Electronics

98700RMK · Joined: 19 Nov 2006 Posts: 2

I am a bit uninformed when it comes to electronics, so I need some help. What I am trying to do is to use a zener diode to regulate a 5 volt reference system so that it wont read more than about 4.5 volts (haven't determined exact voltage yet).

It's actually for a manifold absolute pressure sensor on a turbocharged engine. As boost pressure increases so does voltage at the MAP sensor. The ECM is calibrated to see a maximum of 4.5. I am increasing the boost for more power. However, when the ECM sees too much boost (more than 4.5v) it de-fuels reducing power. So, I need to use the zener diode to allow normal operation below 4.5v, and when voltage gets to 4.5v, it remains there instead of increasing up to a maximum of 5v.

Can anyone pleas help me with this? Very Happy

Mike

neon · Joined: 25 Feb 2006 Posts: 593

ZENERS are simple devices to use but hard to control loads variations and they are passive devices and the voltage of 4.5 is hard to find and establish. there is also temperature to deal with. and when on it would kill the MAP output if it cannot supply zener current it may actualy oscillate.I asume that you have 12v dc then a simple resistor devider to with a diode clamp will work expecialy since you don't know if 4.5v is good. since the 12 v dc is never 12v dc you may use an LM337 regulator to establish a good voltage source so now you may use it and a diode to set it exactly. good luck.

98700RMK · Joined: 19 Nov 2006 Posts: 2

I heard that zener diodes were used for this. Is there a better way to do it? Don't be afraid to dumb it down for me. Wink

Thanks.

Mike

neon · Joined: 25 Feb 2006 Posts: 593

well my concerne if zeners are used as limiters for voltage can the source provide the current? zeners are open circuits until they themself approach the breakdown voltage after that they will limit the voltage. the problem that i see if when you approach the voltage at 4.5 v the breakdown is not gentle and thererfore the limit is not sharp enough at least not for that voltage. you may use a planar transistor Vbe breakdown that will be sharp but the voltage you cannot predict. that is why i sugest a clamp from a voltage source.I f you want a zener as reference clamp that will be fine but use it for a diode clamp.

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