JPS59163919A - Base driving circuit of semiconductor switch - Google Patents

Abstract

PURPOSE:To obtain a base driving circuit with high performance without causing power loss by providing an ON-voltage detector, a setting device of an ON- voltage command and a comparator controlling the switching operation as the result of comparison between the signals from the ON-voltage detector and the setting device. CONSTITUTION:The ON-voltage detector 24 detecting an ON-voltage VCE of a power transistor (TR) 1 with a low loss consists of a resistor 21 having a high resistance value not causing large power loss and a Zener diode 22 for clamping not to give an excessive voltage input to a comparator 13. Further, in order to detect quickly and accurately the ON-voltage VCE, a small diode 23 having several pF of junction capacitance is provided in series with the Zener diode 22. The switch 5 is turned on and off by setting the ON-voltage VCE detected by the voltage detector 24 as, for example, VCE'L for the operating voltage while the VCE falls down and VCE'H for the operating voltage when the VCE is rising in this way, according to the relation of the setting device 20 of a command voltage VCE' and the comparator 13 with hysteresis width.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a base drive circuit for a semiconductor switch used, for example, in a power converter.

Bipolar power transistors used as such semiconductor switches are field effect transistors (F
KT), etc., a considerable amount of power is consumed to drive the base, so a drive circuit with low power loss is desired.

For example, a circuit using a general C chopper as shown in FIG. 1 can be considered as a circuit with low base drive power loss.

In the figure, reference numeral 1 denotes a driven transistor as a main semiconductor switch, which is a power transistor that turns on and off the load current IC of the load 2 and the main circuit power supply 3 constituting the main circuit according to the long signal of the photocoupler 8. When this load current IC is caused to flow, that is, when transistor (2) is turned on, the condition that base current 1B high iB≧i C/h FE is satisfied.

If the current does not exceed the value determined by the current amplification factor hFE of transistor l, the on-voltage of transistor 1 will be sufficiently low (and the voltage drop loss of transistor l will become a problem), so in this circuit, the load current 1c is detected by current detector 11. The base current command IB'7 is then proportionally used as it is, or iB/ is created by anticipating the change in the current amplification factor hFE and providing a circuit for nonlinear correction as shown in 12.

Given iB', this iB/ and the current detector l.

The base current IB detected by the hysteresis width (second
The comparator 13 with α) in the figure compares L
When B'> IB, switch 5 is on, ]B'<I
At the time of B, the switch 5 is turned off, and as shown in FIG. 2, iB, which is approximately equal to the current command value iB', can flow.

In the figure, 4 is a power supply for driving the base, 6 is a reactor, 7 is a freewheeling diode, and 9 is an AND circuit.

As shown in FIG. 1, current control by switching using a C chopper does not include elements such as resistances that generate large amounts of loss, so the loss of the base drive circuit is reduced. Furthermore, the minimum necessary iB commensurate with the load current
It can be said that this is a sufficient energy saving measure against fluctuating loads.

However, the current detector 11 that detects the load current iC is a direct current transformer (DC-CT) that can detect hundreds of currents in a direct current manner.
), and in order to always maintain the relationship IB≧iC/hFE, it is desirable that the delay be several μs or less. Similarly, the current detector 10 is also expensive and poses a problem.

The purpose of the present invention is to eliminate the disadvantages of the conventional example, and provide an inexpensive and high-performance base drive circuit without causing power loss by using a resistor or using expensive equipment such as a DC transformer. It's about doing.

According to the present invention, in a circuit using a switching regulator to drive the base of a main semiconductor switch, the on-voltage detector and on-voltage command setter of the main semiconductor switch and the signals received from these are compared. This is achieved by providing a comparator for controlling switch operation within the regulator.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 3 is a circuit diagram showing an embodiment of the present invention, and FIG. 4 is an operating waveform diagram thereof. Components that are the same as those in FIG. 1 are given the same reference numerals.

24 is a detector for detecting the on-voltage VCP of the power transistor with low loss, and 20 is a setting device for the command voltage VCE'. The base drive circuit is shown.

The on-voltage detector 24 is composed of a high resistance 21 that does not cause large power loss, and a clamping Zener diode 22 that prevents excessive voltage input from being input to the comparator.

This Zener diode has a junction capacitance of several hundred pF (picofarads), so in relation to the high resistance 21, the CR
In many cases, the VCB becomes a filter and cannot be detected accurately and quickly.

For this reason, it would be better to reduce the resistance of the high resistance 21, but since the power loss when off increases, a small diode 2 with a junction capacitance of several pF may be used.
3 were installed in series.

In this way, the on-voltage vcE detected by the voltage detector 24 is determined by the relationship between the setting device 20 and the comparator 13 with hysteresis width.
cg'r, If the operating voltage during % increase is ■cEh, then
The switch 5 is turned on and off by the operation shown in FIG.

FIG. 5 is a circuit diagram showing another embodiment in which the voltage detector 24 is improved, and the voltage detector 24' is a Zener diode 2.
2. In addition to the small current source resistor 26, a high voltage diode 25 is used to achieve no loss. In this circuit, when the power transistor 1 is off, the diode 25 is in a blocking state, so when the transistor l is on, vc
E can be detected. In that case, diode 25
Since the forward drop of is affected by temperature and other factors, a compensation diode of 27 and a resistor of 2F for the small current source are required. It is preferable to add the forward drop of VCE' to the command voltage VCE' for correction.

FIG. 6 is a circuit diagram showing another embodiment of the present invention. In contrast to the previous embodiment, which focused on the collector-emitter voltage "CE" of the power transistor 1, it focused on the collector-base voltage "VCB". It controls the current on and off.

In other words, the voltage detector 31 that detects VCB has a high resistance 2.
1 and a small diode 23, and this vcB is appropriately about -0.5V when the transistor 1 is on, and is a negative value, so a Zener diode is not necessary.

In the figure, 30 indicates a setter for the command voltage vCB'. In this embodiment, the power transistor 1 is suitable for both simple and Darlington, and since cB is almost the same, the base drive circuit is set according to the type and characteristics of the transistor 1. The advantage is that you don't have to change anything.

Figure 7 is a circuit diagram showing a simplified version of Figure 6, in which the voltage detector 3
By selecting elements constituting the diode 1' such that the forward drop of the diode 25 is approximately equal to the appropriate VcB, constant VcB control can be performed with a very simple circuit.

It is noteworthy that almost all the functions shown in FIG. 1 can be satisfied with such a simple control circuit. In other words, if the change in hl is corrected by the iB' generating circuit 12 in FIG. 1, a base drive circuit with higher performance can be obtained, but in the example shown in FIG. 6 or 7, the influence of this change in hFFi is completely corrected. , an appropriate base current IB for properly turning on the transistor 1 is automatically supplied.

Furthermore, as shown in FIG. 8, the setting device 30 for setting the designated voltage VcB' can be subjected to various nonlinear corrections due to the influence of load current, etc., like the generator circuit 12, so that cB'
It may be configured as a correction circuit 32.

In the present invention, as mentioned above, IB automatically flows according to the load current, so by doing this, vBE will increase or decrease according to the load current, and VCB' can be adjusted according to the value of VBE. This correction is effective in improving the load characteristics of the power transistor 1.The input for this ■CB' correction is directly input to the
It may be iB, it may be iB, or a combination thereof.

As mentioned above, the base drive circuit of the semiconductor switch of the present invention, when using a switching regulator,
Instead of flowing a base current commensurate with the load current, the appropriate base current is made to flow only by detecting the voltage related to the on-voltage of the main semiconductor switch, so an expensive current detector such as a DC transformer is used. It is inexpensive and has high performance without any power loss due to resistance.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventional example, FIG. 2 is an operation waveform diagram of the circuit shown in FIG. 1, FIG. 3 is a circuit diagram showing a first embodiment of the base drive circuit of the present invention, and FIG. Figure 5 is a circuit diagram showing an improved example of the circuit in Figure 3, Figure 6 is a circuit diagram showing another embodiment of the present invention, Figure 7 is a partial diagram of the circuit in Figure 6. FIG. 8 is a circuit diagram showing another modification of the circuit shown in FIG. 6. ■...Power transistor, 2...Load, 3...Main circuit power supply, 4
...Base drive power supply, 5...Switch, 6...
Reactor, 7...Freewheeling diode, Photocoupler, 9...AND circuit, 10, II...Current detector, 12...Specified current generation circuit, 13...Comparator, 2o...On voltage setter, 21...High resistance, 22...Zener diode, 23...Small diode, 24.24', 30, 31...On voltage detector, 25
...High voltage diode, 26.28...Resistor for small current source, 27...Compensation diode 32...Correction circuit. Applicant Fuji Electric Manufacturing Co., Ltd. Figure 1 8 Figure 2 7ts Figure 3 Figure 4 11 Houses Figure 5 4 Figure 6 Figure 7 31' Figure 8

Claims (1)

[Claims] ゛In a circuit that uses a switching regulator to drive the base of a main semiconductor switch, the on-voltage detector and on-voltage command setter of the main semiconductor switch, and the signals received from these, control the switch operation in the regulator based on the comparison results. A base drive circuit for a semiconductor switch, comprising a control comparator.