JPS6262619A - Speed-up circuit of transistor - Google Patents

Abstract

PURPOSE:To obtain a circuit having excellent operating efficiency with comparatively simple constitution by providing an absorber circuit provided with a resistor and a capacitor to the titled circuit and utilizing a current flowing to the absorber circuit so as to apply conduction control of a discharge transistor (TR). CONSTITUTION:The absorber circuit 12 connected in parallel with a switching TR Q1 consists of a series circuit composing of a capacitor C1 and resistors R7, R8. In applying a drive current to a base of the TR Q1, the TR Q1 is turned on and a current flows to the primary winding of a transformer T1. The switching TR Q1 is turned on rapidly. When a capacitor C3 is charged, a base current keeps flowing through a resistor R2. When the supply of the drive current is stopped, the TR Q1 is turned off. The current flows through the capacitor C1 and the resistors R7, R8 and the emitter-collector voltage of the switching TR Q1 is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a circuit for improving the switching speed of a switching transistor that drives a KM AT type negative load such as a transformer or a coil.

[Prior art] In order to efficiently drive a switching transistor, an excessive base current is injected when the transistor is turned on to shorten the on time, and a reverse bias voltage is applied when the transistor is turned off to reduce the amount of current accumulated in the base when the transistor is turned on. The accumulated charge is extracted to shorten the accumulation time.

The simplest speed amplifier circuit has a configuration in which a capacitor is inserted in parallel with the base resistor of the L transistor, and when the transistor is turned on, overdrive is applied by the charging current of the capacitor, and when the transistor is turned off, the transistor is reverse biased by the charging voltage of the capacitor. It is.

This circuit is the simplest, but in order to operate efficiently, it is necessary to use a large number of capacitors with appropriate capacitance values depending on the base resistance and the constant of the transistor, and it is not always possible to achieve satisfactory performance. The drawback is that it is difficult.

Therefore, in the prior art, a speed-up circuit 10 as shown in FIG. 3 has been used. Here, the switching transistor Q1 is a transformer T.

It drives an inductive load such as a capacitor C to absorb the spike voltage that occurs at turn-off.
3 and a resistor R, are connected in series.
2 is installed in parallel with the switching transistor Q1. A base bias circuit consisting of resistors Rz and Ri is connected as an input circuit to such a switching transistor Q, and is driven via a pulse transformer T's.

Here, the speed-up circuit 10 is composed of a capacitor C2, a transistor Qz, a diode D1, and three resistors R, , R, , R,.

When a driving pulse is supplied to the pulse transformer T2, the switching transistor Q turns on, and the transformer T1
Current flows through the negative winding.

At the same time, current flows through resistor R7 and diode DI to charge capacitor Cm.

At this time, the base-emitter of the transistor Q2 is reverse biased and is non-conductive.

When the drive signal to the pulse transformer T2 is inverted, the charge stored in the capacitor C2 makes the transistor Q2 conductive, and the switching transistor Q is turned on through the resistor R4.
Subtract the base accumulated charge of l. As a result, the switching transistor Q is reverse biased and turned off, and part of the energy stored in the transformer T is consumed as a current passing through the absorber circuit 12.

[Problems to be Solved by the Invention] In the speed-up circuit 10 as described above, when the switching transistor Q1 is turned on, the charging current to the capacitor C2 is overdriven to shorten the on time, and when the switching transistor Q1 is turned off, the base accumulated charge is Although the extraction accumulation time can be shortened and the efficiency can be improved, as can be seen from the drawings, the disadvantage is that the number of parts is quite large and the circuit is complicated.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the drawbacks of the prior art as described above and to provide a transistor speed-up circuit with a relatively simple configuration and high operating efficiency.

[Means for Solving the Problems] The present invention, which can achieve the above-mentioned objects, does not apply to inductive loads. A series circuit of a diode and a capacitor is connected in parallel with the base resistor of a switching transistor that controls the on-off of the current, and a discharge transistor is connected between the connection point of the diode and the capacitor and the emitter of the transistor. This is a transistor speed-up circuit in which the discharge transistor is connected to an absorber circuit, and the base of the discharge transistor is connected to an absorber circuit.

The inductive load here refers to a coil, a transformer, etc. When switching an inductive load, an absorber circuit including a resistor and a capacitor is provided to absorb the flyback voltage generated when the switching transistor is turned off and protect the transistor. The present invention utilizes the current flowing through this absorber circuit to control the conduction of the discharge transistor.

Therefore, the present invention is suitable for driving switching transistors such as switching power supplies, for example.

[Function] As described above, the absorber circuit absorbs the spike voltage generated by the inductive load when the switching transistor is turned off, and the current flowing through it is consumed by the resistor and is completely lost as heat. The present invention
A portion of the current that would normally be wasted is used to control the conduction of the discharge transistor, and the charge accumulated in the base of the switching transistor is extracted to shorten the accumulation time.

Furthermore, at turn-on, the capacitor is overdriven by the charging current that passes through the diode, shortening the on-time (rise time + delay time).

[Embodiment] FIG. 1 is a circuit diagram showing an example of a switching power supply to which a transistor speed-up circuit according to the present invention is applied. For ease of explanation, parts corresponding to those of the prior art shown in FIG. 3 are given the same reference numerals. The switching transistor Q+ controls on/off the primary side current of the transformer T. A rectifying and smoothing circuit 14 is connected to the secondary side of the transformer T1, and the power supply connected between the output terminal C-4 is connected to the switching transistor Q+. Power is supplied to the load.

Note that resistors R2 and R3 are base bias resistors of the switching transistor Q.

The absorber circuit 12 connected in parallel with the switching transistor Q+ includes a capacitor C and a resistor Rt.
, Re. This resistance R1, RI
l is for dividing the terminal voltage of the absorber circuit 12,
The sum of these resistance values corresponds to the resistance value of resistor R5 in FIG.

The speed-up circuit 10 according to the present invention connects a series circuit of a diode D2 and a capacitor C3 in parallel with the base resistance R2 of the switching transistor Q, and connects a connection point e between the diode D2 and the capacitor C3. A discharge transistor Q3 is connected between the emitter of the transistor Q1, and its base is connected to the connection point f between the resistor R1 and the resistor R8 of the absorber circuit 12.

Direct current is supplied between input terminals a and b as a power source, and a pulsed drive signal is supplied from a control circuit or the like to a pulse transformer T2 connected to the input terminal of the switching transistor Q.

When a drive current is supplied to the base of the switching transistor Q1, it is turned on and current flows through the primary winding of the transformer T. Since the base current at turn-on flows through diode D2 and capacitor C3, it is overdriven and the switching transistors Q,
turns on rapidly. Once capacitor C3 is charged, base current continues to flow through resistor R2.

Next, when the supply of drive current is stopped, the switching transistor Q is turned off. At this time, due to the inductance of the transformer T1, the switching transistor Q1
The emitter-collector voltage of tries to rise, but
Since the absorber circuit 12 is connected in parallel with it, current flows through the capacitors C1, Rt, and Ra, reducing the voltage between the emitter and collector of the switching transistor Q1, thereby protecting the transistor and protecting it from unnecessary noise flowing outside. decreases.

Further, in the present invention, since a current flows through the resistor R when the switching transistor Q1 is turned off, the current causes a voltage drop and a positive voltage is generated at the connection point f between the resistors R1 and R6. As a result, a pulse current flows to the base of the discharging transistor Q3, which momentarily turns the capacitor C1
The charge accumulated in the base of the switching transistor Q is extracted through the switching transistor Q and turned off rapidly, shortening the accumulation time.

When the drive current is again supplied to the base of the switching transistor Ql, the above-described operation turns on the transistor Ql, and the charge in the capacitor CI of the absorber circuit 12 is discharged. At this time, a current also flows through the resistor R8, but the voltage at the connection point f caused by the current becomes lower than the voltage at the other end of the resistor RIl, so the discharging transistor Q3 becomes reverse biased and becomes non-conductive. It is maintained.

The above operation waveforms are collectively shown in FIG. 2.

As shown in the figure, the base current of the switching transistor Q is overdriven by the charging current of the capacitor C4 when it is turned on, so the on time is shortened, and the switching transistor Q1 is reverse biased when it is turned off, so the storage time is reduced. This enables short driving times.

Although the above description has been made using a one-way switching power supply as an example, the present invention is not limited thereto, and can be applied to a half-bridge type, full-bridge type, or Buchspull type power supply, and can also be applied when driving an inductive load such as a coil. Needless to say, it can also be applied.

Further, in the above embodiment, the absorber circuit is connected in parallel to the switching transistor, but the present invention can be applied to other cases as well.

[Effects of the Invention] As described above, the present invention provides a series circuit of a diode and a capacitor in parallel with the base circuit, which improves the on-characteristics of the switching transistor, and also actively diverts a portion of the current flowing through the absorber circuit. When the switching transistor is turned off, the discharging transistor is momentarily controlled by R1ffl to draw out the base accumulated charge, so the accumulation time of the switching transistor can be shortened, and the combination of these two effects increases the switching speed. can significantly improve efficiency.

Further, since the discharge transistor is driven using energy that would normally be consumed as heat in the absorber circuit, efficiency is not impaired.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an example of the application of the present invention to a switching power supply, FIG. 2 is a voltage and current waveform diagram of each part of the circuit, and FIG. 3 is a circuit diagram showing an example of the prior art. 10... Speed-up circuit, 12... Absorber circuit, 14... Rectifier smoothing circuit, T... Transformer,
Q,...Switching transistor, Q□...Discharge transistor, D2...Diode, C1...
capacitor. Patent applicant: Fuji Electrochemical Co., Ltd. Agent: Shigeru Mi 1 Figure 1 Date==m2゜Figure 3

Claims (1)

[Claims] 1. A series circuit of a diode and a capacitor is connected in parallel with the base resistor of a switching transistor that controls on-off the current flowing through the inductive load, and a discharge is caused between the connection point of the diode and the capacitor and the emitter of the transistor. The base of the discharge transistor is connected to an absorber circuit that absorbs a spike voltage generated when the switching transistor is turned off, and the conduction of the discharge transistor is controlled by the current flowing through the absorber circuit. Features a transistor speed-up circuit.