JPH04239814A - Current detection circuit for mosfet - Google Patents

Abstract

PURPOSE:To detect a current at other part than a main current path in a current detection circuit of a MOSFET. CONSTITUTION:The series connection of a limit resistor 2, a transistor(TR) 3 and a current sensing resistor 4 is connected in parallel between a drain D and a source S of a MOSFET 1. In this case, the limit resistor 2 is connected to a collector of the TR, the sense resistor 4 is connected to the emitter, and a gate G of the MOSFET1 is connected to the base G1 respectively and the operation of the MOSFET1 is made stable to detect a current by eliminating a current sensing component from the main current path.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a MOSFET switching circuit.

0002

[Prior Art] A conventional MOSFET current detection circuit is
As shown in FIG. 3, in the switching circuit of MOSFET 1, a current transformer 8 and limiting resistors 9a and 9b are connected.
, a diode 10, and an electrolytic capacitor 11 (for example, μPC1094C, 1094G Application Note, NEC, IEA-631A, 1990).
．． 4).

First, when the switching element MOSFET 1 is turned on and a main current flows, the current flows through the primary side of the current transformer 8. In this case, a voltage is generated on the secondary side of the current transformer 8 in accordance with the amount of change in the current.

The voltage generated on the secondary side of the current transformer 8 is converted into a half-wave rectified waveform by a smoothing diode 10 and a limiting resistor 9a, and further by a smoothing electrolytic capacitor 1.
1 to convert it into a DC voltage. The limiting resistor 9b is a limiting resistor for adjusting the level of the DC voltage. In the case of this circuit, the voltage generated in the sense increases according to the change in the main current, allowing current detection.

[0005]

[Problem to be solved by the invention] This conventional MOSFE
The T current detection circuit is effective when the load is a transformer, but cannot be used when the load is a resistive load or a capacitive load. Furthermore, since the current transformer 8 is used, the current detection section is large, which poses problems in terms of economy and space.

In order to solve these problems, as shown in FIG. 4, a sense resistor 4 is inserted between the source S and GND of MOSFET 1 as a switching element, and the voltage (current is converted into voltage by the resistor) is sensed directly. There was a method called (for example, μPC1099C×1GS Application Note NEC IEA-647A, 1990
/4). In the case of this current detection circuit, the source S of MOSFET 1 floats above GND, resulting in poor operational stability and the voltage applied to the gate G must also be higher than usual. Furthermore, since there is a sense resistor on the main current route, there is a problem in that noise voltage is easily generated and accurate current detection cannot be performed.

An object of the present invention is to provide a MOSFET current detection circuit that detects the current of the MOSFET based on the on-voltage of the MOSFET.

[0008]

[Means for Solving the Problems] In order to achieve the above object, a MOSFET current detection circuit according to the present invention includes a MOSFET, a limiting resistor, a second transistor, and a current detecting sense resistor. In this current detection circuit, the MOSFET is switched by the output of an IC, the second transistor is turned on and off by the same input signal as the MOSFET, and the limiting resistor and the second transistor are switched on and off by the same input signal as the MOSFET. The transistor and the current detection sense resistor are connected in series and in parallel between the drain and source of the MOSFET.

Furthermore, the current detection sense resistor is removed, and the limiting resistor and the current detection sense resistor are connected in series and in parallel between the drain and source of the MOSFET.

0010

[Operation] A limiting resistor 2 and a transistor 3 (as a second switching element) are connected in parallel between the drain D and source S of MOSFET 1 as a switching element from the drain side.
A collector C is connected to the limiting resistor 2 side, an emitter E is connected to the sense resistor side, and a base G1 is connected to the gate G of the MOSFET 1. ) and a sense resistor 4 are connected in series, and the on-voltage of MOSFET 1 turns on the MOSFET.
It detects the current.

[0011]

[Embodiments] Hereinafter, embodiments of the present invention will be explained with reference to the drawings.

(Embodiment 1) FIG. 1 is a circuit diagram showing Embodiment 1 of the present invention. In the figure, a limiting resistor 2, a transistor 3 as a second switching element, and a sense resistor 4 are provided between the drain D and source S of a MOSFET 1 as a first switching element, which are connected in series. Transistor 3 has its gate G1 connected to the gate G of MOSFET 1 and is turned on and off by the same input signal as MOSFET 1. A sense resistor 4 is connected to its emitter E, and a limiting resistor 2 is connected to its collector C. has been done.

MOSF as the first switching element
ET1 is turned on and off by IC output, etc.
The output of the IC and the like are simultaneously turned on and off by interlocking the transistor 3 as a second switching element. However, in this case, the switching time of MOSFET 1 and transistor 3 is MOSFET 1<<transistor 3, so MOSFET 1 is turned on → transistor 3 is turned on, and MOSFET 1 is turned off → transistor 3 is turned off. First, when MOSFET1 is turned on by the output of the IC, the drain D and source S of MOSFET1 are
The voltage between the two terminals suddenly decreases to an on-voltage (usually several volts). On voltage (after a while after MOSFET1 turns on)
At this stage, the transistor 3 as the second switching element turns on, and the on-voltage is divided by the limiting resistor 2, the collector saturation voltage of the transistor 3, and the sense resistor 4. In this case, if a sense terminal 5 is provided between the sense resistor 4 and the emitter E of the transistor 3, a voltage proportional to the ON voltage of the MOSFET 1 can be sensed.

Since MOSFET 1 is a semiconductor having an on-resistance that is approximately constant depending on the gate voltage (output voltage of the IC), if the current is not large, the on-state voltage of the MOSFET will also be large, and therefore the sense voltage will also be large.

[0015] The output of the IC is turned off, and MOSFET1
When turned off, the drain voltage rises to VCC (circuit voltage). In this case, the sense voltage also increases until the transistor 3 is turned off. normal MOSFE
When detecting the current of T, it is used as a protection circuit that turns off MOSFET1, which is the first switching element, if a current exceeding a certain level flows due to some abnormality. Turn on and off. Therefore, if the sense voltage increases while MOSFET 1 is on, the IC output is turned off, but the increase in the sense voltage when MOSFET 1 is off has no meaning. In other words, the fact that transistor 3 turns off later than MOSFET 1 does not pose a problem in actual use.

(Example 2) FIG. 2 is a diagram showing Example 2 of the present invention, in which (a) is a circuit diagram and (b) is a cross section of a pellet when the circuit in (a) is configured as one semiconductor. It is a diagram.

In this embodiment, only the sense resistor 4 in Embodiment 1 is removed, and the other connection configurations are the same as in the embodiment.

Next, the case where the circuit shown in (a) is manufactured as one semiconductor will be explained. First, by partially diffusing impurities such as phosphorus into the N-type substrate, MOSFET1
, the transistor 3 is formed (this is similar to the conventional manufacturing method). Next, the gate of MOSFET 1 and the base of transistor 3 are connected with aluminum wiring on the surface of the pellet. 7 is SiO2. Since the drain of MOSFET 1 and the collector of transistor 3 are on a common substrate, they are automatically connected. Limiting resistance 2 of transistor 3
The manufacturing methods are: ■ method using epitaxial resistivity, and ■ method of lowering the back surface impurity concentration of the N substrate to provide resistance (Fig. 2(b)
)), ■Reducing the effective emitter area of the transistor,
There are ways to create resistance. Regarding the operation in Figure 2,
This is similar to FIG. Note that although it is possible to form the sense resistor by diffusing it as a polysilicon resistor on the pellet surface, it is provided externally in order to increase the degree of freedom in design using a MOSFET.

[0019]

[Effects of the Invention] As explained above, the present invention provides a MOSFET
Since the current of the MOSFET is detected based on the ON voltage of the ET, the current can be detected regardless of the load, and since no transformer is used, space efficiency and economy can be improved. In addition, since only the switching element MOSFET is present in the main current path, it has excellent operational stability.
This has the effect that there is no need to increase the output voltage of the IC. Further, in the invention of claim 2, there are two switching elements on one pellet, and the only external component is the sense resistor, so there is an effect that space can be further saved compared to the invention of claim 1.

[Brief explanation of the drawing]

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

FIG. 2 is a diagram showing a second embodiment of the present invention, in which (a) is a circuit diagram of the second embodiment, and (b) is a cross-sectional view of a pellet when the circuit in (a) is made into a semiconductor.

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

FIG. 4 is a circuit diagram showing a conventional example.

[Explanation of symbols]

1 MOSFET 2 Limiting resistance 3 Transistor 4 Sense resistance 5 Sense terminal 6 Aluminum electrode

Claims (2)

[Claims] [Claim 1] MO comprising a MOSFET, a limiting resistor, a second transistor, and a current detection sense resistor.
SFET current detection circuit, MOSFET is I
The second transistor is turned on and off by the same input signal as the MOSFET, and the limiting resistor, the second transistor, and the sense resistor for current detection are: Connect in series,
A MOSFET current detection circuit, characterized in that the MOSFET is connected in parallel between its drain and source. 2. The current detection sense resistor is removed, and the limiting resistor and the current detection sense resistor are connected in series and connected in parallel between the drain and source of the MOSFET. M according to claim 1,
OSFET current detection circuit.