JPH03195212A - Semiconductor device - Google Patents

Abstract

PURPOSE:To allow the semiconductor device to take no notice of the performance of a current sending comparator without increasing an output impedance by detecting an output current depending on a gatesource voltage of an output transistor(TR). CONSTITUTION:Suppose that the reference voltage Vr of a reference voltage generator 5 is set to Vr=VGS2, when a current flowing to an output TR 4 is larger than ID2, the voltage VGS2 is larger than the voltage VGS2. Thus, a comparator 6 compares the gate-source voltage with the voltage Vr, outputs a signal to a gate drive circuit 7 to turn off the output TR 4. Since the voltage VGS when a current flowing to the output TR is smaller than the ID2 is smaller than the voltage VGS2, the TR keeps turning on. Thus, when a current larger than the current depending on the reference voltage Vr flows, the output TR 4 is turned off and when the current smaller than the current depending on the reference voltage Vr flows conversely, the output TR is turned on as it is. Thus, so-called overcurrent protection is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor device, and particularly to a current detection circuit for an output transistor in a source type output circuit using an N-channel field effect transistor.

[Conventional technology]

Conventionally, a current detection circuit of this type of output circuit uses a detector 38 to detect a voltage drop across a sense resistor 30 connected in series to an output transistor 34, as shown in FIG.

[Problem to be solved by the invention]

In the conventional output circuit described above, the sense resistor 30 for detecting current is connected in series with the output transistor 34, and the output impedance seen from the output terminal 33 becomes high, resulting in power loss. If the sense resistor 30 is set to a very small value, the voltage drop will be small and the performance of the detector 38 will become a problem.

[Means to solve the problem]

The output circuit of the present invention includes a gate-source voltage (VOS) detection circuit for detecting the current flowing through the output transistor; 8 judgment circuit, and a gate drive circuit that controls the output transistor to turn on/off (ON-OFF) according to the V(is judgment result).

In contrast to the conventional output circuit described above, the present invention detects current based on the voltage between the gate and source of the output transistor.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention.

4 is an output N-channel transistor, 5 is a reference voltage generator, 6 is a comparator, 7 is a gate drive circuit, 8
1 is a gate-source voltage detector, 1.2 is a power supply, 3 is an output terminal, and 9 is a control signal input terminal.

The output transistor 4 can flow a drain current corresponding to the gate-source voltage (VOS) as shown in FIG. A certain V, such as In++ for VGSI and ID2 for VQB2. ID that can be sent to 8
is decided.

Now the reference voltage VrO value of the reference voltage generator is V r =VG
82, when the current flowing through the output transistor 4 is larger than ID2, ■. ll is V. Since the value is larger than S□, the comparator 6 compares it with Vr, sends a signal to the gate drive circuit 7, and operates to turn off the output transistor 4. Also, V when the current flowing through the output transistor is smaller than ■1□. S is V. Since the value is smaller than s2, it remains in the ON state.

Therefore, when a current larger than the current determined by the value of the reference voltage Vr flows, the output transistor 4 is turned off (OF'F) L,
On the other hand, if the value is small, the operation is turned on (ON). This is a so-called overcurrent protection operation.

The current detection method using this circuit detects the voltage between the gate and source of the output transistor, so a relatively large voltage is detected, so the performance of the comparator is not a problem. Also, there is no need for a sense resistor to be placed in series with the output transistor.

FIG. 2 is a block diagram of another embodiment of the invention. 26
．． 26' is a comparator, 20 is a latch circuit, and the other configurations are the same as in the first embodiment.

This embodiment has two reference voltages, one being the maximum current value ID2 and the other being the minimum current value ID2. , if an overload is connected to output terminal 3, Ifll and ID
It becomes an on-off (ON-OF'F) operation between 20 and 20 seconds.

〔Effect of the invention〕

As explained above, the present invention has the advantage that by detecting the output current using the gate-source voltage of the output transistor, the output impedance does not increase and the performance of the current detection comparator does not become a problem. be.

29.39...Control signal input terminal.

Claims (1)

[Claims] A semiconductor device characterized in that a potential difference between a gate and a source of an output transistor is detected, and the output transistor is controlled depending on the magnitude of the potential difference.