Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Automotive power supply: how much filtering needed?

Status
Not open for further replies.
Hi -

I am new to electronics and this board. I have built a little circuit to install in a motorcycle. It provides an extra turn signal indicator. I'm wondering how much I need to filter the 12v power I feed it.

The circuit is very basic. It uses just two 555 timers plus LEDs and several passives. No microcontrollers. It all runs on 12 volts and less than 150 mA.

Can I hook it directly to the 12V supply from the bike or do I need filtering?

Thanks,
David
 
If your motorcycle is like my car, the 12V bus voltage varies from 12.0VDC to about 14.7VDC, with occasional spikes that might go higher, and alternator ripple which might be 250mVAC riding on the DC level. During cranking, the voltage can sag as low as 8V.

The 555s are ratiometric devices, meaning that their internal trip points are pegged to 1/3 and 2/3 of the voltage at the the 555's VCC pin. Bypassing the 555's Vcc to Vss pin with 10uF to 100uF will help hold that voltage steady. I would use a 100nF ceramic in parallel with a 10uF to 100uF electrolytic.
 
Thanks, Mike.

Will the caps be enough? I have heard there is a part called a transient voltage suppression diode. Do I need this as well?
 
A TVS like a 1N6277 will offer protection against inductive spikes. You should have 1 to 5Ω of series resistance in the input power lead to your timer circuit so that the clamp has some upstream impedance.

I would start with just the bypass cap and try it in the vehicle. If you run into problems, I would make the circuit operate on 10V, and use an automotive adjustable LDO regulator. The "automotive" LDOs are designed to cope with automotive electrical environment.
 
also, the automotive LDO's as Mike stated usually have a much better temperature range of use.
 
I don't think you need a regulator with that circuit. Also if you put a ten ohm resistor from the battery in series with a 470uF filter capacitor, that should provide sufficient spike protection.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top