Mauriscivic's Pulser

[gyulasun]

Hi Garry,

One test you could do if you happen to have an oscilloscope is that feed coil L1 directly via the bulb (omit MOSFET for this test) from any AC voltage source between 8-12V and couple L2 coil to it to see the induced voltage amplitude across the latter on the scope, it must be over at least 10V peak to peak so that its positive half wave, 5V peak would already trigger the gate-source electrodes of the MOSFET(s).  Do you have ferrite cores on the coils?  For AC source, you can use a normal mains transformer with 9-12V secondary coil output or a function generator with sine wave output if you happen to have. If you do not have an oscilloscope, you can use a normal AC voltmeter which is good for 50Hz.

Gyula

[garrypm]

Thanks Gyula,

Yes I have a scope and will setup as you suggest using 12ac

I had noted previously that the signal generated on the trigger coil is only a couple of volts at most - thats why I thought of using a higher wattage bulb.

Many thanks, Garry

[garrypm]

@Tinselkoala,

Any chance you caould spare a couple of minutes and take a look at that video for me.

It may be that N-Channel IRF840 are not suitable.

Many Thanks. Garry

[gyulasun]

Hi Garry,

I have redrawn Groundloop's original schematic to show how I would suggest testing your IRF840 MOSFETs, see Fig. A  below. After assembling the circuit, rotate the wiper of the potmeter to mid-position, so that it would give about +6V to the gate (with respect to the source) if the main supply voltage is 12V.  And giving this 12V to the circuit, the 12V lamp should bright almost fully because as per its data sheet it has less than 1 Ohm ON resistance.  This way you could test both IRF840s to see they are not faulty i.e. they are controllable by the potmeter:  turning down the wiper towards lower voltages the lamp should get dark at less than 2 to 4V gate-source voltage levels (from data sheet the gate-source threshold voltage range is any value between 2 to 4V). Such test can also show you whether the two IRF840s has too much difference in their threshold voltage levels or you can select the lower threshold voltage types, besides checking their normal operation.

As a next step, please assemble circuit in Fig. B and use the same potmeter at R1 and R2, leave the wiper at a position which just extinguishes the lamp in circuit Fig. A  because this bias voltage just under the threshold level will help start the oscillator in Fig. B.  Remember to check winding sense of L1 or L2 and always switch on and off and on the 12V supply voltage to give a kick, helping start oscillation.
If the oscillator still does not start, then please build circuit in Fig. C   hopefully you will have success.

rgds,  Gyula

[garrypm]

Hi Gyula,

Thanks for that.

Fig A. Setup and tested both the 840's - Result > the pot acts like a dimmer and controls the intensity of the 5 watt lamp.

Now to move on to Fig B.

Thanks, Garry