Which Way to Connect Regulator Chip?

Since it is doubtful that any other forum members are going to have the exact databook you used, you are going to have to provide more details on your circuit, and the wattage of your headlamp.

Tom

Well said Tom. We also need his final circuit(s) too......!

It sounds as if the regulator is only to provide a reference for the transisitor, maybe similar to a emitter follower circuit using a high power transistor. I'm assuming the power components are being mounted on suitable heatsinks? Unable to provide any more help, as the guys above have pointed out, too many variables.

How do you know the pins are wrong? The pin-out on negative regulators are different than the positive regulators in some cases. Here are the 78/79 family of linear regulators. ( I apologize for the cruddy graphics but I am trying to keep the bandwidth low.)

Thanks, you are correct about the connections.

Why dont you use a bridge rectifier on your magneto output then you can use the same polarity for all your lamps and charging.

Also your V regulators are probably a bit on the small side for the current to your lamps you could use them to bias some power transitors whiich can handle the current. Normaly regulation is cotrolled by a simple Zenner bridge tapped across the battery which stabilises the charge rate.

GA, it is the method which works that gets the most attention

Hi Garth,

I tried to use a bridge, but couldn't locate the proper ground. Had it hooked to the ignition. They may be combined in a strange way.

The positive regulator chip also failed once before I added the 1K resistor (there is also a 0.1uF cap on the output pin). I have adequate heat sink for the power devices. The chips themselves shouldn't get hot, but are mounted on the same aluminum plate.

regards,

S

you circuit is no problem. if it fails, please check your input voltage, to insure it lower than 35 or 45V ( depend on manufacturer). otherwise, it will break out.

I was told, if you use motorcycle generator, it has very large voltage range and it will vey higher than 60v. so it will break out the 3 terminal device. so you hve to add a zener to keep it lower than 35v.

next, check output current to keep lewer than the output cutrrnt of the transistorl.

Hi,

You may be right about the voltage being too much. I have used your suggestion about a zener, but built a simpler circuit as I started out to do in the first place. I just have a power zener and two transistors in a Darlington arrangement. Took it for a test ride today, and so far so good. The heat sink gets a little hot, so I may make some improvements to that.

Thanks everybody for your suggestions.

S

I assume you have the tabs of the regulators insulated as the tab of the 7812 is GND and the tab of the 7912 is its input and therefore would be shorted to GND through the heatsink.

http://passthrough.fw-notify.net/download/684113/http://www.fairchildsemi.com/ds/LM/LM7805.pdf

Hope of some use.

Craig.

Hi,

The second link doesn't work. The first one is great, but doesn't answer the question because it doesn't have the high current application.

S

Apologies, I notice there are 2 URL there:

This was the one I intended:

http://www.fairchildsemi.com/ds/LM/LM7805.pdf

Thanks,

I had it connected right, but it failed. I am finished with the project,

S

The idea has some merit I must agree.

If he does it, he should try and find some diodes with a very low loss, not normal silicon as they drop around 0.6 volt.....that can make a significant difference to lamp brightness when running "on the edge"!

I am sure someone here can recommend a diode type that has low loss and enough current handling to suit!

Hi,

you cannot use a bridge rectifier if the magneto is pegged to frame on one side. If the ground termination can be lifted this would give you an isolated ac supply which you couñld then use a bridge rectifier and then connect the neg to chassis, which is the norm. if that is not possible then you could use a small 1:1 transformer to isolate the ac from ground.

Why not add a battery to the system? The difference to a modern system is that you will have to add a "dump" type regulator to stop overcharging the battery. You will need a 14V regulator that opens above that voltage dumping unused power to a resistance. This can be bought as a lump. they are used frequently in small generators.