Chinese Hiland 0-30V/Audioguru PSU build (down the rabbit hole)

[Audioguru]

The transistor datasheet shows how much the chip temperature rises with power dissipation and the datasheet of a heatsink shows how much is the temperature rise of its transistor mounting surface with power dissipation. Add about 0.5 to 1 degree C rise per Watt when an insulator is used between them. The worst case dissipation of the output transistors and bridge rectifier when the transformer produces 28VAC and the output from the circuit is shorted with 3A is 119W.

Pick the spec's of a similar size heatsink as yours from the datasheet of a heatsink manufacturer like Wakefield. They might even show the cooling increase with air speed from a fan.

 

[bushtech]

Time to start assembly and checking what I've missed

Audioguru: Still working my way through Wakefield

 

[bushtech]

Progress:

I first want to check if it works. Will build it into it's box later

 

[bushtech]

When I get to switch on some time can I do the light globe in series setup. Or is there some progressive start up that I can do?

 

[Audioguru]

You can put a 60W light bulb in series with one 240V transformer wire then test the output voltage up and down from the project.

 

[bushtech]

Thanks Audioguru

 

[bushtech]

With the replacement of the 4 onboard rectifier diodes with a bridge rectifier off board on heatsink I am battling to find the correct 2 connection points for the 2 + - leads from the bridge rectifier.

Please can you help

Thanks

 

[bushtech]

Good news is that I am getting 27.5V DC out of bridge rectifier

 

[bushtech]

lol. This is getting rather busy

 

[bushtech]

Houston, we have ignition!

I have a 60W globe in series. On switchon the globe lights up and then dies. The onboard led comes on and stays on. Voltage on outputs 10.6V (no adjustment of pots done) 1A fuse in incoming not blowing. No smoke escaping but a frantic feel around for hot components revealed that U3 is getting very hot.

I have now inserted a dummy load of 5W resistors totalling 7.5kΩ but U3 still getting very hot.

Investigation continuing but a flash of insight as to where/what to check will be highly appreciated

 

[bushtech]

Some readings so far:
Out from bridge rectifier: 40V

Pin 6 readings on TLE2141's:
U1: 11.3V
U2: 7.8V
U3: 5.1V

BD139:
b: 7.5V
c: 40V
e: 12.3V
All readings taken switch on, read, switch off (scared of smoke escaping from U3)

 

[bushtech]

I suspect these are problematic:

U3:
pin 2 = 3.8V
pin 3 = 3.8V

 

[bushtech]

Got my little digital led meter VA meter connected and Voltage not working but the ammeter shows 5.6A. If it's correct............

 

[Audioguru]

I assume that your voltage measurements were with no load on the project and with the voltage and current setting pots were at minimum.

1) The emitter voltage of the NPN BD139 should be about 0.7V less than its base voltage, not 4.8V higher.
2) The load on the output of U3 is a 10k resistor with a current of only 2.7mA with your voltage measurements. Then its heating is only its output voltage of 5.1V x 2.7mA= 0.014W which is nothing since 36 times more power would make it hot. Check that the output of U3 is not shorted to anything, that R20 is 10k and that the anode of D9 is not shorted to something that is a positive voltage.
3) Check the datasheet of the BD139 to see which pin is which, maybe you have base and emitter swapped.

 

[bushtech]

Still have a 7.5kΩ dummy load attached. Pots not set yet. Will check the rest, thanks Audioguru

 

[Audioguru]

Check the datasheet for the output transistors to see its pins.
I hope you did not buy cheap fake or defective transistors and opamps from ebay.

Edit: You never said what the output voltage is. It should go from 0V to +30V with the voltage setting pot and with the current setting pot turned up a little. The LED should light only when the output current is higher than the setting of the current setting pot. The maximum current into your 7.5k load will be 30V/7500= 4mA and much less at lower output voltages.

Where did you measure 5.6A? 5.6A in the 7.5k load needs a voltage of 5.6 x 7500= 42 thousand volts!

 

[bushtech]

I have now turned all pots down. Dummy load still connected. Pinouts on BD 139 checked and correct. R20 is 10k. Can't see any shorts at U3 and D9.

99% of components come from Mantech here in SA including the TLE2141P's which I can see they imported from Mexico.

The Voltage I was measuring on the ouputs was 10.6V.

But with all pots turned down things have gone weird: I now read 40V on output terminals and ALL legs of BD139 also read 40 V

The little meter that was reading 5.6A you can see in post #69. It could be incorrectly wired up, I used Miles K wiring setup for it.

I can't leave it switched on long enough to start fiddling with pots, U3 gets too hot

 

[bushtech]

The 2N3055's could be suspect. I found them in a lot of electronics spares I was given, they look unused but they are at least 20 years old

 

[Audioguru]

Isn't your pcb from Bangood? Then it is for the old original defective Greek kit. My many mods added a 10V zener diode to U3 to reduce its supply voltage and the pcb is made for an Oriental driver transistor (and maybe the little transistors) that have different pin layouts than the Western transistors I use.

With a +40V supply, the maximum output from a TLE2141 is +39V, then the max output from the BD139 driver is +38.4V and the max output from a 2N3055 output transistor is 37.8V with no load.
Fully loaded at 3A the unregulated positive supply is about +35V and the outputs are a little less and produce a maximum output of about +31V or +32V. Calibration limits the output to +30.0V.

How can the base of the BD139 be at 40V when it is connected to the output of U2 that can go no higher than 39V?
How can the emitter of the BD139 be higher than a diode drop less than its base voltage?
How can U3 get hot when it should be dissipating almost no power?

 

[bushtech]

Sorry Audioguru, yes pcb from banggood so all original unchanged parts are those that came with the kit.

Yep something gone pear shaped. BD139:
e: 39.2V
c: 41.6V
b: 39.3V
Tried to get these as accurate as possible. Have to be quick. Tried to wait until readings stabilised

The 10V 1W zener (D13) to U3 is a 1N4740ATR

Busy checking wiring

Thanks a mil for your help