Updating Old PCB Components: 2N3055 to IRG4PC50UD

Apart from the URL's not working, I don't see a problem with the concept. Your gate driver needs to be compatible with the IGBT's however. 2N3055's require enough voltage to force enough current into the Base of the transistor, whereas the insulated gate needs enough current to raise the voltage of the Gate to the ON state as quickly as possible. I didn't get to look at the data sheet for the IRG4PC50UD, but it will "look" like a capacitor to your Gate source -- what value, I don't know.

Attempting to help the OP out with the links;

2N3055 Datasheet link

IRG4PC50UD Datasheet link

I will note that if you could provide a schematic for the original circuit, it would help those knowledgeable in these areas provide a more applicable answer. It would also allow posters to suggest circuit changes that may make the implementation work/work better/prevent smoke egress :)

Tom

lol...well that sux, links worked in the preview, sorry.

thanks people....I will check the values of the 2N's before replacement and then check same again for the IGBT's once in place inside circuit. Was thinking of making an add-on with a 555 timer mock up to see what is needed to trigger the gates of IGBT's.

Will be time consuming to grab a circuit, so I didn't go that way. The gates for the 2N's were triggered from another PCB board and there is like about 10 of them to choose from as to which is the trigger

I will now go back and put in the hard yards to see if I can find the gate trigger source and make a circuit for the master power unit, if only for my own peace of mind...hate frying eggs and burning my bacon

"such as incompatibilities I may have missed?"

Generally no problem, however the terms hard and fast switching do worry me as the gate drive source/sink current impedance would be dependant on the load and frequency of the switching. Should it be inadequate it is possible that the drain source current while switching on starts to "turn" the gate off whilst trying to switch on. This can lead to undesirable transfer characteristics of the device. At a quick glance you need to charge 4000pF of gate capacitance. Dedicated mosfet drivers are usually recommended for this type of application. Whilst i do agree that the gate impedance is exceptionally high, it does experience "gate inversion phenomenon" so carefull attention to the gate drive should be adhered to.

Hope these pointers help

Let me sum up:-

You are taking a piece of equipment that has been working for 20 (?) years or so, that STILL works, and trying to make it work better???

Why not leave well alone (never touch a running machine!)?

Or tell us the REAL reasons for the "improvements" please?

Andy,

The links I posted work OK, post #2

Tom

In agreement with the 2nd previous post,.."If it ain't broke don't fix it."!!!! while 2N 3055s are hardly ideal for discharging a bank of capacitors, they were used in many applications in the 1960- 'til 1970s for regulated power supplies, power inverters and power amplifiers, and are quite adequate up to say 40 KHz, and low power supply voltage. If they haven't failed by now, the design parameters of the early circuit had taken the characteristics of these humble old workhorses, well into consideration. The new (hex fet? devices I'm assuming) switching devices while "superior" in every way, may not be supperior in working with this circuit... For instance the 2N3055 requires about a .6V + bias on the base for turn on and has an exponetial current rise from collector to emitter with a linear increase of the base voltage and also non linear "base impediance" the Fet device will have a linear relationship between Gate voltage and output current. It will also handle higher supply voltage, the gate definately has a higher input impedance and as earlier posters have mentioned the gate voltage will not be discharged through the device because of the high impedance, so make sure that the gate drive circuit covers itself appropriately for the device and the output desired. The FET device will definately have a higher upper frequency limit , but unless these capacitors are driving something that demands really astronomical amount of current,very fast, like a tesla coil primary or high powered Photo-flash tubes ( in which case 2N3055's would (probably) not have been used anyway), maybe you are just guilding a lilly. IF IT AIN'T BROKE DON'T FIX IT.

I humbly accept the adage, "if it ain't broke, don't fix it". Thanks for putting my head on the straight and narrow.

I was previously thinking of improving the transistors operational purpose, keeping in mind the differences related to gate operation.

Think I will apply the adage to other works in progress, related to projects currently in progress inside my evil home laboratory.

I am basically combining old discarded electronic units designed for specific uses to perform a multitude of operations, rather than make a new and complex PCB circuit. I have so far accumulated discrete oscillating timers, amplifiers, voltage regulators (non-linear), inverters (DC/AC) just to name a few. All the units have proved their reliability by still working after many years of service. So I will leave their proven circuits alone without drastic and significant changes to their created purpose.

Thanks again.