# Help with this project

Discussion in 'The Projects Forum' started by j45, Mar 15, 2009.

1. ### j45 Thread Starter New Member

Mar 15, 2009
7
0
I would like some help from you experts out there.

simple project I want to make :

When I apply 9-13.5 VDC to input 1, I get a output A. When I apply 9-13.5VDC to input 2 I get Output A+B .
Using FETs . Output switching need to handle 5-7 Amps is this possable ?

I could use relays but this would make the unit too big .

Deleted email to foil spambots - and we prefer to render assistance in the public forum

Last edited by a moderator: Mar 15, 2009
2. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
Possibly you could define the nature of the outputs - A & B? It's trivial to find FET's that can pass over 100 amps.

3. ### j45 Thread Starter New Member

Mar 15, 2009
7
0
Hi

The output is from the FET's ( 5- 7 Amps 9-13.5 VDC ) When on input 2 a voltage (9-13.5VDC) is applyed the FET is switched ON (ie output A) handling 5-7amps . When on input 2 a voltage (9-13.5VDC) is applyed the FET is switched ON ( ie on both output A and B ) also able to handle 5-7amps.

4. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
The voltage requirement for a FET is 10 volts on the gate relative to the source for full conduction. With no more idea of the circuit, that's about all that can be said. The gate voltage should be 10 - 18 volts.

5. ### j45 Thread Starter New Member

Mar 15, 2009
7
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Hi

The normal running voltage is 12vdc on input 1 and 1 . I'm made a circuit using relays please can you help by using FET's in place of the relays.

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6. ### beenthere Retired Moderator

Apr 20, 2004
15,815
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That is a wiring diagram. The relay common and N/O & N/C contacts are not indicated. A schematic would be very helpful.

Otherwise, if the FET gates can be maintained 10 volts above the source, and those relays are being used as SPST, then yes, they can be used in place of the relays.

7. ### j45 Thread Starter New Member

Mar 15, 2009
7
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Relay coil + no 86 - no 85 . relay contact n/o no 87 and 30. Where no 87 has + input and 30 + output.

8. ### j45 Thread Starter New Member

Mar 15, 2009
7
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schematic attached, sorry had to use paint

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9. ### j45 Thread Starter New Member

Mar 15, 2009
7
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Beenthere any sugestions ?

10. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
If the source pin is at ground and the load is in the drain circuit, it should work. Place a small resistor in series with the gate - baout 22 to 47 ohms. If the drive simply opens up when the FET should be off, place a 470 omm resistor to ground at the gate to insure it turns off.

This may sound vague, but I have no idea of the nature of the load or the circuit away from the relays.

11. ### j45 Thread Starter New Member

Mar 15, 2009
7
0
Any chance of a quick schematic of the circuit ? Which FET would handle 4-7 amps at 12VDC ?