Re: Voltage loss over diodes/transistors

Jan Nielsen wrote:
Hi,

I have a circuit that runs off a 5VDC regulator.
I need to drive 2 relays, and the ones I have are 6Vdc, but ofcause they switch fine at lower voltage.

The problem is, to switch the relay I have a transistor, and then a diode to prevent back current, after the transistor and diode I am left with 3.8V which is very close to the limit of what the relay will accept, so its not that reliable.

Is there a way to limit that loss, or do I have to run at a higher voltage to start with ?


/Jan
Config your circuit using a common emitter for the transistor.
the collector goes to one side of the coil.
the other side of the coil to your 5 VDC.
the base with a resistor in series goes to your switching signal.

Place a protection diode across the relay coil. , the cathode (line side) will go to the 5VDC+ of the coil, the anode to the collector side
of the coil..
Coils will release high voltage energy if allowed to discharge at a
rapid rate. Coils discharge in reverse polarity and thus the diode makes for a component to do the job.

Also, it's good practice to put a bypass diode from the input to the
output of the regulator. many regulators do not like voltages much higher on the output side than on the input side. if you place the
diode with it's cathode to the input and anode on the output. current will only flow when the output is higher than the input and thus force
caps on the output to discharge. etc..


--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

.

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