Problem with LM337 voltage regulator

[stoyanoff]

Greatings! I have a problem with LM337.
This is my schematic.View attachment LM337.pdf
This is working fine, but I decided I need bigger cap on the output. So I exchage the 100uF Cap with 2200uF. But this burns the regulator. What`s happenning here?! Where is the problem?!
Thanks!

 

[FvM]

I don't see a reasonable purpose of a large output capacitor, but if you have it, you should observe the datasheet hints about protection diodes.

Presuming you want a regulated voltage supply, you should firstly use a bridge rectifier instead of a single diode and secondly a sufficient input capacitor.

 

[stoyanoff]

I`m making bipolar power supply using transformer without mid point. Because of that I`m using single diode. I need larger on the output because the supplied schematic drains current on pulses and I need big buffer.
I`ll fix this somehow, but I have another problem. I`m draining about 40mA. In spite of the smaller cap on the input, the regulator increases its heat. This is because the difference Vin-Vout. I can`t put heatsink. There is no space...
Any ideas how I could deal with this problem?!

 

[crutschow]

Check the polarity of the new capacitor. If it is reversed, it will draw high current.

How do you plan to do a bipolar supply with only a single winding on the transformer? For that you would need some type of virtual ground circuit with 1/2 the total rectifier voltage for each output. You can still use a bridge rectifier for that configuration.

One way to reduce the heat dissipated with a linear regulator is to add a power resistor in series with the regulator input to drop some the excess voltage. Size it so that, at maximum output current, its voltage drop still allows the minimum required voltage across the regulator so it can maintain regulation. Otherwise, if you can't use a heatsink, then you would need to go to a more efficient switching regulator.

 

[memarian]

I`m making bipolar power supply using transformer without mid point. Because of that I`m using single diode. I need larger on the output because the supplied schematic drains current on pulses and I need big buffer.
I`ll fix this somehow, but I have another problem. I`m draining about 40mA. In spite of the smaller cap on the input, the regulator increases its heat. This is because the difference Vin-Vout. I can`t put heatsink. There is no space...
Any ideas how I could deal with this problem?!

Hi,

Your Circuit has some problems :

1) if you check LM337 Datasheet , minimum input Recommended Capacitor is 1uf (you used 220nf),even with the Filter Cap (usually around 1000uf) after diode (which you don't have in your circuit). that 1 uf cap is for Stability of LM337.

2) your resistors are too high. adjustment pin current usually is between 65uA..100uA.when you use 2.2kohm resistor your, resistor current is around 500uA( that will add to adjustment pin current and goes to 6.8Komh resistor), so when the temperature changes , your output voltage may change. datasheet recommended 120ohm , but your output current is low (40ma) so some thing around 680ohm will be enough.

3) if your total current is 40ma , but regulator have high temp, you can use one or two Zener diodes in series , before regulator input (with appropriate wattage)., But you should know that instead of regulator those diode will be hot. It's the nature of linear regulation.

 

[stoyanoff]

Zener diode in the entrance is a good idea! I`ll test it! Thanks!