The switch of electronic system of ignition 98.3734. Scheme, description

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The switch of electronic system of ignition 98.3734. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Automobile. Ignition

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The electronic ignition switch 98.3734 developed and manufactured by JSC ChNPPP ELARA (hereinafter referred to as the switch) is designed to switch the current in the primary winding of the coil of the contactless ignition system for cars of the VAZ-2105, VAZ-2108, VAZ-2110, VAZ-21213, VAZ-1111 families , ZAZ-1102 [1] The instrument is protected by a utility model certificate.

The device works in conjunction with ignition coils 3122.3705, 27.3705 and their modifications, having a primary winding resistance of less than 0,7 Ohm and an inductance of not more than 7 mH, a distribution sensor 40.3706, 3810.3706 and their modifications. The rated supply voltage is 12, the maximum is 16, the minimum is 6 V. The switch normalizes the current limiting time through the ignition coil, depending on the operating mode, in the range from 0,6 to 4,5 ms, which is 2 ... 15% of the duration of the period input signal at a frequency of 33 Hz and a supply voltage of 13,5 V. The switching current of the ignition coil (break current) is limited by the switch at the level of 7,3 ... 7,8 A at a supply voltage of 13,5 V. The switch stops the flow of current through the coil ignition 1 s after the stop of the sensor-distributor shaft, preventing sparking. Working range of ambient temperature from -45 to +105 °С.

Electronic ignition switch 98.3734

The switch diagram is shown in fig. 1, and the appearance - in Fig. 2.

Electronic ignition switch 98.3734

Positional designations of all elements correspond to the scheme of the manufacturer. The basis of the device is a specialized integrated circuit L497D from ST Microelectronics, designed to control the switching transistor BU941ZP of the same company. The operation of the microcircuit is described in detail in [2]. Let us consider some features of its operation with a switch-on different from the typical circuit.

Chip DA1 is powered by two current sources. The first source on transistors VT1 and VT2 provides a current of 50 mA to power the Hall sensor and the DA1 chip. Its output current depends on the resistance of the resistor R3 and the voltage at the emitter junction of the transistor VT1. Resistor R2 sets the operating point of the transistor VT2 and the voltage at the collector of the transistor VT1.

In the event of an increase in temperature, the voltage across resistor R3 decreases by approximately 2,1 mV/°C, which leads to a corresponding decrease in the output current. Capacitor C9 suppresses high-frequency oscillations that occur when voltage surges appear in the car's on-board network.

The second current source, made on transistors VT3 and VT4, stabilizes the base current of the transistor VT5 at 40 mA. The use of transistors MJE350 (VT2, VT4) in current sources ensures reliable operation of the switch in the event of impulse noise up to 350 V in the vehicle's on-board network and an increase in ambient temperature up to 105 °C.

The Zener diode VD3 BZX84C9V1 stabilizes the voltage at 9 V to power the Hall sensor.

Diode VD1 protects the device from reverse polarity of the power supply.

Resistor R28 and diode assembly VD5 provide reliable protection of microcircuit inputs from possible voltage surges.

The VD4R13C8R14 circuit protects the VT5 transistor in the event of an increase in voltage in the on-board network. If the voltage exceeds 24 V, the VD4 zener diode opens and current begins to flow through the resistors R13, R14, which leads to an increase in the voltage at the HI input (pin 13) of the current feedback on the DA1 microcircuit and to a decrease in the current limit level in the ignition coil. When the voltage exceeds approximately 70 V, the switch turns off completely.

The switching transistor current sensor (R18-R27) is made of ten 1 ohm surface mount resistors connected in parallel. In previously produced switches, the function of the current sensor was performed by the ASOS resistor with a resistance of 0,1 Ohm ± 5%. However, experiments have shown that the sensor used here has better temperature stability.

The block uses imported element base mainly for surface mounting. Fixed resistors and ceramic capacitors X7R - size 1206. Bipolar transistors BUZ941ZP and MJE350 are replaceable by transistors KT898A (or series KT8131, KT8225, KTD8252) and KT720A, respectively, and transistors BC808 - BC807.

Literature

Pyatkov K. B., Ignatov A. P., Kosarev S. N. et al. Cars VAZ-2110 and VAZ-21102: Maintenance and repair manual. - M.: Behind the wheel, 1996.
Khodasevich A. G., Khodasevich T. I. Handbook on the device and repair of electronic devices in cars. Issue. 1. Electronic ignition systems. - M.: Antelkom, 2001.

Author: A. Pozdeev, Cheboksary

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