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.

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’.

Author : By Jac Hettema – Copyright : Elektor

 

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LM3886 Power Amplifier Schematics

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Amplifier Printed Circuit Board (PCB)

Amplifier Printed Circuit Board Bottom

Amplifier Printed Circuit Board Top

Amplifier Printed Circuit Board

Amplifier Power Supply
The power supply used is a regulated power supply. I used 10000uF per rail before the LT1083 regulator. After the regulator, I have 100uF on the regulator board. The advantage of using regulator is that the power supply ripple voltage is removed. If power regulation is not used, I can hear very little 50/100Hz hum from the speaker.

The high current MUR860 diode is used to ensure high current flow. The voltage regulator used is LT1083, it can provide about 8A of current. Transformer used here is a 500VA 2x 25V. The power supply is then regulated by 2 LT1083, after the regulation, the voltage is 30V.

Power Supply Recomended

I did some DC measurement and the result is quite good, I got 7 mV of DC offset at the speaker terminal. The voltage difference between the output of the 2 chips is less then 1 mV.

The sound of this amplifier is similar to my LM3875 amplifier, which is very clean and detail. It has no hum, no hiss and no noise. Compared to the LM3875 Gainclone, this amp can deliver twice the power to my 4-ohm speaker, and it improves the dynamics and bass punch a lot.

Source :http://www.shine7.com/audio/pa100.htm

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Remotely Adjustable Solid State High-voltage Supply Circuit Diagram

Remotely Adjustable Solid State High-voltage Supply Circuit Diagram

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High-Performance Interruption Detector Circuit diagram :
. 

High-Performance Interruption Detector Circuit Diagram

 

When the IR signal path is blocked, the output of the sensor module still re-mains high. However, when the block is removed, the output of the sensor module briefly goes low to trigger monostable IC3. This is due to the fact that the sensor module is meant for pulsed operation. Thus interruption of the IR path for a brief period gives rise to pulsed operation of the sensor module. Once monostable IC2 gets triggered, its output goes high and stays in that state for the duration of its pulse width that can be controlled by preset VR1. The high output at pin 3 of the monostable makes the musical IC to function. Voltage divider comprising R2 and R3 reduces the 555 output voltage to a safer value (around 3V) for UM66 operation. The du-ration of the musical notes is set by pre-set VR1 as stated earlier. 

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Note. 

 

The heart of the schema is the IR sensor module (usually used in VCRs and TVs with remote); the schema works satisfactorily with various makes of sensors. The entire schema can be fixed in the same cabinet if the connection wires to the sensors are smaller than 1.5 meters. The reflection property of IR signals can also be used for small distance coverage.

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High impedance balance output circuit

Adding the output cathode followers for valve circuits are expensive and consume a lot of extra energy, so that the output is often taken directly from the anode gain-stage, as a result, even loading bridge the so-called 10 k distortion can seriously endanger performance and output swing available from the source equipment.
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Impedance in terms of audio, so the input impedance is determined by the need to R1, R2 bias non-inverting input. A property of remarkable and very useful from this circuit is that the addition of Rg resistance increased profits, but maintain the balance of the circuit. This confidentiality guration can not be set to weaken for the advantages of an op-amp with feedback on the series can not decreases below unity.

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High Voltage DC Generator Circuit Diagram

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