Masteck linear supply, take two.

Joerg

should be

bucks. The

in there.

the price

assume

Lascar

But

voltage.

stuff.

exploded.

We were told a long time ago by Mastech that we could clip out that diode. They showed us where it was too.

He just said to be careful when setting the current source up. Like, raising the voltage slowly or something that made sense.

They will usually pop the output current limit FET when abruptly shorted at any kind of high voltage with that diode in or out anyway.

That part of their protection circuit needs a teeny bit of re-design IMHO.

Sometimes I find it handy to have a broken one that puts out 80+ VDC instead of 50V.

boB

Joerg

should be

bucks. The

in there.

the price

assume

Lascar

of

20

But

voltage.

stuff.

exploded.

Thanks for the hint. Although, I'be got the schematic for the HY3005 here and that doesn't have any FET.

Do you have any experience with their switcher bench supplyies? I am thinking about buying one because I have these occascional assignments to help with the design of a big inverter. Would be cool to be able to supply 12V or 24V at tens of amps without having to schlepp in that massive transformer and working up a back pain.

--
Regards, Joerg

http://www.analogconsultants.com/

at should be

e of bucks. The

lator in there.

of the price

for

that assume

a Lascar

sure of

about 20

, TEC

hing. =A0But

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guys

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urrent

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OK no big tranny in the arb though... And we'll resell it so shipping back from customer to us, then to Sean...

Hey if we open it up to snip a diode we can do a little test, that may catch units that couldn't survive the shipping vibration test.

George H.

:

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ulator in there.

d of the price

g for

s that assume

a Lascar

sure of

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r, TEC

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thankS boB,

Maybe we can add some warning and advice on how to treat the supply with kid gloves.

No yanking the coil out with lot of current on either.

George H.

Or maybe they over teach Muntzing.

?-)

Not really. Sometimes I found that a trace routing was done wrong. Snip, snip, cut, cut, lay down wire -> fixed. The additional cost for routing the traces correctly (not past flyback transformer T3) would have been ... zero. They simply didn't know that flyback transformers have a propensity to sing.

--
Regards, Joerg

http://www.analogconsultants.com/

:

to

d

This particular supply could use more Muntzing. I assume that more parts than just the diode are part of the 'short circiut protection'.

Yeah, the schematic looks incredibly busy. In China the cost of discrete parts is so low that it obviously still deosn't matter. I learned about that when a contract manufacturer there asked me to comb through my design and see which resistors can be eased to 10%, and maybe even 20%. In the end it made a few pennies difference, and times a ton of boards per month it mattered.

But WRT power supplies I have only muntzed switchers so far. Sometimes to the point where the dedicated boost controller chip had to leave the ballfield and make room for a logic chip that cost 15c less.

--
Regards, Joerg

http://www.analogconsultants.com/

Joerg

should be

bucks. The

regulator in there.

the price

assume

Lascar

of

20

But

voltage.

fry stuff.

his

switching

exploded.

I guess I forgot (or didn't know in the first place) that the smaller supplies were different than the 50V 20A supplies like we are using.

We use the smaller Mastech's too but they don't seem to break very much.

We're always breaking the big ones. There is a fairly decent TO-220 FET in the output that is driven very weakly by an op-amp circuit that detects current from an output shunt. This FET is fairly easily replaceable but it looks like the drive is just too weak to react fast enough and I suspect it goes linear when trying to protect things and blows from that. Should be fairly easy to fix that up.

It looks like the main switcher is way before this circuit.

boB

Joerg

should be

of bucks. The

regulator in there.

the price

assume

Lascar

sure of

about 20

But

voltage.

fry stuff.

his

switching

exploded.

Yes, I saw that in the switcher schematic. They are essentially hanging the gate of a big FET (over 4000pF) plus, for whatever reason, another

1000pf in the output of a TL084. That's a big no-no. Looks like some sort of linear post-regulator. The current limit seems to be U401B, via D404.

You could probably hang a FET driver with Schmitt inputs in between so there's more gusto.

--
Regards, Joerg

http://www.analogconsultants.com/

be

bucks. The

there.

price

stuff.

Actually, George, I got mine (YH-305D) through Ebay based on a find by Larkin. No diode to clip. About $75 with free shipping from CA.

John

Joerg

should be

of bucks. The

regulator in there.

of the price

that assume

Lascar

sure of

about 20

something. But

voltage.

fry stuff.

current

his

another

switching

exploded.

That's exactly what I have been thinking.