2MHz Square Wave generator Circuit Diagram

With the values shown the circuit generates a 2-MHz symmetrical square wave. Changing capacitors Cl and C2 to 0.01 µ¥ results in a frequency of 500 Hz. For the particular integrated circuits and power supply voltages (5.0 V), the reliable operating range of Rl = R2 is 2 k ohm to 4 k ohm.

2MHz Square Wave generator Circuit Diagram

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High Voltage Generator

This high voltage generator was designed  with the aim of testing the electrical break-down protection used on the railways. These  protection measures are used to ensure that  any external metal parts will never be at a  high voltage. If that were about to happen,  a very large current would flow (in the order  of kilo-amps), which causes the protection  to operate, creating a short circuit to ground effectively earthing the metal parts. This hap-pens when, for example, a lightning strike hits  the overhead line (or their supports) on the  railways. 

This generator generates a high voltage of  1,000 V, but with an output current that is limited to few milliamps. This permits the electrical breakdown protection to be tested with-out it going into a short circuit state. The circuit uses common parts throughout: a  TL494 pulse-width modulator, several FETs or  bipolar switching transistors, a simple 1.4 VA  mains transformer and a discrete voltage multiplier. P1 is used to set the maximum current  and P2 sets the output voltage. 

Circuit diagram :

High Voltage Generator Circuit Diagram

The use of a voltage multiplier has the advantage that the working voltage of the smoothing capacitors can be lower, which makes them easier to obtain. The TL494 was chosen  because it can still operate at a voltage of  about 7 V, which means it can keep on working even when the batteries are nearly empty.  The power is provided by six C-type batteries, which keeps the total weight at a reason-able level. 

The 2x4 V secondary of AC power transformer  (Tr1) is used back to front. It does mean that  the 4 V winding has double the rated voltage  across it, but that is acceptable because the  frequency is a lot higher (several kilo-Hertz)  than the 50 Hz (60 Hz) the transformer is  designed for. The final version also includes a display of the  output voltage so that the breakdown volt-age can be read. 

From a historical perspective there follows a  bit of background information. In the past a different system was worked  out. Every high-voltage support post has a  protection system, and it isn’t clear when  the protection had operated and went into  a short-circuit state due to a large current  discharge. 

Since very large currents were involved, a certain Mr. Van Ark figured out a solution for this.  He used a glass tube filled with a liquid containing a red pigment and a metal ball. When  a large current discharge occurred the metal  ball shot up due to the strong magnetic field,  which caused the pigment to mix with the liquid. This could be seen for a good 24 hours after the event. After a thunder storm it was  easy to see where a discharge current took  place: one only had to walk past the tubes  and have a good look at them. 

Unfortunately, things didn’t work out as  expected. Since it often took a very long  time before a discharge occurred, the pigment settled down too much. When a dis-charge finally did occur the pigment no  longer mixed with the liquid and nothing was  visible. This system was therefore sidelined,  but it found its place in the (railway) history  books as the ‘balls of Van Ark’.

 

 

Streampowers

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Simple Function Generator

Simple triangle-wave generators have a weakness in that the waveform of their output signal normally cannot be modified. The circuit presented here makes it possible to smoothly alter the waveform of a linearly rising and steeply trailing saw-tooth signal through a symmetrical triangle-wave to a slowly trailing, steeply rising linear sawtooth. The wanted waveform may be selected independently of the frequency, which can also be varied uniformly from 0.2 Hz to 8 kHz. At the same time, a rectangular signal with variable duty cycle (also independent of frequency) is available at the rectangular-signal output of the circuit.

The circuit consists of integrator IC1b, whose output is applied to comparator IC1c. The output of the comparator is a rectangular signal The output of IC1b is raised by amplifier IC1d to a level that allows the full output voltage range of the operational amplifier to be used. Op amp IC1a provides a stable virtual earth, whose level is set to half the supply voltage with P1. The smooth setting of the frequency is made possible by feedback of part of the output of the comparator to the input of the integrator via P2. This preset is usually not provided in standard triangle-wave generators. Network D1-R1-D2-R2-P3 makes it possible to give integrator capacitor C3 different charging and discharge times.

This arrangement enables the output signal at A1 and the duty cycle of the rectangular wave signal at A2 to be varied. Varying the amplification factor with P5 has no effect on the frequency set with P2. The slope of the signal edges, the transient responses, and the output voltage range (rail-to-rail or with some voltage drop) depend on the type of op amp used. The TL084 used in the prototype offers a good compromise between price and meeting the wanted parameters. The circuit is best built on a small piece of prototyping board. The circuit draws a current of not more than 12mA.

Brief parameters:
Provides triangle-wave, sawtooth or rectangular signal
Waveform variable independently of frequency (triangle wave and sawtooth)
Duty cycle of rectangular signal can be set independently of frequency

Applications:
Test and measurement
Pulse-width control

Summary of preset action:
P1 – sets virtual earth to a level equal to Ucc/2;
P2 – sets the frequency;
P3– sets the waveform;
P4 – sets the hysteresis of the comparator (frequency and amplitude of the triangle-wave signal)
P5 – sets the amplification of the triangle-wave and sawtooth signals.

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