JPH03210820A - Protective system for output transistor at load short-circuit - Google Patents

Abstract

PURPOSE:To protect an output transistor(TR) with a simple circuit by using an A/D converter built in a microcomputer to convert a voltage at an output terminal into a digital value and turning off the output TR when the value reaches a prescribed value or below. CONSTITUTION:When an H level signal is outputted to the output terminal 12b of a microcomputer incorporated with an A/D converter, a TR 15 is turned on and a current is supplied to a load 18. When the load 18 is short-circuited due to any cause, the voltage at an output terminal 17 is lowered. The voltage drop is detected by the microcomputer incorporated with the A/D converter and the output terminal 12b of the microcomputer 12 incorporated with the A/D converter is brought into an L level. Thus, the TR 15 is turned off and an output TR 13 is turned off. Thus, even when the load 18 is shortcircuited, since continuance of an overcurrent flowing to the output TR 13 is prevented even when the load 18 is short-circuited, the output TR 13 is protected.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a microcomputer with a built-in analog-to-digital converter (hereinafter simply referred to as an 'A/D built-in microcomputer').
The present invention relates to a load short-circuit protection method for an output transistor that protects the output transistor in the event of a load short-circuit in a device having an output transistor at the output terminal.

[Prior art]

FIG. 3 is a block diagram showing a protection method for a load short circuit of an output transistor in a control device using a conventional microcomputer with a built-in A/D. In the same figure, 31 is a DC power supply;
2 is a microcomputer with a built-in A/D, 33 is an output transistor drive circuit, 34 is a load short-circuit detection circuit, 35 is a PNP type output transistor, 36 is a load detection resistor, 37 is an output terminal, and 38 is a load.

The DC power supply 31 is connected to an A/D built-in microcomputer 32, an output transistor drive circuit 33, a load short circuit detection circuit 34, and is also connected to an emitter terminal of an output transistor 35. The output signal of the A/D built-in microcomputer 32 is input to the output transistor drive circuit 33, and the output signal of the output transistor drive circuit 33 is input to the base terminal of the output transistor 35. As a result, the A/D built-in microcomputer 32
The output transistor 35 is turned ON or OFF by the output signal of
It operates so that F. A collector terminal of the output transistor 35 is connected to a load detection resistor 36, and both ends of the load detection resistor 36 are connected to the load short circuit detection circuit 34. The output of the load short circuit detection circuit 34 is connected to the output transistor drive circuit 33. Further, one end of a load 38 is connected to the output terminal 37, and the other end is connected to ground.

First, if the load 38 is short-circuited while the A/D built-in microcomputer 32 outputs a signal to turn on the output transistor 35 via the output transistor drive circuit 33, a large current flows through the load detection resistor 36. Therefore, the potential difference between both ends becomes large. This potential difference is detected by a load short circuit detection circuit 34, and a signal from the load short circuit detection circuit 34 turns off the output transistor drive circuit 33, and also turns off the output transistor 35, thereby preventing the output transistor 35 from being destroyed.

[Problem to be solved by the invention]

However, in the conventional output transistor load short-circuit protection method described above, the load detection resistor 36 for high power is required to detect a short circuit in the load 38, and the load short-circuit detection circuit 34 is required to detect the potential difference between both ends of the load detection resistor 36. As a protection method for the transistor 35, there are problems in that the circuit configuration is not only complicated, but also the cost is high and the size is large.

The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide a protection method for an output transistor in the event of a load short circuit, which does not require a load detection resistor for high power use and a load short circuit detection circuit as described above. be.

[Means to solve the problem]

In order to solve the above problems, the present invention provides a device having a microcomputer with a built-in analog-to-digital converter and an output transistor at the output terminal, in which the voltage at the output terminal of the device that supplies current from the output transistor to the load is The voltage value of the output terminal is input to the microcomputer and converted to a digital value by the analog-to-digital converter built into the microcomputer, and when the digital value becomes less than a predetermined value, the load is short-circuited. detect,
The feature is that the output transistor is turned off.

[Effect]

By protecting the output transistor in the event of a load short circuit as described above, the analog
A digital converter converts the voltage value of the output terminal into a digital value, and when the digital value becomes less than a predetermined value, a short circuit in the load is detected and the output transistor is turned off. , the output transistor can be protected without requiring a high-power load detection resistor or a load short-circuit detection circuit.

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 is a circuit diagram of a control device having a microcomputer with a built-in A/D to which the output transistor load short-circuit protection method of the present invention is applied. The + side terminal of the DC power supply 11 is connected to the power supply terminal 12a of the A/D built-in microcomputer 12 and the emitter terminal 13e of the PNP type output transistor 13. A resistor 14 is connected to the output terminal 12b of the A/D built-in microcomputer 12, and the other end of the resistor 14 is connected to an NPN transistor 15.
It is connected to the base terminal 15b of. A collector terminal 15c of the transistor 15 is connected to a base terminal 13b of the output transistor 13 via a resistor 16. A collector terminal 13c of the output transistor 13 is connected to an output terminal 17 of the control device and an analog input terminal 12c of the microcomputer 12 with built-in A/D. A load 1B is connected to the output terminal 17. Also, the other end of the load 18, one side terminal of the DC power supply 11, and one side power supply terminal 12d of the A/D built-in microcomputer 12.
The emitter terminal 15e of the transistor 15 and the emitter terminal 15e of the transistor 15 are respectively connected to ground. The A/D built-in microcomputer 12 has input/output terminals other than the output terminal 12b and the analog input terminal 12c, and various signal lines are connected thereto, but since they are not directly related to the present invention, their explanation will be omitted.

First, H(
When a high) level signal is output, the transistor 15 is turned on, and the output transistor 13 is also turned on, so that current is supplied to the load 18 via the output terminal 17.

The A/D built-in microcomputer 12 takes in the voltage of the output terminal 17 through the analog input terminal 12c.

If the load 18 is short-circuited for some reason, the output terminal 17
This voltage drop is detected by the A/D built-in microcomputer 12, and the output terminal 12b of the A/D built-in microcomputer 12 is set to L (low) level. As a result, the transistor 15 is turned off, and the output transistor 13 is turned off.
Becomes FF.

As a result, even if the load 18 is short-circuited, the output transistor 1
Since overcurrent can be prevented from continuing to flow through transistor 3, output transistor 13 is protected.

Figure 2 shows the output terminal 17 by the A/D built-in microcomputer 12.
12 is a diagram illustrating a processing flow for measuring the voltage, determining whether it is less than a predetermined value (when the load is short-circuited), and determining the output state of the output terminal 12b of the A/D built-in microcomputer 12. FIG.

In FIG. 2, the voltage value of the analog input terminal 12c of the A/D built-in microcomputer 12 is converted into a digital value (step 201), and then it is determined whether the converted digital value is less than a predetermined value. If the digital value is less than a predetermined value, it is assumed that the load 1B is short-circuited, the output terminal 12b is set to L (low) level, and the process returns to step 203).

If the digital value is not below a predetermined value in step 202, the output terminal 12b is set to H (high) level, and step 2
04), return to step 201.

〔Effect of the invention〕

As explained above, according to the present invention, the voltage value of the output terminal is converted into a digital value by the analog-to-digital converter built in the micro combinator, and when the digital value becomes less than a predetermined value, the load is Since a short circuit is detected and the output transistor is turned OFF, the output transistor can be protected with a simple circuit that does not require a conventional high-power load detection resistor or load short circuit detection circuit, and it also has a compact size. Extremely excellent effects can be obtained in that it is possible to reduce costs and reduce costs.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a control device having a microcomputer with a built-in A/D to which the output transistor load short-circuit protection method of the present invention is applied, and Fig. 2 is a diagram showing the processing flow of the microcomputer with a built-in A/D of the above control device. , FIG. 3 is a block diagram showing a protection method for a load short circuit of an output transistor in a control device using a conventional microcomputer with a built-in A/D. In the figure, 11...DC power supply, 12...A/D built-in microcomputer, 13...output transistor, 14...
-Resistor, 15...Transistor, 16...Resistor, 17...Output terminal, 18...Load.

Claims (1)

[Scope of Claim] A device having a microcomputer with a built-in analog-to-digital converter and an output transistor at an output terminal, wherein a voltage at an output terminal of the device that supplies current from the output transistor to a load is controlled by the microcomputer. input to the computer, convert the voltage value of the output terminal into a digital value with the analog-to-digital converter, and when the digital value becomes less than a predetermined value, a short circuit in the load is detected and the output transistor is switched on. A protection method for the output transistor in the event of a load short circuit, which is characterized by being turned OFF.