LCD-LED Displayvoltage converter

One-transistor Voltage Converter Schematic Circuit Diagram

Taking apart a solar-powered lamp revealed a single-transistor voltage converter circuit that allowed an LED to be driven from a 1.2 V cell. The l/h diagram shows the circuit (with slight modifications). The circuit oscillates at about 500 kHz and, at a cell voltage of 1.4 V, draws 11 mA with a respectably bright LED. The circuit works down to a supply voltage of 0.8 V.

One-transistor Voltage Converter Schematic Circuit Diagram

One-transistor Voltage Converter Schematic Circuit Diagram 2

The oscilloscope shows 3 Vpp at the LED, as expected. The left-hand coil and the capacitor form a series of resonant circuits, excited by the collector of the transistor which alternates periodically between conducting and blocking. When the transistor is of the upper coil dumps its stored energy so that the voltage on the collector rises to about double the cell voltage.

A sine wave voltage of 35 Vpp (!) was measured across the capacitor in the resonant circuit. Using a two-channel oscilloscope showed the phase relationships: the resonant circuit shifts the phase by about 90 degrees. The base resistor coupled with the base capacitance and the Miller capacitance ( effect) of the transistor adds a further phase shift.

The voltage increase obtained using the series resonant circuit can be used to make a bipolar voltage converter, for example to power operational amplifiers (see r/h diagram). Two electrolytic capacitors and two diodes rectify the voltage. The circuit can deliver a voltage difference of 9 V at 0.2 mA, which is enough for a low-power opamp.

A sine wave, sinusoidal wave, or just sinusoid is a mathematical curve defined in terms of the sine trigonometric function, of which it is the graph. It is a type of continuous wave and also a smooth periodic function. and is defined by the function y = sin x. In other words, it is an s-shaped, smooth wave that oscillates above and below zero.
The sine function and sine waves are widely used to model economic and financial data that exhibit cyclic or periodic behavior. The variable in such modeling exercises is time. For example, a business selling consumer discretionary goods is likely to experience strong seasonality in its sales and revenues.

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