Simple switching power supply help.

[Scott Wiper]

I am trying to design a simple switching power supply with transistors. I
have put together a schmatic for you to look at and I would like to know
would it be better to use a power supply controller. This is for a big
project for my website I am trying to keep it simple as the other projects
are. Can you look at the sheet and point out if it can be done with a pair
of 555 timers that are pwm from the 120 Hz off the bridge. that is in the
circuit. I could use a 556 dual timer with triggered PWM for volts out. The
4N37 is to trigger from it's collector on the low volt part.

http://www.travel-net.com/~swiper/switch.gif

 

[Jan Panteltje]

I am trying to design a simple switching power supply with transistors. I
have put together a schmatic for you to look at and I would like to know
would it be better to use a power supply controller. This is for a big
project for my website I am trying to keep it simple as the other projects
are. Can you look at the sheet and point out if it can be done with a pair
of 555 timers that are pwm from the 120 Hz off the bridge. that is in the
circuit. I could use a 556 dual timer with triggered PWM for volts out. The
4N37 is to trigger from it's collector on the low volt part.

http://www.travel-net.com/~swiper/switch.gif

First look makes me wonder... looks like total nonsense.
In some sequence of seeing it...
Where is the output.,
You need a fuse in the 120 V ac
78V after the bridge... remember the peak there is sqrt(2)x 120.
The timers may perhaps run, but why the strange constructions q1 q2 and q3 q4.
3055 cannot handle the collector voltage of 170 V and will short, taking the
ciruits on the +12 V and +5V with it.
DO NOT TRY ANY OF THIS.
JP

 

[Ken Smith]

I am trying to design a simple switching power supply with transistors.

You really need to restart your thinking. The design you show has many
errors in the specifics and several errors in the general ideas.

Q4 will be scrap when power is applied.

D6 and D7 serve no purpose as installed.

Q3's turn off time will be measured in weeks due to a lack of E-B
discharge path.

Depending on what T1 is, D2 will be destroyed.

Phase control regulation is a good trick to lower power but it puts a lot
of noise back out onto the mains. If you are running logic from the +5,
you'd better make +7V or so and then make a series regulator from that.

 

[Scott Wiper]

On a sunny day (Tue, 18 May 2004 11:12:41 -0400) it happened "Scott Wiper"

I am scarping takng the volts down from the mains at 120 volts. I will be
useing a 28vac toriod step coil rated a 5.6amp Your point is taken.


First look makes me wonder... looks like total nonsense.
In some sequence of seeing it...
Where is the output.,
You need a fuse in the 120 V ac
78V after the bridge... remember the peak there is sqrt(2)x 120.
The timers may perhaps run, but why the strange constructions q1 q2 and q3
q4.
3055 cannot handle the collector voltage of 170 V and will short, taking the
ciruits on the +12 V and +5V with it.
DO NOT TRY ANY OF THIS.
JP