JPS61296508A - Circuit for detecting open head of digital magnetic circuit - Google Patents

Abstract

PURPOSE:To detect an open head and a fault of the titled circuit with a small- sized and simplified circuit by utilizing the change in a bias voltage generated in a recording circuit at data recording. CONSTITUTION:Suppose that a transistor (TR) 3 is turned off when a level of an input terminal is at +V, an output of an inverter goes to +V when the level of the input terminal is OV and OV when +V, then a TR 4 is conductive, a current flows from a current source 5 to diodes 10, 12 and a magnetic head 20 and a magnetic head is excited invertedly. Diodes 13-15, resistors 16-18 and a TR 19 constitute a head open detection circuit. Each anode voltage of diodes 9, 10 is a repetitive waveform with a voltage amplitude of 2ED+EF with a bias of 2ED, where ED is an on-voltage of the diodes and EF is flyback voltage of a coil. When the head is opened, a collector voltage of the TR 19 is nearly OV and detected by the change in the collector voltage.

Description

Detailed Description of the Invention 1. Field of Application of the Invention The present invention provides a digital magnetic recording device that detects circuit abnormalities caused by disconnection of a magnetic head coil or an open state between a recording circuit and a coil in response to a data input signal. This invention relates to a circuit that detects when recording data.

[Background of the Invention] Conventionally, a method for detecting an abnormality in the data recording circuit of a digital magnetic recording device is to detect the occurrence of a flyback voltage that occurs at one end or both ends of a magnetic head coil during recording, and to detect an abnormality in the head. Methods are known for detecting changes in flyback voltage over time. Furthermore, a method is known in which a voltage difference occurring between both ends of the head is sensed, a change in output voltage at the time of an abnormality is detected, and an abnormality is reported.

However, since the sensing circuit is placed in the head, there is a problem in that the connection between the head and the circuit becomes complicated.

A technique for checking abnormalities in recorded information is described in, for example, Japanese Patent Application Laid-open No. 129918/1983. [Object of the Invention] An object of the present invention is to use a circuit that is smaller and simpler than the above-mentioned method. Another object of the present invention is to provide a method for detecting an open state of a head section by sensing an abnormality in a circuit section and reporting the abnormality.

[Summary of the invention]

If the head coil is disconnected or an open state occurs between the head and the recording circuit, the bias voltage changes in the recording circuit connected in series to the head during data recording. The present invention can detect the open state of the head by sensing this change in bias voltage.

Embodiments of the Invention Embodiments of the invention will now be described with reference to FIG. terminal 1
For example, the digital recording signal input from
When this input is Ov, the transistor 3 is turned on and the recording current source 5
-it insertion current flows through the diode 9.11 and the magnetic head 20. Furthermore, when the input terminal becomes +■, the transistor 6 turns off, and the output of the inverter 2 performs an inversion operation in which the output becomes @+V when the input terminal is Ov, and Ov when the input terminal is +V. , current source 5
As a result, current flows through the diodes 10 and 12 and the magnetic head 20, and the magnetic head is excited in the above-mentioned reverse manner. Diodes 13 to 15, resistors 16 to 18, and transistor 19 constitute a head open detection circuit. When recording data, the input terminal repeatedly changes between Ov and +■. At this time, the anode voltage of each of the diodes 9 and 100 is, if the on voltage of the diode is ED1 and the flyback voltage of the coil is EF, the voltage amplitude is 2·HD− with 2·ED as the bias.
The repeated waveform of 1-EF is shown in FIG. 2(a). Now, suppose that the head coil 20 is disconnected or the connection between the circuit section and the head becomes open. During recording, the current of the current source 5 is changed to the transistor 3 due to the signal reversal of the data input 1.
, 40 flow to resistors 6 and 7.8, respectively, when they are on. Here, the resistance values of resistors 6 and 7.8 are respectively R, and R mat n
a, the resistor 6 is a damping resistor, the resistor 7°8 is a reverse bias resistor, R, >> R,, R, (R.

=R, =R). Therefore, for example, when transistor 3 is turned on, the collector connection resistance becomes R/2, where resistor 7 is connected in parallel with the series value of resistor 6 and resistor 8 (approximately 10 R, R). . Therefore, since the head is in an open state, the anode voltage of the diode 9 is determined only by this resistance value R/2 since the diode is not conductive.
It becomes 几・I/2−■. By setting the resistance value R to several Ω to several tens of Ω, it is possible to easily achieve 2ED+EF<几·I/2−V. With the head coil open,
When data is recorded, the anode voltage when the diodes 9 and 100 are non-conducting has the waveform shown in FIG. 2(b). Here, if the on-voltage between the emitter and base of the diodes 16 to 15 and the switching transistor 19 is Vl)t, and the voltage across the resistor 16 is R, then the transistor 19
The anode voltage of diode 9 that turns on is 3VD1+
It will be VR.

Adjust the value of resistor 16.17, 2ED +Ep < 3V old +VB < ReI/2-
V, the transistor 19 will be turned off under normal conditions due to changes in the anode bias voltage of the diodes 9 and 10, and the collector output of the transistor 19 will be 5.
v, and if the head is open, transistor 19
The collector becomes almost Ov, and opening of the head can be detected by a change in the collector voltage.

(Effect of the Invention J According to the present invention, when the head coil is disconnected or the head and the recording circuit section are in an open state, an abnormal state can be detected by detecting the change in bias voltage that occurs in the recording circuit when recording data. The method of detecting flyback voltage and detecting the voltage between terminals across the head requires a circuit that combines a time constant circuit, a comparator, an amplifier, etc., but the present invention detects excessive bias voltage. Therefore, the abnormality detection circuit can be made small and inexpensive, and by not directly detecting the head coil, the configuration of the connection part between the recording circuit section and the head coil can be reduced. It has the advantage of being simple.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of an embodiment of the present invention, Figure 2 (a) is a voltage waveform diagram of the diode 9,100 anode during normal recording operation, and Figure 2 (b) is in the recording state with the head open. 2 is a voltage waveform diagram of the anodes of diodes 9 and 10 in FIG. DESCRIPTION OF SYMBOLS 1... Recording data input terminal, 2... Analog inverter, 5... Recording current source circuit, 9-15... Diode, 19... Transistor for detection.

Claims (1)

[Claims] 1. In a data recording magnetic head of a digital signal recording device and a data recording circuit that records data with the head, the bias of each of the recording circuit sections connected in series to both ends of the data head during recording is detected. A digital magnetic circuit characterized in that a circuit is provided in the recording circuit to detect and display a change in bias voltage generated in the recording circuit in the event of an abnormality due to a disconnection of the head or an open state of the circuit and the head. head open detection circuit.