output of the phase comparison circuit 3 is fed back to the horizontal drive circuit to stop the switching operation.
The position to be fed back can also be implemented in the horizontal oscillation circuit before the horizontal drive circuit.

[0036]

According to the present invention, the following effects can be expected. a. As described above, since the loss of the switching transistor can be reduced, a high output voltage resonance type switching circuit can be obtained with a transistor having a small output.

B. MOSF for switching transistor
If a MOS gate type such as ET is used, the driving method is facilitated, and if a MOSFET is used, a parasitic diode can be used for the object diode of the present invention, and the number of parts can be reduced. .

C. Further, by using the SENSE FET, the parasitic diode can be used, and the current can be easily monitored and the circuit can be simplified. d. The abnormal operation of the circuit can be prevented by the current detecting means and the operation stopping means.

[Brief description of drawings]

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

FIG. 2 is an explanatory view of a reverse recovery time of a diode and a voltage and a current of a circuit for explaining the operation of the embodiment.

FIG. 3 is a circuit diagram showing a configuration of a second embodiment.

FIG. 4 is a circuit diagram showing a configuration of a third embodiment.

[Explanation of symbols]

1 ... Horizontal deflection output circuit, 1a ... Transistor, 1b ... Diode, 1c ... Deflection coil, 1d ... Capacitor, 2 ...
Horizontal drive circuit 3 ... Phase comparison circuit, 3a ... Detection coil, 3b ... Diode, 3c ... Capacitor, 3d ... Reference voltage, 3e ... Comparator, 3f ... Inverter, 3g ... AND circuit, De ... Diode, R ... Resistor.

Claims (5)

[Claims] 1. A diode having a reverse recovery time which is substantially the same as the ON operation time of a switching transistor is provided in parallel between the collector (drain) and the emitter (source) of the switching transistor in a polarity opposite to the power supply voltage. A voltage resonance type switching circuit characterized in that 2. The voltage resonance type switching circuit according to claim 1, wherein the diode is an external diode, an internal diode parasitic on the switching transistor, or both of the diodes. 3. A current detecting means for detecting the current of the diode when the switching transistor is off, and the switching operation of the switching transistor is stopped when the current of the diode is detected by the current detecting means during the off operation. The voltage resonance type switching circuit according to claim 1 or 2, further comprising: an operation stopping means for causing the operation. 4. The voltage resonance type switching circuit according to claim 1, wherein the switching transistor is a MOS gate type transistor. 5. The switching transistor is SENS.
The voltage resonance type switching circuit according to any one of claims 1 to 3, which is an E FET.