JPH01261919A - Power output circuit - Google Patents

Abstract

PURPOSE:To speed up the switching of an output MOSFET to an off state by providing driving MOSFET between the gate and the source of the output MOSFET in a source follower type so as to attain switch control. CONSTITUTION:The driving MOSFETQ2 is provided between the gate and the source of the power output MOSFETQ1. When a control signal is switched from an H level to an L level, the output signal of an inverter circuit N1 comes to the H level and makes FETQ2 in an on state. Since the gate and the source in FETQ1 are shortened, FETQ1 is switched from the on-state to the off-state. At that time, a back electromotive voltage occurs in an inductive load L and an output terminal OUT connected to the source of FETQ1 is reduced to a negative and lower order. Energy accumulated in a load L can be released in a short time by a voltage clamping circuit consisting of a diode D3 and a Zener diode ZD.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a power output circuit, and relates to a technique that is effective when applied to an output circuit that drives an inductive load using, for example, a source follower type output MOSFET. It is.

[Conventional technology]

As an example of a power output circuit that drives an inductive load, there is, for example, Magazine R Electronics Technology J, November 1987 issue, pages 22 to 25. This power MOSFET has a source grounded and a drain connected to an inductive load such as a motor.

[Problem to be solved by the invention]

Power output circuits installed in automobiles, such as electronic fuel injection solenoids, have power output elements on the power supply voltage side.
It is desirable to use a high-side drive circuit (source follower circuit) in which the load is placed on the ground potential side of the circuit. because,
This is because if the load is connected to the power supply voltage side and the load is grounded due to a collision or the like, there is a risk that an overcurrent will flow there and cause a fire.

However, in the source follower output circuit as shown in FIG. 4, when the drive MOSFET Q2 is turned on,
The gate of the output MOSFET QI is set to a low level like the ground potential of the circuit. This causes the output MOS F
ETQ 1 is switched from the on state to the off state, but a back electromotive voltage is generated in the load. As a result, as shown in FIG. 5, the source potential of the output MOSFETQI becomes a negative potential, and when it reaches the effective threshold voltage vth of the output MOSFETQI, the output MOSFETQI
turns on and clamps the potential of the output terminal OUT. Since the threshold voltage vth is a relatively small voltage in absolute value, it takes time to release the energy stored in the load, and the actual output MOS
'Slow down the switching of FET to the off state. This means that when the load is driven by a pulse width modulation signal, the longer the back electromotive voltage period, in other words, the longer the time for switching the output MOS FET to the substantially off state, the longer the pulse width. The pulse width duty of the modulation signal is restricted and the control range becomes narrower.

The purpose of this invention is to provide an output MOSFET in the form of a source follower.
An object of the present invention is to provide a power output circuit that can quickly switch an ET to a substantially OFF state.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Means to solve the problem]

A brief overview of typical inventions disclosed in this application is as follows.

That is, a drive MOSFET is provided between the gate and source of the source follower type output MOSFET to perform switch control.

[For production]

According to the above means, when the drive MOSFET is turned on, the gate and source of the output MOSFET are short-circuited, so even if a back electromotive force is generated due to an inductive load, the output MOSFET can be maintained in an off state, and an appropriate With a voltage clamp circuit, it is possible to release the energy stored in an inductive load in a short time.

〔Example〕

FIG. 1 shows a circuit diagram of an embodiment in which the power output circuit according to the present invention is used in a high-side drive circuit (source follower circuit) that drives an inductive load such as a motor or a solenoid. It is shown.

The power output circuit of this embodiment is formed as one integrated circuit IC as shown by the broken line in the figure. Although not particularly limited, the power MOSFET QI uses the substrate as its drain region, and the power MOSFET QI is formed on the back side of the substrate. The structure is such that a drain electrode is provided.

The drain of the power MOSFET QI is connected to the power supply voltage Vcc
is combined with The source of the MOSFET QI is coupled to an external terminal OUT, to which an inductive load such as the motor or solenoid is provided. Therefore, power output MOSFET Q1 is a source follower output MOS
Operates as a FET. □ A drive MOSF is installed at the gate of the power MOSFETQI above.
A drive circuit consisting of ETQ2 and a load resistor RL is provided. As the operating voltage of the drive circuit, a voltage Vcc+V obtained by boosting the power supply voltage Vcc by a booster circuit BST is used.

Although not particularly limited, a control signal in is supplied to the gate of the drive MOSFET Q2 through an inverter circuit N1.

Although not particularly limited, the operating voltage of the inverter circuit N1 is a 5V voltage that is relatively lower than the power supply voltage Vcc. Accordingly, the control signal in has a high level of 5V, and is set to a relatively low logic level such as the ground potential of a low level circuit. Therefore, the drive circuit consisting of the inverter circuit N1, MOSFET Q'2, and resistor R performs a type of level conversion operation.

In this embodiment, the following configuration is adopted to increase the substantial switching speed of the output MOSFET QI to the off state. That is, the drive MOSFETQ2
The source of MOSFET QI is coupled to the source of the power output MOSFET QI, rather than being coupled to the circuit's ground potential point. In other words, the drive MOSFET Q2 is provided between the gate and source of the power output MOSFET QI.

For example, when the control signal in is at a high level, the output signal of the inverter circuit N1 is at a low level such as the ground potential of the circuit. Drive MOS according to the low level of this output signal.
FETQ2 is turned off and the power MOS FET
A boosted operating voltage Vcc+V is supplied to the gate of Q1 through a resistor R. The boosted voltage +■ formed by the booster circuit BST is set to be equal to or higher than the substantial threshold voltage of MOSFET QI. Therefore, as shown in the waveform diagram of FIG. 2, when MOSFET QI is in the on state, the power supply voltage Vcc is directly output from its source, so that a high output voltage without voltage loss can be obtained. When the output MOS FETQl is turned on in this way, the voltage at the output terminal OUT becomes a high voltage such as the power supply voltage Vcc, and the drive MOSFETQ2 is turned on accordingly.
The source voltage of will also be high. Therefore, the drive MOSFET Q2 can be maintained in the off state by the low level of the output signal of the inverter circuit N1 as described above.

When the control signal in changes from high level to low level, the output signal of the inverter circuit N1 becomes high level and turns on the drive MOSFET Q2. As a result, the gate and source of the power MOSFET QI are short-circuited, so that the power MOSFET QI is switched from the on state to the off state. At this time, a back electromotive voltage is generated in the load, lowering the output terminal OUT to which the source of the power MOSFET QI is connected to a negative potential.

In this embodiment, a voltage clamp circuit consisting of a diode D3 and a Zener diode ZD is provided for the above load. Therefore, as shown in the waveform diagram of FIG. 2, the potential of the output terminal OUT when the output MOSFET Q1 is turned off is -(VD3+VZD
) becomes a large voltage with negative polarity. Here, VD3 is the forward voltage of diode D3, and VZD is the Zener voltage of Zener diode ZD. By setting the clamp voltage to a high absolute value, the energy stored in the inductive load can be released in a short time.

Even if the output terminal OUT is set to a large negative voltage as described above, the off state can be maintained because the gate and source of the power output MOSFET QI are short-circuited by the drive MOSFET Q2. At this time, the drive MOS
The gate of FETQ2 is supplied with a high level voltage such as +5■ formed by the inverter circuit N1, and since the back electromotive force generated by the above load has negative polarity, the voltage between the gate and source is The voltage applied to becomes thicker to maintain the above-mentioned on state.

Although not particularly limited, MOSFET Q3 and diode D2 are provided for the following reason. In other words, the MOSFET is
When driving MOSFET Q2, when MOSFET Q2 is off, its source potential is VVcc, so MOSFET
ETQ2 cannot be switched from off state to on state.

Therefore, the source potential of MOSFETQ2 is first lowered to the ground potential by MOSFETQ3. Further, the diode D2 is provided to prevent the gate voltage of the MOSFETQI from being clamped at -v by the drain-source diode of the MOSFETQ2.

FIG. 3 shows a circuit diagram of another embodiment of the power output circuit. In this embodiment, a voltage clamp circuit is built into a semiconductor integrated circuit IC. That is, the power output M
A diode DI and a Zener diode ZD similar to those described above are provided between the gate of OSFET QI and an appropriate internal voltage Vx. Further, the load of the drive circuit uses a constant current source 1o instead of the resistor RL as described above. A resistor R is inserted between the drain of the drive MOSFET Q2 and the gate of the output MOSFET QI.

In this configuration, the output voltage is Vx-(VDI+VZD
+Vth) (7), the transistor 7-M03FET Q1 turns on again and releases the electrical energy stored in the load. In other words, the voltage drop at the resistor R becomes
When the effective threshold of OSFETQI (a voltage is reached,
The capacitor 7-M03FETQI turns on again and performs a voltage clamp operation.In this case, the clamp voltage can be set high, so the back electromotive voltage period can be shortened.In this case, Since the power of the back electromotive voltage is consumed by the output MOSFET QI, the built-in diode D1 and Zener diode ZD can be used for small signals.Therefore, in the circuit of this example,
Compared to the first leap circuit, external components such as a large signal diode and a Zener diode ZD constituting the voltage clamp circuit are unnecessary.

Power MOSFETQ1 shown in Figure 1 or Figure 3 above
Although not particularly limited, the drain region thereof is an N-type substrate. Therefore, the drain electrode is provided on the back side of the substrate. A P-type channel region constituting power MOSFET 0.1 is formed in a ring shape on the surface of the substrate.

Similarly, a ring-shaped N is formed on the surface of this P-type channel region.
A source region of the mold is formed. A gate electrode is formed on the surface of the channel region sandwiched between the source region and the substrate serving as the drain region, with a gate insulating film (not shown) interposed therebetween. The source region and the channel region are commonly connected to form a source electrode.

MOSFET as a drive circuit for the above power MOSFETQI
Each circuit element such as ETQ2, booster circuit BST, and constant current source Io is formed in a P-type isolation region formed on the front surface side of the substrate. That is, N in the P-type isolation region.
A transistor (diode) is obtained by forming a P-type collector region in the collector region, a P-type base region in the collector region, and an N-type emitter region in the base region. In addition, the N-channel region SFET is
It may be formed in the P-type isolation region.

The effects obtained from the above examples are as follows. That is, (1) a drive MOSFET is provided between the gate and source of the source follower type output MOSFET to perform switch control thereof. In this configuration, the drive MO
When S FET turns on, the output MOS F E
By short-circuiting the gate and source of the T, the output MOSFET can be kept off even if a back electromotive force is generated by the inductive load, and an appropriate voltage clamp circuit can be used to quickly remove the energy stored in the inductive load. This has the effect that it can be released at

(2) Due to (1) above, the output MOSFET can be switched from the OFF state to the ON state at high speed, and when the output MOSFET is switch-controlled by a pulse width modulation signal, the control range is This has the effect of allowing a wide range of settings.

(3) By using the source follower output MO8FET, it is possible to obtain a power output circuit suitable for mounting on a vehicle.

(4) Power output MOS with built-in voltage clamp circuit
By turning the FET on again and clamping the back electromotive force, an effect can be obtained in that the number of external components can be reduced.

Although the invention made by the present inventor has been specifically explained based on Examples above, the present invention is not limited to the above-mentioned Examples, and various changes can be made without departing from the gist thereof. For example, a plurality of power MOS FETs may be provided on one semiconductor substrate. In this case, a power MOSFET whose drain is the substrate is inevitably used as a high-side drive circuit (source follower circuit) with a common drain. The above power MOSFET is an electronic type that can replace conventional mechanical switching elements, in addition to those that drive inductance loads such as motors and solenoids as shown in Figure 1, as well as drive circuits that drive lamps such as automobile headlamps. This makes it suitable for power switch circuits.

In addition, when configuring a low side drive circuit, the output M
P-channel M as OSFET and drive MOSFET
An OSFET may be used. In this configuration,
Since the ground potential of the circuit is applied to the drain of the P-channel MOSFET, a low-side drive circuit with a load on the power supply voltage Vcc side can be configured.

The present invention can be widely used as a power output circuit with a source follower configuration.

〔Effect of the invention〕

A brief explanation of the effects obtained by typical inventions disclosed in this application is as follows. That is, a drive MOSFET is provided between the gate and source of the source follower type output MOSFET to perform switch control. In this configuration, when the drive MOSFET turns on, the output MOSFET
Since the gate and source of the MOSFET are short-circuited, the output MOSFET can be kept off even if a back electromotive force is generated by the inductive load, and an appropriate voltage clamp circuit can be used to quickly remove the energy stored in the inductive load. It becomes possible to release it.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of this invention, FIG. 2 is a waveform diagram for explaining its operation, and FIG. 3 is a circuit diagram showing another embodiment of this invention. FIG. 4 is a circuit diagram showing an example of a source follower output circuit, and FIG. 5 is a waveform diagram for explaining its operation. IC: Semiconductor integrated circuit, L: Load (inductive), BS
T: Boost circuit, N1: Inverter circuit, Io: Constant current source

Claims (1)

[Claims] 1. An output MOSFET in the form of a source follower, a drive MOSFET provided between the gate and source of this output MOSFET, and a load provided between the drain of the drive MOSFET and an operating voltage. A power output circuit comprising means. 2. The power output circuit according to claim 1, wherein the source of the output MOSFET is provided with an inductive load and a voltage clamp circuit for a back electromotive force generated therein. 3. The power output circuit according to claim 2, wherein the drive MOSFET is driven by a pulse width modulation signal.