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Gate VOltage for the Power MOSFET IRF530

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Nancy1985

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Friends,
I want to use power MOSFET IRF530 as a switch to turn ON/OFF a (12V, 5W) heater coil. The gate is driven by about 4 dc voltage from another low power IC. This pin however cannot source more than 1mA current. In addition this IC is driven by 5V voltage source which is different from the 12V DC supply that drives the heater. I would like someone to let me know if:
1) Do I need separate gate driver for the MOSFET or the 4Vdc is sufficient to turn on the IRF530 to allow the required 2.4 A current by heating coil?
2) Switching speed is not a very critical. Even if the IRF530 takes about a second to turn ON/OFF, it is fine. But to protect that can I use unity gain buffer before the gate?
 

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Gate voltage for IRF530 MOSFET swithcing

Dear All,
My earlier post was somewhat incomplete. I want to use IRF530 to switch on/off a heater that draws about 2.5 A current. The gate voltage to the IRF530 comes from a digital logic pin (about 5Vdc) from another IC. The maximum current that this low power IC can source out is only 1mA. Will that (5Vdc, 1mA) be sufficient to turn on the MOSFET into saturation (2.5 A)? Please note that I do not have any special MOSFET gate driver IC.

I also want to know what type of isolation would be required between IRF530 and low power IC that supplies 5Vdc gate?

thanks in advance....

Nancy

---------- Post added at 12:14 ---------- Previous post was at 12:12 ----------

Do I need to put any resister between the the digital 5Vdc and the IRF530 gate?

Threads merged [alexan_e]
Click to expand...
 

Re: Gate voltage for IRF530 MOSFET swithcing

In brief, I don't think it will work.
1) 5V will not drive that mosfet into saturation.
2) At 5V, the current will be limited to less than 2A (see Figure 3 of the Fairchild datasheet)
3) 1mA will give slow switching, which may not be a concern in your application, but at switch on, the mosfet will appear as a short on the IC, so you will/may need a current limiting resistor.

You might find a logic-level mosfet that will work. Such mosfets saturate at 5V or less. There are many options. Check out the IRLZ44 as just one example. What resources do you have available?

John
 
Re: Gate voltage for IRF530 MOSFET swithcing

Hi John,
Many thanks for your reply. Will it be OK if I amplify the 5Vdc with some non-inverting op-amp?

Nancy
 

Re: Gate voltage for IRF530 MOSFET swithcing

You are basically asking whether a gate driver will help. Yes it will. Do you have ≥ 10V available? The op-amp will not increase the voltage above the supply. You can use a simple transistor to drive the gate too. Remember, it is the voltage that you need. The current will affect how fast it turns on and off, but for occasional switching, the heat generated during slow-speed switching may not be a problem.

John
 
Re: Gate voltage for IRF530 MOSFET swithcing

Hi John
IRLZ44 certainly looks a better choice.
I will try to procure one and use it.
Once again many thanks for pointing that out to me.

-Nancy
 

Re: Gate voltage for IRF530 MOSFET swithcing

Remember the IRLZ44 was only one example of many. You may want to look around. The IRLZ34 has a lower gate charge (35 nC compared to 66 nC for the IRLZ44) and could still handle the current and voltage (?) you need. I have assumed that voltage will be ≤12V DC. What will be your drain-source voltage? It will e DC, right?

I asked what sort of resources you have for parts, because often as the saturation voltage for Vgs goes down, the capacitance/charge for the gate goes up. With the low driving current you have available (i.e., without any sort of op-amp or driver added), you probably want to keep that charge as low as practical.

John
 

Re: Gate VOltage for the Power MOSFET IRF53-

Hi, in the STM datasheet,
1)ON (*)
VGS(th) Gate Threshold Voltage VDS = VGS ID = 250 µA Min=2V Typ=3V Max=4 V
So, you should use a VGS greater than 4V to be sure to turn on the MOSFET.
2) you do not need any buffer to protect the gate, perhaps a resistance in parallel to the gate is quite sufficient.
JoseMiguel
 

Re: Gate VOltage for the Power MOSFET IRF53-

joseMiguel said:
Hi, in the STM datasheet,
1)ON (*)
VGS(th) Gate Threshold Voltage VDS = VGS ID = 250 µA Min=2V Typ=3V Max=4 V
So, you should use a VGS greater than 4V to be sure to turn on the MOSFET.
2) you do not need any buffer to protect the gate, perhaps a resistance in parallel to the gate is quite sufficient.
JoseMiguel
Click to expand...
DO NOT look at the threshold voltage. It shows when the Mosfet is almost turned OFF (its current is only 0.25mA), not when it is turned ON.
The on-resistance spec for the IRF530 is shown when the Vgs is 10V. So use 10V.
 

Finally I used a non-inverting amplifier(powered with +/ 12Vdc) to amplify the 5Vdc logic level to 10Vdc which then drives the gate of the power MOSFET. The switch worked fine. Thanks one and all for the help!!!!

-Nancy
 

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