Voltage regulator.

[jimbo84]

I’m trying to trouble shoot a bench power supply, it looks like a bit of a DIY creation.

Whenever any kind of load is put on it the regulator shuts down the output.

The supply from the transformer is using the 31.9vAC output which with no load gives 35vAC measured then after the bridge rectifier it’s giving 46vDC into the regulator. The max I can get out of the reg with the variable resistors set to max is 13vDC when according to the data sheet it should give 26-35v.

Even a tiny bulb shuts off the output from the regulator. The input power remains constant.

Does it sound like the regulator has gone bad?

Probe showing which transformer output is being used.


The reg itself


The data sheet for the reg

 

[David_W]

Have you put a short circuit across the terminals showing R1 in the datasheet?

 

[voipio]

Make sure that the jumper wire between the regulator's pins 3 and 4 is soldered properly to the pins. A dry joint there would cause those symptoms.

 

[jimbo84]

Have you put a short circuit across the terminals showing R1 in the datasheet?

Yeah the link was already in place.

 

[jimbo84]

Make sure that the jumper wire between the regulator's pins 3 and 4 is soldered properly to the pins. A dry joint there would cause those symptoms.

It seemed ok but I’ve resoldered it anyway and it’s still the same sadly.

 

[David_W]

If it's not in fold back, the other check I'd suggest is that you are putting too high a voltage into it from the sounds of it, 46 just above 45. Doubt it's an issue, but worth using a couple of diodes to drop the voltage to inside spec

 

[jimbo84]

If it's not in fold back, the other check I'd suggest is that you are putting too high a voltage into it from the sounds of it, 46 just above 45. Doubt it's an issue, but worth using a couple of diodes to drop the voltage to inside spec

I’ve used one of the other transformer windings so the reg is now getting 27v input and putting out 6.7v

The input/outputs according to this table are way off.

 

[Seadog]

Replace the reg.

 

[jimbo84]

This thing really isn't worth spending any money on but I'm learning as I go with this kind of stuff so does it need to be an equivalent of the rather large voltage reg (approx 4 inch square and 1.5 inch deep) already in there or can it be something like the below, obviously with some form of heat sync?

 

[David_W]

Short answer, because it's a linear regulator all the excess voltage is being turned to heat. That's the voltage difference multiplied by the current, so roughly that's 45V-35V, multiplied by 2A, so 20W.
That linear regulator will take around 1W.
If it's an interesting challenge, then adding in a circuit around it with a heatsink like,

With a heavily heatsinked to3 or To220 transistor like a 2n3055 might do, but much easier and efficient would be looking for a buck regulator module

 

[David_W]

This is a bit too low on the input voltage, but as a reference,
Buck reg

Added, this one will handle the voltage. And as an electronic engineer, I can't make it for that price,
60V Buck reg

 

[voipio]

This thing really isn't worth spending any money on but I'm learning as I go with this kind of stuff so does it need to be an equivalent of the rather large voltage reg (approx 4 inch square and 1.5 inch deep) already in there or can it be something like the below, obviously with some form of heat sync?

View attachment 515315

The RS 305-989 regulator basically consists of a black anodised extruded aluminium heatsink, onto which have been mounted a handful of components, at most, in a simple circuit, and some connection pins, and then the components encapsulated in epoxy resin, to protect the circuit, and hide its true identity. The construction shown in the photographs does not make the best use of heatsink positioning, from a dissipation point of view. The heatsink really should be mounted externally to the case, or inside the case with adequate ventilation, with the fins oriented vertically. The heatsink could be re-utilised, with all the existing pins disconnected, to mount something like the LM338 device.

 

[jimbo84]

Thanks everyone. I've removed the existing reg and will use it as a heat sync when I have a go at putting together another.