Automotive digital clock power supply. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power Supplies
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Agree, it is very convenient when there is a digital electronic clock on the dashboard of your car, with a clearly visible contrast display with clear numbers that do not irritate your eyes, in harmony with the design of the dashboard.
Unfortunately, it is almost impossible to find car watches in the distribution network that meet such requirements. All that trade "generously" offers us is Chinese "consumer goods" on "blind" liquid crystal indicators. You can also buy a rather expensive, so-called "on-board computer", of domestic production, with a LED display, and use it as a clock.
But this is not an option either - apart from the unreasonably high price, the LED indicators of such devices are hard to read during the day, and the design leaves much to be desired.
In my opinion, the best option for a car is a watch with a vacuum luminescent indicator of the IVL type. The readings of such an indicator are equally well visible both day and night, with excellent clarity and a pleasant blue-green color. In the radio engineering literature from the 80s until recently, there are many descriptions of watches on such indicators made on the BIS K145IK1901, KA1035KhL1, KR1016VI1. But the use of these very good and time-tested circuits in a car is hindered by too high a supply voltage (not lower than 24 V), which is necessary for the operation of a fluorescent indicator. Of course, a ventilator can also work with 12 V litanium, but all its advantages will be lost.
In my car, I installed a clock on K145IK1901 and IVL2-7 / 3, made according to a typical scheme, and used a 28 V voltage source on the MC34Q63A DC-DC converter chip for power.
The converter is made according to the typical MC34063A switching circuit to increase the voltage (Step-Up). The voltage from the car battery is supplied to terminal 6A1. Through the resistor R1 to the pump output stage on the inductance L1. The microcircuit has a generator with an output key transistor.
The emitter of this transistor is connected to pin 2, the collector is connected to pin 1.
In this circuit, the emitter is connected to a common minus (pin 2), and the collector is loaded on the inductance L1. The pulse frequency is about 100 kHz. Self-induction EMF appears on L1, the magnitude of the pulses of which significantly exceeds the supply voltage. This alternating voltage is rectified by the diode VD1 and a constant voltage appears on C3.
To stabilize the output voltage, the comparator input A1 is used - pin 5. The voltage on it should be 1,25 V. If the voltage differs from this value, the parameters of the pulses on the collector of the output transistor change so as to compensate for the change.
The output voltage can be higher - up to 40 V, its value depends on the ratio of the resistances of the divider R4-R3. Coil L1 contains 35 turns of SEW 0,35 on a K13x7x5 ferrite ring.
With an output voltage of 28V, the maximum output current is 100mA. The filament target of the ventilator indicator must be powered directly from the car battery (through a quenching resistor or by means of an alternating voltage generator, as suggested in the typical K145IK1901 circuit).
Author: Krivenko P.A.
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