Hi, is there a way to use for example two 15v regulators to get 30v?? if so how is it done??
thanx
thanx
Hi, cascading (totem pole) two 7815 regs may work, but starting up from zero volts could take out one or other.
Better to use a 317 adjustable type, they work up to 36V or so.
But to get 30Vdc from it, the input voltage when mains is high could be above the chip maximum.
Better to use a 317 adjustable type, they work up to 36V or so.
But to get 30Vdc from it, the input voltage when mains is high could be above the chip maximum.
OK...is there a way to use two 15v Zener diodes to regulate to 30v ??? Could i put 2 15v zeners in series with a resistor in paralell with each zenner for current limiting to get 30v ??(Dont series diodes increase voltage and paralell diodes increase current??)
i have 6 transformer Ballanced Mic preamp modules that need a regulated 24v - 32v DC supply and i don"t have any LM317 left but i have a lot of 7815 regulators and some 15v zenner diodes and lots of transistors i can use for a Pass transistor....
The Preamp modules will consume about 20-30mA of current each(about 15mA for the Opamp and another 10mA for phantom power) so i only need max 200mA of current for all 6 modules and i have some 250mA 26v (38v DC) transformers that should be perfect for these modules......
Thanx
i have 6 transformer Ballanced Mic preamp modules that need a regulated 24v - 32v DC supply and i don"t have any LM317 left but i have a lot of 7815 regulators and some 15v zenner diodes and lots of transistors i can use for a Pass transistor....
The Preamp modules will consume about 20-30mA of current each(about 15mA for the Opamp and another 10mA for phantom power) so i only need max 200mA of current for all 6 modules and i have some 250mA 26v (38v DC) transformers that should be perfect for these modules......
Thanx
You can, in theory, "jack up" the output voltage with a resistor or zener in series with the common terminal to ground.
E.G a 10V zener will lift the output to 25V.
You have to beware of maximun ratings and fault (ie output short circuit - it WILL happen!) conditions.
Read the data sheet here
http://www.fairchildsemi.com/ds/LM/LM7815.pdf
Given that a 317 costs so little - is it worth it?
E.G a 10V zener will lift the output to 25V.
You have to beware of maximun ratings and fault (ie output short circuit - it WILL happen!) conditions.
Read the data sheet here
http://www.fairchildsemi.com/ds/LM/LM7815.pdf
Given that a 317 costs so little - is it worth it?
Hi,
A Zener is in effect a shunt regulator.
Feed in through a resistor or CCS, and let the zener pull sufficient current to hold the pre-amp supplies at your chosen (total Zener) voltage.
Add a cap in parallel to the Zener string and that's it.
A Zener is in effect a shunt regulator.
Feed in through a resistor or CCS, and let the zener pull sufficient current to hold the pre-amp supplies at your chosen (total Zener) voltage.
Add a cap in parallel to the Zener string and that's it.
Hi, so would something like the attached curcuit work??
It uses two 1n4007 diodes for rectification and two 15v zeners in series to get the 30v regulation, I also added a Pass transistor ,i"m thinking i"ll use a 2n2222 which is a 600mA NPN transistor......
I also made it 2 regulators to share the current....
so does the curcuit look OK?? are there any changes I should make??
Thanx
PS: i would gladly use a LM317 but were i live you can not buy electronic components so i have to order them on line and i am not about to Pay $10 shipping for a single regulator....
It uses two 1n4007 diodes for rectification and two 15v zeners in series to get the 30v regulation, I also added a Pass transistor ,i"m thinking i"ll use a 2n2222 which is a 600mA NPN transistor......
I also made it 2 regulators to share the current....
so does the curcuit look OK?? are there any changes I should make??
Thanx
PS: i would gladly use a LM317 but were i live you can not buy electronic components so i have to order them on line and i am not about to Pay $10 shipping for a single regulator....
Attachments
Hi,
the 100r feeding the Zener string needs to be re-calculated.
If you use 400mW Zeners Imax=400/15=26mA.
Add on a little base current say 4mA.
the voltage drop across the 100r is V=(0.026+0.004)*100=3V
Vinput =Zener string +3V=33V
this is the maximum voltage that that the input can take before the zeners are overloaded.
They will be happy running at 10% to 20% of maximum rating.
the 100r feeding the Zener string needs to be re-calculated.
If you use 400mW Zeners Imax=400/15=26mA.
Add on a little base current say 4mA.
the voltage drop across the 100r is V=(0.026+0.004)*100=3V
Vinput =Zener string +3V=33V
this is the maximum voltage that that the input can take before the zeners are overloaded.
They will be happy running at 10% to 20% of maximum rating.
Be carefull with that large 1000uF at the emitter of the transistors. That thansistor has to charge the cap at turn-on which can draw a LOT of current and damage the transistor.
The 1000uF doesn't do anything anyway because the output Z of that emitter is very low and parallels the 1000uF and is MUCH smaller in impedance than the cap.
For stability you may use a small cap there, say 10uF
Jan Didden
The 1000uF doesn't do anything anyway because the output Z of that emitter is very low and parallels the 1000uF and is MUCH smaller in impedance than the cap.
For stability you may use a small cap there, say 10uF
Jan Didden
If you are trying to power all 6 modules from the proposed circuit, it won't work. The power rating of a 2n2222 is around 1 watt so at 200 mA the voltage needs to be less than 5 volts.
Re: Minion
There are a number of ways to get a house keeping supply boosted up.
Start with the first requirement:
How much current does your 30V rail need or your split +15/-15 rails need?
There are a number of ways to get a house keeping supply boosted up.
Start with the first requirement:
How much current does your 30V rail need or your split +15/-15 rails need?
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