MOSFET

[Rajinder]

Hi all,
I have the circuit connected below, I am using the following AQY222R2T MOS Relay. Basically I am using the MOS relay to switch an output of 10V @ 400mA. The device is AQY222R2TY

I have worked out the input resistor as

R = Vin - VF
----------
IF

From the datasheet this works out as

10V - 1.05V
------------ = 1.79K or 1.8K
5mA

I have a few questions:

1. Is my calculation for R correct? I have used the following (drop out voltage waveform diagram 7 in the datasheet i.e. at 5mA the VF is around 1.05V). Or should I be using 3mA (led operate current) instead of 5mA?
2. The Output power is rated at 250mW, I believe that my output of 10V @ 400mA = 400mW - hence the device is not suitable.
3. The FET used to switch the FET led has a RDS max of 3R, which I can add to the calculation, but is that really going to matter.
4. I can't see a max input voltage, so will the 10V be ok?

Finally will a G3VM-63G be a better choice? This has an output capability of 500mA @ 60V. I can't however see the output power dissipation of this device.
Any help would be appreciated.

 

[Bluejets]

The fet will need to be a logic level fet.

 

[bertus]

Hello,

As @Bluejets said, you will need a logic level mosfet.
That will have a lower Vth as a standard mosfet.
The resistor to ground on the gate must have a high value like 10K.
The resistor in series with the gate should have a low value like 22 Ohms.

Bertus

 

[Audioguru]

You do not need a Fet if you use the 3V input signal (with a series resistor to limit the current to about 5mA) to turn on the opto-input of the relay.

 

[Bluejets]

10v might be too much for any micro output pin...??

 

[Audioguru]

10v might be too much for any micro output pin...??

IRFxxx Mosfets are fully turned on when the Vgs is 10V.
IRLxxx Mosfets are "logic level" and are fully turned on when the Vgs is 5V.

 

[Rajinder]

Hi all,
The 3V is driven from a micro, I will make sure it is a logic level FET.
The 10V is the voltage I have available and is also what I am switching on the relay output.

 

[Harald Kapp]

The 3V is driven from a micro, I will make sure it is a logic level FET.
The 10V is the voltage I have available and is also what I am switching on the relay output.

As @Audioguru stated: You can drive the LED of the PhotoMOS relay from 3 V directly (with a suitable series resistor, of course).There is no need at all for the intervening FET stage. Save components and money, increase reliability.

 

[Bluejets]

Yes, I was thinking the Op may try to use the micro to sink the LED circuit from 10v.

 

[Harald Kapp]

Yes, I was thinking the Op may try to use the micro to sink the LED circuit from 10v.

I see, that would indeed require a transistor interface.

@Rajinder ; Do us a favor, please: next time use the correct symbols for your circuit elements so we can identify how you are going to connect the components. A MOSFET isn't a square with 3 unlabeled pins as in your original post. Depending on the type and polarity of the MOSFET different symbols are used, see e.g. here, section "circuit symbols".

 

[Audioguru]

A little 2N7000 or 2N7002 will work if you find a sensitive one.