# Pulse Generator

Discussion in 'General Electronics Discussion' started by sihaam, Nov 28, 2012.

1. ### sihaam

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Nov 28, 2012
Hello All,
I am building a small 5 amp spark eroder. It will use 50V DC. The power supply provides straight 50VDC, but I need a variable square wave pulse generator to take this 50VDC and pulse it for me. All help will be appreciated

2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
We need to know a bit more.

Presumably the 50V is pulsed into some sort of load. What is that load (capacitive, inductive, expected max current, etc.)?

Also, what frequency, and since we're talking pulses, what mark/space ratio?

3. ### sihaam

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Nov 28, 2012
Spark erosion is the process whereby you use set "sizes" of sparks to cut away metal. In spark erosion, you need to "chip" the workpiece with sparks of a uniform amperage, eg 3amps x 50VDC. Every time a spark is generated, it "eats away" a precise amount of the workpiece. The time space between the sparks (the on time must be able to be varied from 1 millisec to 500 millisecs). Similarly, the off time must also be able to be varied. So I assume that the circuit will have two knobs, one to control the ON time and the other to control the off time. I am no an expert in electronics, but everyone in spark erosion tells me that the wave must be square. I assume the square means that the entire period of the "on" pulse will be eg 3 amps x 50V and when off, it is abruptly zero. In this manner we will be generating a set size of the spark. I need a simple circuit to take the 50VDC and make it into controlled pulse lengths. No special power supply is needed. Standard regulated 5 amp x 50VDC power supplies are commonly used. It is definitely not like a welder. In a welder the arc is continuous. In a spark eroder, the arc is simply a controlled burst of a spark jumping from the cathode onto the work piece. See attached pic to get a better idea.

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4. ### Harald KappModeratorModerator

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Nov 17, 2011
You could use a 555 timer in astable configuration.
This will allow you to set the on time and the on+off time separately.

It will, in this configuration, not allow you to set both times independently. If you explicitely need this feature (as stated in your post), put two 555 in monostable configuration in series as shown here (page 6)..

In any case you will need a suitable power stage (transistor) tp drive the 3 A / 50 V power to the head of the eroder.

Harald

5. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
Or with a circuit like this:

You can vary the mark and space independently. (R1 should NOT be allowed to go to zero).

Then the output of the 555 needs to be used to control a mosfet which will switch your 50V.

Last edited: Nov 29, 2012
6. ### CDRIVEHauling 10' pipe on a Trek Shift3

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May 8, 2012
Steve, you have a typo in there.

Chris