JP3035401B2 - Semiconductor integrated 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 driving circuit for a switching transistor used in a switching regulator or the like.

In recent years, switching regulators are required to be small, light, and highly efficient. For this reason, even during high-frequency operation in which the size of the smoothing filter can be reduced, it is required to reduce the loss at the time of turning on and off the switching transistor and realize high efficiency operation at the same time as size reduction.

[0003]

2. Description of the Related Art A conventional switching transistor driving circuit will be described with reference to FIG.
in is input to the bases of the transistors Tr1 and Tr2, and the current sources 2a and 2b are connected to the collectors of the transistors Tr1 and Tr2.
And the emitter is connected to the ground GND.

The collector of the transistor Tr1 is connected to the base of the transistor Tr3, and the collector of the transistor Tr3 is connected to the power supply Vcc via the resistors R1 and R2.
The emitter is connected to the ground GND.

The collector of the transistor Tr2 is connected to the base of the transistor Tr4, the emitter of the transistor Tr4 is connected to the base of the transistor Tr5, and the collectors of both the transistors Tr4 and Tr5 are connected to each other and connected to the output terminal t1 so that both transistors are connected. The transistors Tr4 and Tr5 have a Darlington configuration.

The emitter of the transistor Tr5 is connected to a terminal t2 for connecting an external element, and a speed-up capacitor CE and a resistor RE connected in parallel as external elements are connected between the terminal t2 and the ground GND. ing.

The base of the transistor Tr4 is connected to the emitter of a PNP transistor Tr6 via a diode D1, and the base of the transistor Tr6 has a reference voltage VR.
And the collector is connected to the ground GND. Therefore, when the transistor Tr2 is turned off, the base potential of the transistor Tr4 becomes higher than the reference voltage VR by the threshold value of two diodes, and the potential of the terminal t2 becomes almost the reference voltage VR.

Between the resistors R1 and R2, the emitter of the transistor Tr7 is connected via a resistor R3 and the transistor T7 is connected via the resistor R3 and a diode D2.
The collector of the transistor Tr7 is connected to the power supply Vcc. Also, the transistor Tr7
Is connected to the collectors of the transistors Tr4 and Tr5 and the output terminal t1.

The output terminal t1 is connected to the base of a PNP type switching transistor Tr8, which is an external element. The emitter of the switching transistor Tr8 is connected to the power supply Vcc, and the output current Iout is output from the collector.

A terminal t3 is connected between the resistors R1 and R2, and a terminal t4 is connected to the base of the transistor Tr7. A bootstrap capacitor CBS is connected between the terminals t3 and t4 as an external element.

In the driving circuit 1 configured as described above, when the input signal Vin rises from the L level to the H level, the transistors Tr1 and Tr2 are turned on, and accordingly, the transistors Tr3, Tr4 and Tr5 are turned off, and the switching transistor is turned off. The base current IB of Tr8 is cut off, and the switching transistor Tr8 is also turned off.

At this time, when the transistors Tr4 and Tr5, which have been in the on state, are turned off, the potential of the terminal t3 rises momentarily, and the transistor Tr7 is turned on momentarily based on the bootstrap capacitor CBS. The potential of the output terminal t1 is rapidly increased to near the level of the power supply Vcc. Therefore, the switching transistor Tr8 is quickly turned off, and the turn-off loss is reduced.

On the other hand, when the input signal Vin falls from the H level to the L level, the transistors Tr1 and Tr2 are turned off,
Accordingly, the transistors Tr3 and Tr
4, Tr5 and Tr6 are turned on, a base current IB flows through the switching transistor Tr8, and the switching transistor Tr8 is turned on to output an output current Iout.

At this time, the speed-up capacitor CE
The base current IB of the switching transistor Tr8 sharply rises by the action of the switching transistor Tr8, and the switching transistor Tr8 is quickly turned on to reduce the turn-on loss. After the switching transistor Tr8 is turned on, a constant base current I set by the resistor RE is set.
At B, the switching transistor Tr8 is driven in a saturated state, and a constant driving state independent of the power supply Vcc is obtained.

[0015]

However, in the above-described drive circuit, there are four terminals t1 and t2 for connecting the output terminal t1 to the speed-up capacitor CE and the resistor RE and the bootstrap capacitor CBS which are external elements. Terminals are required. Further, since the speed-up capacitor CE and the bootstrap capacitor CBS have large capacities, it is difficult to incorporate them in the drive circuit 1.
Since the resistance value of the resistor RE needs to be adjusted by a load connected to the collector of the switching transistor Tr8, it is difficult to incorporate the resistor RE in the drive circuit 1.

Accordingly, the number of terminals of the drive circuit 1 increases, and when a large number of such drive circuits 1 are used, there is a problem that the increase in the number of terminals becomes an obstacle to downsizing the system.

An object of the present invention is to provide a drive circuit capable of reducing the number of terminals while achieving high efficiency and thereby achieving downsizing of the system.

[0018]

FIG. 1 is a diagram illustrating the principle of the present invention. That is, in claim 1, the switching transformer
The drive circuit 5 of the transistor Tr8 has three terminals t5, t6, t
7, a first terminal t5 and a third terminal of the drive circuit 5.
Connect bootstrap capacitor CBS to child t7
And the first terminal t5 and the second terminal of the drive circuit 5
Speed up capacitor CE and resistor RB between t6
And one end of the resistor RB is connected to the switch
Connected to the base of the switching transistor Tr8.

According to a second aspect, the drive circuit includes the switch.
Boot that reduces the turn-off loss of the switching transistor
A strap circuit, the first terminal and the second terminal
And a clamp circuit that clamps a constant voltage between
Was. In claim 3, the clamp circuit is connected in series in a plurality of stages.
It consisted of connected diodes. In claim 4, the block
The heat strap circuit includes a transistor and the transistor.
And a resistor connected between the collector and base of the
Was.

[0020]

According to the first aspect, the three terminals are external elements.
Bootstrap capacitor and speed-up capacitor
When the switching transistor is connected to the
Data is controlled. According to claim 2, a bootstrap circuit
As a result, the turn-off loss of the switching transistor
Switching transistor by the clamp circuit
The base current of the capacitor is maintained at a constant current. In claim 3,
Clamp voltage is generated by diodes connected in series in multiple stages
And the switching transistor
The base current of the capacitor is maintained at a constant current. In claim 4,
Based on the charge on the bootstrap capacitor,
Transistor is turned on, and the transistor is turned on.
The switching transistor is turned off.
You.

[0021]

FIG. 2 shows an embodiment of the present invention.
It will be described according to. The input signal Vin is the NPN of the drive circuit 5.
The input is input to the base of the transistor Tr11. The collector of the transistor Tr11 is connected to the current source 3a, the collector and the base of the NPN transistor Tr12, and the emitter is connected to the ground GND.

The base of the transistor Tr12 is NPN
The transistor Tr13 is connected to the base and the emitter is connected to the ground GND. The collector of the transistor Tr13 has a resistor R11 and three-stage diodes D3 and D3.
Power supply Vcc is supplied via the terminals D4 and D5, and the emitter is connected to the ground GND.

The collector of the transistor Tr13 has P
The base of the NP transistor Tr14 is connected, the collector of the transistor Tr14 is connected to the ground GND, and the emitter is connected to the output terminal t5.

NPN is connected to the anode of the diode D3.
The emitter of the transistor Tr15 and the terminal t6 are connected, the power supply Vcc is supplied to the collector of the transistor Tr15, the power supply Vcc is supplied via the resistor R12, and the base is connected to the terminal t7.

The output terminal t5 is connected to the base of a switching transistor Tr8 via a speed-up capacitor CE and a resistor RB connected in parallel, the power supply Vcc is connected to the emitter of the switching transistor Tr8, and the output switching from the collector. The current Iout is output.

The terminal t6 is connected to the base of the switching transistor Tr8, and a bootstrap capacitor CBS is connected between the terminal t7 and the output terminal t5.

Now, the driving circuit 5 configured as described above
When the input signal Vin rises from the L level to the H level, the transistor Tr11 is turned on, the transistors Tr12 and Tr13 are turned off, and the transistor Tr14 is also turned off. As a result, the bootstrap capacitor CBS
Is supplied to the base of the transistor Tr15,
A collector current hFE times the discharge current is supplied to the base of the switching transistor Tr8 via the terminal t6. Therefore, the base potential of the switching transistor Tr8 is quickly raised and the switching transistor Tr8 is quickly turned off, so that the turn-off loss is reduced.

On the other hand, when the input signal Vin falls from the H level to the L level, the transistor Tr11 is turned off, the transistors Tr12 and Tr13 are turned on, and the transistor Tr14 is turned on. As a result, the speed-up capacitor C is shifted from the base of the switching transistor Tr8.
The switching transistor T
A large base current IB instantaneously flows through r8, and the switching transistor Tr8 is quickly turned on, so that the turn-on loss is reduced.

Then, since the voltage between both terminals of the resistor RB is clamped by the forward voltage drop of the diodes D3 and D4, the base current IB of the switching transistor Tr8 becomes constant, and the constant drive independent of the power source Vcc. The state is obtained.

At this time, the bootstrap capacitor CBS is charged from the power supply Vcc via the resistor R12.
As described above, in the driving circuit 5, when the input signal Vin rises, the switching transistor T is connected by the bootstrap capacitor CBS connected between the terminals t5 and t7.
The turn-off loss of r8 is reduced. Also, the input signal Vin
At the time of falling, the turn-on loss is reduced by the speed-up capacitor CE connected between the terminals t5 and t6.

The three terminals t5, t6, and t7 can connect the bootstrap capacitor CBS, the speed-up capacitor CE, and the resistor RB, which are external elements, and drive the switching transistor Tr8.

Therefore, the drive circuit 5 having a high efficiency and a small number of terminals can be constructed.

[0033]

As described in detail above, the present invention has an excellent effect of providing a drive circuit capable of reducing the number of terminals and increasing the size of the system while improving the efficiency.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is a circuit diagram showing one embodiment of the present invention.

FIG. 3 is a circuit diagram showing a conventional example.

[Description of Signs] 5 Drive circuit 6 Clamp circuit 7 Bootstrap circuit Vin Binary input signal t5 Output terminal t6 terminal t7 terminal CBS Bootstrap capacitor RB Resistance RE Resistance CE Speed-up capacitor Tr8 PNP switching transistor

Continuation of the front page (72) Inventor Yoshiaki Sano 1015 Uedanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Prefecture Inside Fujitsu Limited (56) References JP-A-1-168119 (JP, A) JP-A-3-272218 (JP, A) JP-A-2-279017 (JP, A) JP-A-5-153768 (JP, A) JP-A-4-140059 (JP, A) JP-A-2-280662 (JP, A) (58) Survey Field (Int.Cl. ⁷ , DB name) H03K 17/00-17/693 H02M 3/00-3/44

Claims (4)

(57) [Claims] 1. A switching transformer having three terminals.
A semiconductor integrated circuit including a driver circuit , wherein a boot is provided between a first terminal and a third terminal of the driver circuit.
Connecting a strap capacitor , between the first terminal and the second terminal of the drive circuit,
A speed-up capacitor and a resistor are connected in parallel, and one end of the resistor is connected to the base of the switching transistor.
A semiconductor integrated circuit connected to the semiconductor integrated circuit. 2. The drive circuit according to claim 1, wherein the drive circuit reduces a turn-off loss of the switching transistor.
Bootstrap circuit, the first terminal, and the second terminal.
And a clamp circuit that clamps to a constant voltage
2. The semiconductor integrated circuit according to claim 1, further comprising:
Road. 3. The clamp circuit is connected in series in a plurality of stages.
3. A diode according to claim 2, wherein:
3. The semiconductor integrated circuit according to claim 1. 4. The bootstrap circuit includes a transistor
Connected between the transistor and the collector and base of the transistor
3. A resistor according to claim 2, wherein
Semiconductor integrated circuit.