Hi there I'm new to this. So here it goes. Has anybody tried to swap the irf520 for the ERF 7530? Can it be done without a lot of modification? Stryker 497. Thanks in advance.
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irf520 replacement with erf7530
- Thread starter jbullard85
- Start date
Nope: won't work. Because the 7530 needs to use another transistor in front of it in order to amp it up to the proper input level of that the 7530 requires to get full output..
It is possible. Check the specifications of the two fets.
The VGS on threshold voltage for the ifr520 is 2.0 V to 2.9 V with a maximum of 4 Volts.
The erf7530 is the same with the exception of the various letters after the part number. If you use the ERF7530 be sure toget the same last letter since that is the on voltage matching.
ie: ERF7530A is the minimum of 2 volts to 2.199 with an absolute maximum of 4 volts. A through J each letter denotes a different Vth voltage combination.
Physical size might need to be considered as well.
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Does anybody know how much power (watts) it takes to drive an irf520? I can't seem to find it on the data sheets that I'm looking at.
FETs are not "Watt" driven. FETs are voltage controlled with very; very little current that just charges the Gate Capacitance. It is a "Field Effect Transistor". No measurable DC current flows into the gate. Only a extremely small leakage current, if you have anything more than Picoamps you have a defective part that will soon fail. The gate is isolated from the circuit like a capacitor. Conducts AC signal but not DC.
The drive required: The VGS on threshold voltage for the ifr520 is 2.0 V to 2.9 V with a maximum of 4 Volts.
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The thing is, as I understand it, is that you want to replace the final on a radio that has the 520 final. It also probably has a 520 in the driver position as well, as most radios do today. Well, the driver isn't putting out a hot enough signal to fully drive that 7530. It may work; but not have the 75w output - if that is what you are expecting. I thought about doing this at one time - too.
The power amp section of any CB radio usually has the mixer chip first. This has a very low output. It then usually goes into a pre-driver, then the driver, and then the final output transistor. Each device is gradually upping the amplitude of the RF signal. Each device is matched to accept a load that it designed to do just that.
Be interested in hearing your results once you mount that device and then set the gate voltage to an optimal level, as tallman described.
The RFX-75 already has been designed to accept the output of the final transistor in order to achieve full output of the 7530 device . . .
BTW - Even if you did the circuit right to use a 7530 on a radio chassis, it would need a large heat sink to displace all of the heat buildup.
The power amp section of any CB radio usually has the mixer chip first. This has a very low output. It then usually goes into a pre-driver, then the driver, and then the final output transistor. Each device is gradually upping the amplitude of the RF signal. Each device is matched to accept a load that it designed to do just that.
Be interested in hearing your results once you mount that device and then set the gate voltage to an optimal level, as tallman described.
The RFX-75 already has been designed to accept the output of the final transistor in order to achieve full output of the 7530 device . . .
BTW - Even if you did the circuit right to use a 7530 on a radio chassis, it would need a large heat sink to displace all of the heat buildup.
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Or even the rfx150. Might as well get the power out of it. Make sure if you do get the rfx75,85, or the 150, to get a fan kit to add to it!! Good luck with whatever you do. Having fun and modding and seeing for yourself the difference is sometimes the best way to learn.
Have a good day and be safe.
Have a good day and be safe.
The original question was would it work. Not more power. The driver transistor only needs to swing the driving signal from two to four volts. If you use "Military design methods" the erf7530 would be loafing and get no where close to failure parameters. Heat build up would be minimal. The power output would be limited to the circuit resistances of small traces and other circuit limits. It would be better to install the RFX75 for power gain. The RFX150 needs a 40 watt drive to get any where close to the150 watt output.
I appreciate all of the responses. I was looking for simple replacement and power gain but that would not work.
An irf-520 can usually deliver up to 25w if the radio is tuned right. They are very inexpensive, usually about a buck or so to replace each one. I converted an old Cobra 148GTL with a irf-520 just to see what it would do. With a gate voltage of 3.8v, I got around 25w and it didn't get hot.
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