went and got some IRF510's from radio shack, but I didn't notice until I got home that there were 2 1MΩ resistors in the schematic posted. What are those for and do I need them? The biggest I have is 100KΩ, will that work?

 

As I recall your Collector resistors were 470 Ohms. If so, changing the Gate resistors to 100K won't change much. So yes.

Edit: They're used to keep the Gate from floating and it's just good practice since MOSFETs Gates are extremely sensitive (Hi z). The circuit would probably work without them but I wouldn't recommend it though.

 

My problem is that I used to know this stuff. I did circuit card repair in the military, but that was a couple years ago and I haven't really messed with any of it since then

 

Try these drivers with the 555s. Use 5V to 8V zeners, and 100Ω resistors. The LED version shown is for 5-8V power supplied circuits.

Wire the LEDs the same way as you wired the 555 output.

 

My problem is that I used to know this stuff. I did circuit card repair in the military, but that was a couple years ago and I haven't really messed with any of it since then

You didn't carry your MOS over to civilian life? Why not?

 

Ok went after the 1M ohm resistors. Had the circuit hooked up with the 100K resistors tho and it didn't even come on.

on yours there bill, what are the transistors?

 

Would it be possible for you to draw the schematic and post it?

 

Any transistor that can handle the current will work. You said 300ma? I'd use 2N2222A and 2N2907A (or similar). If it is more current then you need transistors that can handle more power.

The Zeners (or LEDs) are dual purpose. The high side of a 555 is not to rail, it is about 1.4 V from power supply, this allows Q1 to turn off anyhow. The other job is they limit shoot through, a condition where both transistor are on at the same time, and cause a large current surge that isn't good for the power source or the transistors.

The resistors need to be ½W.

Have you read this?

LEDs, 555s, Flashers, and Light Chasers

 

Ok went after the 1M ohm resistors. Had the circuit hooked up with the 100K resistors tho and it didn't even come on.

on yours there bill, what are the transistors?

Did you move your LED Pods out of the Collectors of the NPNs and into the Drain circuit of the FETs as shown? If so, did you remember to connect one end of both 470 Ohm resistors to the collectors?

 

My problem is that I used to know this stuff. I did circuit card repair in the military, but that was a couple years ago and I haven't really messed with any of it since then

Thanks for your Service, bro.

Stuff goes quick if you don't use it.

It's late and I'm tired, but I'll get back to this tomorrow to help you get your stuff wired.

 

Did you move your LED Pods out of the Collectors of the NPNs and into the Drain circuit of the FETs as shown? If so, did you remember to connect one end of both 470 Ohm resistors to the collectors?

I did move the LED Pods.
the 470Ω resistors were dropped long ago. Let me try to throw together a schematic to show what I'm working with now.

 

OK, here is what I have hooked up.
The LED's are those pods.
Q1 and Q2 are the IRF510's
Q3 and Q4 are either 2N3904 or 2N2222, usually 2N2222
C1, C2, R3, and R4 are changing based on the flash rate I'm trying to achieve.

Hooked up like that I get nothing, no lights at all.

I hate that I'm getting like this. I was never an electronics engineer or anything, but I'd know what components were being used for what. At the same time, it's kind of nice as I'm getting back into it and starting to remember quite a bit.

 

You didn't carry your MOS over to civilian life? Why not?

Where I moved to after leaving the military, there wasn't much available. Now I'm running into the problem you see here: I don't much know the stuff anymore. I had a job interview about a year ago that required an electronics test and I did do pretty good on that. The hiring manager said he just didn't think I sounded confident enough with the material.

 

OK, here is what I have hooked up.
The LED's are those pods.

Ouch! You've got a couple of things wrong there:
(1) Led Pod 1 & 2 are (reversed biased) backward.
(2) You omitted the 470R collector resistors that existed in your original schematic. They are absolutely required to limit collector current and thereby not fry the device. They are also needed to produce a voltage drop at the collectors and passing that signal to the Gates of the FETs. Warning! Before powering it up again please post your corrected schematic. This way we may be able to avert smoke! Auto batteries can do some major damage and are totally unforgiving a mistake. They can hurt you too!

By the way, I should have done this before but the most honorable Sgt. Wookie was not remiss on this account... Thank you for your service!!

 

Here's a complete schematic that I spiced. Note the addition of R9 & R10 and the change in R9 & R10. You may have to play with these values but I doubt it. Also note that my spice run indicates nearly 1A flowing through each LEDPOD when they're on. You will not pull 1A though. I spiced it this way to demonstrate that those FETs can power a bunch of those LEDPODs if necessary. Any questions, just ask.

EDIT:
The omission of a voltage divider (R1 & R10) and (R2 & R9) was a screw up on my part. I should have realized the the collectors of Q1 & Q2 would not pull to zero. Let us know if you understand what they're for. Here's an exercise for you:
Find the value (using Ohms Law) of the max and min Gate to Source voltages. This can be calculated by looking at the max and min collector voltages of Q1 & Q2 as shown in the graph.

 

OK, attached is one way that you could drive your LED array using some additional components.

I've only added them to the right side to keep things simple. R5, R6, D1, and Q3. Rload represents your LED array.

R5 limits the current flowing through D1 to the base of Q3, an NPN Darlington power transistor.
R6 keeps the base of Q3 pulled low when Q2's collector voltage falls below around 7.3v.
D1's Vf is subtracted from Q2's collector voltage. As you'll notice from the yellow plot below the schematic, Q2's collector voltage spends about half the time at 7.3v, the other half at nearly 12v. This is why you can't successfully drive the gate of a MOSFET directly from the collectors of Q1 or Q2.

 

Woops! I forgot to post the schematic. It's there now.

 

Here's one way you could do it using your 555 timer circuit and a couple of power MOSFETs. Refer to the attached.

With your chosen values for R3, R4, and C3, the flash rate will be about 7Hz. To decrease the flash rate, increase R4.

R1 helps to prevent Q1's gate from "ringing" when it's charged or discharged by the 555's output.

R5 and D1 represent one of your LED arrays.

When Q1 is conducting, Q2's gate is discharged via Q1's drain-source. R2 keeps Q2's gate from ringing during the gate discharge.

When Q1 turns off, R7 pulls Q2's gate high so that it turns on.

 

As you'll notice from the yellow plot below the schematic, Q2's collector voltage spends about half the time at 7.3v, the other half at nearly 12v. This is why you can't successfully drive the gate of a MOSFET directly from the collectors of Q1 or Q2.

Yes Sgt. that's why I added a voltage divider but I failed to post the schematic because.... because I'm brain dead! LED's in series with R9 & R10 would also help but I don't think he needs them.

 

Here's a complete schematic that I spiced. Note the addition of R9 & R10 and the change in R9 & R10. You may have to play with these values but I doubt it. Also note that my spice run indicates nearly 1A flowing through each LEDPOD when they're on. You will not pull 1A though. I spiced it this way to demonstrate that those FETs can power a bunch of those LEDPODs if necessary. Any questions, just ask.

The omission of a voltage divider (R1 & R10) and (R2 & R9) was a screw up on my part. I should have realized the the collectors of Q1 & Q2 would not pull to zero. Let us know if you understand what they're for. Here's an exercise for you:
Find the value (using Ohms Law) of the max and min Gate to Source voltages. This can be calculated by looking at the max and min collector voltages of Q1 & Q2 as shown in the graph.

That's the thing about this particular astable MV; the collectors of Q1/Q2 do momentarily go to nearly 0v. However, they spend most of their time at about Vcc/2 and Vcc-2v.

In order to reliably switch the gate of a standard power MOSFET, you need to drive it from nearly 0v to at least 10v.