variable switch mode power supply

switch mode power supply

I want to make a switch mode power supply to convert -48 VDC to -30/+15/-15/+5 VDC. please help me to design the circuit with 555 timer.
thank u anybody

Re: switch mode power supply

I don't think so, it is good idea to build a SMPS for multi-outputs with a simple 555 timer. Try to think of using LM3524 or SG3525 etc (PWM based) and design for specifically for SMPS. Any how following is a circuit based on 555 for tube light conversion. You can pick an idea and modify this circuit.(if you insist on 555 only). Second circuit is based on discrete transistors, you can also look.

Regards

switch mode power supply

thank u Awarapunshee, i want using 555 as a pwm. u think that LM3524 or SG3525 are more than useful. please send me an SMPS scheme that uses these components if u have.
regards

Re: switch mode power supply

You can find many circuit for these IC's (and application notes etc), anyway following is one DC DC converter using 3525.

What is purpose of transistor output feeding transformer in two of these circuits...the one with the 555 timer, IRF510, 555 switching circuit.GIF and the other one (M3) SG3525 SMPS.gif
?
Thanks!

Nora said:

What is purpose of transistor output feeding transformer in two of these circuits...the one with the 555 timer, IRF510, 555 switching circuit.GIF and the other one (M3) SG3525 SMPS.gif
?
Thanks!

Click to expand...

It is quite basic question. These are power MOSFETs that are quickly switched between the saturation (full-on) and the cutoff (full-off) states. They serve as a “gate” for the energy entering the supply that is subsequently delivered to the load. The energy flow is regulated by the control circuit, which senses the energy demanded by the load and then varies the percentage of on-time for the power switches, which then “regulate” the delivery of the energy to the load to match the load’s demands.

Regards

Thanks for the reply.

I have built a similar circuit to the 555 timer one pictured above. I don't have a 10nF cap is across the primary, and am using a 2222 bjt.
My circuit doesn't work please help me to understand the theory and troubleshoot this.

With the transformer removed, and with power removed from the bjt, I get pulse of ~100kHz at the transistor base/ pin 3 of 555.
When I put power on the bjt (transformer still removed), the pulse at the base stops, and I read Vcc at the collector. With a resistor in place of the transformer, I am still reading no pulse at the bjt.

Can someone help me to understand how to choose a transistor? And should I still see a pulse once power is applied? What kind of voltage/wave should I expect to see at the collector (input to transformer)?
Thanks!
N_N

Use MOSFET, Instead of BJT (2N2222), It cannot handle the load. 10nF is also necessary

Regards

Hi Nora,
Post your circuit pls...
Btw; I think that your transistor has a failure...
K.

K.
you were totally right, I swapped the transistor and the circuit works. Thanks!!!
I've posted the circuit here and still have questions about the how/ why operation.

How do I design for the transistor/ mosfet? what values am I looking for?
How do I know if I should use a BJT or a mosfet?
Anything else I need to look out for?

I know that my transformer needs switching freq around 100kHz, so I designed the 555 circuitry for that (will eventually be microprocessor based).

On the input power to TR1 I have an electrolytic capacitor, the original 470uF didn't seem to work so I switched to 220uF.
How do I choose the capacitor value? Should it be electrolytic?
Thanks!
N_N

hi
in ur circuit the output pin no 3 drive the junction of base-emitter without any
resistore u must add RB resistore to protect 2N3904