Stabilized voltage converter on the YX8018 chip. Scheme, description

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Stabilized voltage converter on the YX8018 chip. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Voltage converters, rectifiers, inverters

The YX8018 chip is widely used in low-cost LED lawn lamps, where an unstabilized boost converter is built on it. It provides power to the lighting LED (or LEDs) from a Ni-Cd battery. The current through the LED (from fractions to several milliamps) is set by the inductance of the storage choke in the converter. Therefore, there is no need to stabilize the voltage.

A feature of the YX8018 and similar microcircuits is the presence of a control input, with which you can also turn on the switch of the voltage converter. It is this input that is used in LED lawn lights to turn them on automatically at nightfall. The same input can be used to build a stabilized boost converter.

Stabilized voltage converter on the YX8018 chip
Fig. 1

A diagram of such a converter on the YX8018 chip is shown in fig. 1. It can be used to power a single Ni-Cd, Ni-Mh battery or a galvanic cell of various electronic devices that require a supply voltage of 2 to 5 V. In the initial state, at the CE input (pin 3) of the microcircuit, there is a voltage close to the voltage nutrition. This is due to the presence of a built-in resistor connecting this pin to the power plus. Therefore, the converter turns on, the voltage pulses at its output L (pin 1) rectifies the diode VD1, and the smoothing capacitors C2 and C3 are charged - the output voltage rises.

When the voltage at the gate of the transistor VT1 reaches the threshold value (about 2 V), the resistance of the transistor channel will decrease and the voltage at its source (and the CE input of the microcircuit) will also decrease - the converter will turn off. The output voltage will begin to decrease, which will lead to the closing of the field effect transistor and turning on the converter.

Stabilized voltage converter on the YX8018 chip
Fig. 2

Thus, the converter periodically turns on and off, maintaining the output voltage set by the tuning resistor R1. The operating frequency of the converter is about 200 kHz, and the on / off frequency depends on the output current and the capacitance of the capacitor C2 (the greater the current and the lower the capacitance of the capacitor, the greater the frequency) and can be from several hertz to tens of kilohertz. The dependences of the output voltage of the converter (2,7 V) on the input voltage for different values of the load current are shown in fig. 2.

The amplitude of the ripples is about 10 mV, it remains practically unchanged and, to a small extent, depends on the output voltage and the parameters of the field-effect transistor. The pulsation frequency depends on the operating frequency of the converter and the on/off frequency of the converter and can vary over a wide range. Thermal stability is determined primarily by the parameters of the field effect transistor. In this case, the voltage temperature coefficient is negative and amounts to several millivolts per degree Celsius.

Stabilized voltage converter on the YX8018 chip
Fig. 3

All elements can be mounted on a single-sided printed circuit board made of foil fiberglass, its drawing is shown in fig. 3. A tuning resistor SP3-19 was used, an oxide capacitor was imported, the rest were K10-17. Instead of the 1N5817 diode, low-power pulse or detector germanium diodes or Schottky diodes can be used. The inductor is wound on a ferrite ring with a diameter of 6 ... 9 mm from the transformer of the electronic ballast of a compact fluorescent lamp and contains 5 turns of wire PEV-2 0,4.

The output voltage in the range of 2,2.5 V is set with a tuning resistor, it can be replaced with a resistive divider with a total resistance of at least 1 MΩ. To reduce ripples with a frequency of 200 kHz between capacitors C2 and C3, a choke, for example EC24, with an inductance of 470 ... 1000 μH, must be installed in the positive power line.

Author: I. Nechaev

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