JP2001156607A - High voltage switch protection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high voltage switch protection circuit that prevents a voltage applied to semiconductor elements from being excessive so as to protect a switch circuit because the semiconductor elements may be employed for a high voltage switch placed between a high voltage power supply and a load, a voltage is not uniformly distributed to the elements due to a stray capacitance or the like in a transient-state such as transition from on to off and the voltage exceeding the rated voltage of the elements and damaging the elements. SOLUTION: Switching transistors(TRs) Qj are connected in series and equalization resistors Rj are connected between each collector and each emitter of each TR. A base current adjustment TR Qc is connected to a base Gj of the TR Qj of each stage. The equalization resistance is divided to connect a voltage division point Kj to a base of a base current adjustment TR Qc, and when the collector-emitter voltage of the switch TR Qj rises, a very small current flows from the base current adjustment TR Qc to the base of the switch TR Qj to decrease the collector-emitter voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for protecting a semiconductor switch element of a DC power supply using a high voltage switch formed by connecting a large number of semiconductor switch elements in series. The voltage of the power supply targeted by the present invention is several tens kV to several tens.
It is a high voltage of 00 kV. A high-voltage DC power supply drives a high-voltage load such as an ion source, a high-frequency electron tube, and an electron accelerator. Depending on load, current value is several mA-10
0 mA. In the case of pulse driving, the current may be several A.

A problem is a switch that connects a high-voltage power supply to a high-voltage load. A simple mechanical switch that opens and closes a piece of metal has difficulties when turned off. Discharge occurs due to high voltage, so current cannot be cut off. Special switches are used because of the high voltage. If only a high voltage is applied, a gap switch or the like may be used in which two metal spheres are opposed to each other to cause a discharge between the metal spheres by a trigger voltage and conduct between the switches by plasma. It closes spontaneously when the charge stored in the power supply is completely discharged. This can be turned on but difficult to turn off. Current cannot be interrupted during application.

In order to allow the switch to be freely opened and closed, a vacuum tube element having a high withstand voltage may be used. For example, it is a vacuum electron tube such as a thyratron. However, vacuum electron tubes have the disadvantage that they are bulky and expensive and have a short life.
Therefore, a high-voltage semiconductor switch element is sometimes used. However, there is no semiconductor element that can withstand a high voltage alone, which is a problem in the present invention, even if it has a high breakdown voltage. Therefore, a number of equivalent switch elements are connected in series to form one switch.

[0004]

2. Description of the Related Art High voltage circuits (several tens kV to several hundreds k)
When the semiconductor element is used as a high-voltage switch in V), the withstand voltage of the semiconductor element is low, so that the semiconductor elements are connected in series to form one switch. Here, the semiconductor element is a transistor, a thyristor, or the like. Thyristor, SCR (silicon controlled rectifier) withstand voltage 2kV ~
Some are as high as 10 kV, but several tens of kV to several hundred k
It is still insufficient to open and close the V power supply. In the case of a thyristor, power cannot be controlled only by a switch operation (on / off). When a power transistor is used, power can be continuously controlled. For a transistor, the breakdown voltage is about 1 kV to 4 kV.

Assuming that the breakdown voltage of the semiconductor element is Vs and the power supply voltage is Vq, an integer ratio m = [Vq / Vs] is obtained, and n is a larger integer and (m <n) n semiconductor elements are connected in series. By connecting, it becomes possible to withstand the power supply voltage Vq. Here, [x] is a symbol representing only an integer part except a decimal part of x. For example, in the case of a 50 kV power supply, a switch in which five semiconductor elements with a withstand voltage of 10 kV are connected in series can be used as a switch. Alternatively, a device in which ten devices with a withstand voltage of 5 kV are connected in series is used.

[0006] The semiconductor element has a control terminal (gate electrode). When an ON signal voltage is applied to the control terminal, the semiconductor element conducts (ON, closes, closes). When an off signal is given to the control terminal, the semiconductor element becomes non-conductive (open, off, open). By applying an on / off control signal to the gate electrode, the semiconductor element can be closed (closed, on) or opened (open, off).
Not all SCRs can do this. There are only a few devices that can turn off the device by introducing an off signal to the gate. For example, a turn-off type SCR can be used.

Semiconductor devices connected in series must be opened and closed simultaneously. Therefore, it is necessary to simultaneously supply a control signal to the control terminals of all the semiconductor elements. If the time of the control signal is different, a voltage higher than the withstand voltage is applied to one of the elements, and the element may be destroyed. The problem is particularly when the switch is off.

[0008]

FIG. 1 is a schematic wiring diagram of a switch element portion according to a conventional example. The DC power supply 1 boosts a commercial AC by a transformer and combines it with a rectifier to generate a high voltage. So DC power supply 1 is a transformer,
It is a collective device including many rectifiers and capacitors. The power supply voltage is several tens kV to several hundred kV.

The power supply 1 may be bypassed by a resistor 2 having a large resistance value. Power supply 1 is a low resistance resistor 3
To the semiconductor element row via The semiconductor element array is obtained by connecting equivalent semiconductor switch elements Q1, Q2,..., Qn in series. These are, for example, SCRs (thyristors). The cathode of each device is connected to the anode of the next device. Each is a control terminal (gate)
have. On and off signals are simultaneously input to the control terminal. All elements open or close at the same time. The element array forms one switch as a whole. The cathode of the last element Qn is connected to a load directly or through a transformer.

When an ON signal is simultaneously applied to the control terminals G1, G2,..., Gn, all the elements Q1, Q2,. Conversely G
, Gn are simultaneously turned off, and all the switching elements Q1, Q2,. Since the semiconductor elements are connected in series and have a common current, the voltage is always equally distributed if they are closed and opened at the same time. At the time of off, a voltage of V / n, which is obtained by dividing the power supply voltage V by the number n of elements, should be applied.

There are two problems here. In the case of a change to off and a load flash. (1) When the switch is turned off (from on to off) In order to stop the load drive, the switches must be shut off all at once. An off signal is given to the control terminals G1, G2,..., Gn of the n elements. However, since a signal is applied to n elements, a time lag may occur. For example, a time lag occurs due to a stray capacitance of a circuit. If there is a time lag in the change from ON to OFF of the switch element, a voltage is applied to the element that is quickly turned off, but the voltage is not applied to the element that is delayed. An element that is quickly turned off may be destroyed by a voltage higher than the withstand voltage.

(2) In the case of load flashover In some cases, discharge may occur inside the load and the load resistance may become substantially zero. Since the switch is closed and a current is flowing, the current flowing through the semiconductor element increases when the load resistance approaches zero. Also in this case, the voltage applied to the semiconductor element may not be uniform but may be non-uniform. The stray capacitance of the circuit is as small as several pF, but may be affected by the stray capacitance when the control pulse signal is sharp. Variations in transistor performance may occur due to aging as well as stray capacitance. For example, if the current amplification factor is different, the collector current is different even if the control current is used as the base, and the voltage applied to the transistor is different.

In some cases, an equalizing resistor is inserted between the anode and the cathode of the semiconductor device in order to apply a voltage evenly when the semiconductor device is turned off. R1 to R in FIG.
n is an equalizing resistance. The resistance values are the same and have considerably higher resistance values. R1 = R2 =... = Rn and are connected to points M0, M1, M2,. Since no current flows through the semiconductor elements Q1 to Qn when the semiconductor device is turned off, a voltage obtained by equally dividing the power supply voltage V by n is applied to these resistors. Therefore, the voltage applied to the element Qj is the same, that is, V / n. When turned off, the voltage applied to the elements becomes equal because of the equalizing resistance.

However, a current flows through the equalizing resistor, which results in a loss. Since the smaller the loss, the better the resistance value of the equalizing resistance. Although the voltage equalizing resistor as shown in FIG. 1 can prevent the abnormal voltage at the time of off, it is ineffective for the above-mentioned (1) transition from on to off and (2) non-uniform voltage due to load flash. There is no other choice.

As described above, a voltage may not be applied evenly to a plurality of series semiconductor elements. If the voltages are unequal, it is possible that the element with the higher voltage will be destroyed. SUMMARY OF THE INVENTION It is an object of the present invention to provide a protection circuit for making a voltage applied to a semiconductor element always uniform in a high-voltage switch circuit in which semiconductor elements are connected in series.

[0016]

A high-voltage switch protection circuit according to the present invention comprises a plurality of switching transistors connected in series between a DC power supply and a load, and a collector-emitter (drain-source) of the transistor. A high-voltage switch circuit including a plurality of stages of voltage-balancing resistors connected between them, and simultaneously opening and closing the transistors by simultaneously applying on-signals and off-signals to the bases (gates) of the transistors. A base (gate voltage) current adjusting transistor connected to the base (gate) of the transistor in the stage is provided, and a voltage equalizing resistor connected between the collector and the emitter (between the drain and the source) of the transistor is divided. The voltage is connected to the base (gate) of the base (gate voltage) current adjustment transistor, and the voltage is divided by the equalizing resistor. When the voltage rises, a base current is applied from the base (gate voltage) current adjusting transistor to the switching transistor (gate voltage is applied), and the collector-emitter (drain-source) voltage of the transistor is decreased. I have.

In the present invention, the switching semiconductor element Q
j is limited to a transistor. This is because the load power is controlled continuously. SC with only ON / OFF operation described above
It cannot be used for R (thyristor). The transistor may be a bipolar transistor or a field effect transistor (FET).

Since the names of the anode, the cathode and the control electrode are different between the two, it is somewhat complicated. In the case of bipolar, the space between the anode and the cathode should be called the space between the collector and the emitter. In the case of FET, it should be called between drain and source. The control electrode is bipolar base and the control means is base current. In the case of an FET, the control electrode is a gate and the control means is a gate voltage. The present invention can be applied in any case. That is, a set of switch element = bipolar, adjustment element = bipolar, and switch element = FE
A set of T and adjustment element = FET is possible.

Although it is written to include both, it is complicated. Therefore, the term “between the collector and the emitter or between the drain and the source” is generically referred to as between the anode and the cathode. Then, it is called a control electrode instead of the base or the gate. The base current adjusting transistor or the gate voltage adjusting transistor is simply referred to as an adjusting transistor. Then, the present invention can be more generally expressed as follows.

A high-voltage switch protection circuit according to the present invention comprises a plurality of stages of switch transistors connected in series between a DC power supply and a load, and a plurality of stages of voltage equalization connected between the anode and cathode of the transistor. Including resistance and
In a high-voltage switch circuit in which a transistor is simultaneously opened and closed by simultaneously applying a control signal to a control electrode of the transistor, an adjustment transistor connected to the control electrode of the transistor at each stage is provided, and an anode of the switching transistor is provided. The voltage dividing resistor connected between the cathodes is divided, and the voltage at the voltage dividing point is connected to the control electrode of the adjusting transistor.When the voltage dividing point voltage of the voltage equalizing resistor increases, the voltage from the adjusting transistor to the control electrode of the switching transistor is increased. An excess current or voltage is applied to lower the anode-cathode voltage of the switching transistor.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention employs a semiconductor element for a switch as a transistor (bipolar, FET) and uses a semiconductor switch capable of continuous power control. A voltage applied to the transistor is detected by dividing the equalizing resistor Rj, and a small current is caused to flow from the base current adjusting transistor to the control terminal (base, gate) of the switching transistor so that the voltage does not exceed the rated voltage. I have to. This prevents the voltage applied to the semiconductor element from exceeding the rated voltage.

In the transition from ON to OFF, an extra voltage is applied to the element which has been turned off quickly, but the voltage at the voltage dividing point rises at that time, and a minute voltage is applied from the base current adjusting transistor to the control electrodes (base, gate). Current flows, delaying the transition to off. Thereby, the element can be protected.

In the case of a load flash, the voltage drop at the load is zero.
, And all the power supply voltages V are applied to the n series semiconductor elements. That is, since the control current (gate signal) to which the voltage of V / n is applied still flows, the element remains conductive (ON). Since the current value is large, the voltage cannot be returned to a uniform value depending on the equalizing resistor having a large resistance value.

In this case, a voltage higher than the average voltage (V / n)
+ Δ) is applied to the j-th element, the base current adjusting transistor works to increase the control current. Therefore, it returns to the average voltage V / n. That is, the non-uniform voltage can be prevented even in the case of a load flash. Of course, the load flash should not be left for a long time, and the control current must be cut off immediately to turn off the transistor. As described above, the present invention exerts its effects in the case of a change from ON to OFF or in the case of a load flash (short circuit).

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a switch circuit connecting the semiconductor elements of FIG. 1, a circuit as shown in FIG. 2 is provided independently for all the semiconductor elements. In FIG. 1, n semiconductor elements Q
1, Q2,... Qn are connected in series. DC power supply 1
Is connected through a resistor 3 having a small resistance value to a series body Q1 of semiconductor elements,
Q2,... Qn. Each of the semiconductor elements has control electrodes G1, G2,..., Gn. .., R between the anode and the cathode of the semiconductor element.
n are connected. When the same control signal is applied to the control electrodes G1, G2,..., Gn at the same time, the whole is turned on / off.

Although the semiconductor element and the resistor have an n-stage configuration,
Since the semiconductor element and the equalizing resistor use the same thing,
Only one stage will be described. That is enough to understand the operation of the whole protection circuit.

In the present invention, the equalizing resistor Rj connected between the anode and the cathode of the semiconductor device is further divided into two. Ra and Rb. The combined resistance Rj becomes an equalized resistance value (Rj = Ra + Rb). This is the anode of the element Qj.
The voltage between the cathodes (the voltage between Mj-1 and Mj) is divided by the ratio of the resistance value ratio. A voltage signal line is taken out from the division point Kj and connected to the base of the transistor Qc. The collector of transistor Qc is connected to voltage V _CC . V _DD is obtained from the emitter potential Mj of the semiconductor element Qj. V _CC is a constant voltage higher than that,
_An appropriate DC power supply is required to _generate the voltage of V _CC from _DD .

The cathode of the diode D1 is connected to the gate terminal (base) of the semiconductor device. A gate signal Ig is input from the anode of D1. This is the same as in the conventional example, in which a control signal is input to the gate (base).

Here, a case where both the switch element and the adjusting device are bipolar will be exemplified. A circuit can be similarly configured with an FET.

The cathode of the second diode D2 is connected to the base Gj of the semiconductor element Qj. The adjustment current Ic flows through this. Therefore, a base current adjusting transistor Qc is newly provided. D1 and D2 are necessary to separate the control signal and the adjustment signal. The collector of the base adjustment transistor Qc is connected to V _CC . The emitter of Qc is connected to the anode of diode D2 via variable resistor VR1. The base of Qc is connected to a voltage dividing point Kj via a resistor Rc.

It is assumed that the collector-emitter voltage of Qj is Vj. Since this is divided by the resistors Ra and Rb, the point Kj becomes RaVj / Rb. Assuming that the voltage drop at Qj or D1 is δ, a current of Ib = {(RaVj / Rb) −δ} / Rc flows to the base of the adjustment transistor Qj.

When the power supply voltage V is evenly distributed (V
j = V / n), the base current Ib is set to 0. (RaV / nRb) −δ <0 When the voltage Vj between the anode and the cathode of the transistor is V / n
, A base current flows, which is amplified by Qc and enters the base Gj of Qj. The collector current of Qj increases and the voltage drops. Therefore, Qj is free from destruction.

The maximum value of the adjustment current Ic sent from Qc to Gj depends on the rated voltage Vm of the transistor, the load resistance RL,
It is appropriately determined by the power supply voltage V, but is much smaller than the control signal Ig applied through D1.

[0034]

According to the circuit of the present invention, in a semiconductor switch circuit in which transistors are connected in series and an equalizing resistor is provided in parallel with each transistor, the equalizing resistor is divided and a voltage is taken out from a dividing point. The voltage applied to the transistor is detected, and a base current is added so that the voltage does not abnormally increase. When the base current is increased, the voltage between the collector and the emitter of the transistor decreases, and the transistor can be protected. When a semiconductor element is used as a switch for opening and closing a high-voltage power supply, a large number of elements are connected in series because the withstand voltage is insufficient. However, it is difficult to maintain a balance between the elements, and the elements are easily damaged.
However, the present invention can protect a semiconductor device and maintain a circuit.

In the circuit of FIG. 1, in order to make the voltage applied to the semiconductor element in an off state (open, non-conductive) constant, a voltage equalizing resistor R1 is used.
To Rn. Each of them is simply drawn with one dashed line, but in reality, several resistors are connected in series. This is because the permissible heating value is not sufficient with one resistor. Therefore, the number of components does not increase even if dividing the equalizing resistance. Although the number of adjusting transistors and the number of power supplies therefor increase, the withstand voltage of the adjusting transistors may be low and the rated current may be small, so that they are inexpensive. In addition, the newly required power source is small and inexpensive. The protection circuit of the present invention does not significantly increase the cost as compared with the conventional example.

[Brief description of the drawings]

FIG. 1 is a schematic circuit diagram of a semiconductor high-voltage switch circuit according to a conventional example.

FIG. 2 is a protection circuit diagram according to an embodiment of the present invention, which is added at each stage of the circuit of FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DC power supply 2 Resistance 3 Resistance Q1-Qn Switch semiconductor element R1-Rn Equalization resistance G1-Gn Control electrode Qc Base current adjustment transistor VR1 Variable resistance D1, D2 Diode Ig Control current Ic Adjustment current Ib Base of adjustment transistor Current

Continued on the front page F-term (reference) 5J055 AX32 AX56 AX65 BX16 CX04 CX07 DX04 DX12 DX42 DX53 DX61 DX72 DX83 DX84 DX88 EX24 EY01 EY02 EY03 EY12 EY17 EY21 FX02 FX04 FX09 FX32 FX33 GX01

Claims (1)

[Claims] 1. A transistor control device comprising: a plurality of stages of switching transistors connected in series between a DC power supply and a load; and a plurality of stages of voltage equalizing resistors connected between an anode and a cathode of the transistors. In a high-voltage switch circuit that simultaneously opens and closes a transistor by simultaneously applying a control signal to the electrode, an adjusting transistor connected to the control electrode of the transistor in each stage is provided, and between the anode and cathode of the switching transistor. Divide the connected equalizing resistor, connect the voltage at the voltage dividing point to the control electrode of the adjusting transistor, and when the voltage at the dividing point of the equalizing resistor rises, the excess current or the excess current is applied to the control electrode of the switching transistor from the adjusting transistor. Voltage to reduce the anode-cathode voltage of the switch transistor. High voltage switch protection circuit characterized by the following.